The use of nuclear energy in the modern world turns out to be so important that if we woke up tomorrow and the energy from the nuclear reaction had disappeared, the world as we know it would probably cease to exist. Peace forms the basis of industrial production and life in countries such as France and Japan, Germany and Great Britain, the USA and Russia. And if the last two countries are still able to replace nuclear energy sources with thermal stations, then for France or Japan this is simply impossible.

The use of nuclear energy creates many problems. Basically, all these problems are related to the fact that using the binding energy of the atomic nucleus (which we call nuclear energy) for one’s benefit, a person receives a significant evil in the form of highly radioactive waste that cannot simply be thrown away. Waste from nuclear energy sources must be processed, transported, buried, and stored for a long time in safe conditions.

Pros and cons, benefits and harms of using nuclear energy

Let's consider the pros and cons of using atomic-nuclear energy, their benefits, harm and significance in the life of Mankind. It is obvious that nuclear energy today is needed only by industrialized countries. That is, peaceful nuclear energy is mainly used in facilities such as factories, processing plants, etc. It is energy-intensive industries that are remote from sources of cheap electricity (such as hydroelectric power plants) that use nuclear power plants to ensure and develop their internal processes.

Agrarian regions and cities do not have much need for nuclear energy. It is quite possible to replace it with thermal and other stations. It turns out that the mastery, acquisition, development, production and use of nuclear energy is for the most part aimed at meeting our needs for industrial products. Let's see what kind of industries they are: automotive industry, military production, metallurgy, chemical industry, oil and gas complex, etc.

Does a modern person want to drive a new car? Want to dress in fashionable synthetics, eat synthetics and pack everything in synthetics? Want colorful products in different shapes and sizes? Wants all new phones, TVs, computers? Do you want to buy a lot and often change the equipment around you? Do you want to eat delicious chemical food from colored packages? Do you want to live in peace? Want to hear sweet speeches from the TV screen? Does he want there to be a lot of tanks, as well as missiles and cruisers, as well as shells and guns?

And he gets it all. It does not matter that in the end the discrepancy between word and deed leads to war. It doesn't matter that recycling it also requires energy. For now the man is calm. He eats, drinks, goes to work, sells and buys.

And all this requires energy. And this also requires a lot of oil, gas, metal, etc. And all these industrial processes require nuclear energy. Therefore, no matter what anyone says, until the first industrial thermonuclear fusion reactor is put into production, nuclear energy will only develop.

We can safely list everything that we are used to as the advantages of nuclear energy. The downside is the sad prospect of imminent death due to the collapse of resource depletion, problems of nuclear waste, population growth and degradation of arable land. In other words, nuclear energy allowed man to begin to take control of nature even more, raping it beyond measure to such an extent that in a few decades he overcame the threshold of reproduction of basic resources, launching the process of collapse of consumption between 2000 and 2010. This process objectively no longer depends on the person.

Everyone will have to eat less, live less and enjoy the natural environment less. Here lies another plus or minus of nuclear energy, which is that countries that have mastered the atom will be able to more effectively redistribute the scarce resources of those who have not mastered the atom. Moreover, only the development of the thermonuclear fusion program will allow humanity to simply survive. Now let’s explain in detail what kind of “beast” this is - atomic (nuclear) energy and what it is eaten with.

Mass, matter and atomic (nuclear) energy

We often hear the statement that “mass and energy are the same thing,” or such judgments that the expression E = mс2 explains the explosion of an atomic (nuclear) bomb. Now that you have a first understanding of nuclear energy and its applications, it would be truly unwise to confuse you with statements such as “mass equals energy.” In any case, this way of interpreting the great discovery is not the best. Apparently, this is just the wit of young reformists, “Galileans of the new time.” In fact, the prediction of the theory, which has been verified by many experiments, only says that energy has mass.

We will now explain the modern point of view and give a short overview of the history of its development.
When the energy of any material body increases, its mass increases, and we attribute this additional mass to the increase in energy. For example, when radiation is absorbed, the absorber becomes hotter and its mass increases. However, the increase is so small that it remains beyond the accuracy of measurements in ordinary experiments. On the contrary, if a substance emits radiation, then it loses a drop of its mass, which is carried away by the radiation. A broader question arises: is not the entire mass of matter determined by energy, i.e., is there not a huge reserve of energy contained in all matter? Many years ago, radioactive transformations responded positively to this. When a radioactive atom decays, a huge amount of energy is released (mostly in the form of kinetic energy), and a small part of the atom's mass disappears. The measurements clearly show this. Thus, energy carries away mass with it, thereby reducing the mass of matter.

Consequently, part of the mass of matter is interchangeable with the mass of radiation, kinetic energy, etc. That is why we say: “energy and matter are partially capable of mutual transformations.” Moreover, we can now create particles of matter that have mass and are capable of being completely converted into radiation, which also has mass. The energy of this radiation can transform into other forms, transferring its mass to them. Conversely, radiation can turn into particles of matter. So instead of “energy has mass,” we can say “particles of matter and radiation are interconvertible, and therefore capable of interconversion with other forms of energy.” This is the creation and destruction of matter. Such destructive events cannot occur in the realm of ordinary physics, chemistry and technology, they must be sought either in the microscopic but active processes studied by nuclear physics, or in the high-temperature crucible of atomic bombs, in the Sun and stars. However, it would be unreasonable to say that "energy is mass." We say: “energy, like matter, has mass.”

Mass of ordinary matter

We say that the mass of ordinary matter contains within itself a huge supply of internal energy, equal to the product of mass by (the speed of light)2. But this energy is contained in the mass and cannot be released without the disappearance of at least part of it. How did such an amazing idea come about and why was it not discovered earlier? It had been proposed before - experiment and theory in different forms - but until the twentieth century the change in energy was not observed, because in ordinary experiments it corresponds to an incredibly small change in mass. However, we are now confident that a flying bullet, due to its kinetic energy, has additional mass. Even at a speed of 5000 m/sec, a bullet that weighed exactly 1 g at rest will have a total mass of 1.00000000001 g. White-hot platinum weighing 1 kg will only add 0.000000000004 kg and practically no weighing will be able to register these changes. It is only when enormous reserves of energy are released from the atomic nucleus, or when atomic "projectiles" are accelerated to speeds close to the speed of light, that the mass of energy becomes noticeable.

On the other hand, even a subtle difference in mass marks the possibility of releasing a huge amount of energy. Thus, hydrogen and helium atoms have relative masses of 1.008 and 4.004. If four hydrogen nuclei could combine into one helium nucleus, the mass of 4.032 would change to 4.004. The difference is small, only 0.028, or 0.7%. But it would mean a gigantic release of energy (mainly in the form of radiation). 4.032 kg of hydrogen would produce 0.028 kg of radiation, which would have an energy of about 600000000000 Cal.

Compare this to the 140,000 Cals released when the same amount of hydrogen combines with oxygen in a chemical explosion.
Ordinary kinetic energy makes a significant contribution to the mass of very fast protons produced in cyclotrons, and this creates difficulties when working with such machines.

Why do we still believe that E=mc2

Now we perceive this as a direct consequence of the theory of relativity, but the first suspicions arose towards the end of the 19th century, in connection with the properties of radiation. It seemed likely then that the radiation had mass. And since radiation carries, as if on wings, at a speed with energy, or rather, it itself is energy, an example of mass has appeared that belongs to something “immaterial”. The experimental laws of electromagnetism predicted that electromagnetic waves should have "mass." But before the creation of the theory of relativity, only unbridled imagination could extend the ratio m=E/c2 to other forms of energy.

All types of electromagnetic radiation (radio waves, infrared, visible and ultraviolet light, etc.) share some common features: they all propagate in vacuum at the same speed and all transfer energy and momentum. We imagine light and other radiation in the form of waves propagating at a high but certain speed c = 3*108 m/sec. When light strikes an absorbing surface, heat is generated, indicating that the stream of light carries energy. This energy must propagate along with the flow at the same speed of light. In fact, the speed of light is measured exactly this way: by the time it takes a portion of light energy to travel a long distance.

When light hits the surface of some metals, it knocks out electrons that fly out just as if they had been hit by a compact ball. , apparently, is distributed in concentrated portions, which we call “quanta”. This is the quantum nature of the radiation, despite the fact that these portions are apparently created by waves. Each piece of light with the same wavelength has the same energy, a certain “quantum” of energy. Such portions rush at the speed of light (in fact, they are light), transferring energy and momentum (momentum). All this makes it possible to attribute a certain mass to the radiation - a certain mass is assigned to each portion.

When light is reflected from a mirror, no heat is released, because the reflected beam carries away all the energy, but pressure similar to the pressure of elastic balls or molecules acts on the mirror. If, instead of a mirror, the light hits a black absorbing surface, the pressure becomes half as much. This indicates that the beam carries the amount of motion rotated by the mirror. Therefore, light behaves as if it had mass. But is there any other way to know that something has mass? Does mass exist in its own right, such as length, green color, or water? Or is it an artificial concept defined by behavior like Modesty? Mass, in fact, is known to us in three manifestations:

• A. A vague statement characterizing the amount of “substance” (Mass from this point of view is inherent in matter - an entity that we can see, touch, push).
• B. Certain statements linking it with other physical quantities.
• B. Mass is conserved.

It remains to determine the mass in terms of momentum and energy. Then any moving thing with momentum and energy must have "mass". Its mass should be (momentum)/(velocity).

Theory of relativity

The desire to link together a series of experimental paradoxes concerning absolute space and time gave rise to the theory of relativity. Two kinds of experiments with light gave conflicting results, and experiments with electricity further aggravated this conflict. Then Einstein proposed changing the simple geometric rules for adding vectors. This change is the essence of his “special theory of relativity.”

For low speeds (from the slowest snail to the fastest of rockets), the new theory agrees with the old one.
At high speeds, comparable to the speed of light, our measurement of lengths or time is modified by the movement of the body relative to the observer, in particular, the mass of the body becomes greater the faster it moves.

Then the theory of relativity declared that this increase in mass was completely general. At normal speeds there is no change, and only at a speed of 100,000,000 km/h does the mass increase by 1%. However, for electrons and protons emitted from radioactive atoms or modern accelerators, it reaches 10, 100, 1000%…. Experiments with such high-energy particles provide excellent confirmation of the relationship between mass and velocity.

At the other edge there is radiation that has no rest mass. It is not a substance and cannot be kept at rest; it simply has mass and moves with speed c, so its energy is equal to mc2. We talk about quanta as photons when we want to note the behavior of light as a stream of particles. Each photon has a certain mass m, a certain energy E=mc2 and momentum (momentum).

Nuclear transformations

In some experiments with nuclei, the masses of atoms after violent explosions do not add up to the same total mass. The released energy carries with it some part of the mass; the missing piece of atomic material appears to have disappeared. However, if we assign the mass E/c2 to the measured energy, we find that the mass is conserved.

Annihilation of matter

We are accustomed to thinking of mass as an inevitable property of matter, so the transition of mass from matter to radiation - from a lamp to an escaping ray of light - looks almost like the destruction of matter. One more step - and we will be surprised to discover what is actually happening: positive and negative electrons, particles of matter, joining together, are completely converted into radiation. The mass of their matter turns into an equal mass of radiation. This is a case of disappearance of matter in the most literal sense. As if in focus, in a flash of light.

Measurements show that (energy, radiation during annihilation)/ c2 is equal to the total mass of both electrons - positive and negative. An antiproton combines with a proton and annihilates, usually releasing lighter particles with high kinetic energy.

Creation of matter

Now that we have learned to manage high-energy radiation (ultra-short-wave X-rays), we can prepare particles of matter from the radiation. If a target is bombarded with such rays, they sometimes produce a pair of particles, for example positive and negative electrons. And if we again use the formula m=E/c2 for both radiation and kinetic energy, then the mass will be conserved.

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University of Management"
Department of Innovation Management
in the discipline: “Concepts of modern natural science”
Presentation on the topic: Nuclear
energy: its essence and
use in technology and
technologies

Presentation plan

Introduction
Nuclear energy.
History of the discovery of nuclear energy
Nuclear reactor: history of creation, structure,
basic principles, classification of reactors
Areas of nuclear energy use
Conclusion
Sources used

Introduction

Energy is the most important sector of the national economy,
covering energy resources, generation, transformation,
transmission and use of various types of energy. This is the basis
state economy.
The world is undergoing a process of industrialization, which requires
additional consumption of materials, which increases energy costs.
With population growth, energy consumption for soil cultivation increases,
harvesting, fertilizer production, etc.
Currently, many natural resources are readily available
planets are running out. It takes a long time to extract raw materials
deep or on sea shelves. Limited world reserves
oil and gas, it would seem, pose humanity with the prospect of
energy crisis.
However, the use of nuclear energy gives humanity
the opportunity to avoid this, since the results of fundamental
research into the physics of the atomic nucleus makes it possible to avert the threat
energy crisis by using the energy released
in some reactions of atomic nuclei

Nuclear energy

Nuclear energy (atomic energy) is energy
contained in atomic nuclei and released
during nuclear reactions. Nuclear power plants,
those generating this energy produce 13–14%
world production of electrical energy. .

History of the discovery of nuclear energy

1895 V.K. Roentgen discovers ionizing radiation (X-rays)
1896 A. Becquerel discovers the phenomena of radioactivity.
1898 M. Sklodowska and P. Curie discover radioactive elements
Po (Polonium) and Ra (Radium).
1913 N. Bohr develops the theory of the structure of atoms and molecules.
1932 J. Chadwick discovers neutrons.
1939 O. Hahn and F. Strassmann study the fission of U nuclei under the influence of
slow neutrons.
December 1942 - First self-sustaining
controlled chain reaction of nuclear fission at the SR-1 reactor (Group
physicists of the University of Chicago, headed by E. Fermi).
December 25, 1946 - The first Soviet reactor F-1 was put into operation
critical state (a group of physicists and engineers led by
I.V. Kurchatova)
1949 - The first Pu production reactor was put into operation
June 27, 1954 - The world's first nuclear power plant went into operation
power plant with an electrical capacity of 5 MW in Obninsk.
By the beginning of the 90s, more than 430 nuclear power plants operated in 27 countries around the world.
power reactors with a total capacity of approx. 340 GW.

History of the creation of a nuclear reactor

Enrico Fermi (1901-1954)
Kurchatov I.V. (1903-1960)
1942 in the USA, under the leadership of E. Fermi, the first
nuclear reactor.
1946 The first Soviet reactor was launched under the leadership
Academician I.V. Kurchatov.

NPP reactor design (simplified)

Main elements:
Active zone with nuclear fuel and
retarder;
Neutron reflector surrounding
active zone;
Coolant;
Chain reaction control system,
including emergency protection
Radiation protection
Remote control system
The main characteristics of the reactor are
its power output.
Power of 1 MW - 3·1016 divisions
in 1 sec.
Schematic structure of a nuclear power plant
Cross-section of a heterogeneous reactor

Structure of a nuclear reactor

Neutron multiplication factor

Characterizes the rapid growth of the number
neutrons and is equal to the ratio of the number
neutrons in one generation
chain reaction to the number that gave birth to them
neutrons of the previous generation.
k=Si/Si-1
k<1 – Реакция затухает
k=1 – The reaction proceeds stationary
k=1.006 – Controllability limit
reactions
k>1.01 – Explosion (for a reactor at
thermal neutrons energy release
will grow 20,000 times per second).
Typical chain reaction for uranium;

10. The reactor is controlled using rods containing cadmium or boron.

The following types of rods are distinguished (according to the purpose of application):
Compensating rods – compensate for the initial excess
reactivity, extend as fuel burns out; up to 100
things
Control rods - to maintain critical
states at any time, for stopping, starting
reactor; several pieces
Note: The following types of rods are distinguished (according to purpose
applications):
Control and compensating rods are optional
represent different structural elements
registration
Emergency rods - reset by gravity
to the central part of the core; several pieces. Maybe
Additionally, some of the control rods are also reset.

11. Classification of nuclear reactors by neutron spectrum

Thermal neutron reactor (“thermal reactor”)
A fast neutron moderator (water, graphite, beryllium) is required to reach thermal
energies (fractions of eV).
Small neutron losses in the moderator and structural materials =>
natural and slightly enriched uranium can be used as fuel.
Powerful power reactors can use uranium with high
enrichment - up to 10%.
A large reactivity reserve is required.
Fast neutron reactor ("fast reactor")
Uranium carbide UC, PuO2, etc. is used as a moderator and moderation
There are much fewer neutrons (0.1-0.4 MeV).
Only highly enriched uranium can be used as fuel. But
at the same time, the fuel efficiency is 1.5 times greater.
A neutron reflector (238U, 232Th) is required. They return to the active zone
fast neutrons with energies above 0.1 MeV. Neutrons captured by nuclei 238U, 232Th,
are spent on obtaining fissile nuclei 239Pu and 233U.
The choice of construction materials is not limited by the absorption cross section, Reserve
much less reactivity.
Intermediate Neutron Reactor
Fast neutrons are slowed down to an energy of 1-1000 eV before absorption.
High load of nuclear fuel compared to thermal reactors
neutrons
It is impossible to carry out expanded reproduction of nuclear fuel, as in
fast neutron reactor.

12. By fuel placement

Homogeneous reactors - fuel and moderator represent a homogeneous
mixture
Nuclear fuel is located in the reactor core in the form
homogeneous mixture: solutions of uranium salts; suspension of uranium oxides in
light and heavy water; solid moderator impregnated with uranium;
molten salts. Options for homogeneous reactors with
gaseous fuel (gaseous uranium compounds) or suspension
uranium dust in gas.
The heat generated in the core is removed by the coolant (water,
gas, etc.) moving through pipes through the core; or a mixture
fuel with a moderator itself serves as a coolant,
circulating through heat exchangers.
Not widely used (High corrosion of structural
materials in liquid fuel, the complexity of reactor design
solid mixtures, more loading of weakly enriched uranium
fuel, etc.)
Heterogeneous reactors - fuel is placed in the core discretely in
in the form of blocks between which there is a moderator
The main feature is the presence of fuel elements
(TVELs). Fuel rods can have different shapes (rods, plates
etc.), but there is always a clear boundary between fuel,
moderator, coolant, etc.
The vast majority of reactors in use today are
heterogeneous, which is due to their design advantages in terms of
compared to homogeneous reactors.

13. By nature of use

Name
Purpose
Power
Experimental
reactors
Study of various physical quantities,
whose values ​​are necessary for
design and operation of nuclear
reactors.
~103W
Research
reactors
Fluxes of neutrons and γ-quanta created in
active zone, used for
research in the field of nuclear physics,
solid state physics, radiation chemistry,
biology, for testing materials,
designed to work in intensive conditions
neutron fluxes (including nuclear parts
reactors) for the production of isotopes.
<107Вт
Standouts
I'm energy like
usually not
used
Isotope reactors
To produce isotopes used in
nuclear weapons, for example, 239Pu, and in
industry.
~103W
Energy
reactors
To obtain electrical and thermal
energy used in the energy sector, with
water desalination, for power drive
ship installations, etc.
Up to 3-5 109W

14. Assembling a heterogeneous reactor

In a heterogeneous reactor, nuclear fuel is distributed in the active
zone discretely in the form of blocks, between which there is
neutron moderator

15. Heavy water nuclear reactor

Advantages
Smaller absorption cross section
Neutrons => Improved
neutron balance =>
Use as
natural uranium fuel
Possibility of creating
industrial heavy water
reactors for production
tritium and plutonium, as well as
wide range of isotopic
products, including
medical purposes.
Flaws
High cost of deuterium

16. Natural nuclear reactor

In nature, under conditions like
artificial reactor, can
create natural areas
nuclear reactor.
The only known natural
nuclear reactor existed 2 billion
years ago in the Oklo region (Gabon).
Origin: a very rich vein of uranium ores receives water from
surface, which plays the role of a neutron moderator. Random
decay starts a chain reaction. When it is active, the water boils away,
the reaction weakens - self-regulation.
The reaction lasted ~100,000 years. Now this is not possible due to
uranium reserves depleted by natural decay.
Field surveys are being carried out to study migration
isotopes – important for the development of underground disposal techniques
radioactive waste.

17. Areas of use of nuclear energy

Nuclear power plant
Scheme of operation of a nuclear power plant on a double-circuit
pressurized water power reactor (VVER)

18.

In addition to nuclear power plants, nuclear reactors are used:
on nuclear icebreakers
on nuclear submarines;
during the operation of nuclear missiles
engines (in particular on AMS).

19. Nuclear energy in space

Space probe
Cassini, created by
project of NASA and ESA,
launched 10/15/1997 for
series of studies
objects of Solar
systems.
Electricity generation
carried out by three
radioisotope
thermoelectric
generators: Cassini
carries 30 kg 238Pu on board,
which, disintegrating,
releases heat
convertible to
electricity

20. Spaceship "Prometheus 1"

NASA is developing a nuclear reactor
able to work in conditions
weightlessness.
The goal is to supply power to space
ship "Prometheus 1" according to the project
search for life on the moons of Jupiter.

21. Bomb. The principle of uncontrolled nuclear reaction.

The only physical need is to obtain critical
masses for k>1.01. No control system development required –
cheaper than nuclear power plants.
The "gun" method
Two uranium ingots of subcritical masses when combined exceed
critical. The degree of enrichment 235U is not less than 80%.
This type of “baby” bomb was dropped on Hiroshima 06/08/45 8:15
(78-240 thousand killed, 140 thousand died within 6 months)

22. Explosive crimping method

A bomb based on plutonium, which, using complex
systems for simultaneous detonation of conventional explosives is compressed to
supercritical size.
A bomb of this type "Fat Man" was dropped on Nagasaki
09/08/45 11:02
(75 thousand killed and wounded).

23. Conclusion

The energy problem is one of the most important problems that
Today humanity has to decide. Such things have already become commonplace
achievements of science and technology as a means of instant communication, fast
transport, space exploration. But all this requires
huge expenditure of energy.
The sharp increase in energy production and consumption has brought forward a new
acute problem of environmental pollution, which represents
serious danger to humanity.
World energy needs in the coming decades
will increase rapidly. No one source of energy
will be able to provide them, so it is necessary to develop all sources
energy and use energy resources efficiently.
At the nearest stage of energy development (the first decades of the 21st century)
Coal energy and nuclear power will remain the most promising
energy with thermal and fast neutron reactors. However, you can
hope that humanity will not stop on the path of progress,
associated with energy consumption in ever-increasing quantities.

When German chemists Otto Hahn and Fritz Strassmann first succeeded in splitting a uranium nucleus using neutron irradiation in 1938, they were in no hurry to inform the public about the scale of their discovery. These experiments laid the foundation for the use of atomic energy for both peaceful and military purposes.

A by-product of the atomic bomb

Otto Hahn, who collaborated with the Austrian physicist Lise Meitner before his death in 1938, was well aware that the fission of the uranium nucleus - an unstoppable chain reaction - meant an atomic bomb. The United States, eager to get ahead of Germany in the creation of nuclear weapons, launched the Manhattan Project, an enterprise of unprecedented scope. Three cities have grown up in the Nevada desert. 40,000 people worked here in deep secrecy. Under the leadership of Robert Oppenheimer, the “father of the atomic bomb,” about 40 research institutions, laboratories and factories emerged in record time. To extract plutonium, the first nuclear reactor was created under the stands of the University of Chicago football stadium. Here, under the leadership of Enrico Fermi, the first controlled self-sustaining chain reaction was launched in 1942. No useful use had yet been found for the resulting heat.

Electrical energy from a nuclear reaction

In 1954, the world's first nuclear power plant was launched in the USSR. It was located in Obninsk, about 100 km from Moscow, and had a capacity of 5 MW. In 1956, the first large nuclear reactor began operating in the English town of Calder Hall. This nuclear power plant had gas cooling, which ensured relative operational safety. But on the world market, pressurized water-cooled water-cooled nuclear reactors, developed in the USA in 1957, have become more widespread. Such stations can be built at relatively low costs, but their reliability leaves much to be desired. At the Ukrainian nuclear power plant Chernobyl, the melting of the reactor core led to an explosion with the release of radioactive substances into the environment. The disaster, which led to the death and serious illness of thousands of people, led to many protests against the use of atomic energy, especially in Europe.

• 1896: Henri Bequerel discovered radioactive emissions from uranium.
• 1919 Ernest Rutherford was the first to artificially cause a nuclear reaction by bombarding nitrogen atoms with alpha particles, which turned into oxygen.
• 1932: James Chadwick fired alpha particles at beryllium atoms and discovered neutrons.
• 19.38: Otto Hahn achieves a chain reaction in the laboratory for the first time, splitting a uranium nucleus with neutrons.

1.Introductions

2.Radioactivity

3.Nuclear reactors

4.Engineering aspects of a fusion reactor

5.Nuclear reaction. Nuclear energy.

6.Gamma radiation

7.Nuclear reactor

8.Principles of building nuclear energy

9. Nuclear fusion tomorrow

10.Conclusion

11.References

INTRODUCTION: What does physics study?

Physics is the science of nature that studies the simplest and at the same time the most general laws of nature, the structure and laws of motion of matter. Physics is classified as an exact science. Its concepts and laws form the basis of natural science. The boundaries separating physics and other natural sciences are historically arbitrary. It is generally accepted that physics is fundamentally an experimental science, since the laws it discovers are based on experimentally established data. Physical laws are presented in the form of quantitative relationships expressed in the language of mathematics. In general, physics is divided into experimental, which deals with conducting experiments in order to establish new facts and test hypotheses and known physical laws, and theoretical, focused on the formulation of physical laws, the explanation of natural phenomena based on these laws and the prediction of new phenomena.

The structure of physics is complex. It includes various disciplines or sections. Depending on the objects being studied, there are physics of elementary particles, nuclear physics, physics of atoms and molecules, physics of gases and liquids, plasma physics, and solid state physics. Depending on the processes or forms of motion of matter being studied, the mechanics of material points and solid bodies, the mechanics of continuous media (including acoustics), thermodynamics and statistical mechanics, electrodynamics (including optics), the theory of gravity, quantum mechanics and quantum field theory are distinguished. Depending on the consumer focus of the knowledge obtained, fundamental and applied physics are distinguished. It is also customary to distinguish the doctrine of vibrations and waves, which considers mechanical, acoustic, electrical and optical vibrations and waves from a single point of view. Physics is based on fundamental physical principles and theories that cover all branches of physics and most fully reflect the essence of physical phenomena and processes of reality.

From the early civilizations that arose on the banks of the Tigris, Euphrates and Nile (Babylon, Assyria, Egypt), there is no evidence of achievements in the field of physical knowledge, with the exception of those embodied in architectural structures, household items, etc. products of knowledge. When erecting various kinds of structures and making household items, weapons, etc., people used certain results of numerous physical observations, technical experiments, and their generalizations. We can say that there was certain empirical physical knowledge, but there was no system of physical knowledge.

Physical concepts in Ancient China also appeared on the basis of various types of technical activity, during which various technological recipes were developed. Naturally, mechanical concepts were developed first of all. Thus, the Chinese had ideas about force (what makes you move), reaction (what stops movement), lever, block, comparison of scales (comparison with a standard). In the field of optics, the Chinese had the idea of ​​​​forming a reverse image in a "camera obscura". Already in the sixth century BC. they knew the phenomena of magnetism - the attraction of iron by a magnet, on the basis of which the compass was created. In the field of acoustics, they knew the laws of harmony and the phenomena of resonance. But these were still empirical ideas that had no theoretical explanation.

In Ancient India, the basis of natural philosophical ideas was the doctrine of the five elements - earth, water, fire, air and ether. There was also a guess about the atomic structure of matter. Original ideas were developed about such properties of matter as heaviness, fluidity, viscosity, elasticity, etc., about movement and the causes that cause it. By the 6th century BC Empirical physical concepts in some areas show a tendency to transform into unique theoretical constructions (in optics, acoustics).

The phenomenon of radioactivity, or spontaneous decay of nuclei, was discovered by the French physicist A. Becquerel in 1896. He discovered that uranium and its compounds emit rays or particles that penetrate through opaque bodies and can illuminate a photographic plate; Becquerel established that the intensity of radiation is proportional only to the concentration uranium and does not depend on external conditions (temperature, pressure) and on whether uranium is in any chemical compounds.

English physicists E. Rutherford and F. Soddy proved that in all radioactive processes mutual transformations of the atomic nuclei of chemical elements occur. A study of the properties of radiation accompanying these processes in magnetic and electric fields showed that it is divided into a-particles (helium nuclei), b-particles (electrons) and g-rays (electromagnetic radiation with a very short wavelength).

An atomic nucleus emitting g-quanta, a-, b- or other particles is called radioactive nucleus. There are 272 stable atomic nuclei in nature. All other nuclei are radioactive and are called radioisotopes.

The binding energy of a nucleus characterizes its resistance to disintegration into its component parts. If the binding energy of a nucleus is less than the binding energy of its decay products, this means that the nucleus can spontaneously decay. During alpha decay, alpha particles carry away almost all the energy and only 2% of it goes to the secondary nucleus. During alpha decay, the mass number changes by 4 units and the atomic number by two units.

The initial energy of an alpha particle is 4-10 MeV. Since alpha particles have a large mass and charge, their mean free path in air is short. For example, the mean free path in air for alpha particles emitted by a uranium nucleus is 2.7 cm, and those emitted by radium is 3.3 cm.

This is the process of transformation of an atomic nucleus into another nucleus with a change in the atomic number without changing the mass number. There are three types of b-decay: electron, positron, and capture of an orbital electron by an atomic nucleus. The last decay type is also called TO-capture, since in this case the electron closest to the nucleus is most likely to be absorbed TO shells. Absorption of electrons from L And M shells is also possible, but less likely. The half-life of b-active nuclei varies over a very wide range.

The number of beta-active nuclei currently known is about one and a half thousand, but only 20 of them are naturally occurring beta-radioactive isotopes. All others are obtained artificially.

The continuous distribution of kinetic energy of electrons emitted during decay is explained by the fact that, along with the electron, an antineutrino is also emitted. If there were no antineutrinos, then the electrons would have a strictly defined momentum, equal to the momentum of the residual nucleus. A sharp break in the spectrum is observed at a kinetic energy value equal to the beta decay energy. In this case, the kinetic energies of the nucleus and antineutrino are equal to zero and the electron carries away all the energy released during the reaction.

During electronic decay, the residual nucleus has an order number one greater than the original one, while maintaining the mass number. This means that in the residual nucleus the number of protons increased by one, and the number of neutrons, on the contrary, became smaller: N=A-(Z+1).

During positron decay, the full number of nucleons is retained, but the final nucleus has one more neutron than the initial one. Thus, positron decay can be interpreted as the reaction of the transformation of one proton inside the nucleus into a neutron with the emission of a positron and a neutrino.

TO electronic capture refers to the process of an atom absorbing one of the orbital electrons of its atom. Since the capture of an electron from the orbit closest to the nucleus is most likely, electrons are most likely to be absorbed TO-shells. Therefore this process is also called TO-capture.

It is much less likely that electrons will be captured from L-,M-shells. After capturing an electron from TO-shell, a series of electron transitions from orbit to orbit occurs, a new atomic state is formed, and an X-ray quantum is emitted.

Stable nuclei are in a state corresponding to the lowest energy. This state is called basic. However, by irradiating atomic nuclei with various particles or high-energy protons, a certain energy can be transferred to them and, therefore, transferred to states corresponding to higher energy. Transitioning after some time from the excited state to the ground state, the atomic nucleus can emit either a particle, if the excitation energy is high enough, or high-energy electromagnetic radiation - a gamma quantum.

Since the excited nucleus is in discrete energy states, gamma radiation is characterized by a line spectrum.

When heavy nuclei fission, several free neutrons are produced. This makes it possible to organize the so-called fission chain reaction, when neutrons, propagating in a medium containing heavy elements, can cause their fission with the emission of new free neutrons. If the environment is such that the number of newly created neutrons increases, then the fission process increases like an avalanche. In the case when the number of neutrons decreases during subsequent fissions, the nuclear chain reaction fades.

To obtain a stationary nuclear chain reaction, it is obviously necessary to create conditions such that each nucleus that absorbs a neutron, upon fission, releases on average one neutron, which goes towards the fission of the second heavy nucleus.

A nuclear reactor is a device in which a controlled chain reaction of fission of certain heavy nuclei is carried out and maintained.

A nuclear chain reaction in a reactor can only occur with a certain number of fissile nuclei, which can fission at any neutron energy. Of the fissile materials, the most important is the 235 U isotope, the share of which in natural uranium is only 0.714%.

Although 238 U is fissile by neutrons whose energy exceeds 1.2 MeV, a self-sustaining chain reaction on fast neutrons in natural uranium is not possible due to the high probability of inelastic interaction of 238 U nuclei with fast neutrons. In this case, the neutron energy becomes below the threshold fission energy of 238 U nuclei.

The use of a moderator leads to a decrease in resonant absorption in 238 U, since a neutron can pass through the region of resonance energies as a result of collisions with moderator nuclei and be absorbed by nuclei 235 U, 239 Pu, 233 U, the fission cross section of which increases significantly with decreasing neutron energy. Materials with a low mass number and a small absorption cross section (water, graphite, beryllium, etc.) are used as moderators.

To characterize a fission chain reaction, a quantity called the multiplication factor K is used. This is the ratio of the number of neutrons of a certain generation to the number of neutrons of the previous generation. For a stationary fission chain reaction K=1. A breeding system (reactor) in which K = 1 is called critical. If K >1, the number of neutrons in the system increases, and in this case it is called above critical. At K< 1 происходит уменьшение числа нейтронов, и система называется под критической. В стационарном состоянии реактора число вновь образующихся нейтронов равно числу нейтронов, покидающих реактор (нейтроны утечки) и поглощающихся в его пределах. В критическом реакторе присутствуют нейтроны всех энергий. Они образуют так называемый энергетический спектр нейтронов, который характеризует число нейтронов различных энергий в единице объема в любой точке реактора. Средняя энергия спектра нейтронов определяется долей замедлителя, делящихся ядер (ядра горючего) и других материалов, которые входят в состав активной зоны реактора. Если большая часть делений происходит при поглощении тепловых нейтронов, то такой реактор называется реактором на тепловых нейтронах. Энергия нейтронов в такой системе не превышает 0.2 эВ. Если большая часть делений в реакторе происходит при поглощении быстрых нейтронов, такой реактор называется реактором на быстрых нейтронах.

In the core of a thermal neutron reactor, along with nuclear fuel, there is a significant mass of moderator-substance, characterized by a large scattering cross section and a small absorption cross section.

The active zone of a reactor is almost always, with the exception of special reactors, surrounded by a reflector that returns some of the neurons to the active zone due to multiple scattering.

In fast neuron reactors, the active zone is surrounded by reproduction zones. They accumulate fissile isotopes. In addition, the reproduction zones also serve as a reflector.

In a nuclear reactor, fission products accumulate, which are called slag. The presence of slags leads to additional losses of free neutrons.

Nuclear reactors, depending on the relative placement of fuel and moderator, are divided into homogeneous and heterogeneous. In a homogeneous reactor, the core is a homogeneous mass of fuel, moderator and coolant in the form of a solution, mixture or melt. A reactor in which fuel in the form of blocks or fuel assemblies is placed in a moderator, forming a regular geometric lattice in it, is called heterogeneous.

During operation of the reactor, heat is released in various quantities in the heat-removing elements (fuel rods), as well as in all its structural elements. This is due, first of all, to the inhibition of fission fragments, their beta and gamma radiation, as well as nuclei interacting with neurons, and, finally, to the slowing down of fast neurons. Fragments from the fission of a fuel core are classified according to velocities corresponding to temperatures of hundreds of billions of degrees.

Indeed, E = mu 2 = 3RT, where E is the kinetic energy of fragments, MeV; R = 1.38·10 -23 J/K - Boltzmann's constant. Considering that 1 MeV = 1.6 10 -13 J, we obtain 1.6 10 -6 E = 2.07 10 -16 T, T = 7.7 10 9 E. The most probable energy values ​​for fragments fissions are 97 MeV for a light fragment and 65 MeV for a heavy fragment. Then the corresponding temperature for a light fragment is 7.5 10 11 K, for a heavy fragment 5 10 11 K. Although the temperature achievable in a nuclear reactor is theoretically almost unlimited, in practice the restrictions are determined by the maximum permissible temperature of structural materials and fuel elements.

The peculiarity of a nuclear reactor is that 94% of fission energy is converted into heat instantly, i.e. during the time during which the power of the reactor or the density of the materials in it does not have time to change noticeably. Therefore, when the reactor power changes, heat release follows the fuel fission process without delay. However, when the reactor is turned off, when the fission rate decreases by more than tens of times, sources of delayed heat release (gamma and beta radiation from fission products) remain in it, which become predominant.

The power of a nuclear reactor is proportional to the flux density of neurons in it, so any power is theoretically achievable. In practice, the maximum power is determined by the rate of heat removal released in the reactor. The specific heat removal in modern power reactors is 10 2 - 10 3 MW/m 3, in vortex reactors - 10 4 - 10 5 MW/m 3.

Heat is removed from the reactor by a coolant circulating through it. A characteristic feature of the reactor is the residual heat release after the fission reaction stops, which requires heat removal for a long time after the reactor is shut down. Although the decay heat power is significantly less than the nominal power, the coolant circulation through the reactor must be ensured very reliably, since the decay heat cannot be controlled. Removing coolant from a reactor that has been operating for some time is strictly prohibited in order to avoid overheating and damage to the fuel elements.

A nuclear power reactor is a device in which a controlled chain reaction of fission of the nuclei of heavy elements is carried out, and the thermal energy released during this process is removed by a coolant. The main element of a nuclear reactor is the core. It houses nuclear fuel and carries out a fission chain reaction. The core is a collection of fuel elements containing nuclear fuel placed in a certain way. Thermal neutron reactors use a moderator. A coolant is pumped through the core to cool the fuel elements. In some types of reactors, the role of moderator and coolant is performed by the same substance, for example, ordinary or heavy water. For

To control the operation of the reactor, control rods made of materials with a large neutron absorption cross section are introduced into the core. The core of power reactors is surrounded by a neutron reflector - a layer of moderator material to reduce the leakage of neutrons from the core. In addition, thanks to the reflector, the neutron density and energy release are equalized throughout the volume of the core, which makes it possible to obtain greater power for a given zone size, achieve more uniform fuel burnout, increase the operating time of the reactor without overloading the fuel, and simplify the heat removal system. The reflector is heated by the energy of slowing down and absorbed neutrons and gamma quanta, so its cooling is provided. The core, reflector and other elements are housed in a sealed housing or casing, usually surrounded by biological shielding.

The reactor core must be designed in such a way that the possibility of unintended movement of its components, leading to an increase in reactivity, is excluded. The main structural part of a heterogeneous core is the fuel rod, which largely determines its reliability, size and cost. Power reactors typically use fuel rods with fuel in the form of compressed uranium dioxide pellets enclosed in a steel or zirconium alloy shell. For convenience, fuel elements are assembled into fuel assemblies (FA), which are installed in the core of a nuclear reactor.

The main share of thermal energy is generated in fuel rods and transferred to the coolant. More than 90% of all the energy released during the fission of heavy nuclei is released into the fuel elements and is removed by the coolant flowing around the fuel elements. Fuel rods operate in very severe thermal conditions: the maximum heat flux density from the fuel rod to the coolant reaches (1 - 2) 10 6 W/m 2, whereas in modern steam boilers it is equal to (2 - 3) 10 5 W/m 2. In addition, a relatively small volume of nuclear fuel releases a large amount of heat, i.e. The energy density of nuclear fuel is also very high. The specific heat release in the active zone reaches 10 8 -10 9 W/m 3, while in modern steam boilers it does not exceed 10 7 W/m 3.

Large heat flows passing through the surface of fuel rods and significant energy intensity of the fuel require exceptionally high durability and reliability of fuel rods. In addition, the operating conditions of fuel rods are complicated by the high operating temperature, reaching 300 - 600 C o on the surface of the cladding, the possibility of thermal shocks, vibration, and the presence of a neutron flux (fluence reaches 10 27 neutron/m 2).

High technical requirements are imposed on fuel rods: simplicity of design; mechanical stability and strength in the coolant flow, ensuring preservation of dimensions and tightness; low neutron absorption by the structural material of the fuel element and a minimum of structural material in the core; absence of interaction of nuclear fuel and fission products with the fuel cladding, coolant and moderator at operating temperatures. The geometric shape of the fuel element must ensure the required ratio of surface area to volume and the maximum intensity of heat removal by the coolant from the entire surface of the fuel element, as well as guarantee a large burnup of nuclear fuel and a high degree of retention of fission products. Fuel elements must be radiation resistant, have the required dimensions and design, ensuring the ability to quickly carry out reloading operations; have simple and economical regeneration of nuclear fuel and low cost.

For safety reasons, reliable tightness of the fuel element cladding must be maintained throughout the entire period of operation of the core (3-5 years) and the subsequent storage of spent fuel elements before being sent for reprocessing (1-3 years). When designing a core, it is necessary to establish and justify in advance the permissible limits of damage to fuel elements (quantity and degree of damage). The core is designed in such a way that during operation throughout its entire design service life the established limits for damage to fuel elements are not exceeded. Fulfillment of these requirements is ensured by the design of the core, the quality of the coolant, the characteristics and reliability of the heat removal system. During operation, the tightness of the cladding of individual fuel elements may be compromised. There are two types of such a violation: the formation of microcracks through which gaseous fission products escape from the fuel element into the coolant (gas density type defect); the occurrence of defects in which direct contact of the fuel with the coolant is possible.

The operating conditions of fuel rods are largely determined by the design of the core, which must ensure the design geometry of the placement of fuel rods and the coolant distribution required from the point of view of temperature conditions. When the reactor is operating from power, a stable flow of coolant must be maintained through the core, guaranteeing reliable heat removal. The core must be equipped with sensors inside the reactor control that provide information on power distribution, neutron flux, fuel rod temperature conditions and coolant flow.

The core of a power reactor must be designed so that the internal mechanism of interaction between neutronic and thermal physical processes, under any disturbances in the multiplication factor, establishes a new safe power level. In practice, the safety of a nuclear power plant is ensured, on the one hand, by the stability of the reactor (a decrease in the multiplication factor with increasing temperature and power of the core), and, on the other hand, by the reliability of the automatic control and protection system.

In order to ensure safety in depth, the design of the core and the characteristics of nuclear fuel must exclude the possibility of the formation of critical masses of fissile materials during the destruction of the core and the melting of nuclear fuel. When designing the core, it must be possible to introduce a neutron absorber to stop the chain reaction in any cases associated with a violation of the core cooling.

The core, containing large volumes of nuclear fuel to compensate for burnup, poisoning and temperature effects, has several critical masses. Therefore, each critical volume of fuel must be provided with means of reactivity compensation. They must be placed in the core in such a way as to exclude the possibility of local critical masses.

Reactors are classified according to the energy level of the neutrons involved in the fission reaction, according to the principle of placement of fuel and moderator, intended purpose, type of moderator and coolant and their physical state.

According to the level of energetic neutrons: reactors can operate on fast neutrons, on thermal and on neutrons of intermediate (resonance) energies and, according to this, are divided into rectors on thermal, fast and intermediate neutrons (sometimes for brevity they are called thermal, fast and intermediate).

IN thermal neutron reactor Most nuclear fission occurs when the nuclei of fissile isotopes absorb thermal neutrons. Reactors in which nuclear fission is carried out mainly by neutrons with energies greater than 0.5 MeV are called fast neutron reactors. Reactors in which most fissions occur as a result of the absorption of intermediate neutrons by the nuclei of fissile isotopes are called intermediate (resonant) neutron reactors.

Currently, thermal neutron reactors are most widespread. Thermal reactors are characterized by concentrations of 235 U nuclear fuel in the core from 1 to 100 kg/m 3 and the presence of large masses of moderator. A fast neutron reactor is characterized by concentrations of nuclear fuel 235 U or 239 U of the order of 1000 kg/m 3 and the absence of a moderator in the core.

In intermediate neutron reactors, there is very little moderator in the core, and the concentration of 235 U nuclear fuel in it is from 100 to 1000 kg/m 3 .

In thermal neutron reactors, fission of fuel nuclei also occurs when fast neutrons are captured by the nucleus, but the probability of this process is insignificant (1 - 3%). The need for a neutron moderator is due to the fact that the effective fission cross sections of fuel nuclei are much larger at low neutron energies than at large ones.

The core of a thermal reactor must contain a moderator - a substance whose nuclei have a low mass number. Graphite, heavy or light water, beryllium, and organic liquids are used as a moderator. A thermal reactor can even operate on natural uranium if the moderator is heavy water or graphite. Other moderators require the use of enriched uranium. The required critical dimensions of the reactor depend on the degree of fuel enrichment; as the degree of enrichment increases, they become smaller. A significant disadvantage of thermal neutron reactors is the loss of slow neutrons as a result of their capture by the moderator, coolant, structural materials and fission products. Therefore, in such reactors it is necessary to use substances with small cross sections for slow neutron capture as a moderator, coolant and structural materials.

IN intermediate neutron reactors, in which most fission events are caused by neutrons with energies above thermal (from 1 eV to 100 keV), the moderator mass is less than in thermal reactors. The peculiarity of the operation of such a reactor is that the fuel fission cross section with increasing neutron fission in the intermediate region decreases less than the absorption cross section of structural materials and fission products. Thus, the probability of fission events increases compared to absorption events. The requirements for the neutron characteristics of structural materials are less stringent and their range is wider. Consequently, the core of an intermediate neutron reactor can be made of more durable materials, which makes it possible to increase the specific heat removal from the heating surface of the reactor. The enrichment of fuel with a fissile isotope in intermediate reactors, as a result of a decrease in cross-section, should be higher than in thermal ones. The reproduction of nuclear fuel in intermediate neutron reactors is greater than in a thermal neutron reactor.

Substances that weakly moderate neutrons are used as coolants in intermediate reactors. For example, liquid metals. The moderator is graphite, beryllium, etc.

In the core of a fast neutron reactor, fuel rods with highly enriched fuel are placed. The core is surrounded by a breeding zone, consisting of fuel elements containing fuel raw materials (depleted uranium, thorium). Neutrons escaping from the core are captured in the breeding zone by nuclei of fuel raw materials, resulting in the formation of new nuclear fuel. A special advantage of fast reactors is the possibility of organizing expanded reproduction of nuclear fuel in them, i.e. simultaneously with energy generation, produce new nuclear fuel instead of burnt-out nuclear fuel. Fast reactors do not require a moderator, and the coolant does not need to slow down the neutrons.

Depending on the method of placing fuel in the core, reactors are divided into homogeneous and heterogeneous.

IN homogeneous reactor nuclear fuel, coolant and moderator (if any) are thoroughly mixed and are in the same physical state, i.e. The core of a completely homogeneous reactor is a liquid, solid or gaseous homogeneous mixture of nuclear fuel, coolant or moderator. Homogeneous reactors can be either thermal or fast neutron. In such a reactor, the entire active zone is located inside a steel spherical body and represents a liquid homogeneous mixture of fuel and moderator in the form of a solution or liquid alloy (for example, a solution of uranium sulfate in water, a solution of uranium in liquid bismuth), which simultaneously serves as a coolant.

The nuclear fission reaction occurs in the fuel solution inside the spherical reactor vessel, resulting in an increase in the temperature of the solution. The flammable solution from the reactor enters the heat exchanger, where it transfers heat to the water of the secondary circuit, is cooled and is sent back to the reactor by a circular pump. To ensure that a nuclear reaction does not occur outside the reactor, the volumes of the circuit pipelines, heat exchanger and pump are selected so that the volume of fuel located in each section of the circuit is much lower than the critical one. Homogeneous reactors have a number of advantages over heterogeneous ones. This is a simple design of the core and its minimal dimensions, the ability to continuously remove fission products and add fresh nuclear fuel during operation without stopping the reactor, the ease of preparing fuel, and also the fact that the reactor can be controlled by changing the concentration of nuclear fuel.

However, homogeneous reactors also have serious disadvantages. The homogeneous mixture circulating through the circuit emits strong radioactive radiation, which requires additional protection and complicates reactor control. Only part of the fuel is in the reactor and is used to generate energy, while the other part is in external pipelines, heat exchangers and pumps. The circulating mixture causes severe corrosion and erosion of reactor and circuit systems and devices. The formation of an explosive explosive mixture in a homogeneous reactor as a result of radiolysis of water requires devices for its combustion. All this led to the fact that homogeneous reactors are not widely used.

IN heterogeneous reactor fuel in the form of blocks is placed in the moderator, i.e. fuel and moderator are spatially separated.

Currently, only heterogeneous reactors are designed for energy purposes. Nuclear fuel in such a reactor can be used in gaseous, liquid and solid states. However, now heterogeneous reactors operate only on solid fuel.

Depending on the moderating substance, heterogeneous reactors are divided into graphite, light water, heavy water and organic. According to the type of coolant, heterogeneous reactors are light water, heavy water, gas and liquid metal. Liquid coolants inside the reactor can be in single-phase and two-phase states. In the first case, the coolant inside the reactor does not boil, but in the second, it does.

Reactors in the core of which the temperature of the liquid coolant is below the boiling point are called pressurized water reactors, and reactors in which the coolant boils inside are called boiling water reactors.

Depending on the moderator and coolant used, heterogeneous reactors are designed according to different designs. In Russia, the main types of nuclear power reactors are water-water and water-graphite.

Based on their design, reactors are divided into vessel and channel reactors. IN vessel reactors the coolant pressure is carried by the housing. A common coolant flow flows inside the reactor vessel. IN channel reactors The coolant is supplied to each channel with the fuel assembly separately. The reactor vessel is not loaded with coolant pressure; this pressure is carried by each individual channel.

Depending on their purpose, nuclear reactors can be power reactors, converters and multipliers, research and multipurpose, transport and industrial.

Nuclear power reactors are used to generate electricity at nuclear power plants, in ship power plants, at nuclear combined heat and power plants (CHPs), as well as at nuclear heat supply plants (HPPs).

Reactors designed to produce secondary nuclear fuel from natural uranium and thorium are called converters or times multipliers. In a converter reactor, secondary nuclear fuel produces less than what was initially consumed.

In the multiplier reactor, expanded reproduction of nuclear fuel is carried out, i.e. it turns out more than was spent.

Research reactors are used to study the processes of interaction of neutrons with matter, study the behavior of reactor materials in intense fields of neutron and gamma radiation, radiochemical and biological research, the production of isotopes, and experimental research into the physics of nuclear reactors.

Reactors have different powers, stationary or pulsed operating modes. The most widespread are pressurized water research reactors using enriched uranium. The thermal power of research reactors varies over a wide range and reaches several thousand kilowatts.

Multipurpose reactors are those that serve several purposes, such as generating energy and producing nuclear fuel.

If keff >< 1, ряд благополучно сходится и по формуле суммы геометрической прогрессии имеем

where to<1 - коэффициент, равный отношению числа нейтронов, вызвавших деление, к полному их числу. Этот коэффициент зависит от конструкции установки, используемых материалов и т.д. Он надёжно вычисляется. В примерах k=0,6. Осталось выяснить, как можно получить первоначальный поток нейтронов N 0 . Для этого можно использовать ускоритель, дающий достаточно интенсивный поток протонов или других частиц, которые, реагируя с некоторой мишенью, порождают большое кол-во нейтронов. Действительно, например, при столкновении с массивной свинцовой мишенью каждый протон, ускоренный до энергии 1ГэВ (10 9 эВ), производит в результате развития ядерного каскада в среднем n = 22 нейтрона. Энергии их составляют несколько мега электрон -вольт, что как раз соответствует работе реактора на быстрых

in the form

Engineering aspects of a fusion reactor:

The thermonuclear tokamak reactor consists of the following main parts: magnetic, cryogenic and vacuum systems, power supply system, blanket, tritium circuit and protection, system for additional heating of the plasma and replenishing it with fuel, as well as a remote control and maintenance system.

The magnetic system contains coils of a toroidal magnetic field, an inductor for maintaining current and induction heating of the plasma, and windings that form a poloidal magnetic field, which is necessary for the operation of the divertor and maintaining the equilibrium of the plasma cord.

To eliminate Joule losses, the magnetic system, as stated earlier, will be completely superconducting. For the windings of the magnetic system, it is proposed to use alloys of niobium - titanium and niobium - tin.

Creation of a magnetic system of a superconductor reactor with IN 12 Tesla and a current density of about 2 kA is one of the main engineering problems in the development of a thermonuclear reactor, which will have to be solved in the near future.

The cryogenic system includes a magnetic system cryostat and cryopanels in the additional plasma heating injectors. The cryostat looks like a vacuum chamber in which all cooled structures are enclosed. Each coil of the magnetic system is placed in liquid helium. Its vapors cool special screens located inside the cryostat to reduce heat flows from surfaces at the temperature of liquid helium. The cryogenic system has two cooling circuits, in one of which liquid helium circulates, providing the temperature required for normal operation of superconducting coils of about 4 K, and in the other - liquid nitrogen, the temperature of which is 80 - 95 K. This circuit serves to cool the partitions, separating parts with helium and room temperatures.

Cryopanels of injectors are cooled with liquid helium and are designed to absorb gases, which allows maintaining a sufficient pumping speed at a relatively high vacuum.

The vacuum system ensures pumping of helium, hydrogen and impurities from the divertor cavity or from the space surrounding the plasma during reactor operation, as well as from the working chamber in pauses between pulses. To prevent pumped tritium from being released into the environment, it is necessary to provide a closed circuit in the system with a minimum amount of circulating tritium. Gas can be pumped out using turbomolecular pumps, the productivity of which should slightly exceed that achieved today. The duration of the pause to prepare the working chamber for the next impulse does not exceed 30 s.

The power supply system significantly depends on the operating mode of the reactor. It is noticeably simpler for a tokamak operating in continuous mode. When operating in pulse mode, it is advisable to use a combined power supply system - a network and a motor-generator. The generator power is determined by pulsed loads and reaches 10 6 kW.

The reactor blanket is located behind the first wall of the working chamber and is designed to capture neutrons generated in the DT reaction, reproduce “burnt” tritium and convert neutron energy into thermal energy. In a hybrid thermonuclear reactor, the blanket also serves to produce fissile substances. A blanket is essentially something new that distinguishes a thermonuclear reactor from a conventional thermonuclear installation. There is no experience yet in the design and operation of a blanket, so engineering and design development of lithium and uranium blankets will be required.

The tritium circuit consists of several independent units that ensure the regeneration of the gas pumped out from the working chamber, its storage and supply for plasma replenishment, the extraction of tritium from the blanket and its return to the power system, as well as the purification of exhaust gases and air from it.

Reactor protection is divided into radiation and biological. Radiation shielding weakens the neutron flux and reduces the energy release in the superconducting coils. For normal operation of the magnetic system with minimal energy consumption, it is necessary to weaken the neutron flux by 10 s -10 6 times. Radiation protection is located between the blanket and the toroidal field coils and covers the entire surface of the working chamber, with the exception of the diverter channels and injector inputs. Depending on the composition, the thickness of the protection is 80-130 cm.

The biological shield coincides with the walls of the reactor hall and is made of concrete 200 - 250 cm thick. It protects the surrounding space from radiation.

Systems for additional plasma heating and feeding it with fuel occupy significant space around the reactor. If plasma heating is carried out by beams of fast atoms, then radiation protection must surround the entire injector, which is inconvenient for the location of equipment in the reactor hall and for servicing the reactor. Heating systems with high-frequency currents are more attractive in this sense, since their input devices (antennas) are more compact, and generators can be installed outside the reactor hall. Research on tokamaks and the development of antenna designs will allow us to make the final choice of the plasma heating system.

The control system is an integral part of a thermonuclear reactor. As with any reactor, due to the fairly high level of radioactivity in the space surrounding the reactor, control and maintenance in it are carried out remotely - both during operation and during shutdown periods.

The source of radioactivity in a thermonuclear reactor is, firstly, tritium, which decays with the emission of electrons and low-energy 7-quanta (its half-life is about 13 years), and secondly, radioactive nuclides formed during the interaction of neutrons with the structural materials of the blanket and working cameras. For the most common of them (steel, molybdenum and niobium alloys), the activity is quite high, but still approximately 10-100 times less than in nuclear reactors of similar power. In the future, it is planned to use materials with low induced activity, such as aluminum and vanadium, in a thermonuclear reactor. In the meantime, the tokamak thermonuclear reactor is designed taking into account remote maintenance, which imposes additional requirements on its design. In particular, it will consist of identical sections interconnected, which will be filled with various standard blocks (modules). This will make it possible, if necessary, to relatively easily replace individual components using special manipulators.

Nuclear reactions. Nuclear energy.

Atomic nucleus

The atomic nucleus is characterized by charge Ze, mass M, spin J, magnetic and electric quadrupole moment Q, a certain radius R, isotonic spin T and consists of nucleons - protons and neutrons.

The number of nucleons A in a nucleus is called mass number. The Z number is called charge number nucleus or atomic number. Since Z determines the number of protons, and A - the number of nucleons in the nucleus, the number of neurons in the atomic nucleus is N = A-Z. Atomic nuclei with the same Z but different A are called isotopes. On average, there are about three stable isotopes for every Z value. For example, 28 Si, 29 Si, 30 Si are stable isotopes of the Si nucleus. In addition to stable isotopes, most elements also have unstable isotopes, which are characterized by a limited lifetime.

Nuclei with the same mass number A are called isobars, and with the same number of neutrons - isotones.

All atomic nuclei are divided into stable and unstable. The properties of stable nuclei remain unchanged indefinitely. Unstable nuclei undergo various kinds of transformations.

Experimental measurements of the masses of atomic nuclei, carried out with great accuracy, show that the mass of a nucleus is always less than the sum of the masses of its constituent nucleons.

Binding energy is the energy that must be expended to separate a nucleus into its constituent nucleons.

The binding energy related to the mass number A is called average nucleon binding energy in the atomic nucleus (binding energy per nucleon).

The binding energy is approximately constant for all stable nuclei and is approximately equal to 8 MeV. The exception is the region of light nuclei, where the average binding energy increases from zero (A = 1) to 8 MeV for the 12 C nucleus.

Similarly, the binding energy per nucleon can be used to enter the binding energy of the nucleus relative to its other constituent parts.

In contrast to the average binding energy of nucleons, the amount of binding energy between a neuron and a proton varies from nucleus to nucleus.

Often, instead of binding energy, a quantity called mass defect and equal to the difference between the masses and mass number of the atomic nucleus.

Gamma Radiation

Gamma radiation is short-wave electromagnetic radiation. On the scale of electromagnetic waves, it borders on hard X-ray radiation, occupying the region of higher frequencies. Gamma radiation has an extremely short wavelength (λhν (ν – χ radiation frequency, h – Planck’s constant).

Gamma radiation occurs during the decay of radioactive nuclei, elementary particles, during the annihilation of particle-antiparticle pairs, as well as during the passage of fast charged particles through matter.

Gamma radiation, which accompanies the decay of radioactive nuclei, is emitted when a nucleus transitions from a more excited energy state to a less excited one or to the ground one. The energy of a γ quantum is equal to the energy difference Δε ρ of the states between which the transition occurs.

Excited state

Ground state of the E1 nucleus

The emission of a γ-quantum by a nucleus does not entail a change in the atomic number or mass number, unlike other types of radioactive transformations. The width of the gamma radiation lines is extremely small (~10 -2 eV). Since the distance between the levels is many times greater than the width of the lines, the gamma radiation spectrum is lined, i.e. consists of a number of discrete lines. The study of gamma radiation spectra makes it possible to establish the energies of excited states of nuclei. High-energy gamma rays are emitted during the decay of certain elementary particles. Thus, during the decay of a resting π 0 - meson, gamma radiation with an energy of ~70 MeV appears. Gamma radiation from the decay of elementary particles also forms a line spectrum. However, elementary particles undergoing decay often move at speeds comparable to the speed of light. As a result, Doppler line broadening occurs and the gamma radiation spectrum becomes blurred over a wide energy range. Gamma radiation, produced when fast charged particles pass through matter, is caused by their deceleration to the Coulomb field of the atomic nuclei of the matter. Bremsstrahlung gamma radiation, like bremsstrahlung X-ray radiation, is characterized by a continuous spectrum, the upper limit of which coincides with the energy of a charged particle, for example an electron. In charged particle accelerators, bremsstrahlung gamma radiation with a maximum energy of up to several tens of GeV is produced.

In interstellar space, gamma radiation can arise as a result of collisions of quanta of softer long-wave electromagnetic radiation, such as light, with electrons accelerated by the magnetic fields of space objects. In this case, the fast electron transfers its energy to electromagnetic radiation and visible light turns into harder gamma radiation.

A similar phenomenon can occur under terrestrial conditions when high-energy electrons produced at accelerators collide with photons of visible light in intense beams of light created by lasers. The electron transfers energy to a light photon, which turns into a γ-quantum. Thus, it is possible in practice to convert individual photons of light into high-energy gamma-ray quanta.

Gamma radiation has great penetrating power, i.e. can penetrate large thicknesses of matter without noticeable weakening. The main processes that occur during the interaction of gamma radiation with matter are photoelectric absorption (photoelectric effect), Compton scattering (Compton effect) and the formation of electron-positron pairs. During the photoelectric effect, a γ-quantum is absorbed by one of the electrons of the atom, and the energy of the γ-quantum is converted (minus the binding energy of the electron in the atom) into the kinetic energy of the electron flying out of the atom. The probability of a photoelectric effect is directly proportional to the fifth power of the atomic number of the element and inversely proportional to the 3rd power of gamma radiation energy. Thus, the photoelectric effect predominates in the region of low-energy γ-rays (£100 keV) on heavy elements (Pb, U).

With the Compton effect, a γ-quantum is scattered by one of the electrons weakly bound in the atom. Unlike the photoelectric effect, with the Compton effect the γ quantum does not disappear, but only changes the energy (wavelength) and direction of propagation. As a result of the Compton effect, a narrow beam of gamma rays becomes wider, and the radiation itself becomes softer (long-wavelength). The intensity of Compton scattering is proportional to the number of electrons in 1 cm 3 of a substance, and therefore the probability of this process is proportional to the atomic number of the substance. The Compton effect becomes noticeable in substances with low atomic number and at gamma radiation energies exceeding the binding energy of electrons in atoms. Thus, in the case of Pb, the probability of Compton scattering is comparable to the probability of photoelectric absorption at an energy of ~ 0.5 MeV. In the case of Al, the Compton effect predominates at much lower energies.

If the energy of the γ-quantum exceeds 1.02 MeV, the process of formation of electron-positron pairs in the electric field of nuclei becomes possible. The probability of pair formation is proportional to the square of the atomic number and increases with hν. Therefore, at hν ~10 MeV, the main process in any substance is the formation of pairs.

0,1 0,5 1 2 5 10 50

Energy of γ-rays (MeV)

The reverse process, annihilation of an electron-positron pair, is a source of gamma radiation.

To characterize the attenuation of gamma radiation in a substance, the absorption coefficient is usually used, which shows at what thickness X of the absorber the intensity I 0 of the incident beam of gamma radiation is attenuated in e once:

Here μ 0 is the linear absorption coefficient of gamma radiation. Sometimes a mass absorption coefficient is introduced, equal to the ratio of μ 0 to the density of the absorber.

The exponential law of attenuation of gamma radiation is valid for a narrow direction of the gamma ray beam, when any process, both absorption and scattering, removes gamma radiation from the composition of the primary beam. However, at high energies, the process of gamma radiation passing through matter becomes much more complicated. Secondary electrons and positrons have high energy and therefore can, in turn, create gamma radiation due to the processes of braking and annihilation. Thus, a series of alternating generations of secondary gamma radiation, electrons and positrons arises in the substance, that is, a cascade shower develops. The number of secondary particles in such a shower initially increases with thickness, reaching a maximum. However, then the absorption processes begin to prevail over the processes of particle reproduction and the shower fades. The ability of gamma radiation to develop showers depends on the relationship between its energy and the so-called critical energy, after which a shower in a given substance practically loses the ability to develop.

To change the energy of gamma radiation in experimental physics, gamma spectrometers of various types are used, mostly based on measuring the energy of secondary electrons. The main types of gamma radiation spectrometers: magnetic, scintillation, semiconductor, crystal diffraction.

Studying the spectra of nuclear gamma radiation provides important information about the structure of nuclei. Observation of effects associated with the influence of the external environment on the properties of nuclear gamma radiation is used to study the properties of solids.

Gamma radiation is used in technology, for example, to detect defects in metal parts - gamma flaw detection. In radiation chemistry, gamma radiation is used to initiate chemical transformations, such as polymerization processes. Gamma radiation is used in the food industry to sterilize food. The main sources of gamma radiation are natural and artificial radioactive isotopes, as well as electron accelerators.

The effect of gamma radiation on the body is similar to the effect of other types of ionizing radiation. Gamma radiation can cause radiation damage to the body, including its death. The nature of the influence of gamma radiation depends on the energy of γ-quanta and the spatial characteristics of the irradiation, for example, external or internal. The relative biological effectiveness of gamma radiation is 0.7-0.9. In industrial conditions (chronic exposure in small doses), the relative biological effectiveness of gamma radiation is assumed to be equal to 1. Gamma radiation is used in medicine for the treatment of tumors, for the sterilization of premises, equipment and medications. Gamma radiation is also used to obtain mutations with subsequent selection of economically useful forms. This is how highly productive varieties of microorganisms (for example, to obtain antibiotics) and plants are bred.

Modern possibilities of radiation therapy have expanded primarily due to the means and methods of remote gamma therapy. The successes of remote gamma therapy have been achieved as a result of extensive work in the use of powerful artificial radioactive sources of gamma radiation (cobalt-60, cesium-137), as well as new gamma drugs.

The great importance of remote gamma therapy is also explained by the comparative accessibility and ease of use of gamma devices. The latter, like X-rays, are designed for static and moving irradiation. With the help of mobile irradiation, one strives to create a large dose in the tumor while dispersing irradiation of healthy tissues. Design improvements have been made to gamma devices aimed at reducing penumbra, improving field homogenization, using blind filters and searching for additional protection options.

The use of nuclear radiation in crop production has opened up new, broad opportunities for changing the metabolism of agricultural plants, increasing their productivity, accelerating development and improving quality.

As a result of the first studies by radiobiologists, it was established that ionizing radiation is a powerful factor influencing the growth, development and metabolism of living organisms. Under the influence of gamma irradiation, the well-coordinated metabolism of plants, animals or microorganisms changes, the course of physiological processes accelerates or slows down (depending on the dose), and shifts in growth, development, and crop formation are observed.

It should be especially noted that during gamma irradiation, radioactive substances do not enter the seeds. Irradiated seeds, like the crop grown from them, are non-radioactive. Optimal doses of irradiation only accelerate the normal processes occurring in the plant, and therefore any fears or warnings against using crops obtained from seeds that have been subjected to pre-sowing irradiation are completely unfounded.

Ionizing radiation began to be used to increase the shelf life of agricultural products and to destroy various insect pests. For example, if grain, before loading into an elevator, is passed through a bunker where a powerful radiation source is installed, then the possibility of pests breeding will be eliminated and the grain can be stored for a long time without any losses. The grain itself as a nutritional product does not change at such doses of radiation. Its use as food for four generations of experimental animals did not cause any deviations in growth, ability to reproduce, or other pathological deviations from the norm.

Nuclear reactor.

The reactor's energy source is the fission process of heavy nuclei. Recall that nuclei consist of nucleons, that is, protons and neutrons. In this case, the number of protons Z determines the charge of the nucleus Ze: it is equal to the number of the element from the periodic table, and the atomic weight of the nucleus A is the total number of protons and neutrons. Nuclei that have the same number of protons but different numbers of neutrons are different isotopes of the same element and are indicated by the element's atomic weight symbol at the top left. For example, the following isotopes of uranium exist: 238 U, 235 U, 233 U,...

The mass of the nucleus M is not simply equal to the sum of the masses of its constituent protons and neutrons, but is less than it by the value M, which determines the binding energy

(in accordance with the relation) M=Zm p + (A-Z)m n -(A)A, where (A)c is the binding energy per nucleon. The value (A) depends on the details of the structure of the corresponding nucleus... However, there is a general tendency for it to depend on the atomic weight. Namely, neglecting small details, we can describe this dependence as a smooth curve, increasing for small ones. A, reaching a maximum in the middle of the periodic table and decreasing after the maximum to large values ​​of A. Let us imagine that a heavy nucleus with atomic weight A and mass M is divided into two nuclei A 1 and A 2 with masses M 1 and M 2, respectively, and A 1 + A 2 is equal to A or slightly less than it, since several neutrons can be emitted during the fission process. For clarity, let us take the case A 1 + A 2 = A. Consider the difference between the masses of the initial nucleus and the two final nuclei, and we will assume that A 1 = A 2, so that (A 1) = (A 2), M = M- M 1 -M 2 =-(A)A+ (A 1)(A 1 +A 2) =A((A 1)- (A 1)). If A corresponds to the heavy nucleus at the end of the Periodic Table, then A 1 is in the middle and has a maximum value (A 2). This means M>0 and, therefore, energy E d =Mc 2 is released during the fission process. For heavy nuclei, for example for uranium nuclei, ((A 1) - (A))c 2 = 1 MeV. So at A = 200 we have an estimate of E d = 200 MeV. Let us recall that the electron-volt (eV) is an extra-system unit of energy, equal to the energy acquired by an elementary charge under the influence of a potential difference of 1V (1eV = 1.6*10 -19 J). For example, the average energy released during nuclear fission 235 U

E d = 180 MeV = 180 10 6 eV.

Thus, heavy nuclei are potential sources of energy. However, spontaneous nuclear fission occurs extremely rarely and has practically no significance. If a neutron hits a heavy nucleus, the fission process can accelerate sharply. This phenomenon occurs with different intensities for different nuclei, and is measured by the effective cross section of the process. Let us recall how effective cross sections are determined and how they are related to the probabilities of certain processes. Let's imagine a beam of particles (for example, neutrons) falling on a target consisting of certain objects, say nuclei. Let N 0 be the number of neutrons in the beam, n be the density of nuclei per unit volume (1 cm 3). Let us be interested in events of a certain type, for example, the fission of target nuclei. Then the number of such events N will be determined by the formula N=N 0 nl eff, where l is the length of the target and eff is called the cross section of the fission process (or any other process) with a given energy E, corresponding to the energy of incident neutrons. As can be seen from the previous formula, the effective cross section has the dimension of area (cm 2). It has a completely understandable geometric meaning: it is a platform, upon entering which the process of interest to us occurs. Obviously, if the cross section is large, the process proceeds intensively, and a small cross section corresponds to a low probability of hitting this area, therefore, in this case the process occurs rarely.

So, even if for a certain nucleus we have a sufficiently large effective cross section for the fission process, during fission, along with two large fragments A 1 and A 2, several neutrons can be emitted. The average number of additional neutrons is called the multiplication factor and is symbolized by k. Then the reaction goes according to the scheme

n+A A 1 +A 2 +kn.

The neutrons born in this process, in turn, react with A nuclei, which gives new fission reactions and a new, even larger number of neutrons. If k > 1, such a chain process occurs with increasing intensity and leads to an explosion with the release of a huge amount of energy. But this process can be controlled. Not all neutrons will necessarily fall into nucleus A: they can go out through the outer boundary of the reactor, or they can be absorbed in substances that are specially introduced into the reactor. Thus, the value of k can be reduced to a certain k eff, which is equal to 1 and only slightly exceeds it. Then you can manage to remove the generated energy and the operation of the reactor becomes stable. However, in this case the reactor operates in critical mode. Problems with energy dissipation would lead to an increasing chain reaction and disaster. All operating systems have safety measures in place, but accidents are very unlikely to occur and, unfortunately, do occur.

How is the working substance selected for a nuclear reactor? It is necessary that fuel cells contain isotope nuclei with a large effective fission cross section. The unit of measurement of the section is 1 barn = 10 -24 cm 2. We see two groups of cross-section values: (233 U, 235 U, 239 Pu) and small (232 Th, 238 U). To imagine the difference, let's calculate how far a neutron must travel for a fission event to occur. For this we use the formula N=N 0 nl eff. For N=N 0 =1 we have Here n is the density of nuclei, , where p is the usual density and m =1.66*10 -24 g is the atomic mass unit. For uranium and thorium n = 4.8. 10 22 cm 3. Then for 235 U we have l = 10 cm, and for 232 Th l = 35 m. Thus, for the actual implementation of the fission process, isotopes such as 233 U, 235 U, 239 Pu should be used. The 235 U isotope is contained in small amounts in natural uranium, which consists mainly of 238 U, so uranium enriched with the 235 U isotope is usually used as nuclear fuel. In this case, during the operation of the reactor, a significant amount of another fissile isotope is produced - 239 Pu. Plutonium is produced through a chain of reactions

238 U + n () 239 U () 239 Np () 239 Pu,

where means the emission of a photon, and is the decay according to the scheme

Here Z determines the charge of the nucleus, so that during decay it occurs to the next element of the periodic table with the same A, e-electron and v-electron antineutrino. It should also be noted that the isotopes A 1, A 2 obtained during the fission process, as a rule, are radioactive with half-lives from a year to hundreds of thousands of years, so waste from nuclear power plants, which is burnt fuel, is very dangerous and requires special measures to storage Here the problem of geological storage arises, which must ensure reliability for millions of years to come. Despite the obvious benefits of nuclear energy, based on the operation of nuclear reactors in critical mode, it also has serious disadvantages. This is, firstly, the risk of accidents similar to Chernobyl, and, secondly, the problem of radioactive waste. The proposal to use reactors operating in subcritical mode for nuclear energy completely resolves the first problem and greatly facilitates the solution of the second.

Nuclear reactor in subcritical mode as an energy amplifier.

Let's imagine that we have assembled a nuclear reactor with an effective neutron multiplication factor keff slightly less than unity. Let us irradiate this device with a constant external neutron flux N 0. Then each neutron (minus those emitted and absorbed, which is taken into account in k eff) will cause fission, which will give an additional flux N 0 k 2 eff. Each neutron from this number will again produce on average k eff neutrons, which will give an additional flux N 0 k eff, etc. Thus, the total flux of neutrons producing fission processes turns out to be equal to

N = N 0 (1 + k eff + k 2 eff + k 3 eff + ...) = N 0 k n eff.

If keff > 1, the series in this formula diverges, which is a reflection of the critical behavior of the process in this case. If k eff< 1, ряд благополучно сходится и по формуле суммы геометрической прогрессии имеем

The release of energy per unit time (power) is then determined by the release of energy during the fission process,

where to<1 - коэффициент, равный отношению числа нейтронов, вызвавших деление, к полному их числу. Этот коэффициент зависит от конструкции установки, используемых материалов и т.д. Он надёжно вычисляется. В примерах k=0,6. Осталось выяснить, как можно получить первоначальный поток нейтронов N 0 . Для этого можно использовать ускоритель, дающий достаточно интенсивный поток протонов или других частиц, которые, реагируя с некоторой мишенью, порождают большое кол-во нейтронов. Действительно, например, при столкновении с массивной свинцовой мишенью каждый протон, ускоренный до энергии 1ГэВ (10 9 эВ), производит в результате развития ядерного каскада в среднем n = 22 нейтрона. Энергии их составляют несколько мега электрон -вольт, что как раз соответствует работе реактора на быстрых

neutrons It is convenient to imagine the neutron flux through the accelerator current

where e is the charge of protons, equal to the elementary electric charge. When we express energy in electron-volts, this means that we take the representation E = eV, where V is the potential corresponding to this energy, containing as many volts as electron-volts contain energy. This means that, taking into account the previous formula, we can rewrite the energy release formula in the form

Finally, it is convenient to represent the power of the installation in the form

where V is the potential corresponding to the energy of the accelerator, so that VI, according to the well-known formula, is the power of the accelerator beam: P 0 = VI, and R 0 in the previous formula is the coefficient for k eff = 0.98, which provides a reliable subcriticality margin. All other quantities are known, and for a proton accelerator energy of 1 GeV we have . We got a gain of 120, which is, of course, very good. However, the coefficient of the previous formula corresponds to the ideal case, when there are completely no energy losses both in the accelerator and in the production of electricity. To obtain the real coefficient, you need to multiply the previous formula by the efficiency of the accelerator r y and the efficiency of the thermal power plant r e. Then R=r y r e R 0 . The acceleration efficiency can be quite high, for example, in a real project of a high-current cyclotron with an energy of 1 GeV r y = 0.43. The power generation efficiency can be as low as 0.42. The final real gain is R = r y r e R 0 = 21.8, which is still quite good, because only 4.6% of the energy produced by the installation needs to be returned to maintain the operation of the accelerator. In this case, the reactor operates only when the accelerator is turned on and there is no danger of an uncontrolled chain reaction.

The principle of constructing nuclear energy.

As you know, everything in the world consists of molecules that

are complex complexes of interactions

howling atoms. Molecules are the smallest particles

substances that preserve its properties. The composition of molecules

includes atoms of various chemical elements.

Chemical elements are made up of one type of atom.

Atom, the smallest particle of a chemical element, co-

it consists of a “heavy” core and rotating around electro-

The nuclei of atoms are formed by a combination of positive

charged protons and neutral neutrons.

These particles, called nucleons, are held together

in nuclei by short-range attractive forces,

arising due to meson exchanges,

particles of smaller mass.

The nucleus of element X is denoted as or X-A, for example uranium U-235 -,

where Z is the charge of the nucleus, equal to the number of protons, determining the atomic number of the nucleus, A is the mass number of the nucleus, equal to

the total number of protons and neutrons.

The nuclei of elements with the same number of protons but different numbers of neutrons are called isotopes (for example, uranium

has two isotopes U-235 and U-238); nuclei at N=const, z=var - isobars.

Hydrogen nuclei, protons, as well as neutrons, electrons (beta particles) and single helium nuclei (called alpha particles), can exist autonomously outside nuclear structures. Such nuclei or otherwise elementary particles, moving in space and approaching the nuclei at distances of the order of the transverse dimensions of the nuclei, can interact with the nuclei, as they say, participate in the reaction. In this case, particles can be captured by nuclei, or after a collision they can change the direction of movement and give up part of the kinetic energy to the nucleus. Such acts of interaction are called nuclear reactions. A reaction without penetration of the nucleus is called elastic scattering.

After the particle is captured, the compound nucleus is in an excited state. The nucleus can “free itself” from excitation in several ways - by emitting some other particle and a gamma ray, or by dividing into two unequal parts. According to the final results, reactions are distinguished - capture, inelastic scattering, fission, nuclear transformation with the emission of a proton or alpha particle.

Additional energy released during nuclear transformations often takes the form of gamma ray fluxes.

The probability of a reaction is characterized by the size of the “cross section” of a reaction of a given type.

The fission of heavy nuclei occurs during the capture

neutrons. At the same time, new particles are emitted

and the nuclear binding energy transferred

fission fragments. This is a fundamental phenomenon

was discovered at the end of the 30s by German scientists

by the famous Hahn and Strassman, which laid the foundation

for the practical use of nuclear energy.

The nuclei of heavy elements - uranium, plutonium and some others intensively absorb thermal neutrons. After the act of capturing a neutron, a heavy nucleus with a probability of ~0.8 is divided into two parts of unequal mass, called fragments or fission products. In this case, fast neutrons are emitted (on average about 2.5 neutrons for each fission event), negatively charged beta particles and neutral gamma quanta, and the binding energy of particles in the nucleus is converted into the kinetic energy of fission fragments, neutrons and other particles. This energy is then spent on thermal excitation of the atoms and molecules that make up the substance, i.e. to heat up the surrounding matter.

After the act of nuclear fission, the fragments of nuclei produced during fission, being unstable, undergo a series of successive radioactive transformations and, with some delay, emit “delayed” neutrons, a large number of alpha, beta and gamma particles. On the other hand, some fragments have the ability to intensively absorb neutrons.

A nuclear reactor is a technical installation in which a self-sustaining chain reaction of fission of heavy nuclei is carried out with the release of nuclear energy. A nuclear reactor consists of a core and a reflector located in a protective casing. The core contains nuclear fuel in the form of a fuel composition in a protective coating and a moderator. Fuel cells usually take the form of thin rods. They are collected in bunches and enclosed in covers. Such prefabricated compositions are called assemblies or cassettes.

A coolant moves along the fuel elements, which absorbs the heat of nuclear transformations. The coolant heated in the core moves along the circulation circuit due to the operation of pumps or under the influence of Archimedes forces and, passing through a heat exchanger or steam generator, transfers heat to the coolant of the external circuit.

The transfer of heat and the movement of its carriers can be represented in the form of a simple diagram:

1.Reactor

2. Heat exchanger, steam generator

3. Steam turbine plant

4.Generator

5. Capacitor

The development of industrial society is based on an ever-increasing level of production and consumption

various types of energy.

As is known, the production of thermal and electrical energy is based on the process of burning fossil fuels

energy resources -

• oil

and in nuclear energy - the fission of the nuclei of uranium and plutonium atoms during the absorption of neutrons.

The scale of production and consumption of fossil energy resources, metals, consumption of water, air to produce the amount of energy necessary for humanity is enormous, and, alas, resource reserves are limited. The problem of rapid depletion of organic natural energy resources is especially acute.

1 kg of natural uranium replaces 20 tons of coal.

World energy reserves are estimated at 355 Q, where Q is a unit of thermal energy equal to Q = 2.52 * 1017 kcal = 36 * 109 tons of standard fuel /tce/, i.e. fuel with a calorific value of 7000 kcal/kg, so energy reserves are 12.8 * 1012 t.e.

Of this amount, approximately 1/3 i.e. ~ 4.3*1012 t.e.f. can be extracted using modern technology at a moderate cost of fuel extraction. On the other hand, modern energy needs are 1.1 * 1010 t.e./year, and are growing at a rate of 3-4% per year, i.e. double every 20 years.

It is easy to estimate that organic fossil resources, even taking into account the likely slowdown in energy consumption growth, will be largely used up in the next century.

By the way, we note that when burning fossil coals and oil, which have a sulfur content of about 2.5%, up to 400 million tons are formed annually. sulfur dioxide and nitrogen oxides, i.e. about 70 kg. harmful substances per inhabitant of the earth per year.

The use of the energy of the atomic nucleus and the development of nuclear energy relieves the severity of this problem.

Indeed, the discovery of the fission of heavy nuclei by neutron capture, which made our age atomic, added a significant treasure trove of nuclear fuel to the reserves of energy fossil fuels. Uranium reserves in the earth's crust are estimated at a huge figure of 1014 tons. However, the bulk of this wealth is in a dispersed state - in granites and basalts. In the waters of the world's oceans the amount of uranium reaches 4*109 tons. However, relatively few known rich uranium deposits where mining would be inexpensive. Therefore, the mass of uranium resources that can be extracted with modern technology and at reasonable prices is estimated at 108 tons. The annual demand for uranium is, according to modern estimates, 104 tons of natural uranium. So these reserves make it possible, as Academician A.P. Aleksandrov said, “to remove the sword of Damocles of fuel shortage for an almost unlimited time.”

Another important problem of modern industrial society is ensuring the preservation of nature, clean water, and air.

Scientists are well-known about the “greenhouse effect” arising from carbon dioxide emissions from the combustion of fossil fuels and the corresponding global warming of the climate on our planet. And the problems of air pollution, acid rain, and river poisoning have approached a critical point in many areas.

Nuclear power does not consume oxygen and has negligible emissions during normal operation. If nuclear energy replaces conventional energy, then the possibility of a “greenhouse” with severe environmental consequences of global warming will be eliminated.

An extremely important circumstance is the fact that nuclear energy has proven its economic efficiency in almost all areas of the globe. In addition, even with a large scale of energy production at nuclear power plants, nuclear energy will not create any special transport problems, since it requires negligible transport costs, which frees societies from the burden of constantly transporting huge quantities of fossil fuels.

Nuclear reactors are divided into several groups:

depending on the average energy of the neutron spectrum - into fast, intermediate and thermal;

according to the design features of the core - into vessel and channel;

by type of coolant - water, heavy water, sodium;

by type of moderator - water, graphite, heavy water, etc.

For energy purposes, for the production of electricity, the following are used:

water-water reactors with non-boiling or boiling water under pressure,

uranium-graphite reactors with boiling water or cooled by carbon dioxide,

heavy water channel reactors, etc.

In the future, fast neutron reactors cooled by liquid metals (sodium, etc.) will be widely used; in which we fundamentally implement the fuel reproduction mode, i.e. creating the number of fissile isotopes of plutonium Pu-239 exceeding the number of consumable isotopes of uranium U-235. The parameter characterizing the reproduction of fuel is called the plutonium coefficient. It shows how many acts of Pu-239 atoms are created during reactions of neutron capture in U-238 per one atom of U-235 that captured a neutron and underwent fission or radiation transformation into U-235.

Pressurized water reactors occupy a prominent place in the world's power reactor fleet. They are also widely used in the navy as power sources for both surface vessels and submarines. Such reactors are relatively compact, simple and reliable in operation. Water, which serves as a coolant and neutron moderator in such reactors, is relatively cheap, non-aggressive and has good neutronic properties.

Pressurized water reactors are also called water-water or light-water reactors. They are made in the form of a cylindrical high-pressure vessel with a removable lid. This vessel (reactor body) houses the core, composed of fuel assemblies (fuel cassettes) and moving elements of the control and protection system. Water enters the housing through pipes, is supplied to the space under the core, moves vertically upward along the fuel elements and is discharged through the outlet pipes into the circulation circuit. The heat of nuclear reactions is transferred in steam generators to secondary circuit water of lower pressure. The movement of water along the circuit is ensured by the operation of circulation pumps, or, as in reactors for heat supply stations, due to the driving pressure of natural circulation.

Nuclear fusion tomorrow.

“For tomorrow” it is planned, first of all, to create the next generation of tokamaks in which self-sustaining fusion can be achieved. For this purpose, an Experimental Thermonuclear Reactor (OTR) is being developed at the I.V. Kurchatov Institute of Atomic Energy and the D.V. Efremov Research Institute of Electrophysical Equipment.

In OTR, the goal is to maintain the reaction at such a level that the ratio of the useful energy output to the expended energy (denoted by Q) is greater than or at least equal to one: Q = 1. This condition is a serious stage in testing all elements of the system on the path to creating a commercial reactor with Q=5. According to available estimates, only at this value of Q is the self-sufficiency of a thermonuclear energy source achieved, when the costs of all service processes, including social and household costs, are recouped. In the meantime, the American TFTR has achieved a value of Q=0.2-0.4.

There are other problems as well. For example, the first wall - that is, the shell of the toroidal vacuum chamber - is the most intense, literally long-suffering part of the entire structure. In OTR, its volume is approximately 300 m 3 and its surface area is about 400 m 2. The wall must be strong enough to withstand atmospheric pressure and mechanical forces arising from the magnetic field, and thin enough to transfer heat flows from the plasma to the water circulating on the outside of the toroid without a significant temperature difference. Its optimal thickness is 2 mm. The materials chosen are austenitic steels or nickel and titanium alloys.

Euratom plans to install NET (Next Europeus Tor), which is in many ways similar to OTR; this is the next generation of tokamaks after JET and T-15.

NET was supposed to be built during 1994-1999. The first stage of research is planned to be carried out over 3-4 years.

They are also talking about the next generation after NET - this is a “real” thermonuclear reactor, conventionally called DEMO. However, not everything is clear yet even with NET, since there are plans to build several international installations.

NUCLEAR ENERGY
Nuclear energy

Nuclear energy- this is the energy released as a result of the internal restructuring of atomic nuclei. Nuclear energy can be obtained from nuclear reactions or radioactive decay of nuclei. The main sources of nuclear energy are fission reactions of heavy nuclei and fusion (combination) of light nuclei. The latter process is also called thermonuclear reactions.
The emergence of these two main sources of nuclear energy can be explained by considering the dependence of the specific binding energy of a nucleus on the mass number A (the number of nucleons in the nucleus). The specific binding energy ε shows what average energy must be imparted to an individual nucleon in order for all nucleons to be released from a given nucleus. The specific binding energy is maximum (≈8.7 MeV) for nuclei in the iron region (A = 50 – 60) and decreases sharply when moving to light nuclei consisting of a small number of nucleons, and smoothly when moving to heavy nuclei with
A > 200. Thanks to this dependence of ε on A, the two above-mentioned methods of obtaining nuclear energy arise: 1) by dividing a heavy nucleus into two lighter ones, and
2) due to the combination (synthesis) of two light nuclei and their transformation into one heavier one. In both processes, a transition occurs to nuclei in which the nucleons are more strongly bound, and part of the nuclear binding energy is released.
The first method of producing energy is used in a nuclear reactor and atomic bomb, the second - in the thermonuclear reactor and thermonuclear (hydrogen) bomb under development. Thermonuclear reactions are also a source of energy for stars.
The two methods of energy production discussed are record-breaking in terms of energy per unit mass of fuel. So, with the complete fission of 1 gram of uranium, energy of about 10 11 J is released, i.e. approximately the same as during the explosion of 20 kg of trinitrotoluene (TNT). Thus, nuclear fuel is 10 7 times more efficient than chemical fuel.