home Social networks Classifications of nuclear power plants in the world. Nuclear power plants. History of improvement of types of nuclear reactors

Classifications of nuclear power plants in the world. Nuclear power plants. History of improvement of types of nuclear reactors

2.2. Classification of nuclear power plants

The most important classification for nuclear power plants is their classification by the number of circuits. Distinguish nuclear power plants single circuit, double circuit and three-circuit. In any case, modern nuclear power plants use steam turbines as the engine.

In the nuclear power plant system, there are coolant and working body. The working fluid, that is, the medium that does the work, with the conversion of thermal energy into mechanical energy, is water vapor. The requirements for the purity of the steam entering the turbine are so high that they can be met with economically acceptable indicators only if all the steam is condensed and the condensate is returned to the cycle. Therefore, the working fluid circuit for a nuclear power plant, as for any modern thermal power plant, is always closed and additional water enters it only in small quantities to make up for leaks and some other condensate losses.

The purpose of the coolant at nuclear power plants is to remove the heat released in the reactor. To prevent deposits on fuel elements, a high purity of the coolant is required. Therefore, it also requires a closed circuit, and especially because the reactor coolant is always radioactive. Resonance scattering is quite different. This is not inelastic scattering. There is potential scattering, there is resonant scattering - this interaction is already at the wave level of neutrons. Here we are now considering elastic scattering as a classical process of collision of two balls

If the circuits of the coolant and the working fluid are not separated, the nuclear power plant is called single-loop(Fig. 2.2 a). Steam generation occurs in the reactor, the steam is sent to the turbine, where it produces work, which is converted into electricity in the generator. After all the steam has condensed in the condenser, the condensate

a- single-circuit; b- double-circuit; v- three-circuit;
1 - reactor; 2 - steam turbine; 3 - electric generator; 4 - capacitor; 5 - feed pump; 6 - circulation pump; 7 - volume compensator; 8 - steam generator; 9 - intermediate heat exchanger

is pumped back into the reactor. Such reactors operate with forced circulation of the coolant, for which a main circulation pump is installed.

In a single-circuit scheme, all equipment operates in radiation conditions, which complicates its operation. The great advantage of such schemes is their simplicity and great efficiency. The steam parameters before the turbine and in the reactor differ only by the value of losses in the steam pipelines. The Leningrad, Kursk and Smolensk nuclear power plants operate according to a single-loop scheme.

If the circuits of the coolant and the working fluid are separated, then the nuclear power plant is called double-circuit(Fig. 2.2 b). Accordingly, the coolant circuit is called first, and the contour of the working body - second. In such a scheme, the reactor is cooled by a coolant pumped through it and the steam generator by the main circulation pump. The coolant circuit formed in this way is radioactive; it does not include all the plant equipment, but only a part of it. The primary system includes volume compensator, since the volume of the coolant varies depending on the temperature.

Steam from the steam generator of a double-circuit nuclear power plant enters the turbine, then to the condenser, and the condensate from it is returned to the steam generator by a pump. The second circuit thus formed includes equipment operating in the absence of radiation; this simplifies station operation. Mandatory at double-loop NPP steam generator - device, separating both contours, so it equally belongs to both the first and second. The transfer of heat through the heating surface requires a temperature difference between the heat carrier and the boiling water in the steam generator. For a water coolant, this means maintaining in the first

higher pressure circuit than the steam pressure supplied to the turbine. The desire to avoid boiling of the coolant in the reactor core leads to the need to have a pressure in the primary circuit that is significantly higher than the pressure in the secondary circuit. The Novovoronezh, Kola, Balakovo and Kalinin NPPs operate according to the two-loop scheme.

As a coolant in the NPP scheme shown in Fig. 2.2 b, gases can also be used. Gas coolant is pumped through the reactor and steam generator blower, which plays the same role as the main circulation pump, but unlike the water for the gas coolant, the pressure in the first circuit can be not only higher, but also lower than in the second.

Each of the two types of NPPs described with a water coolant has its own advantages and disadvantages; therefore, NPPs of both types are being developed. They have a number of common features, including operation of turbines on medium-pressure saturated steam. Single-circuit and double-circuit nuclear power plants with a water coolant are the most common, and in the world, preference is mainly given to double-circuit nuclear power plants.

During operation, leaks may occur in certain sections of the steam generator, especially at the junctions of the steam generator tubes with the collector or due to corrosion damage to the tubes themselves. If the pressure in the primary circuit is higher than in the second circuit, then a coolant overflow may occur, leading to radioactive contamination of the second circuit. Within certain limits, such an overflow does not disturb the normal operation of a nuclear power plant, but there are coolants that intensively interact with steam and water. This may create a risk of release of radioactive substances into the serviced premises. Such a coolant is, for example, liquid sodium. Therefore, they create an additional intermediate circuit so that even in emergency situations, contact of radioactive sodium with water or water vapor can be avoided. Such a nuclear power plant is called three-circuit(Fig. 2.2 v).

The radioactive liquid metal coolant is pumped by a pump through the reactor and an intermediate heat exchanger, in which it transfers heat to the non-radioactive liquid metal coolant. The latter is pumped through the steam generator through the system that forms the intermediate circuit. The pressure in the intermediate circuit is maintained higher than in the first. Therefore, leakage of radioactive sodium from the primary to the intermediate circuit is impossible. In this regard, if a leak occurs between the intermediate and secondary circuits, the contact of water or steam will be only with non-radioactive sodium. Second system

circuit for a three-circuit circuit is similar to a two-circuit circuit. Three-circuit nuclear power plants are the most expensive due to the large amount of equipment.

The Shevchenko NPP and the third block of the Beloyarsk NPP operate according to the three-loop scheme.

In addition to the classification of nuclear power plants by the number of circuits, individual types of nuclear power plants can be distinguished depending on:

- type of reactor - on thermal or fast neutrons;

— parameters and type of steam turbines, for example, nuclear power plants with saturated or superheated steam turbines;

— parameters and type of coolant — gas coolant, pressurized water coolant, liquid metal coolant, etc.;

— design features of the reactor, for example, with reactors of channel or vessel type, boiling water with natural or forced circulation, etc.;

— type of reactor moderator, for example, graphite or heavy water moderator, etc.

The most complete characteristic of a nuclear power plant combines all classifications, for example,

Novovoronezhskaya a double-loop nuclear power plant with a vessel-type thermal neutron reactor with a "water under pressure" coolant and saturated steam turbines;

Leningradskaya a single-circuit nuclear power plant with a channel-type thermal neutron reactor with a graphite moderator and saturated steam turbines;

Shevchenkovskaya a three-loop nuclear power plant with a sodium-cooled fast neutron reactor and superheated steam turbines.

Technical problems of non-proliferation of nuclear materials. Economic aspects of the use of nuclear energy. Components of the costs of electricity production at nuclear power plants. Decommissioning of nuclear power plants. Economic consequences of severe accidents. Social aspects of the development of nuclear energy.

Let us denote the probability that thermal neutrons will be absorbed by uranium θ. This value is called the thermal neutron utilization factor. Then the number of thermal neutrons absorbed by uranium will be equal to n εφθ .

For each absorption of a thermal neutron by uranium, η new fast neutrons. Consequently, at the end of the cycle under consideration, the number of fast neutrons produced from fission turned out to be equal to n εφθη .

The neutron multiplication factor in an infinite medium is thus equal to

Equality (3.4) is called the formula of four factors. It reveals the dependence of K∞ on various factors that determine the development of a nuclear chain reaction in a mixture of uranium and a moderator.

In a real propagating medium with finite dimensions, neutron leakage is inevitable, which was not taken into account when introducing the formula for K∞. The neutron multiplication factor for a medium of finite size is called the effective multiplication factor Keff; moreover, it is still defined as the ratio of the number of neutrons of a given generation to the corresponding number of neutrons of the previous generation. If Ps and Pd denote the probabilities of avoiding neutron leakage during moderation and diffusion, respectively, then we can write

Kef \u003d K∞ Rz Rd. (3.5)

It is obvious that the condition for maintaining a chain reaction in a medium of finite dimensions will be the ratio Kef ≥ 1. The product PzRd is always less than unity, therefore, for the implementation of a self-sustaining chain reaction in a system of finite dimensions, it is necessary that K∞ is always greater than unity.

The leakage of neutrons from the reactor depends on its geometric dimensions. Since the birth of neutrons occurs throughout the entire volume of the core, and their leakage is only through the surface of the reactor, then, obviously, with an increase in the linear dimensions of the reactor, the relative fraction of neutrons lost through the surface decreases, and the probability of avoiding leakage increases.

The minimum reactor size at which a self-sustaining chain reaction can take place is called the critical size.

Thus, the reactor criticality condition can be written as

1 = K∞RzRd.

If condition (3.5) is met, the number of neutrons produced during the fission of uranium is equal to the number of neutrons that left the reactor and were absorbed by the materials during the slowing down and diffusion processes. In the case when Kef>1, the number of neutrons in the reactor will continuously increase. In a subcritical reactor, Kef< 1.

The neutron balance equation (for a critical reactor will be written in the form

, (3.6)

D is the neutron diffusion coefficient

F - neutron flux

S is the number of generated thermal neutrons.

The number of thermal neutrons S is determined based on the following. For one thermal neutron absorbed in the materials of the reactor core, the number of thermal neutrons absorbed by uranium will be θ, and for one absorption of a thermal neutron by uranium, η fast neutrons are formed. This means that the number of fast neutrons will be equal to θη. These neutrons can fission at a multiplication factor ε, then the final number of fast neutrons will be equal to θηε. Fast neutrons in the process of slowing down avoid resonant absorption with a probability φ and leakage with a coefficient P3. This means that the number of generated thermal neutrons will be equal to θηεφРз.

Thus, with a total absorption of thermal neutrons per unit volume by the core materials equal to ΣаФ, thermal neutrons ΣаФθηεφРз are formed again. Finally, the number of thermal neutrons is determined as follows:

(3.7)

Taking into account formula (3.7), the neutron balance equation (3.6) is rewritten in the form

(3.8)

(3.9)

In equation (3.9), the quantity that depends on the properties of the materials is called the material parameter and denoted B2

(3.10)

then dependence (3.8) is rewritten as

(3.11)

Both equations (3.10) and (3.11), obtained on the basis of the neutron balance equation for the stationary case, correspond to a critical reactor in which the effective multiplication factor is equal to unity (Kef = 1). Taking into account that it follows from equation (3.10)

where L is the diffusion length.

It follows from equations (3.12) that the probability of avoiding neutron leakage in the diffusion process is determined by the expression (1 + B2L2)-1. The probability of avoiding neutron leakage during the deceleration process is calculated based on the consideration of the deceleration process and turns out to be equal to

where τ is a quantity called the age of neutrons and has the dimension cm2.

In general, when the multiplication factor in the reactor differs from unity, equation (3.12) will be written as follows:

(3.14)

Equation (3.14) is the main equation of the reactor, revealing the dependence of the effective neutron multiplication factor on the composition and dimensions of the core. This equation is valid for homogeneous and heterogeneous reactors. The peculiarity of the core heterogeneity is reflected in the approach to calculating the parameters of the equation of four factors, namely the values ε, φ and θ.

With a stationary process

(3.15)

where М2 = L2 + τ is the value called the migration area, cm2.

The solution of equation (3.11) makes it possible to determine the value of B2. In this case, this parameter is a function of the size and geometric shape of the core. In particular, for a cylindrical reactor

(3.16)

where R is the radius and H is the core height. In this case, the value of B2 is called a geometric parameter.

Since both values of B2 obtained by equations (3.10) and (3.16) correspond to the critical reactor, then for such a state of the reactor the material parameter should be equal to the geometric one. Based on this, depending on the given conditions, equation (3.15) is used to solve two types of problems: to determine the composition of the core, if its dimensions and geometry are given, and to determine the dimensions of the reactor in the case of a given composition of the core.

When solving problems of the first type, the value of the geometric parameter is calculated. For example, for a cylindrical reactor - according to the formula (3.16). In this case, the composition of the core, for example, the enrichment of uranium with the 235U isotope, is determined from equation (3.15) by preliminary estimation of the enrichment and calculation of the Kef value for each case.

When solving problems of the second type, the order of calculation can be adopted as follows. According to the composition of the core, which is characterized by uranium enrichment, moderator type, structural materials, etc., the values of К∞, τ and L2 are calculated. The value of the geometric parameter B2 for a given value of Kef is found by graphical solution of equation (3.15). In this case, several values of B2 are preliminarily set and a graph of Kef = f(B2) is plotted.

Having determined the value Thermal power "href="/text/category/teployenergetika/" rel="bookmark">thermal energy , and L2 characterizes the straight distance traveled by the thermal neutron to the capture point. The greater these distances, the less likely it is that the neutron will avoid leakage in the processes of slowing down and diffusion, i.e., the larger should be the size of the reactor, which ensures a self-sustaining chain reaction.

For example, a reactor where ordinary water is used as a moderator, ceteris paribus, will be much smaller than a reactor with a graphite moderator, since for water L = 2.73 cm and τ = 31 cm2, and for graphite L = 54 cm and τ = 364 cm2.

3.2.1.3. NEUTRON FLUX

The solution of equation (3.11) also leads to a dependence characterizing the distribution of the neutron flux over the volume of the core. For a cylindrical reactor with height H and radius R, this dependence has the form

(3.17)

where Фmax is the value of the neutron flux in the core center;

h, r – current coordinates along the height and radius of the active zone;

The current value of the zero order Bessel function of the first kind.

The maximum value of the thermal neutron flux in a reactor without a reflector is set at the geometric center of the core and gradually decreases to zero as it approaches its extrapolated boundaries. In a cylindrical reactor, the change in the neutron flux with height at r = 0, when Jo(0) = 1, will occur according to the dependence

(3.18)

The non-uniformity coefficient of the neutron flux along the height of the core is determined as follows:

(3.19)

The non-uniformity coefficient of the neutron flux along the radius of the cylindrical reactor will be equal to

(3.20)

The product of the coefficients Kh and Kr is called the coefficient of non-uniformity of the neutron flux over the volume of the core

(3.21)

By known values coefficients of non-uniformity of the neutron flux and for a given value of the average neutron flux, it is possible to determine the value of the maximum neutron flux in the reactor

Фmax = KvФср, (3.22)

where Фср is the average neutron flux in the reactor, related to the volume of the core. The average value of the neutron flux can be determined based on the following. The number of fissions of uranium in 1 cm3 per 1 s is ΣfFsr, and the total number of fissions in the entire volume of the core will be ΣfFsrVaz. If the power of 1 kW corresponds to 3.1∙1013 divisions per second, then the power of the reactor can be expressed by the equation

, (3.23)

(3.24)

Average values of neutron fluxes in power reactors are within 1012 ÷ 1014 .

In an operating reactor, neutrons leak from the core. To reduce this leakage, the reactor is surrounded by a reflector. Neutrons that hit the reflector are partially scattered back into the core, and thus a “saving” of neutrons is achieved.

The "saving" of neutrons obtained due to the installation of a reflector can be used in two directions: either to reduce the size of the core without changing its composition, or, leaving the dimensions unchanged, to reduce the enrichment of the fuel with fissile isotope. In both cases, a decrease in the total load of the fissile uranium isotope is obtained. An equally important role of the reflector for power reactors is to substantially equalize the distribution of the thermal neutron flux in the core volume.

When fast neutrons leak from the reactor, due to their moderation in the reflector material, the neutrons can get back into the reactor already thermal. This leads to an increase in the thermal neutron flux near the core boundary. The reflector material should have the same qualities as the moderator, namely good moderating and scattering properties. Therefore, the same substance is often used for the moderator and reflector.

The effective multiplication factor of a reactor with a reflector is determined by the same formula (3.14) as for a reactor without a reflector. However, in this case, when calculating the geometric parameter B2, the actual dimensions of the core increase by the value of the effective addition. For example, for a cylindrical reactor will have

(3.25)

R" = R + Δ. (3.26)

With this method of calculation, the reactor with a reflector is, as it were, replaced by a "naked" reactor, the dimensions of which exceed the dimensions of the active zone of the actual reactor by the amount of the effective additive.

The non-uniformity coefficients of the neutron flux of the core of a cylindrical reactor in the presence of a reflector are determined by the formulas:

According to the height of the reactor

Along the radius of the reactor

In the presence of a reflector, as follows from (3.27) and (3.28), the non-uniformity coefficients of the neutron flux decrease, therefore, the energy release over the volume of the core will be more uniform.

SELF-CHECK QUESTIONS

1. What elementary particles does an atom and the nucleus of an atom consist of?

2. What is the mass of the proton and neutron?

3. What is an atomic mass unit?

4. What is the mass defect and the binding energy of the nucleus?

5. How does the binding energy of nucleons in a nucleus change with the mass number of the nucleus?

6. What are fast and thermal neutrons? What are they characterized by?

7. Why does uranium-235 fission, but uranium-238 does not fission when a thermal neutron is captured?

8. What is meant by microscopic and macroscopic effective cross section of nuclei?

9. How do the microscopic cross sections for fission and absorption of uranium-235 and uranium-238 nuclei change depending on the neutron energy?

10. What is meant by a neutron flux?

11. How is the number of absorptions and fissions of uranium nuclei determined when they capture neutrons?

12. Express the power of the reactor in terms of the neutron flux.

13. Write the thermal neutron balance equation and explain its components.

14. What is the source of thermal neutrons in a reactor?

15. How is the leakage of neutrons determined during their moderation and diffusion?

16. What is meant by the effective neutron multiplication factor Kef?

17. Explain the quantities included in the equation for Kef.

18. Tell us the procedure for solving the equation for the Kef of the reactor for a given uranium enrichment?

19. What is the procedure for solving the equation for the Kef of the reactor for given geometric parameters of the core?

20. What dependencies characterize the change in the neutron flux along the height and radius of the reactor core?

21. What is the effect of the neutron reflector on the neutron flux in the reactor?

3.2.2. DESIGNS OF POWER REACTORS

AND TECHNOLOGICAL SCHEMES OF NPP

3.2.2.1. REACTOR DEVICE

The creation of a homogeneous reactor is associated with significant technical difficulties, therefore, at present, all operating, under construction and design power reactors are heterogeneous.

The main part of the reactor is the core. The active zone of a nuclear reactor is a set of assembly units that creates the conditions for initiating and maintaining a controlled nuclear fission chain reaction. The dimensions of the core must be such that the chain reaction with the existing uranium enrichment is maintained throughout the entire period of operation of the reactor and at which reliable heat removal is ensured at a given reactor power.

Nuclear fuel (fuel) is placed in the active zone. Uranium and its alloys, as well as plutonium and its alloys are used as fuel. In heterogeneous reactors, fuel is used in the form of rods, plates, etc. (Fig. 3.2), in homogeneous ones - in the form of a solution of uranium salts, etc. A moderator (water, graphite, beryllium, etc.) is also placed in the core of thermal reactors. .), which serves to reduce the energy of fission neutrons.

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Rice. 3.3. Types of fuel elements:

a - rod; b - lamellar; c - spherical; g - tubular; e - cylindrical block; f – fuel array with tubes;

1 - fuel material; 2 - shell; 3 - tip; 4 - edge; 5 - coolant

Koll" href="/text/category/koll/" rel="bookmark">collectors and coolant flow distribution path, installation parts - tails, casing or frame, protective plugs and parts for transport and technological purposes.

Rice. 3.5. Working cassette of the VVER-440 reactor:

1 - shank; 2, 3 – lower and middle spacer grids; 4 - tube-case of the cassette; 5 - TVEL; 6 - upper spacer grid; 7 - central tube; 8 - head; 9 - spring clamps; 10 - pin

The fuel assembly or cassette is installed in the technological channel of the nuclear reactor, in which the supply, removal and organization of a directed flow of coolant surrounding the fuel element are carried out, and the possibility of loading and unloading fuel assemblies or cassettes is provided.

It consists of a shank, a head and a hexagonal tube-case, with 126 fuel elements placed in it, which are arranged along a triangular lattice with a step of 12.2 mm. The fixation of the TVEL in the cassette is carried out by spacer grids: lower (bearing), upper and middle guide grids made of stainless steel. These gratings are mechanically interconnected by a central tube made of zirconium alloy. The lower ends of the fuel elements are rigidly fixed in the lower carrier grid, the upper ends enter the holes of the upper grid without fixing to ensure their free thermal expansion. The cassette head has six spring clips to keep it from floating up and compensate for thermal expansion. The design of the shank provides orientation and fixation of the cassette according to the angle in the plan and its landing in the nest of the basket. The mass of the working cassette is 220 kg, the mass of VO2 in the cassette is 127 kg.

A part of a nuclear reactor, which is a vessel designed to accommodate the active zone and internal devices in it, having nozzles for supplying and removing coolant, as well as sealing devices for the internal reactor space, is called a nuclear reactor vessel. The removable part of a nuclear reactor, designed to cover the body and perceive the internal pressure in the reactor, is called the nuclear reactor cover.

The assembly of the main seal of a nuclear reactor is an assembly unit with a union flange and a seal between the cover and the nuclear reactor vessel, which ensures the tightness of the nuclear reactor in all modes of its operation.

The ring that connects the cover of the nuclear reactor to the body and crushes the internal gaskets is called the pressure ring of the main seal of the nuclear reactor.

6. What are thermal and fast reactors?

7. What are the advantages and disadvantages of nuclear power plants with boiling water reactors?

8. What are the advantages and disadvantages of reactors using liquid metals as a coolant?

9. Draw the basic technological schemes of nuclear power plants: NPP with VVER; NPP with RBMK; ATEC; NPP and BN; AST; ASPT.

10. What is the purpose of the control rods?

11. What is the purpose of complexing rods?

12. Why are fast neutron reactors promising?

13. What gases are used as heat carriers?

14. What is the purpose of the cassette wall?

15. How is fuel located in TVEL?

Principles of classification of power plants. Classes, subclasses, groups, subgroups.

Classification of power plants

PART TWO

POWER PLANTS,
WORKING FOR
FREE ENERGY

Class- is determined by the main process and the type of initial (consumed) energy.

Subclass- determined by characteristic features and accepted (usual) names.

Group- is determined by the type of produced (produced) energy.

Subgroup- determines the type of installation by design differences.

Depending on the specific features and the state of development, the indicated division can not always be exactly observed. There are eight main classes:

1- thermal power plants: in them the main process of energy release is a phase transition of a higher order (HRPT), that is, partial or complete splitting of atoms into elementary particles - electrino and electrons. The initial energy is the potential binding energy of elementary particles in an atom - the energy accumulated in matter.

2- natural power plants, i.e. plants that use energy natural phenomena directly.

3- coriolis power plants - the main process of energy production is associated with self-rotation of the rotor by Coriolis forces. The initial energy of the radial flow of matter can be different: hydraulic, chemical, magnetic, ...

4- electromagnetic power plants - the main process is the conversion of electrino flows into various types of energy: mechanical, thermal, electrical.

5- vibroresonant power plants - the main process is the energy exchange of the working fluid under resonance vibrations. The source is the energy of the external environment, in particular, the molecules of atmospheric air.

6- essential power plants - the main process is the directed condensation of ether, in particular, electrin gas. The initial energy is ether.

7- rechargeable power plants - the main process is the accumulation of energy (electrical, chemical, thermal, ...) and its return when the battery is discharged.

8- combined power plants - plants with several different types of energy release processes, which are difficult to attribute to one of the indicated classes.

This class includes all traditional fossil fuel, nuclear, hydrogen and new natural energy installations.

The traditional ones include: internal and external combustion engines, gas and steam turbine installations, as well as various thermal and boiler installations.

Nuclear power plants include modern nuclear power and heating plants, where the process of energy release goes with the complete decay of radioactive substances.

Hydrogen power plants use hydrogen, which reacts with oxygen to form water.

The listed power plants are well known and there is a lot of technical literature on them, so there is no need to describe them in detail.

It should be emphasized that they use limited natural resources: coal, oil, gas, uranium... that are not replenished by nature as quickly as they are spent. These installations are characterized by a detrimental ecology, detrimental to humanity.

Natural energy installations /1/ are free from these shortcomings, since they use only partial, sparing, decomposition of a substance (air, water) without changing chemical properties due to a small mass defect of the order of 10 -6%, which is replenished in natural conditions.

Thermonuclear power plants, which have been developed for several decades with zero results, were not included in the classification, since, according to modern theory /1,2/, they are inoperable.

Basically, at present, the division of power plants into IES, CHPP, CCGT, GTPP, NPP, HPP is used. For a more complete description of the power plant can be classified according to a number of main features:

By type of primary energy resources;

On energy conversion processes;

By the number and type of energy carriers;

By types of supplied energy;

By the circle of covered consumers;

By mode of operation.

1. According to the types of primary energy resources used, power plants that use: organic fuel (TPP); nuclear fuel (NPP); hydropower (HPP, PSP and PES); solar energy (SES); wind energy (WPP); underground heat (geothermal GEOPP).

2. According to the applied energy conversion processes, power plants are distinguished in which: the received thermal energy is converted into mechanical and then into electrical energy (TPP, NPP); the received thermal energy is directly converted into electrical energy (power plants with MHD generators, MHD-ES, SES with photocells, etc.); the energy of water and air is converted into mechanical energy of rotation, then into electrical energy (hydroelectric power plants, pumped storage power plants, wind power plants, wind power plants, air-storage gas turbine power plants).

3. According to the number and type of energy carriers used, power plants are distinguished: with one energy carrier (CPP and CHP, nuclear CPP and CHP on steam, nuclear power plants with a gas energy carrier, GTPP); with two energy carriers different in phase state (combined-cycle power plants, including PG-CPP and PG-CHP); with two different energy carriers of the same phase state (binary power plants).

4. According to the types of energy supplied, power plants are distinguished: those that supply only or mainly electric energy (hydroelectric power plants, pumped storage power plants, IES, nuclear IESs, GTPPs, PG-IESs, etc.); producing electrical and thermal energy (CHP, nuclear CHP, GT-CHP, etc.). Recently, IES and nuclear IES have increasingly increased the supply of thermal energy. Combined heat and power plants (CHP), in addition to electricity, generate heat; The use of exhaust steam heat in combined power generation provides significant fuel savings. If the exhaust steam or hot water is used for technological processes, heating and ventilation of industrial enterprises, then CHPPs are called industrial. When heat is used for heating and hot water supply of residential and public buildings in cities, thermal power plants are called communal (heating). Industrial heating CHP plants supply heat as industrial enterprises as well as the population. At heating CHPPs, along with heating turbine plants, there are hot-water boilers for heat supply during periods of heat load peaks.

5. According to the range of covered consumers, the following are distinguished: district power plants (GRES - state district power plant); local power plants for power supply of individual settlements; block stations for power supply of individual consumers.

6. According to the mode of operation in the EPS, power plants are distinguished: basic; maneuverable or semi-peak; peak.

The first group includes large, most economical CPPs, nuclear CPPs, thermal power plants in the heating mode and partly HPPs, the second group includes flexible condensing power plants, SG-CPPs and CHPPs, the third group includes peak HPPs, HDPPs, GTPPs. Partially in peak mode, CHPPs and less economical IESs operate.

In addition to the general main features of the classification of power plants listed above, each type has its own internal classification features. For example, IES and CHPP differ in initial parameters, technological scheme (block and cross-linked), unit capacity of blocks, etc. Nuclear power plants are classified according to the type of reactors (on thermal and fast neutrons), according to the design of the reactors, etc.

Along with the main types of power plants discussed above, combined cycle and purely gas turbine power plants are also being developed in Russia. Combined-cycle power plants (CCPPs) are used in two versions: with a high-pressure steam generator and with discharge of exhaust gases into conventional boilers. In the first option, the combustion products from the combustion chamber under pressure are sent to a high-pressure compact steam generator, where high-pressure steam is generated, and the combustion products are cooled to 750-800ºС, after which they are sent to the gas turbine, and the high-pressure steam is fed into steam turbine.

In the second option, the combustion products from the combustion chamber with the addition of the required amount of air to reduce the temperature to 750-800ºС are sent to the gas turbine, and from there, the exhaust gases at a temperature of approximately 350-400ºС with a high oxygen content enter the conventional boiler units of steam turbine thermal power plants, where they act as an oxidizer and give their warmth.

And in the first scheme, natural gas or special gas turbine liquid fuel should be burned, in the second scheme, such fuel should be burned only in the combustion chamber of a gas turbine, and in boiler units - fuel oil or solid fuel, which is a certain advantage. Combining the two cycles will increase the overall efficiency of the CCPP by about 5-6% compared to the steam turbine CPP. The power of the gas turbines of the CCPP is approximately 20-25% of the power of the combined cycle unit. Due to the fact that the specific investment in the gas turbine part is lower than in the steam turbine part, a reduction in specific investment by 10-12% is achieved in the SGPP. CCGT units have greater maneuverability than conventional condensing units and can be used for operation in the semi-peak zone, as they are more economical than maneuverable CPPs.

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Introduction

2. Nuclear reactor. Types of nuclear reactors

Conclusion

Introduction

In the second half of the 40s. Soviet scientists began to develop the first projects for peaceful use atomic energy, the general direction of which immediately became the electric power industry.

The world's first industrial nuclear power plant with a capacity of 5 MW was launched on June 27, 1954 in the USSR, in the city of Obninsk, located in the Kaluga region.

Modern civilization is unthinkable without electrical energy. The generation and use of electricity is increasing every year. The energy released in nuclear reactions is millions of times higher than that given by ordinary chemical reactions(for example, a combustion reaction), so that the calorific value of nuclear fuel is immeasurably greater than that of conventional fuel. The main principle of operation of a nuclear power plant is the use of nuclear fuel to generate electricity.

This project is dedicated to the topic Nuclear power plants". The relevance of this topic is due to the increasing interest of modern science in nuclear energy due to the increase in human energy needs. The aim of the work is to study the principles of operation of nuclear power plants, equipment used at nuclear power plants, the mechanisms of nuclear reactions, as well as methods for ensuring the safety of nuclear installations. The paper presents: the most important classification of nuclear installations, the structure and principle of operation of a nuclear reactor, the thermodynamic cycles of a steam turbine installation and methods for increasing its efficiency, as well as examples of nuclear reactions and thermonuclear fusion reactions.

1. Classification of nuclear power plants

nuclear power plant nuclear power

Nuclear power plants are subdivided according to the following parameters:

1. The number of circuits.

2. Type of reactors. Reactors are divided into thermal and fast reactors.

3. Type of turbines: saturated or superheated steam.

4. Type of heat carrier - gas, water, liquid metal.

5. Design features reactor, for example channel-type reactors or vessel-type reactors.

6. Moderator type: graphite or heavy water.

The most important classification of nuclear power plants is the classification according to the number of circuits. The number of circuits is chosen taking into account the requirements for ensuring the safe operation of the unit in all possible emergency situations. An increase in the number of circuits is associated with the appearance of additional losses in the cycle and, accordingly, a decrease in the NPP efficiency.

The work of nuclear power plants is based on the conversion of energy obtained during a nuclear reaction into electrical energy. This transformation takes place in several stages.

In the system of any nuclear power plant, a coolant and a working fluid are distinguished. As is known, at operating stations, the process of converting source energy into thermal energy occurs continuously, and in the event of a heat removal termination, the installation will inevitably overheat. Therefore, along with the source, a consumer of thermal energy is needed, which will take heat and either convert it into other forms of energy or transfer it to other systems. The transfer of heat from the source to the consumer is carried out using a coolant, i.e. the purpose of the coolant is to remove the heat that is released in the reactor. Water has become widespread in power reactors, which, due to its high heat capacity, does not require large expenditures, but requires increased pressure. A medium that converts thermal energy into mechanical energy, i.e. does work, is a working body. The working fluid in nuclear power plants is water vapor. The requirements for the purity of the working fluid entering the turbine and the coolant, which is always radioactive, are very high, so they require closed circuits. If the circuits of the coolant and the working fluid are not separated, the nuclear power plant is called single-circuit. Steam generation occurs in the reactor, the steam is sent to the turbine, where it produces work, which is converted into electricity in the generator. After all the steam has condensed in the condenser, the condensate is pumped back into the reactor by a pump. Such reactors operate with forced circulation of the coolant, for which a main circulation pump is installed. Thus, the coolant circuit is also the working fluid circuit. In single-circuit schemes, all equipment operates in radiation-active conditions, which complicates its repair.

Rice. 1 NPP thermal scheme: a - single-loop; b - double-circuit; in - three-circuit; 1 - reactor; 2 - turbine; 3- turbogenerator; 4- condensing unit; 5- condensate pump; b - system of regenerative heating of feed water; 7 - feed pump; 8 - steam generator; 9 - circulation pump of the reactor circuit; 10 - intermediate circuit circulation pump

If the circuits of the coolant and the working fluid are separated, then the nuclear power plant is called a double-circuit one. Accordingly, the coolant circuit is called the first, and the working fluid circuit is called the second. At a double-circuit station, a steam generator is required, which separates the first and second circuits. In such schemes, only the reactor circuit is radioactive, in which the coolant is pumped through the steam generator, in which it gives off heat to the working fluid of the secondary circuit without coming into contact with it, and is fed back to the reactor by a circulation pump. The second circuit includes equipment that operates in the absence of radiation activity - this simplifies the repair of equipment. The steam from the steam generator goes to the turbine, then to the condenser and is returned to the steam generator by a pump. Heat transfer in a steam generator requires a temperature difference between the heat carrier and the working fluid. For a water coolant, this means that the pressure in the first circuit must be higher than in the second.

If a nuclear power plant does not use water as a coolant, but, for example, such a coolant as liquid sodium, then for the normal operation of the plant it is necessary to create an additional, intermediate circuit. During operation, leaks may occur in certain sections of the steam generator due to the pressure difference between the primary and secondary circuits. Thus, a coolant leakage may occur, leading to radioactive contamination of the secondary circuit. Since liquid sodium interacts intensively with steam and water, there is a danger of radioactive substances being released into the serviced premises. Therefore, an additional, intermediate circuit is created so that even in emergency situations, contact of radioactive sodium with water or water vapor can be avoided. Such a nuclear power plant is called a three-loop.

2. Nuclear reactor and its types

The heart of every nuclear power plant is a nuclear reactor, a device in which a controlled nuclear chain reaction takes place. Uranium isotopes - U235 and U238, as well as Pu239 can currently be used as nuclear fuel. Nuclear fission occurs under the action of neutrons with a certain energy (the value of this energy must lie in a certain range: a slower or faster particle will simply bounce off the nucleus without penetrating into it). There are two types of neutrons: fast and slow. Neutrons of different types affect the nuclei of fissile elements in different ways.

In nuclear reactors on thermal neutrons, the uranium isotope U235 is used as nuclear fuel, the fission of which occurs only if the neutrons are slowed down by 3-4 times compared to fast ones. Therefore, to control a chain reaction in reactors, materials are used in which neutrons lose some of their energy. Such materials that reduce the speed of neutrons are called nuclear moderators. Good neutron moderators are graphite, ordinary and heavy water, beryllium compounds.

A nuclear reactor consists of an active zone and a reflector. The core contains the moderator and nuclear fuel, which is in fuel elements called fuel rods. Coolant flows through the reactor core. Typically, this is ordinary water, but liquid graphite and heavy water can also be used. The reactor is started when neutron absorbing rods are removed from its core.

Rice. 2 Schematic arrangement of a thermal neutron reactor: 1 - control rod; 2 - radiation protection; 3 - thermal insulation; 4 -- moderator; 5 - nuclear fuel; 6 -- coolant

At present, there are two types of nuclear reactors VVER (pressure water power reactor) and RBMK (high power channel reactor). The difference is that RBMK is a boiling water reactor, while VVER uses water under pressure of 120 atmospheres.

TVEL is a fuel element. These are rods in a zirconium shell, inside of which there are tablets of uranium dioxide.

Fast neutron reactors use uranium isotope U238 and plutonium Pu239 as nuclear fuel. Such reactors are very different from all other types of reactors. Its main purpose is to provide expanded breeding of fissile plutonium from U238 with the aim of burning all or a significant part of natural uranium, as well as existing depleted uranium reserves. With the development of energy in fast neutron reactors, the problem of self-sufficiency of nuclear energy with fuel can be solved.

First of all, there is no moderator in a fast neutron reactor. In this regard, not U235 is used as fuel, but Pu239 and U238, which can be fissile from fast neutrons. Plutonium is needed to provide sufficient neutron flux density that U238 alone cannot provide. The heat release of a fast neutron reactor is ten to fifteen times greater than the heat release of slow neutron reactors, and therefore, instead of water (which simply cannot cope with such an amount of energy for transfer), sodium melt is used (its inlet temperature is 370 degrees, and at the outlet - 550). Therefore, for the normal operation of a nuclear power plant with a fast neutron reactor, a third circuit is required. During the operation of such a reactor, a very intense release of neutrons occurs, which are absorbed by the layer of U238 located around the core. In this case, uranium is converted into Pu239, which, in turn, can be used in the reactor as a fissile element.

At present, fast neutron reactors are not widely used, mainly due to the complexity of the design and the problem of obtaining sufficiently stable materials for structural parts. It is believed that such reactors will become widespread in the future.

3. Operation of the main technological equipment of the NPP

The main technological equipment of the NPP is shown in Fig.1.

By circulating through the reactor core and washing the fuel rods, the coolant receives heat. This circulation is carried out by the main circulation pump. The single-phase nature of the coolant makes it necessary to include a volume (pressure) compensator in the NPP equipment, the task of which in a single-loop NPP is performed by a separator drum. A mandatory unit of a double-circuit and three-circuit nuclear power plant is a steam generator. Passing inside the heat exchange tubes of the steam generator, the primary circuit coolant gives off heat to the secondary circuit water, which turns into steam. The steam is sent to a steam turbine, a device designed to convert thermal energy into mechanical energy. The principle of operation of any turbine is similar to the principle of operation of a windmill. The steam in the turbine rotates the blades arranged in a circle on the rotor. The turbine rotor is rigidly connected to the generator rotor, which generates electricity. The parameters of the turbine and its design scheme are different - for a water coolant it is a medium-pressure saturated steam turbine, for a liquid metal one - a high-pressure superheated steam turbine. In a turbine, steam expands adiabatically and does work. From there, the exhaust steam is sent to the condenser. The condenser plays a dual role in the installation: firstly, it has a steam and water space separated by a surface through which heat exchange takes place between the exhaust steam and the cooling water. Therefore, steam condensate can be used as an ideal water that does not contain dissolved salts. Secondly, in the condenser, due to a sharp decrease in the specific volume of steam during its transformation into a droplet-liquid state, a vacuum sets in, which, being maintained throughout the entire operation of the installation, allows the steam to expand in the turbine by one more atmosphere and perform additional work due to this.

The resulting condensate is continuously sucked in by the pump from the condenser, compressed and redirected to the steam generating apparatus - reactor or steam generator.

Thus, the technological process of generating electricity at nuclear power plants includes: increasing the temperature of the condensate to saturation temperature and obtaining steam from it, expanding the steam in the turbine with a decrease in pressure and temperature from the initial value in front of the turbine to a value corresponding to the vacuum in the condenser. Thus, a reactor plant can be represented as a heat engine in which a certain thermodynamic cycle is carried out. The theoretical cycle of a modern steam power plant is the Rankine cycle.

The line K on the diagrams is a separating one: with the appropriate parameters, for all points lying on the diagram above this line, there is only steam, below - a steam-water mixture.

Wet steam in the condenser is completely condensed along the p2=const isobar (line 2 - 3). The water is then compressed by the pump from pressure P2 to pressure P1, this adiabatic process is depicted in the T-S diagram by the vertical line 3-4.

The small value of the adiabatic segment 3-4 indicates a small work expended by the pump on compressing water. The small amount of compression work compared to the amount of work produced by water vapor in the expansion process 1-2 is an important advantage of the Rankine cycle.

From the pump, water under pressure P2 enters the steam generator, where heat is supplied to it in isobaric (process 4-5 P1=const). First, the water in the steam generator is heated to boiling (section 4-5 of the isobar P1=const) and then, upon reaching the boiling point, the process of vaporization takes place (section 5-6 of the isobar P1=const). In section 6-1, the steam overheats in the steam generator, after which the steam enters the turbine. The expansion process in the turbine is depicted by the adiabatic 1-2. The exhausted wet steam enters the condenser, and the cycle is closed.

The efficiency of converting heat into work in a reversible cycle is characterized by thermal efficiency, determined by the formula:

where lts is the work of the cycle, q1 is the supplied heat.

In this cycle, the cycle work lc is the difference between the work - received in the turbine lt and expended in the pump lн.

Therefore, the expression for the thermal efficiency of the cycle will take the form:

Lt - ln / q1

All processes that make up the cycle of a steam turbine plant occur in the flow of matter. Therefore, when analyzing them, one should apply the equation of the first law of thermodynamics for the flow:

q1 = i2 - i1 + w22 / 2 - w12/2 + ltex

We consider the work of the turbine and pump as technical work ltech. In this case, the work of the process of adiabatic expansion of steam in the turbine, provided that its kinetic energy at the inlet and outlet of the turbine is equal to:

Under the same condition, the absolute value of the work of the adiabatic process of water compression in the pump will be:

Then the thermal efficiency of the Rankine cycle can be represented as:

? =[(i2 - i1) - (i3 - i2)]/(i1 - i3)

Specific work of the pump according to absolute value is usually less than 3-4% of the turbine work, so sometimes this work is neglected in the calculations.

ii are the enthalpies of water and steam at the corresponding points in the cycle, they can be found or using the appropriate tables.

The possibility of increasing the thermal efficiency of the Rankine cycle by increasing the initial steam pressure is limited by the requirement not to exceed the limit value of steam moisture at the end of the expansion in the turbine due to the safety of its operation. This can be avoided by changing the configuration of the cycle by introducing a secondary superheat of the steam at some intermediate pressure. For this, a two-stage turbine is used, consisting of a high-pressure cylinder and several low-pressure cylinders. The so-called superheating of the steam takes place in a special element of the installation - the superheater, where the steam is heated to a temperature exceeding the saturation temperature at a given pressure P1. In this case, the average heat input temperature increases compared to the heat input temperature in the cycle without superheating and, therefore, the thermal efficiency of the cycle increases. The Rankine cycle with steam superheating is the main cycle of thermal power plants used in modern thermal power engineering.

Rice. 3 Rankine cycle with reheating of steam in T-S diagram

Steam from the steam generator is sent to the high pressure cylinder (HPC), part of the steam is taken for overheating. As it expands in the high-pressure cylinder (the process in diagram 1-a), the steam does work. After the HPC, the steam is sent to the superheater, where, due to the cooling of the part of the steam selected at the beginning, it is dried and heated to a higher temperature (but already at a lower pressure, process a-b in the diagram) and enters the low-pressure cylinders of the turbine (LPC) . In the low pressure cylinder, the steam expands, again does work (process b-2 in the diagram) and enters the condenser. The remaining processes correspond to the processes in the Rankine cycle considered above. The efficiency of a cycle with reheating of steam is determined by the formula:

? \u003d (lHVD + lHND - lH) / q1 \u003d ((i1 - ia) + (ib - i2) - (i3 - i2)) / ((i1 - i3) + (ib - ia)

Depending on the choice of pressure at which the steam is reheated, the efficiency of the cycle with reheat can be greater or less than the efficiency of the cycle without reheat. Indeed, a cycle with secondary superheating of steam can be represented as a combination of two cycles - the initial cycle 1-с-2ґ-3-1 and additional a-b-2-c-a. Since both cycles have the same heat removal temperature T2, the total cycle will have a higher thermal efficiency than the initial one, provided that the average heat supply temperature Tav in the additional cycle is higher than in the original one. In turn, the average temperature of heat supply in the additional cycle depends on the temperature of the beginning of secondary overheating, which is determined by the pressure at which this overheating occurs. With a decrease in pressure and, accordingly, temperature, the average temperature of heat supply in the additional cycle decreases, but the work obtained in this cycle and its contribution to the total work of the complex cycle increase. Due to the opposite influence of these two factors, there is an optimal value for the temperature at which the secondary superheating of steam begins, at which the maximum increase in the thermal efficiency of the cycle with intermediate steam superheating is ensured. The use of secondary steam superheating makes it possible to increase the efficiency of a steam turbine plant by 4–5%.

Regenerative feed water heating

In heat engineering, the word "regeneration" means the return of part of the waste heat for its further use in the installation. Regenerative heating of feed water is the heating of condensate coming from the condenser to the reactor (in the case of a single-circuit NPP) or to the steam generator (in the case of a double-circuit NPP). The low efficiency of the Rankine cycle compared to the Carnot cycle is due to the fact that a large number of The heat energy from the condensation of steam is transferred to the cooling water in the condenser.

To reduce losses, part of the steam is extracted from the turbine and sent to regeneration heaters, where the thermal energy released during the condensation of the extracted steam is used to heat the water obtained after the main steam stream condenses. In real steam power cycles, regeneration is carried out using regenerative, surface or mixing heat exchangers, each of which receives steam from the intermediate stages of the turbine (the so-called regenerative extraction).

4. Nuclear reactions. Thermonuclear fusion

The atom is the building block of the universe. There are only about a hundred atoms of various types. Most elements are stable (for example, oxygen and nitrogen of the atmosphere; carbon, oxygen and hydrogen are the main components of our body and all other living organisms). Other elements, mostly very heavy ones, are unstable, which means that they spontaneously decay, giving rise to other elements. This transformation is called a nuclear reaction.

Nuclear reactions - transformations of atomic nuclei in interaction with elementary particles, g-quanta or with each other.

Nuclear reactions are divided into two types: nuclear fission and thermonuclear fusion.

A nuclear fission reaction is the process of splitting an atomic nucleus into two (rarely three) nuclei with similar masses, called fission fragments. As a result of fission, other reaction products can also appear: light nuclei (mainly alpha particles), neutrons and gamma quanta. Division is spontaneous (spontaneous) and forced.

Spontaneous (spontaneous) is nuclear fission, during which some fairly heavy nuclei break up into two fragments with approximately equal masses.

Spontaneous fission was first discovered for natural uranium. Like any other type of radioactive decay, spontaneous fission is characterized by a half-life (fission period). The half-life for spontaneous fission varies for different nuclei over a very wide range (from 1018 years for 93Np237 to several tenths of a second for transuranium elements).

Forced nuclear fission can be caused by any particles: photons, neutrons, protons, deuterons, b-particles, etc., if the energy they bring into the nucleus is sufficient to overcome the fission barrier. For nuclear energy, fission caused by neutrons is of greater importance. The fission reaction of heavy nuclei was carried out for the first time on uranium U235. In order for the uranium nucleus to disintegrate into two fragments, an activation energy is imparted to it. The uranium nucleus receives this energy by capturing a neutron. The nucleus enters an excited state, deforms, a "bridge" appears between the parts of the nucleus, and under the influence of the Coulomb repulsive forces, the nucleus is divided into two fragments of unequal mass. Both fragments are radioactive and emit 2 or 3 secondary neutrons.

Rice. 4 Uranium nuclear fission

Secondary neutrons are absorbed by neighboring uranium nuclei, which causes them to fission. Under appropriate conditions, a self-developing process of massive nuclear fission, called a nuclear chain reaction, can occur. This reaction is accompanied by the release of enormous energy. For example, complete combustion of 1 g of uranium releases 8.28 1010 J of energy. A nuclear reaction is characterized by a thermal effect, which is the difference between the rest masses of the nuclei entering into a nuclear reaction and the nuclei formed as a result of the reaction, i.e. the energy effect of a nuclear reaction is determined mainly by the difference in the masses of the final and initial nuclei. Based on the equivalence of energy and mass, it is possible to calculate the energy released or expended in the course of a nuclear reaction, if you know exactly the mass of all the nuclei and particles participating in the reaction. According to Einstein's law:

E = (mA + mx - mB - my)c2

where mА and mх are the masses of the target nucleus and the bombarding nucleus (particle) respectively;

mB and my are the masses and of the nuclei formed as a result of the reaction.

The more energy released during the formation of the nucleus, the stronger it is. The binding energy of the nucleus is the amount of energy required to decompose the nucleus of an atom into its component parts - nucleons (protons and neutrons).

An example of an uncontrolled fission chain reaction is the explosion of an atomic bomb; a controlled nuclear reaction is carried out in nuclear reactors.

Thermonuclear fusion is the reverse reaction of atomic fission, the fusion of light atomic nuclei into heavier nuclei, occurring at superhigh temperatures and accompanied by the release of huge amounts of energy. The implementation of controlled thermonuclear fusion will give mankind a new environmentally friendly and practically inexhaustible source of energy, which is based on the collision of nuclei of hydrogen isotopes, and hydrogen is the most common substance in the universe.

The fusion process proceeds with noticeable intensity only between light nuclei with a small positive charge and only at high temperatures, when the kinetic energy of the colliding nuclei is sufficient to overcome the Coulomb potential barrier. Reactions between heavy isotopes of hydrogen (deuterium 2H and tritium 3H) proceed at an incomparably greater rate with the formation of strongly bound helium nuclei.

2D + 3T > 4He (3.5 MeV) + 1n (14.1 MeV)

These reactions are of the greatest interest for the problem of controlled thermonuclear fusion. Deuterium is found in sea water. Its reserves are publicly available and very large: deuterium accounts for about 0.016% of the total number of hydrogen atoms that make up water, while the world's oceans cover 71% of the Earth's surface area. The reaction involving tritium is more attractive, because it is accompanied by a large release of energy and proceeds at a significant rate. Tritium is radioactive (half-life 12.5 years) and does not occur naturally. Therefore, to ensure the operation of the proposed thermonuclear reactor using tritium as a nuclear fuel, the possibility of breeding tritium must be provided.

The reaction with the so-called lunar isotope 3He has a number of advantages over the most achievable deuterium-tritium reaction under terrestrial conditions.

2D + 3He > 4He (3.7 MeV) + 1p (14.7 MeV)

Advantages:

1. 3He is not radioactive.

2. Dozens of times lower neutron flux from the reaction zone, which dramatically reduces the induced radioactivity and degradation of the reactor structural materials;

3. The resulting protons, unlike neutrons, are easily captured and can be used to generate additional electricity.

The natural isotopic abundance of 3He in the atmosphere is 0.000137%. Most of the 3He on Earth has been preserved since its formation. It is dissolved in the mantle and gradually enters the atmosphere. On Earth, it is mined in very small quantities, estimated at several tens of grams per year.

Helium-3 is a by-product of reactions taking place on the Sun. As a result, on the Moon, which has no atmosphere, this valuable substance is up to 10 million tons (according to minimum estimates- 500 thousand tons). In thermonuclear fusion, when 1 ton of helium-3 reacts with 0.67 tons of deuterium, energy is released that is equivalent to the combustion of 15 million tons of oil (however, the technical feasibility of this reaction has not been studied at the moment). Consequently, the lunar resource of helium-3 should be enough for the population of our planet for at least the next millennium. The main problem remains the reality of extracting helium from lunar soil. The content of helium-3 in regolith is ~1 g per 100 tons. Therefore, to extract a ton of this isotope, at least 100 million tons of soil should be processed. The temperature at which the thermonuclear fusion reaction is possible reaches a value of the order of 108 - 109 K. At this temperature, the substance is in a completely ionized state, which is called plasma. Thus, the construction of the reactor involves: obtaining plasma heated to temperatures of hundreds of millions of degrees; preservation of the plasma configuration over time, for the occurrence of nuclear reactions.

Thermonuclear energy has important advantages over nuclear power plants: it uses absolutely non-radioactive deuterium and the helium-3 isotope and radioactive tritium, but in volumes thousands of times smaller than in nuclear energy. And in possible emergency situations, the radioactive background near the thermonuclear power plant will not exceed natural indicators. At the same time, per unit weight of thermonuclear fuel, approximately 10 million times more energy is obtained than from the combustion of organic fuel, and approximately 100 times more than from the fission of uranium nuclei. Under natural conditions, thermonuclear reactions take place in the interiors of stars, in particular in the inner regions of the Sun, and serve as that constant source of energy that determines their radiation. The combustion of hydrogen in stars proceeds at a low rate, but the gigantic size and density of stars ensure the continuous emission of huge energy flows for billions of years.

All the chemical elements of our planet and the universe as a whole were formed as a result of thermonuclear reactions that occur in the cores of stars. Thermonuclear reactions in stars lead to a gradual change in the chemical composition of stellar matter, which causes the restructuring of the star and its advance along the evolutionary path. The first stage of evolution ends with the depletion of hydrogen in the central regions of the star. Then, after an increase in temperature caused by compression of the central layers of the star, devoid of energy sources, thermonuclear reactions of helium combustion become effective, which are replaced by the combustion of C, O, Si and subsequent elements - up to Fe and Ni. Certain thermonuclear reactions correspond to each stage of stellar evolution. Hydrogen thermonuclear reactions are the first in the chain of such nuclear reactions. They flow in two ways depending on the initial temperature at the center of the star. The first way is the hydrogen cycle, the second way is the CNO cycle.

Hydrogen cycle:

1H + 1H = 2D + e+ + v +1.44 MeV

2D + 1H = 3He + g +5.49 MeV

I: 3He + 3He = 4He + 21H + 12.86 MeV

or 3He + 4He = 7Be + g + 1.59 MeV

7Be + e- = 7Li + v + 0.862 MeV or 7Be + 1H = 8B + g + 0.137 MeV

II: 7Li + 1H = 2 4He + 17.348 MeV 8B = 8Be* + e+ + v + 15.08 MeV

III. 8Be* = 2 4He + 2.99 MeV

The hydrogen cycle begins with a collision reaction of two protons (1H, or p) to form a deuterium nucleus (2D). Deuterium reacts with a proton, forming a light (lunar) isotope of helium 3He with the emission of a gamma photon (g). The lunar isotope 3He can react in two different ways: two 3He nuclei collide to form 4He with the splitting off of two protons, or 3He combines with 4He and gives 7Be. The latter, in turn, captures either an electron (e-) or a proton and another branching of the proton occurs - the proton chain of reactions. As a result, the hydrogen cycle can end in three different ways I, II and III. For the implementation of branch I, the first two reactions of V. c. must occur twice, since in this case two 3He nuclei disappear at once. Particularly energetic neutrinos are emitted in branch III during the decay of the 8B boron nucleus with the formation of an unstable excited beryllium nucleus (8Be*), which almost instantly decays into two 4He nuclei. CNO-cycle is a set of three linked to each other or, more precisely, partially overlapping cycles: CN, NO I, NO II. The synthesis of helium from hydrogen in the reactions of this cycle proceeds with the participation of catalysts, the role of which is played by small impurities of C, N, and O isotopes in the stellar matter.

The main reaction route of the CN cycle:

12C + p = 13N + g +1.95 MeV

13N = 13C + e+ + n +1.37 MeV

13C + p = 14N + g +7.54 MeV (2.7 106 years)

14N + p = 15O + g +7.29 MeV (3.2 108 years)

15O = 15N + e+ + n +2.76 MeV (82 seconds)

15N + p = 12C + 4He +4.96 MeV (1.12 105 years)

The essence of this cycle is the indirect synthesis of a b-particle from four protons during their successive captures by nuclei, starting from 12C.

In the reaction with the capture of a proton by the 15N nucleus, one more outcome is possible - the formation of the 16O nucleus and a new NO I-cycle is born.

It has exactly the same structure as the CN cycle:

14N + 1H = 15O + g +7.29 MeV

15O = 15N + e+ + n +2.76 MeV

15N + 1H = 16O + g +12.13 MeV

16O + 1H = 17F + g +0.60 MeV

17F = 17O + e+ + n +2.76 MeV

17O + 1H = 14N + 4He +1.19 MeV

The NO I cycle increases the rate of energy release in the CN cycle by increasing the number of CN cycle catalyst nuclei.

The last reaction of this cycle can also have a different outcome, giving rise to another NO II cycle:

15N + 1H = 16O + g +12.13 MeV

16O + 1H = 17F + g +0.60 MeV

17F = 17O + e+ + n +2.76 MeV

17O + 1H = 18F + g +5.61 MeV

18O + 1H = 15N + 4He +3.98 MeV

Thus, the CN, NO I, and NO II cycles form a triple CNO cycle.

There is another very slow fourth cycle, the OF cycle, but its role in power generation is negligible. However, this cycle is very important in explaining the origin of 19F.

17O + 1H = 18F + g + 5.61 MeV

18F = 18O + e+ + n + 1.656 MeV

18O + 1H = 19F + g + 7.994 MeV

19F + 1H = 16O + 4He + 8.114 MeV

16O + 1H = 17F + g + 0.60 MeV

17F = 17O + e+ + n + 2.76 MeV

During the explosive combustion of hydrogen in the surface layers of stars, for example, during supernova explosions, very high temperatures, and the nature of the CNO cycle changes dramatically. It turns into the so-called hot CNO cycle, in which the reactions are very fast and intricate.

Chemical elements heavier than 4He begin to be synthesized only after the complete burning out of hydrogen in the central region of the star:

4He + 4He + 4He > 12C + g + 7.367 MeV

Carbon combustion reactions:

12C + 12C = 20Ne + 4He +4.617 MeV

12C + 12C = 23Na + 1H -2.241 MeV

12C + 12C = 23Mg + 1n +2.599 MeV

23Mg = 23Na + e+ + n + 8.51 MeV

12C + 12C = 24Mg + g +13.933 MeV

12C + 12C = 16O + 24He -0.113 MeV

24Mg + 1H = 25Al + g

When the temperature reaches 5 109 K, a large number of various reactions proceed in stars under conditions of thermodynamic equilibrium, resulting in the formation of atomic nuclei up to Fe and Ni.

5. Nuclear power and the environment

The expediency of building and operating nuclear power plants is often called into question because of the danger of accidents leading to the release of radioactive substances into the atmosphere. It is well known that radioactive substances (radionuclides) have a harmful effect on the environment and humans. Radionuclides can enter the body through the lungs when breathing, along with food, or act on the skin. The consequences of exposure are varied and very dangerous. The most severe radiation damage causes radiation sickness, which can lead to death. This disease manifests itself very quickly - from several minutes to a day. Mankind already has the bitter experience of familiarity with the catastrophic consequences of the release of radioactive substances. An example of this is the accident at the Chernobyl nuclear power plant in 1986. As a result of the explosion at the station, a colossal amount of radioactive substances was thrown into the surrounding space. The movement of a radioactive cloud in the atmosphere, the deposition of radionuclides with dust and rain, the spread of soil and surface waters contaminated with radioactive isotopes - all this led to the exposure of hundreds of thousands of people over an area of more than 23 thousand km2.

If we abandon nuclear energy altogether, the danger of irradiation of people and the threat of nuclear accidents will be completely eliminated. But then, in order to meet energy needs, it will be necessary to increase the construction of thermal power plants and hydroelectric power stations. And this will inevitably lead to a large pollution of the atmosphere with harmful substances, to the accumulation of an excess amount of carbon dioxide in the atmosphere, and to disruption of the heat balance on a global scale. Radiation is a formidable and dangerous force, but with the proper attitude it is quite possible to work with it. Characteristically, those who constantly deal with it and are well aware of all the dangers associated with it are the least afraid of radiation. At present, the safety of reactors is given a lot of attention. This is evidenced, in particular, by the following figure: about 70% of all costs for the reactor are related to the protection of people on the territory of the nuclear power plant and beyond. Questions of the safety of the operation of nuclear reactors are discussed in detail and justifiably, and guarantees of the safety of the population near nuclear power plants are no less heated.

Strict requirements for environmental protection lead to the fact that experts propose to build in suitable places some kind of nuclear centers, where several large-capacity reactors could be concentrated, as well as a fuel processing plant and a radioactive waste storage facility. Around such nuclear centers would be industrial and agricultural complexes that use the generated energy (including in the form of hydrogen and fresh water). Such a complex would not only be more efficient and economical, but also better protected from possible accidents (or sabotage) than separate, dispersed power plants and enterprises.

Nuclear power plants of the third generation are much safer, as they have many protective systems. During the operation of a nuclear power plant, safety is primarily based on appropriate methods of detection and control, which guarantee the possibility of timely prevention of dangerous situations. In the event of an accident, the safety system must limit the time of leakage of fission products and contribute to the fastest restoration of normal operating conditions for the equipment, primarily the so-called barriers, which should prevent or limit leakage.

Conclusion

Having studied the operation of nuclear power plants, one can come to the conclusion that they are the most reliable and efficient way to generate electricity. Nuclear power plants do not produce carbon dioxide and other harmful impurities formed during its combustion, which are primarily from coal and oil, especially since these resources are exhaustible and will end in the foreseeable future. It is impossible to rely on alternative energy sources, such as wind, sunlight, tides, because they cannot provide humanity with energy in full. Nuclear energy is an industry that is at the initial stage of its development.

At present, double-loop nuclear power plants are the most common, as they are safer than single-loop ones and more economical than three-loop ones. The main cycle of the steam turbine plant is the Rankine cycle with secondary steam superheating, supplemented by a regenerative feedwater heating system.

The presence of various nuclear technologies, proven economic competitiveness and technical safety, the prospect of developing nuclear reactors on thermal neutrons, as well as reactors carrying out a controlled fusion reaction, in my opinion, make nuclear energy a favorite in providing a significant share of energy production in the present and in the future.

Bibliography

1. T.Kh. Margulov "Nuclear power plants". 1978

2. A.A. Alexandrov "Thermodynamic fundamentals of cycles of thermal power plants" M.: MPEI Publishing House, 2004

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