Classification of nuclear power plants. Thermal power plants Bring the classification of nuclear power plants in the world

Basically, the division of power plants into IES, CHPP, CCGT, GTES, NPP, HPP is currently used. For more full characteristics power plants can be classified according to a number of basic characteristics:

By the type of primary energy resources;

Energy conversion processes;

By the number and type of energy carriers;

By types of supplied energy;

By the circle of consumers covered;

According to the mode of operation.

1. According to the types of used primary energy resources, power plants are distinguished using: fossil fuel (TPP); nuclear fuel (NPP); hydropower (HPP, PSPP and TPP); solar energy (SES); wind energy (WPP); underground heat (geothermal GEOES).

2. According to the applied energy conversion processes, power plants are distinguished, in which: the received thermal energy is converted into mechanical energy, and then into electrical energy (TPP. NPP); the obtained 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 plant, pumped storage power plant, tidal power plant, wind power wind power plants, air-storage gas turbine power plants).

3. By the number and type of energy carriers used, power plants differ: with one energy carrier (IES and CHPP, nuclear IES and CHPP on steam, NPP with a gas energy carrier, GTPP); with two energy carriers different in phase state (combined-cycle power plants, including PG-KES and PG-CHP); with two different energy carriers of the same phase state (binary power plants).

4. By the types of energy supplied, power plants differ: supplying only or mainly electrical energy (HPP, PSPP, IES, nuclear IES, GTES, PG-KES, etc.); releasing electrical and thermal energy(CHP, nuclear CHP, GT-CHP, etc.). Recently, IES and nuclear power plants are increasingly increasing the supply of thermal energy. Combined heat and power plants (CHP), in addition to electricity, generate heat; The utilization of waste steam heat in cogeneration provides significant fuel savings. If exhaust steam or hot water is used for technological process s, heating and ventilation of industrial enterprises, the CHP plants are called industrial. When heat is used for heating and hot water supply of residential and public buildings in cities, CHPs are called communal (heating) plants. Industrial heating CHP plants supply heat as industrial enterprises and the population. At heating CHPPs, along with heating turbine plants, there are hot water boilers for supplying heat during periods of heat load peaks.

5. According to the range of consumers covered, 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. Power plants differ according to the mode of operation in EPS: basic; maneuverable or semi-peak; peak.

The first group includes large, most economical IESs, nuclear IESs, combined heat and power plants in heating mode and partially hydroelectric power plants, the second group includes flexible condensing power plants, PG-IES and CHP, and the third group includes peak hydroelectric power plants, GDES, and GTPP. Thermal power plants and less economical IESs operate partially in peak mode.

In addition to the above general basic features of the classification of power plants, each type has its own internal classification features. For example, IES and CHPP differ in initial parameters, technological scheme (block and with cross-linked), unit capacity of blocks, etc. NPPs are classified by the type of reactors (thermal and fast neutrons), by 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 (PGPPs) are used in two versions: with a high-pressure steam generator and with discharge of exhaust gases into conventional boilers. In the first variant, 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 750-800 ° C, after which they are sent to a gas turbine, and high-pressure steam is supplied to steam turbine.

In the second variant, the combustion products from the combustion chamber with the addition of the required amount of air to reduce the temperature to 750-800 ° C are sent to the gas turbine, and from there exhaust gases at a temperature of about 350-400 ° C with a high oxygen content are fed to conventional boilers of steam turbine TPPs, where they perform the function of an oxidizer and give off their warmth.

And the first scheme should burn natural gas or a special gas turbine liquid fuel, in the second scheme such fuel should be burned only in the combustion chamber of a gas turbine, and in boilers - fuel oil or solid fuel, which is a definite advantage. The combination of the two cycles will increase the overall efficiency of the CHPP by about 5-6% compared to the steam-turbine IES. Power gas turbines The combined-cycle power plant accounts for approximately 20-25% of the capacity of the combined-cycle unit. Due to the fact that the specific capital investment in the gas turbine section is lower than in the steam turbine section, the SGPP achieves a decrease in the specific capital investment by 10-12%. Combined cycle gas units are more maneuverable than conventional condensing units, and can be used to operate in the semi-peak zone, as they are more economical than maneuverable IESs.

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

Nuclear reactors are divided into several groups:

1) Depending on the average energy of the neutron spectrum - into fast, intermediate and thermal;

2) According to the design features of the core - into hull and channel;

3) By the type of heat carrier - water, heavy water, sodium;

4) By the type of moderator - for water, graphite, heavy water, etc.

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

1) Water-cooled reactors with non-boiling or boiling water under pressure,

2) Uranium-graphite reactors with boiling water or cooled with carbon dioxide,

3) 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 that characterizes the breeding of fuel is called the plutonium ratio. It shows how many acts of Pu-239 atoms are created during neutron capture reactions in U-238 per one U-235 atom that has captured a neutron and underwent fission.

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

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

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

In thermal 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.

In the core of a thermal reactor, there must be a moderator - a substance whose nuclei have a small mass number. Graphite, heavy or light water, beryllium, organic liquids are used as moderators. A thermal reactor can even run on natural uranium if heavy water or graphite is used as a moderator. For other moderators, enriched uranium must be used. The required critical dimensions of the reactor depend on the degree of fuel enrichment; with an increase in the degree of enrichment, they are smaller. A significant drawback of thermal 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 capture cross sections for slow neutrons as a moderator, coolant, and structural materials.

The three essential elements for thermal reactors are the heat release, the moderator, and the coolant. This figure shows a typical core layout.

A coolant is pumped through the reactor with the help of pumps (called circulation pumps), which then flows either to the turbine (in RBMK) or to the heat exchanger (in other types of reactors). The heated coolant of the heat exchanger enters the turbine, where it loses part of its energy to generate electricity. From the turbine, the coolant enters the steam condenser so that the coolant with the parameters required for optimal operation is supplied to the reactor. The reactor also has a control system for it, which consists of a set of rods with a diameter of several centimeters and a length comparable to the height of the core, consisting of a material highly absorbing neutrons, usually boron compounds. The rods are located in special channels and can be raised or lowered into the reactor. In the raised state, they contribute to the acceleration of the reactor, in the lowered state, they drown it out. The rod drives are independently adjustable, so they can be used to configure the reaction activity in different parts of the core.

The peculiarity of a nuclear reactor is that 94% of the fission energy is converted into heat instantly, i.e. during the time during which the power of the reactor or the density of materials in it does not have time to change noticeably. Therefore, when the reactor power changes, the heat release follows without delay the fuel fission process.

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 residual heat release after the termination of the fission reaction requires the removal of heat for a long time after the shutdown of the reactor. Although the power of the residual heat release is much less than the nominal one, the circulation of the coolant through the reactor must be ensured very reliably, since the residual heat release cannot be controlled. Removal of the coolant from the reactor that has been operating for some time is strictly prohibited in order to avoid overheating and damage to the fuel elements.

IN intermediate neutron reactors, in which most fission events are caused by neutrons with energies higher than thermal (from 1 eV to 100 keV), the moderator mass is less than in thermal reactors. A specific feature of the operation of such a reactor is that the fission cross section of the fuel with an increase in neutron fission in the intermediate region decreases weaker than the absorption cross section of structural materials and fission products. Thus, the likelihood of fission acts increases compared to takeover acts. Requirements for neutron characteristics of structural materials are less stringent, 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 due to a decrease in the cross section should be higher than in thermal ones. Reproduction of nuclear fuel in reactors using intermediate neutrons is greater than in a reactor using thermal neutrons.

A substance that weakly moderates neutrons is used as coolants in intermediate reactors. For example, liquid metals. The moderator is graphite, beryllium, etc.

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

Reactors are divided into homogeneous and heterogeneous depending on the method of fuel placement in the core.

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 both thermal and fast neutrons. In such a reactor, the entire core is located inside a steel spherical vessel and is a liquid homogeneous mixture of fuel and moderator in the form of a solution or liquid alloy (for example, a solution of uranyl sulfate in water, a solution of uranium in liquid bismuth), which simultaneously serves as a coolant.

A nuclear fission reaction occurs in a fuel solution inside a spherical reactor vessel, as a result of which the temperature of the solution rises. The combustible solution from the reactor enters the heat exchanger, where it gives off heat to the water of the secondary circuit, is cooled and is sent back to the reactor by a circular pump. In order to prevent a nuclear reaction from occurring outside the reactor, the volumes of the pipelines of the loop, heat exchanger and pump are selected so that the volume of fuel in each section of the loop 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 simplicity of fuel preparation, and the fact that the reactor can be controlled by changing the concentration of nuclear fuel.

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

IN heterogeneous reactor the 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 agent, heterogeneous reactors are divided into graphite, light water, heavy water, and organic. By 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, and in the second, it boils.

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

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

By design, reactors are subdivided into vessel and channel reactors. IN pressurized reactors the pressure of the coolant is carried by the body. The general flow of the coolant flows inside the reactor vessel. IN channel reactors the coolant is supplied to each channel with a fuel assembly separately. The reactor vessel is not loaded with the coolant pressure; this pressure is carried by each separate channel.

Depending on the purpose, nuclear reactors are power, converters and breeders, 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 (ATEC), as well as at nuclear power plants (AST).

Reactors designed for the production of secondary nuclear fuel from natural uranium and thorium are called converters or breeders... In the reactor - converter of secondary nuclear fuel, less of the initially consumed fuel is formed. In the breeder reactor, an expanded breeding of nuclear fuel is carried out, i.e. it turns out more than it was spent.

Research reactors serve 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, production of isotopes, experimental research of the physics of nuclear reactors. The reactors have different capacities, stationary or pulsed operation. 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 called that serve several purposes, for example, to generate power and obtain nuclear fuel.

2.2. Classification of nuclear power plants

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

The NPP system distinguishes coolant and working body... The working fluid, that is, the medium that performs work, with the conversion of thermal energy into mechanical energy, is water vapor. The requirements for the purity of the steam supplied to the turbine are so high that they can be met with economically acceptable indicators only by condensing the entire steam and returning the condensate to the cycle. Therefore, the working fluid circuit for a nuclear power plant, as well as for any modern thermal power plant, is always closed and additional water enters it only in small amounts to replenish leaks and some other condensate losses.

The purpose of the coolant at a nuclear power plant 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 loop, and especially because the reactor coolant is always radioactive. Resonant scattering is another matter entirely. This is not inelastic scattering. There is potential scattering, there is resonance scattering - this interaction is already at the wave level of neutrons. Now we are 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 NPP is called single-circuit(fig. 2.2 but). Steam generation occurs in the reactor, the steam is sent to the turbine, where it produces work that is converted into electricity in the generator. After condensation of all the steam in the condenser, the condensate

but- single-circuit; b- double-circuit; in- 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

pump is fed 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 under radiation conditions, which complicates its operation. The great advantage of such schemes is simplicity and high efficiency. Steam parameters in front of the turbine and in the reactor differ only by the value of losses in steam lines. The Leningrad, Kursk and Smolensk NPPs operate according to a single-loop scheme.

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

Steam from the steam generator of a two-circuit NPP enters the turbine, then into the condenser, and the condensate from it is pumped back to the steam generator. The secondary circuit thus formed includes equipment operating in the absence of radiation; this simplifies the operation of the station. At a double-circuit NPP, it is mandatory steam generator - device separating both contours, so it belongs equally to both the first and the second. The transfer of heat through the heating surface requires a temperature difference between the coolant and the boiling water in the steam generator. For a water heat carrier, this means maintaining in the first

a 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 first loop that is significantly higher than the pressure in the second loop. Novovoronezh, Kola, Balakovskaya and Kalininskaya NPPs operate according to a two-circuit 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 gas blower, which plays the same role as the main circulation pump, but in contrast to the water for the gas heat carrier, the pressure in the first circuit can be not only higher, but also lower than in the second.

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

During operation, leaks may occur in certain sections of the steam generator, especially at the joints of the steam generator tubes with the collector or due to corrosion damage to the tubes themselves. If the pressure in the first circuit is higher than in the second, then a coolant overflow may occur, leading to radioactive contamination of the second circuit. Within certain limits, such overflow does not disrupt the normal operation of the nuclear power plant, but there are coolants that intensively interact with steam and water. This can create the danger of the release of radioactive substances into the manned 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. This nuclear power plant is called three-circuit(fig. 2.2 in).

A radioactive liquid-metal coolant is pumped through a reactor and an intermediate heat exchanger, in which it gives off heat to a non-radioactive liquid-metal coolant. The latter is pumped through a steam generator through a system that forms an intermediate circuit. The pressure in the intermediate circuit is kept higher than in the first. Therefore, the overflow of radioactive sodium from the primary circuit 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 scheme 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 unit operate according to a three-circuit scheme. Beloyarsk NPP.

In addition to the classification of nuclear power plants by the number of circuits, separate types NPP depending on:

- type of reactor - thermal or fast neutrons;

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

- parameters and type of heat carrier - with gas heat carrier, heat carrier "water under pressure", liquid metal, etc .;

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

- the type of reactor moderator, for example, a graphite or heavy water moderator, etc.

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

Novovoronezh a two-circuit nuclear power plant with a vessel-type thermal reactor with a "pressurized water" coolant and saturated steam turbines;

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

Shevchenkivska a three-circuit nuclear power plant with a sodium-cooled fast reactor and turbines with superheated steam.

Technical problems of nonproliferation of nuclear materials. Economic aspects of the use of nuclear energy. Cost components of electricity generation at nuclear power plants. Decommissioning of a nuclear power plant. Economic consequences of severe accidents. Social aspects of the development of nuclear power.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

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 the peaceful use of 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 inconceivable without electrical energy. The production and use of electricity is increasing every year. The energy released in nuclear reactions is millions of times higher than that which is given by conventional 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 operating principle 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 increased interest modern science towards nuclear energy in connection with the increasing needs of mankind in energy. The aim of the work is to study the principles of operation of nuclear power plants, equipment used at nuclear power plants, mechanisms of nuclear reactions, as well as methods of ensuring safety nuclear plants... The paper presents: the most important classification of nuclear installations, the structure and principle of operation of a nuclear reactor, 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 classified according to the following parameters:

1. The number of contours.

2. Type of reactors. Reactors are subdivided 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 reactors, such as channel-type reactors or tank-type reactors.

6. Moderator type: graphite or heavy water.

The most important classification of nuclear power plants is the classification by the number of circuits. The number of circuits is selected taking into account the requirements for ensuring the safe operation of the unit at 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 operation of a nuclear power plant 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 you know, at operating stations, the process of converting the source energy into heat occurs continuously and in case of termination of heat removal, inevitable overheating of the installation will occur. Consequently, 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. Heat transfer from the source to the consumer is carried out with the help of a heat carrier, 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 medium at a nuclear power plant is water vapor. The requirements for the cleanliness of the working fluid supplied to the turbine and the coolant, which is always radioactive, are very high, therefore, they require closed circuits. If the circuits of the coolant and the working fluid are not separated, the NPP 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 in the condenser has condensed, the condensate is pumped back into the reactor. Such reactors operate with forced circulation of the coolant, for which a main circulation pump is installed. Thus, the coolant circuit is at the same time the working fluid circuit. In single-loop circuits, all equipment operates in radiation-active conditions, which complicates its repair.

Rice. 1 Thermal diagram of the NPP: a - single-circuit; b - double-circuit; в - three-circuit; 1 - reactor; 2 - turbine; 3- turbo generator; 4- condensing unit; 5- condensate pump; b - feed water regenerative heating system; 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 NPP is called double-circuit. 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 second circuit, without contacting it, and is fed back to the reactor by the circulation pump. The second circuit includes equipment that works in the absence of radiation activity - this simplifies equipment repair. Steam from the steam generator enters the turbine, then to the condenser and returns to the steam generator by a pump. The transfer of heat in a steam generator requires a temperature difference between the coolant and the working fluid. For a water heat carrier, this means that the pressure in the first circuit must be higher than in the second.

If a nuclear power plant uses not 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 first and second circuits. Thus, a coolant overflow may occur, leading to radioactive contamination of the second circuit. Since liquid sodium intensively interacts with steam and water, there is a danger of the release of radioactive substances into the serviced premises. Therefore, an additional intermediate circuit is created in order to avoid contact of radioactive sodium with water or water vapor even in emergency situations. Such a nuclear power plant is called three-circuit.

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. At present, uranium isotopes - U235 and U238, as well as Pu239 can be used as nuclear fuel. Fission of nuclei 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 be repelled from the nucleus without penetrating into it). There are two types of neutrons: fast and slow. Neutrons different types affect the nuclei of fissile elements differently.

In nuclear reactors using thermal neutrons, the isotope of uranium U235 is used as a nuclear fuel, the fission of which occurs only if the neutrons are slowed down by 3-4 times in comparison with fast ones. Therefore, to control the 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 reaction moderators. Good neutron moderators are graphite, ordinary and heavy water, beryllium compounds.

A nuclear reactor consists of a core and a reflector. The core contains a moderator and nuclear fuel, which is contained in fuel cells called fuel rods. The coolant flows through the reactor core. Typically this is normal water, but liquid graphite and heavy water can also be used. The reactor starts up when the neutron absorbing rods are removed from its core.

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

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

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

Fast reactors use the isotope of uranium 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 in order to burn all or a significant part of natural uranium, as well as the available reserves of depleted uranium. With the development of the power of fast reactors, the problem of self-sufficiency of nuclear power 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 fissioned 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 higher than the heat release of slow neutron reactors, and therefore, instead of water (which simply cannot cope with such a volume of energy for transfer), sodium melt is used (its inlet temperature is 370 degrees, and at the outlet - 550). Therefore, for 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 U238 layer located around the core. This converts uranium into Pu239, which, in turn, can be used in the reactor as a fissile element.

Currently, fast 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 The NPP is shown in Fig. 1.

By circulating through the reactor core and washing the fuel elements, 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-circuit NPP is performed by a separator drum. A steam generator is an obligatory unit of a two-circuit and three-circuit NPP. Passing inside the heat exchange tubes of the steam generator, the primary coolant gives off heat to the secondary water, which turns into steam. 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 an electric current. The parameters of the turbine and its design scheme differ - 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, expanding adiabatically, does work. From there, the exhaust steam is directed to the condenser. The condenser plays a double role in the installation: firstly, it has steam and water spaces separated by a surface through which heat exchange between the exhaust steam and the cooling water takes place. Therefore, steam condensate can be used as ideal water free of 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 occurs, which, being maintained during the entire operation time of the installation, allows the steam to expand in the turbine by one more atmosphere and thereby perform additional work.

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

Thus, the technological process of electricity generation at nuclear power plants includes: raising the temperature of the condensate to the 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 the value corresponding to the vacuum in the condenser. Thus, the 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.

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

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

The small value of the segment of the adiabat 3-4 indicates a small amount of work expended by the pump to compress the water. The small amount of work of compression compared to the amount of work produced by steam during expansion 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 isobarically (process 4-5 P1 = const). First, the water in the steam generator is heated to boiling (section 4-5 isobars P1 = const) and then, upon reaching the boiling point, the process of vaporization occurs (section 5-6 isobars P1 = const). In section 6-1, the steam is overheated in the steam generator, after which the steam enters the turbine. The expansion process in the turbine is depicted by the adiabat 1-2. Waste 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 lc is the work of the cycle, q1 is the supplied heat.

In this cycle, the work of the cycle lc is the difference between the work received in the turbine lt and spent in the pump ln.

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

Lт - lн / q1

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

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

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 from the turbine is equal:

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)

The specific work of the pump in absolute value is usually less than 3-4% of the work of the turbine, therefore, sometimes this work is neglected in the calculations.

ii are the values of the enthalpy of water and steam at the corresponding points in the cycle, they can be found either using the corresponding 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 limiting value of steam moisture at the end of the expansion in the turbine under the condition of its safe operation. This can be avoided by changing the configuration of the cycle by introducing secondary superheating of steam at a certain intermediate pressure. For this, a two-stage turbine is used, consisting of a high-pressure cylinder and several cylinders. low pressure... The so-called superheating of steam occurs in a special element of the installation - a superheater, where the steam is heated to a temperature exceeding the saturation temperature at a given pressure P1. In this case, the average temperature of the heat supply increases in comparison with the temperature of the heat supply in the cycle without overheating and, therefore, the thermal efficiency of the cycle increases. The Rankine cycle with steam superheating is the main cycle of heat power plants used in modern heat power engineering.

Rice. 3 Rankine cycle with secondary superheating of steam in the T-S diagram

Steam from the steam generator is directed to a high pressure cylinder (HPC), part of the steam is taken for superheating. Expanding in the high pressure cylinder (process in diagram 1-a), steam does work. After the HPC, the steam is sent to the superheater, where, due to the cooling of the part of the steam taken 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 LPC, the steam expands, performs work again (process b-2 in the diagram) and enters the condenser. The rest of the processes correspond to the processes in the above Rankine cycle. The efficiency of a cycle with intermediate superheating of steam is determined by the formula:

? = (lChVD + lChND - lH) / q1 = ((i1 - ia) + (ib - i2) - (i3 - i2)) / ((i1 - i3) + (ib - ia)

Depending on the choice of pressure at which secondary superheating of steam is performed, the efficiency of the cycle with secondary superheating can be greater or less than the efficiency of the cycle without secondary superheating. 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 thermal efficiency higher than that of the initial one, provided that the average temperature Tav of heat supply in the additional cycle will be higher than in the initial one. In turn, the average temperature of the heat supply in the additional cycle depends on the temperature of the onset 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 the 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 of the temperature of the onset of secondary superheating of steam, at which the maximum increase in the thermal efficiency of the cycle with intermediate superheating of steam is provided. The use of secondary superheating of steam makes it possible to increase the efficiency of the steam turbine plant by 4 -5%.

Regenerative feed water heating

In heating 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 called 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 value of the efficiency of the Rankine cycle in comparison with the Carnot cycle is due to the fact that a large amount of thermal energy during the condensation of steam is transferred to the cooling water in the condenser.

To reduce losses, a part of the steam from the turbine is taken and sent to regeneration heaters, where the heat energy released during the condensation of the extracted steam is used to heat the water obtained after the condensation of the main steam stream. 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 of the elements are stable (for example, oxygen and nitrogen in the atmosphere; carbon, oxygen and hydrogen are the main constituents 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 are transformations of atomic nuclei when interacting with elementary particles, r-quanta or with each other.

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

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

Spontaneous (spontaneous) is fission of nuclei, during which some rather heavy nuclei disintegrate 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 over a very wide range for different nuclei (from 1018 years for 93Np237 to several tenths of a second for transuranic elements).

Forced fission of nuclei 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 power greater importance fission caused by neutrons plays. 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 action of the Coulomb repulsive forces, the nucleus fission into two fragments of unequal mass. Both fragments are radioactive and emit 2 or 3 secondary neutrons.

Rice. 4 Fission of a uranium nucleus

Secondary neutrons are absorbed by neighboring uranium nuclei, which causes their fission. Under appropriate conditions, a self-developing process of mass nuclear fission, called a nuclear chain reaction, can occur. This reaction is accompanied by the release of colossal energy. For example, with the complete combustion of 1 g of uranium, 8.28 · 1010 J of energy is released. 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 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 nuclei formed as a result of the reaction.

The more energy is released during the formation of a 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 constituent 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 of atomic fission, the fusion of light atomic nuclei into heavier nuclei, which occurs at an ultrahigh temperature and is accompanied by the release of huge numbers 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 widespread substance in the Universe.

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

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 seawater. Its reserves are generally available and very large: the share of 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 with the participation of tritium is more attractive, since 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 deuterium-tritium reaction most attainable under terrestrial conditions.

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

Advantages:

1.3He is not radioactive.

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

3. The resulting protons, in contrast to neutrons, are easily captured and can be used for additional generation of electricity.

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

Helium-3 is a byproduct of solar reactions. As a result, the Moon, which has no atmosphere, contains up to 10 million tons of this valuable substance (according to the minimum estimates, 500 thousand tons). During thermonuclear fusion, when 1 ton of helium-3 with 0.67 tonnes of deuterium enters the reaction, energy is released equivalent to the combustion of 15 million tons of oil (however, the technical feasibility of this reaction has not yet been studied). 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 the extraction of helium from the lunar soil. The content of helium-3 in the 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 reaction of thermonuclear fusion 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 presupposes: obtaining plasma heated to temperatures of hundreds of millions of degrees; preservation of the plasma configuration for a period of time for the occurrence of nuclear reactions.

Thermonuclear power engineering has important advantages over nuclear power plants: it uses absolutely non-radioactive deuterium and the helium-3 isotope and radioactive tritium, but in volumes that are thousands of times smaller than in nuclear power. And in possible emergency situations, the radioactive background near a thermonuclear power plant will not exceed natural indicators. In this case, per unit weight of thermonuclear fuel, approximately 10 million times more energy is obtained than when burning fossil fuel, and approximately 100 times more than when fission of uranium nuclei. IN natural conditions thermonuclear reactions take place in the interior of stars, in particular in the inner regions of the sun, and serve as the 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 the stars ensure the continuous emission of huge streams of energy for billions of years.

Everything chemical elements 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 progress 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 the 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. The first in the chain of such nuclear reactions are hydrogen thermonuclear reactions. They proceed 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 + r +5.49 MeV

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

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

7Be + e- = 7Li + v + 0.862 MeV or 7Be + 1H = 8B + r + 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 the collision reaction of two protons (1H, or p) with the formation of 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: when two 3He nuclei collide, they 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 - the proton chain of reactions arises. 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. of c. must be realized twice, since in this case two 3He nuclei disappear at once. In branch III, especially energetic neutrinos are emitted during the decay of the 8B boron nucleus with the formation of an unstable beryllium nucleus in an excited state (8Be *), which decays almost instantly 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 the isotopes C, N, and O in the stellar matter.

The main reaction path of the CN-cycle:

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

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

13C + p = 14N + r +7.54 MeV (2.7106 years)

14N + p = 15O + r +7.29 MeV (3.2108 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 consists in the indirect synthesis of a b-particle from four protons during their sequential capture 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 a 16O nucleus and a new cycle NO I-cycle is born.

It has exactly the same structure as the CN loop:

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

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

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

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

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

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

NO I-cycle increases the rate of energy release in the CN-cycle, increasing the number of CN-cycle catalyst cores.

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 + r +0.60 MeV

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

17O + 1H = 18F + r +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 energy production is negligible. However, this cycle is very important in explaining the origin of 19F.

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

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

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

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

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

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

With the explosive combustion of hydrogen in the surface layers of stars, for example, during supernova explosions, very high temperatures can develop, 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 confusing.

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

4He + 4He + 4He> 12C + r + 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 + r +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 take place in stars under thermodynamic equilibrium conditions, as a result of which atomic nuclei up to Fe and Ni are formed.

5. Nuclear power and the environment

The feasibility of the construction and operation of nuclear power plants is often called into question due to 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 during breathing, along with food, or act on the skin. The effects of radiation exposure are varied and very dangerous. The most severe radiation damage causes radiation sickness, which can lead to the death of a person. This disease manifests itself very quickly - from several minutes to a day. Humanity already has a bitter experience of acquaintance 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 over 23 thousand km2.

If nuclear power is abandoned altogether, the danger of human exposure 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 plants. 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, to a violation of the heat balance on a global scale. Radiation is a formidable and dangerous force, but with proper treatment it is quite possible to work with it. It is characteristic that the least afraid of radiation are those who constantly deal with it and are well aware of all the dangers associated with it. Currently, the safety of reactors is receiving a lot of attention. This is evidenced, in particular, by the following figure: about 70% of all expenses for the reactor are associated with the protection of people on the territory of the nuclear power plant and beyond. The issues of the safety of operation of nuclear reactors are discussed in detail and reasonably, and guarantees of the safety of the population near nuclear power plants are no less hot.

The strict requirements for environmental protection lead to the fact that experts propose to build in suitable places some kind of nuclear centers, where it would be possible to concentrate several high-power reactors, as well as a fuel reprocessing plant and a radioactive waste storage facility. Around such atomic centers would be industrial and agricultural complexes using 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 assurance is based primarily on appropriate methods of detection and control, which guarantee the possibility of timely warning of dangerous situations. In the event of an accident, the safety system should limit the time of fission products leakage and facilitate the fastest restoration of normal operating conditions of 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 effective way electricity production. The nuclear power plant does not produce carbon dioxide and other harmful impurities formed during its combustion, which are available, first of all, from coal and oil, especially since these resources will be exhausted and will run out in the foreseeable future. Count on alternative sources energies such as the energy of wind, sunlight, ebb and flow, it is impossible, because they cannot provide humanity with energy in full. Nuclear energy is an industry that is at an early stage of its development.

Currently, the most common are two-circuit nuclear power plants, since they are safer than single-circuit, and more economical than three-circuit. The main cycle of a steam turbine plant is a Rankine cycle with secondary superheating of steam, supplemented by a system of regenerative heating of feed water.

The presence of various nuclear technologies, proven economic competitiveness and technical safety, the prospect of developing nuclear reactors using 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. Margulova "Nuclear Power Plants". 1978 year

2. A.A. Aleksandrov "Thermodynamic foundations of cycles of thermal power plants" M .: Publishing house of MPEI, 2004

Posted on Allbest.ru

...

The history of nuclear energy in our country and abroad

The second half of the 40s was marked by the beginning of work on the creation of the first project involving the use of a peaceful atom to generate electricity. In 1948, I.V. Kurchatov, guided by the instructions of the party and the Soviet government, made a proposal to start work on the practical use of atomic energy to generate electricity.

Two years later, in 1950, not far from the village of Obninskoye, located in the Kaluga region, the construction of the first nuclear power plant on the planet was started. The launch of the world's first industrial nuclear power plant, with a capacity of 5 MW, took place on June 27, 1954. The Soviet Union became the first power in the world that managed to use the atom for peaceful purposes. The station was opened in Obninsk, which had received the status of a city by that time.

But Soviet scientists did not stop there, they continued work in this direction, in particular, only four years later, in 1958, the operation of the first stage of the Siberian nuclear power plant began. Its capacity was several times higher than the station in Obninsk and amounted to 100 MW. But for domestic scientists this was not the limit, upon completion of all work, the design capacity of the station was 600 MW.

In the vastness of the Soviet Union, the construction of a nuclear power plant, at that time, took on a massive scale. In the same year, the construction of the Beloyarsk NPP was launched, the first stage of which, already in April 1964, supplied the first consumers. The geography of the construction of nuclear power plants enveloped the whole country with its network, in the same year the first unit of the nuclear power plant in Voronezh was launched, its capacity was 210 MW, the second unit, launched five years later in 1969, boasted a capacity of 365 MW. the boom in the construction of nuclear power plants did not subside throughout Soviet era... New stations, or additional blocks of those already built, were launched at intervals of several years. So, already in 1973, Leningrad received its own nuclear power plant.

However, the Soviet state was not the only one in the world who was able to master such projects. In Great Britain, they also did not sleep and, realizing the prospects of this direction, they actively studied this issue. After only two years, after the opening of the station in Obninsk, the British launched their own project to develop the peaceful atom. In 1956, in the town of Calder Hall, the British launched their own station, the capacity of which exceeded the Soviet counterpart and amounted to 46 MW. They did not lag behind on the other side of the Atlantic, a year later, the Americans solemnly put into operation the station in Shippingport. The facility's capacity was 60 MW.

However, the development of a peaceful atom was fraught with hidden threats, which the whole world soon learned about. The first swallow was major accident in Three - Mile - Island that happened in 1979, well, and after it there was a catastrophe that struck the whole world, in the Soviet Union, in the small town of Chernobyl, there was a large-scale catastrophe, it happened in 1986. The consequences of the tragedy were irreparable, but in addition, this fact made the whole world think about the advisability of using nuclear energy for peaceful purposes.

The world's luminaries in this industry are seriously thinking about improving the safety of nuclear facilities. The result was the holding of a constituent assembly, which was organized on 05/15/1989 in the Soviet capital. The assembly decided to create a World Association, which should include all operators of nuclear power plants, its generally recognized abbreviation is WANO. In the course of implementing its programs, the organization systematically monitors the increase in the safety level of nuclear power plants in the world. However, despite all the efforts made, even the most modern and seemingly safe facilities cannot withstand the onslaught of the elements. It is because of the endogenous catastrophe, which manifested itself in the form of an earthquake and the ensuing tsunami in 2011, that an accident occurred at the Fukushima-1 station.

Atomic blackout

NPP classification

Nuclear power plants are classified according to two criteria, the type of energy they produce and the type of reactors. Depending on the type of reactor, the amount of generated energy, the level of safety, and also what kind of raw materials are used at the station are determined.

According to the type of energy that the stations produce, they are divided into two types:

Their main function is to generate electricity.

Nuclear thermal power plants. Due to the heating installations installed there, using heat losses, which are inevitable at the station, it becomes possible to heat the network water. Thus, these stations generate heat energy in addition to electricity.

Having examined many options, scientists have come to the conclusion that the most rational are their three varieties, which are currently used all over the world. They differ in a number of ways:

Fuel used;
Applied heat carriers;
Active zones operated to maintain the required temperature;
A type of moderator that determines a decrease in the speed of neutrons that are released during decay and are so necessary to support a chain reaction.

The most common type is a reactor that uses enriched uranium as fuel. Ordinary or light water is used here as a heat carrier and moderator. Such reactors are called light water reactors; they are known in two varieties. In the first, steam used to rotate the turbines is generated in an active zone called a boiling water reactor. In the second, the formation of steam occurs in the external circuit, which is connected to the first circuit by means of heat exchangers and steam generators. This reactor, began to develop in the fifties of the last century, the basis for them was the US army programs. In parallel, at about the same time, a boiling-water reactor was developed in the Union, in which a graphite rod acted as a moderator.

It is the type of moderated reactor of this type that has found practical application. This is a gas-cooled reactor. Its history began in the late forties, early fifties of the XX century, initially developments of this type were used in the production of nuclear weapons. In this regard, two types of fuel are suitable for it, these are weapons-grade plutonium and natural uranium.

The last project, which was accompanied by commercial success, was a reactor where heavy water is used as a coolant, and the already well-known natural uranium is used as a fuel. Initially, such reactors were designed by several countries, but in the end their production was concentrated in Canada, which is due to the presence of massive uranium deposits in this country.

Thorium NPPs - Energy of the Future?

The history of improving the types of nuclear reactors

The reactor, the first nuclear power plant on the planet, was a very reasonable and viable design, which was proved in the course of many years and flawless operation of the station. Among its constituent elements were distinguished:

side water protection;
masonry casing;
top floor;
prefabricated collector;
fuel channel;
top plate;
graphite masonry;
bottom plate;
distribution manifold.

The main structural material for the fuel element cladding and technological channels was stainless steel; at that time, it was not known about zirconium alloys, which could, in terms of properties, be suitable for working with a temperature of 300 ° C. Cooling of such a reactor was carried out with water, while the pressure under which it was supplied was 100 at. At the same time, steam was released with a temperature of 280 ° C, which is a quite moderate parameter.

The channels of the nuclear reactor were designed in such a way that they could be completely replaced. This is due to the resource limitation, which is due to the time spent by the fuel in the zone of activity. The designers did not find any reason to expect that structural materials located in the irradiated zone of activity will be able to use up their entire resource, namely about 30 years.

As for the TVEL design, it was decided to adopt a tubular version with a one-way cooling mechanism.

This reduced the likelihood that fission products would enter the circuit in the event of fuel rod damage. To regulate the temperature of the fuel element cladding, a fuel composition of a uranium-molybdenum alloy was used, which had the form of grains dispersed by means of a warm-water matrix. The nuclear fuel processed in this way made it possible to obtain highly reliable fuel rods. which were able to operate at high thermal loads.

The infamous Chernobyl nuclear power plant can serve as an example of the next round of development of peaceful nuclear technologies. At that time, the technologies used in its construction were considered the most advanced, and the type of reactor was the most modern in the world. We are talking about the RBMK-1000 reactor.

The thermal power of one such reactor reached 3200 MW, while it has two turbine generators, the electric power of which reaches 500 MW, thus, one power unit has an electric power of 1000 MW. Enriched uranium dioxide was used as fuel for the RBMK. In the initial state, before the start of the process, one ton of such fuel contains about 20 kg of fuel, namely uranium - 235. With a stationary loading of uranium dioxide into the reactor, the mass of the substance is 180 tons.

But the loading process is not a heap; fuel elements, already well-known to us, are placed in the reactor. In fact, they are tubes that are made with a zirconium alloy. As the contents, they contain uranium dioxide tablets, which have a cylindrical shape. In the reactor activity zone, they are placed in fuel assemblies, each of which combines 18 fuel rods.

There are up to 1,700 such assemblies in such a reactor, and they are placed in a graphite stack, where vertical technological channels are specially designed for these purposes. It is in them that the circulation of the coolant takes place, the role of which, in the RMBK, is played by water. The whirlpool of water occurs under the influence of circulation pumps, of which there are eight. The reactor is located inside the shaft, and the graphic masonry is in a cylindrical body 30mm thick. The support of the entire apparatus is a concrete base, under which there is a pool - a bubbler, which serves to localize the accident.

The third generation of reactors uses heavy water

The main element of which is deuterium. The most common design is called CANDU, it was developed in Canada and is widely used around the world. The core of such reactors is located in a horizontal position, and cylindrical tanks play the role of a heating chamber. The fuel channel runs through the entire heating chamber, each of these channels has two concentric tubes. There are outer and inner tubes.

In the inner tube, the fuel is under the pressure of the coolant, which makes it possible to additionally refuel the reactor during operation. D20 heavy water is used as a retarder. In the course of a closed cycle, water is pumped through the pipes of the reactor containing the fuel bundles. As a result of nuclear fission, heat is generated.

The cooling cycle when using heavy water consists in passing through steam generators, where ordinary water boils from the heat generated by the heavy water, as a result of which steam is formed, escaping under high pressure. It is distributed back to the reactor, resulting in a closed cooling cycle.

It was along this path that there was a step-by-step improvement of the types of nuclear reactors that were used and are used in various countries of the world.

Classification of nuclear power plants. Thermal power plants Bring the classification of nuclear power plants in the world

Send your good work in the knowledge base is simple. Use the form below

Similar documents

The history of nuclear energy in our country and abroad

NPP classification

The history of improving the types of nuclear reactors

As for the TVEL design, it was decided to adopt a tubular version with a one-way cooling mechanism.

The third generation of reactors uses heavy water