home » Autumn shoes » Spent nuclear fuel from thermal reactors. Fast neutron reactors and their role in the development of "large" nuclear power

Spent nuclear fuel from thermal reactors. Fast neutron reactors and their role in the development of "large" nuclear power

December 25th, 2013

The stage of the physical start-up of the BN-800 fast neutron reactor began today at the Beloyarsk NPP, a representative of Rosenergoatom told RIA Novosti.

During this phase, which could take several weeks, the reactor will be filled with liquid sodium and then loaded with nuclear fuel. A representative of Rosenergoatom explained that upon completion of the physical start-up, the power unit will be recognized as a nuclear installation.

Power unit No. 4 with the BN-800 reactor of the Beloyarsk Nuclear Power Plant (BNPP) will reach full capacity by the end of 2014, Alexander Lokshin, First Deputy Director General of Rosatom State Corporation, told reporters on Wednesday.

“The unit should reach full capacity by the end of the year,” he said, adding that this is the end of 2014.

According to him, the circuit is currently being filled with sodium, and the end of the physical start-up is planned by mid-April. According to him, the power unit is 99.8% ready for physical start-up. As Evgeny Romanov, General Director of Rosenergoatom Concern OJSC, noted, the facility is scheduled to be energized at the end of summer.

The power unit with the BN-800 reactor is a development of the unique BN-600 reactor at the Beloyarsk NPP, which has been in pilot operation for about 30 years. A very small number of countries in the world have fast reactor technologies, and Russia is the world leader in this area.

Let's find out more about him ...

Reactor (central) hall BN-600

The town of Zarechny is located 40 km from Yekaterinburg, in the midst of the most beautiful Ural forests. In 1964, the first Soviet industrial nuclear power plant was launched here - Beloyarskaya (with the AMB-100 reactor with a capacity of 100 MW). Now Beloyarsk NPP remains the only one in the world where an industrial fast neutron power reactor, BN-600, operates.

Imagine a boiler that evaporates water, and the resulting steam turns a turbine generator that generates electricity. This is roughly how a nuclear power plant works in general terms. Only the "boiler" is the energy of atomic decay. The designs of power reactors can be different, but according to the principle of operation, they can be divided into two groups - thermal reactors and fast reactors.

Low-enrichment uranium is usually used as fuel for thermal reactors, graphite, light or heavy water are used as moderators, and ordinary water is used as a coolant. Most of the operating nuclear power plants are arranged according to one of these schemes.

Fast neutrons produced by forced nuclear fission can be used without any slowdown. The scheme is as follows: fast neutrons formed during the fission of uranium-235 or plutonium-239 nuclei are absorbed by uranium-238 with the formation (after two beta decays) of plutonium-239. Moreover, for 100 separated nuclei of uranium-235 or plutonium-239, 120-140 plutonium-239 nuclei are formed. True, since the probability of fission of nuclei by fast neutrons is less than by thermal ones, the fuel must be enriched to a greater extent than for thermal reactors. In addition, it is impossible to remove heat with the help of water (water is a moderator), so you have to use other coolants: usually these are liquid metals and alloys, from very exotic variants such as mercury (such a coolant was used in the first American experimental reactor Clementine) or lead - bismuth alloys (used in some reactors for submarines - in particular, Soviet boats of Project 705) to liquid sodium (the most common variant in industrial power reactors). Reactors operating in this manner are called fast reactors. The idea of such a reactor was proposed in 1942 by Enrico Fermi. Of course, the military showed the most ardent interest in this scheme: fast reactors in the process of operation generate not only energy, but also plutonium for nuclear weapons. For this reason, fast reactors are also called breeders (from the English breeder - manufacturer).

Zigzags of history

It is interesting that the history of the world atomic energy began precisely with a fast neutron reactor. On December 20, 1951, the world's first fast neutron power reactor EBR-I (Experimental Breeder Reactor) with an electrical capacity of only 0.2 MW was put into operation in Idaho. Later, in 1963, a nuclear power plant with a fast neutron reactor Fermi was launched near Detroit - already with a capacity of about 100 MW (in 1966 there was a serious accident there with the melting of part of the core, but without any consequences for the environment or people) ...

In the USSR, since the end of the 1940s, Alexander Leipunsky has been studying this topic, under whose leadership the foundations of the theory of fast reactors were developed at the Obninsk Institute of Physics and Power Engineering (IPPE) and several experimental stands were built, which made it possible to study the physics of the process. As a result of the research carried out in 1972, the first Soviet fast-neutron nuclear power plant was commissioned in the city of Shevchenko (now Aktau, Kazakhstan) with the BN-350 reactor (originally designated BN-250). It not only generated electricity, but also used heat to desalinate water. Soon, the French nuclear power plant with the Phenix fast reactor (1973) and the British one with the PFR (1974), both with a capacity of 250 MW, were launched.

However, in the 1970s, thermal reactors began to dominate nuclear power. This was due to various reasons. For example, the fact that fast reactors can produce plutonium, which means that this can lead to a violation of the law on the non-proliferation of nuclear weapons. However, most likely the main factor was that thermal reactors were simpler and cheaper, their design was tested on military reactors for submarines, and uranium itself was very cheap. The industrial fast-neutron power reactors that went into operation after 1980 can be counted on the fingers of one hand all over the world: these are Superphenix (France, 1985–1997), Monju (Japan, 1994–1995) and BN-600 (Beloyarskaya NPP, 1980) , which is currently the only operating industrial power reactor in the world.

Construction of BN-800

They come back

However, at present, the attention of specialists and the public is again riveted to nuclear power plants with fast neutron reactors. According to estimates made by the International Atomic Energy Agency (IAEA) in 2005, the total volume of explored uranium reserves, the production costs of which do not exceed $ 130 per kilogram, is approximately 4.7 million tons. According to IAEA estimates, these reserves will last 85 years (if we take as a basis the need for uranium for electricity production at the level of 2004). The content of the isotope 235, which is “burned” in thermal reactors, in natural uranium is only 0.72%, the rest is “useless” for thermal reactors, uranium-238. However, if we switch to the use of fast reactors capable of “burning” uranium-238, these same reserves will last for more than 2500 years!

Moreover, fast reactors make it possible to implement a closed fuel cycle (it has not been implemented in BN-600 at present). Since only uranium-238 is “burned”, after reprocessing (extraction of fission products and adding new portions of uranium-238), the fuel can be reloaded into the reactor. And since more plutonium is produced than decayed in the uranium-plutonium cycle, the excess fuel can be used for new reactors.

Moreover, this method can be used to process surplus weapons-grade plutonium, as well as plutonium and minor actinides (neptunium, americium, curium) recovered from the spent fuel of conventional thermal reactors (minor actinides are currently a very dangerous part of radioactive waste). At the same time, the amount of radioactive waste in comparison with thermal reactors is reduced by more than twenty times.

Smooth on paper only

Why, with all their advantages, fast neutron reactors have not become widespread? This is primarily due to the peculiarities of their design. As mentioned above, water cannot be used as a coolant, since it is a neutron moderator. Therefore, in fast reactors, metals are mainly used in a liquid state - from exotic lead-bismuth alloys to liquid sodium (the most common option for nuclear power plants).

“In fast reactors, thermal and radiation loads are much higher than in thermal reactors,” Mikhail Bakanov, chief engineer of the Beloyarsk NPP, explains to PM. - This leads to the need to use special structural materials for the reactor pressure vessel and in-reactor systems. The bodies of TVEL and fuel assemblies are made not of zirconium alloys, as in thermal reactors, but of special alloyed chromium steels, which are less susceptible to radiation ‘swelling’. On the other hand, for example, the reactor pressure vessel is not subject to internal pressure loads - it is only slightly higher than atmospheric pressure ”.

According to Mikhail Bakanov, in the first years of operation, the main difficulties were associated with radiation swelling and cracking of the fuel. These problems, however, were soon resolved, new materials were developed - both for fuel and for fuel rod casings. But even now the campaigns are limited not so much by the fuel burnup (which reaches 11% on the BN-600), but by the resource of materials from which the fuel, fuel rods and fuel assemblies are made. Further operational problems were mainly associated with leaks of sodium in the secondary circuit, a chemically active and fire hazardous metal that violently reacts to contact with air and water: “Only Russia and France have long experience in operating industrial fast-neutron power reactors. Both we and French specialists faced the same problems from the very beginning. We have successfully solved them, from the very beginning providing for special means of monitoring the tightness of the circuits, localization and suppression of sodium leaks. And the French project turned out to be less prepared for such troubles, as a result, in 2009 the Phenix reactor was finally shut down. "

“The problems were really the same,” adds Nikolai Oshkanov, director of the Beloyarsk NPP, “but they were solved here and in France in different ways. For example, when the head of one of the assemblies was bent on the Phenix to grab and unload it, the French specialists developed a complex and rather expensive system of 'vision' through the sodium layer. And when we had the same problem, one of our engineers suggested using a video camera placed in a simple structure like a diving bell - an open pipe from the bottom with argon blowing from above. When the sodium melt was displaced, the operators were able to grip the machine via video link and the bent assembly was successfully retrieved. ”

Fast future

“There would be no such interest in the technology of fast reactors in the world if it were not for the successful long-term operation of our BN-600,” says Nikolai Oshkanov. “The development of nuclear power, in my opinion, is primarily associated with the serial production and operation of fast reactors. ... Only they make it possible to involve all natural uranium in the fuel cycle and thus increase efficiency, as well as reduce the amount of radioactive waste by tens of times. In this case, the future of nuclear energy will be really bright ”.

Fast breeder reactor BN-800 (vertical section)
What's inside him

The active zone of a fast neutron reactor is arranged like an onion, in layers

370 fuel assemblies form three zones with different enrichment in uranium-235 - 17, 21 and 26% (initially there were only two zones, but in order to equalize the energy release, three were made). They are surrounded by side screens (blankets), or breeding zones, where assemblies containing depleted or natural uranium, consisting mainly of the 238 isotope, are located. reproduction).

Fuel assemblies (FA) are a set of fuel elements (fuel rods) assembled in one housing - tubes made of special steel filled with uranium oxide pellets with different enrichment. So that the fuel rods do not come into contact with each other, and a coolant can circulate between them, a thin wire is wound on the tubes. Sodium enters the fuel assembly through the lower throttling holes and exits through the windows in the upper part.

In the lower part of the fuel assembly there is a shank inserted into the socket of the collector, in the upper part there is a head part, for which the assembly is gripped during overloading. Fuel assemblies of different enrichment have different seats, so it is simply impossible to install the assembly in the wrong place.

To control the reactor, 19 compensating rods are used containing boron (neutron absorber) to compensate for fuel burnup, 2 automatic control rods (to maintain a given power), and 6 active protection rods. Since the intrinsic neutron background of uranium is small, a "backlight" is used for the controlled launch of the reactor (and control at low power levels) - a photoneutron source (gamma emitter plus beryllium).

How the BN-600 reactor works

The reactor has an integral layout, that is, the core (1) is located in the reactor vessel, as well as three loops (2) of the first cooling circuit, each of which has its own main circulation pump (3) and two intermediate heat exchangers (4). The coolant is liquid sodium, which is pumped through the core from the bottom up and heats up from 370 to 550 ° C

Passing through intermediate heat exchangers, it transfers heat to sodium in the second circuit (5), which already enters the steam generators (6), where it evaporates water and superheats the steam to a temperature of 520 ° C (at a pressure of 130 atm). Steam is supplied to the turbines alternately in high (7), medium (8) and low (9) pressure cylinders. The spent steam is condensed by cooling with water (10) from the cooling pond and again enters the steam generators. Three turbine generators (11) of the Beloyarsk NPP provide 600 MW of electrical power. The gas cavity of the reactor is filled with argon under a very low excess pressure (about 0.3 atm).

Blind overload

The refueling process of one assembly takes up to an hour, the refueling of a third of the core (about 120 fuel assemblies) takes about a week (in three shifts), this procedure is performed every micro campaign (160 effective days, in terms of full capacity). True, now the fuel burnup has been increased, and only a quarter of the core is overloaded (approximately 90 fuel assemblies). At the same time, the operator does not have direct visual feedback and is guided only by the indicators of the angles of rotation of the column and grippers (positioning accuracy is less than 0.01 degrees), extraction and setting forces. For safety reasons, certain restrictions are imposed on the operation of the mechanism: for example, it is impossible to simultaneously release two adjacent cells, in addition, during an overload, all control and protection rods must be in the core.

In 1983, on the basis of BN-600, the enterprise developed a project for an improved BN-800 reactor for a power unit with a capacity of 880 MW (e). In 1984, work began on the construction of two BN-800 reactors at the Beloyarsk NPP and the new South Ural NPP. The subsequent delay in the construction of these reactors was used to finalize the design in order to further increase its safety and improve technical and economic indicators. Work on the construction of BN-800 was resumed in 2006 at the Beloyarsk NPP (4th power unit) and should be completed in 2014.

The following important tasks have been set for the BN-800 reactor under construction:

Maintenance of operation on MOX-fuel.
Pilot demonstration of key components of the closed fuel cycle.
Testing in real operating conditions of new types of equipment and improved technical solutions introduced to improve efficiency, reliability and safety.
Development of innovative technologies for future fast neutron reactors with liquid metal coolant:
- testing and certification of advanced fuels and structural materials;
- demonstration of the technology of burning out minor actinides and transmutation of long-lived fission products that make up the most dangerous part of radioactive waste from nuclear power.

The development of a project for an improved commercial reactor BN-1200 with a capacity of 1220 MW is underway.

BN-1200 reactor (vertical section)

The following program for the implementation of this project is planned:

2010 ... 2016 - development of the technical design of the reactor plant and implementation of the R&D program.
2020 - commissioning of the main MOX-fueled power unit and organization of its centralized production.
2023 ... 2030 - commissioning of a series of power units with a total capacity of about 11 GW.

Nuclear energy has always received increased attention due to its potential. In the world, about twenty percent of electricity is obtained with the help of nuclear reactors, and in developed countries this indicator of the product of nuclear energy is even higher - more than a third of all electricity. However, the main type of reactors is still thermal, such as LWR and VVER. Scientists believe that one of the main problems of these reactors in the near future will be the lack of natural fuel, uranium, its isotope 238, which is necessary for the fission chain reaction. Proceeding from the possible depletion of the resources of this natural fuel material for thermal reactors, restrictions are imposed on the development of nuclear energy. More promising is the use of nuclear reactors using fast neutrons, in which fuel breeding is possible.

Development history

Based on the program of the Ministry of Atomic Industry of the Russian Federation, at the beginning of the century, tasks were set to create and ensure the safe operation of nuclear power complexes, modernized nuclear power plants of a new type. One of these facilities was the Beloyarsk nuclear power plant, located 50 kilometers near Sverdlovsk (Yekaterinburg). The decision to create it was made in 1957, and in 1964 the first unit was put into operation.

Thermal nuclear reactors operated in two of its blocks, which had exhausted their resource by the 80-90s of the last century. For the first time in the world, the BN-600 fast neutron reactor was tested at the third block. During his work, the results planned by the developers were obtained. The safety of the process was also up to the mark. During the project period, which ended in 2010, there were no major irregularities or deviations. The final term of his work expires by 2025. It can already be said that fast-neutron nuclear reactors, which include the BN-600 and its successor, the BN-800, have a great future.

Launch of the new BN-800

Scientists OKBM them. Afrikantov from Gorky (now Nizhny Novgorod) prepared a project for the fourth power unit of the Beloyarsk NPP back in 1983. In connection with the accident that occurred at Chernobyl in 1987 and the introduction of new safety standards in 1993, work was stopped and the launch was postponed indefinitely. Only in 1997, after obtaining a license for the construction of Unit 4 with the BN-800 reactor with a capacity of 880 MW from Gosatomnadzor, the process resumed.

On December 25, 2013, the reactor began to warm up for the further entry of the coolant. In June the fourteenth, as planned, there was a mass output sufficient to carry out a minimal chain reaction. Then the matter stalled. MOX fuel, consisting of fissile uranium and plutonium oxides, similar to that used in Unit 3, was not ready. It was he who wanted to use the developers in the new reactor. I had to combine, look for new options. As a result, in order not to postpone the launch of the power unit, it was decided to use uranium fuel in the assembly part. The launch of the BN-800 nuclear reactor and unit No. 4 took place on December 10, 2015.

Process description

During operation in a reactor with fast neutrons, secondary elements are formed due to the fission reaction, which, when absorbed by the uranium mass, form a newly created nuclear material plutonium-239, capable of continuing the process of further fission. The main advantage of this reaction is the production of plutonium neutrons, which is used as fuel for nuclear reactors at nuclear power plants. Its presence makes it possible to reduce the production of uranium, the reserves of which are limited. From a kilogram of uranium-235, a little over a kilogram of plutonium-239 can be obtained, thereby ensuring the breeding of fuel.

As a result, energy production in nuclear power units with the lowest consumption of scarce uranium and the absence of production restrictions will increase hundreds of times. It is estimated that in this case, the uranium reserves will be enough for mankind for several tens of centuries. The best option in nuclear power to maintain a balance in the minimum consumption of uranium will be a ratio of 4 to 1, where four thermal reactors will use one, operating on fast neutrons.

BN-800 targets

During the period of operation in power unit No. 4 of the Beloyarsk NPP, certain tasks were set for the nuclear reactor. The BN-800 reactor is supposed to run on MOX fuel. A slight hitch that occurred at the beginning of the work did not change the plans of the creators. According to the director of the Beloyarsk NPP, Mr. Sidorov, the full transition to MOX fuel will be carried out in 2019. If this is done, the local fast breeder nuclear reactor will be the first in the world to fully operate with such fuel. It should become a prototype for future similar fast reactors with a liquid metal coolant, more efficient and safer. Based on this, the BN-800 is testing innovative equipment under operating conditions, checking the correct application of new technologies that affect the reliability and efficiency of the power unit.

class = "eliadunit">

Testing the operation of the new fuel cycle system.

Long-lived radioactive waste burning tests.

Disposal of weapons-grade plutonium accumulated in large quantities.

BN-800, just like its predecessor, BN-600, should become a starting point for Russian developers to accumulate invaluable experience in the creation and operation of fast reactors.

Fast breeder reactor advantages

The use of BN-800 and similar nuclear reactors in nuclear power engineering allows

Significantly increase the period of uranium reserves, which significantly increases the amount of energy received.

Ability to reduce the lifetime of radioactive fission products to a minimum (from several thousand years to three hundred).

To improve the safety of nuclear power plants. The use of a fast neutron reactor makes it possible to minimize the possibility of core melting to a minimum level, makes it possible to significantly increase the level of self-protection of an object, and to exclude the release of plutonium during reprocessing. Reactors of this type with sodium coolant have an increased level of safety.

On August 17, 2016, power unit No. 4 of the Beloyarsk NPP entered the operating mode of 100% capacity. Since December last year, the united system "Ural" has been receiving the energy generated by the fast reactor.

class = "eliadunit">

The town of Zarechny is located 40 km from Yekaterinburg, in the midst of the most beautiful Ural forests. In 1964, the first Soviet industrial nuclear power plant was launched here - Beloyarskaya (with the AMB-100 reactor with a capacity of 100 MW). Now the Beloyarsk NPP remains the only one in the world where an industrial fast neutron power reactor, BN-600, operates.

At the heart of any reactor is the fission of heavy nuclei under the action of neutrons. True, there are also significant differences. In thermal reactors, uranium-235 is fissioned by low-energy thermal neutrons, thus forming fission fragments and new high-energy neutrons (the so-called fast neutrons). The probability of absorption by the uranium-235 nucleus (followed by fission) of a thermal neutron is much higher than that of a fast one, so the neutrons must be slowed down. This is done with the help of moderators - substances, in collisions with nuclei of which neutrons lose energy. Low-enrichment uranium is usually used as fuel for thermal reactors, graphite, light or heavy water are used as moderators, and ordinary water is used as a coolant. Most of the operating nuclear power plants are arranged according to one of these schemes.

Fast neutrons produced by forced nuclear fission can be used without any slowdown. The scheme is as follows: fast neutrons formed during the fission of uranium-235 or plutonium-239 nuclei are absorbed by uranium-238 with the formation (after two beta decays) of plutonium-239. Moreover, for 100 separated nuclei of uranium-235 or plutonium-239, 120-140 plutonium-239 nuclei are formed. True, since the probability of fission of nuclei by fast neutrons is less than by thermal ones, the fuel must be enriched to a greater extent than for thermal reactors. In addition, it is impossible to remove heat with the help of water (water is a moderator), so you have to use other coolants: usually these are liquid metals and alloys, from very exotic variants such as mercury (such a coolant was used in the first American experimental reactor Clementine) or lead - bismuth alloys (used in some reactors for submarines, in particular, Soviet boats of project 705) to liquid sodium (the most common option in industrial power reactors). Reactors operating in this manner are called fast reactors. The idea of such a reactor was proposed in 1942 by Enrico Fermi. Of course, the military showed the most ardent interest in this scheme: fast reactors in the process of operation generate not only energy, but also plutonium for nuclear weapons. For this reason, fast reactors are also called breeders (from the English breeder - manufacturer).

What's inside him

The active zone of a fast neutron reactor is arranged like an onion, in layers. 370 fuel assemblies form three zones with different enrichment in uranium-235 - 17, 21 and 26% (initially there were only two zones, but in order to equalize the energy release, three were made). They are surrounded by side screens (blankets), or breeding zones, where assemblies containing depleted or natural uranium, consisting mainly of the 238 isotope, are located. reproduction). The BN-600 reactor belongs to breeders, that is, for 100 uranium-235 nuclei separated in the core, 120-140 plutonium nuclei are produced in the side and end screens, which makes it possible to expand the breeding of nuclear fuel. Fuel assemblies (FA) are a set of fuel elements (fuel rods) assembled in one housing - tubes made of special steel filled with uranium oxide pellets with different enrichment. So that the fuel rods do not touch each other and a coolant can circulate between them, a thin wire is wound on the tubes. Sodium enters the fuel assembly through the lower throttling holes and exits through the windows in the upper part. In the lower part of the fuel assembly there is a shank inserted into the socket of the collector, in the upper part there is a head part, for which the assembly is gripped during overloading. Fuel assemblies of different enrichment have different seats, so it is simply impossible to install the assembly in the wrong place. To control the reactor, 19 compensating rods are used, containing boron (neutron absorber) to compensate for fuel burnout, 2 automatic control rods (to maintain a given power), and 6 active protection rods. Since the intrinsic neutron background of uranium is small, a "backlight" is used for the controlled launch of the reactor (and control at low power levels) - a photoneutron source (gamma emitter plus beryllium).

Zigzags of history

It is interesting that the history of the world atomic energy began precisely with a fast neutron reactor. On December 20, 1951, the world's first fast neutron power reactor EBR-I (Experimental Breeder Reactor) with an electrical capacity of only 0.2 MW was put into operation in Idaho. Later, in 1963, a nuclear power plant with a fast neutron reactor Fermi was launched near Detroit - already with a capacity of about 100 MW (in 1966 there was a serious accident with the melting of a part of the core, but without any consequences for the environment or people) ...

However, in the 1970s, thermal reactors began to dominate nuclear power. This was due to various reasons. For example, the fact that fast reactors can produce plutonium, which means that this can lead to a violation of the law on the non-proliferation of nuclear weapons. However, most likely the main factor was that thermal reactors were simpler and cheaper, their design was tested on military reactors for submarines, and uranium itself was very cheap. The industrial fast-neutron power reactors that went into operation after 1980 can be counted on the fingers of one hand all over the world: these are Superphenix (France, 1985-1997), Monju (Japan, 1994-1995) and BN-600 (Beloyarskaya NPP, 1980) , which is currently the only operating industrial power reactor in the world.

They come back

Reactor assembly workshop, where separate parts of the reactor are assembled from separate parts using the SKD method

Blind reboot

Unlike thermal reactors, in the BN-600 reactor the assemblies are located under a layer of liquid sodium; therefore, the removal of spent assemblies and the installation of fresh ones in their place (this process is called refueling) occurs in a completely closed mode. In the upper part of the reactor there are large and small rotary plugs (eccentric relative to each other, that is, their rotational axes do not coincide). A column with control and protection systems, as well as an overload mechanism with a collet-type gripper, is mounted on a small rotary plug. The swivel mechanism is equipped with a "water seal" made of a special fusible alloy. In the normal state, it is solid, and for reloading it is heated to the melting point, while the reactor remains completely sealed, so that the release of radioactive gases is practically excluded. The reloading process turns off many stages. First, the gripper is brought to one of the assemblies located in the in-reactor storage of spent assemblies, retrieves it and transfers it to the unloading elevator. Then it is lifted into the transfer box and placed in the drum of spent assemblies, from where, after cleaning with steam (from sodium), it will enter the holding pool. At the next stage, the mechanism retrieves one of the core assemblies and transfers it to the in-reactor storage. After that, the required one is removed from the drum of fresh assemblies (into which the fuel assemblies that have come from the factory are installed in advance) are installed in the elevator of fresh assemblies, which feeds it to the reloading mechanism. The last stage is the installation of fuel assemblies in the vacant cell. In this case, certain restrictions are imposed on the operation of the mechanism for safety reasons: for example, it is impossible to simultaneously release two adjacent cells, in addition, during an overload, all control and protection rods must be in the core. The refueling process of one assembly takes up to an hour, the refueling of a third of the core (about 120 fuel assemblies) takes about a week (in three shifts), this procedure is performed every micro campaign (160 effective days, in terms of full capacity). True, now the fuel burnup has been increased, and only a quarter of the core is overloaded (approximately 90 fuel assemblies). At the same time, the operator does not have direct visual feedback, and is guided only by the indicators of the angles of rotation of the column and grippers (positioning accuracy is less than 0.01 degrees), extraction and setting forces.

The reloading process includes many stages, is carried out using a special mechanism and resembles a game of "15". The ultimate goal is to get fresh assemblies from the corresponding drum into the desired nest, and the spent assemblies into its own drum, from where, after cleaning with steam (from sodium), they will fall into the holding pool.

Smooth on paper only

“In fast reactors, thermal and radiation loads are much higher than in thermal reactors,” Mikhail Bakanov, chief engineer of the Beloyarsk NPP, explains to PM. - This leads to the need to use special structural materials for the reactor pressure vessel and in-reactor systems. The housings of the fuel rods and fuel assemblies are not made of zirconium alloys, as in thermal reactors, but of special alloyed chromium steels, which are less susceptible to radiation 'swelling.' higher than atmospheric ".

“The problems were really the same,” adds Nikolai Oshkanov, director of the Beloyarsk NPP, “but they were solved in our country and in France in different ways. For example, when the head of one of the assemblies was bent on the Phenix to grab and unload it, the French specialists developed a complex and rather expensive system of 'seeing' through the sodium layer. And when we had the same problem, one of our engineers suggested using a video camera. housed in the simplest design, such as a diving bell, an open tube at the bottom with argon blown from above. When the sodium melt was expelled, the operators were able to grip the mechanism using video link and the bent assembly was successfully retrieved. "

Fast future

And those perspectives that leadership in this area brings.

Nuclear technologies in Russia have always occupied a special place: they ensured strategic security, maintained global parity at the stages of the superiority of opponents in the world arena in the field of military technologies, and ensured energy security. In the modern world, the development of nuclear and radiation technologies is one of the engines of industrial and social development (a large technological project inevitably turns out to be a pole of influence on education, ecology, economy and culture).

At present, the world owes about 13% of all electricity produced to nuclear technologies, with the lowest cost per kilowatt-hour and the lowest indicators of environmental pollution.

During the construction of a nuclear power plant, even the emissions of builders' diesel generators are taken into account in order to achieve at least some figures regarding the environmental impact and CO2 emissions.

From a purely technological point of view, it is worth noting that enviable indicators of nuclear power were achieved using reactors that operate on "thermal" or "slow" neutrons - neutrons that passed through a special moderator (water, heavy water or graphite), threw off excess energy and launched self-sustaining nuclear chain reaction. Accordingly, the rate of the reaction and many engineering and design problems that must be solved for the successful operation of a nuclear reactor depend on the number of free neutrons available for a nuclear reaction and the ability of the fuel to capture them. According to the observations of scientists, in the technology of so-called fast reactors (a.k.a. "breeders" or "breeder reactors") there is an excess of neutrons, a neutron flux of 2.3 free neutrons is formed against 1 for thermal reactors. This colossal potential, in addition to direct energy-generating applications, can be used for the reproduction of nuclear fuel and for solving other problems: cogeneration of electricity and heat, water desalination, hydrogen production, and others.

Nuclear power in operation today uses almost exclusively uranium-235 as fuel, the content of which is only 0.7% in fossil uranium. The percentage of uranium-235 in fuel cells is brought to an operable amount due to special enrichment procedures. Fast reactors can produce plutonium, which is used to generate and go to warehouses / dumps uranium-238, the content of which in the mined ore is the remaining 99.3%; and plutonium, in turn, is excellent as a fuel for thermal reactors operated today, that is, more fuel is generated in fast reactors than is consumed!

According to IAEA estimates, the proven reserves of uranium-235 will last for about 85 years, which is an order of magnitude less than oil or gas. Such nuclear power obviously does not have a long-term future. But the picture changes drastically when considering the large-scale deployment of fast reactors and closing the fuel cycle.

This version of development opens up to use all the natural resources of uranium (235 and 238), as well as thorium and the accumulated weapons-grade plutonium, and then the explored reserves will last for (according to various estimates) about 2500 years, taking into account the steady growth of energy consumption and the resource deficit according to Malthus. Unsurprisingly, from the very beginning of nuclear power development, breeders have relied on the future backbone of the global nuclear generating industry. The level of technology development acts as a "limiter": working with fast reactors, which implies closing the fuel cycle, still requires an expensive and complex complex for the processing and recycling of irradiated nuclear fuel. But, despite the higher unit costs for reprocessing spent nuclear fuel from fast reactors, the smaller amounts of reprocessable materials required to obtain a unit of plutonium make this process devilishly profitable compared to today's reprocessing of waste from thermal reactors.

Speaking of accumulated radioactive waste: fast reactors make it possible to process weapons-grade plutonium and minor actinides (neptunium, americium, curium) recovered from the spent fuel of conventional thermal reactors (minor actinides are currently a very dangerous part of radioactive waste). Spent fuel from slow reactors is a new fuel for the future of nuclear power, and such a future is already coming. And as many as two enterprises capable of reprocessing irradiated nuclear fuel are located in Russia. There are not many more such factories in the world than two Russian ones.

World Race for Fast Reactors

The world's first nuclear reactor was "slow": it was built by Enrico Fermi under the western stands of the football field of the University of Chicago from graphite and uranium blocks, for 28 minutes with the help of such a mother it was launched in 1942 and had absolutely no protection against radiation and cooling systems. According to a fairly accurate description of Mr. Fermi himself, this development looked like "a damp pile of black bricks and wooden logs", which in fact it was. But even then he dreamed of building a fast reactor.

The first fast reactors, respectively, appeared in America: in Los Alamos in 1946, the Clementine stand was launched, in which mercury acted as a rather exotic coolant; and in 1951, the first power reactor EBR-1 (Experimental Breeder Reactor) with a capacity of only 0.2 MW was launched in Idaho, which demonstrated the possibility of simultaneous production of electricity and nuclear fuel in one device and launched the history of nuclear power. Later, in 1963, an experimental industrial fast neutron reactor "Enrico Fermi" with a capacity of about 100 MW was launched in Detroit, but after only three years there was a serious accident with the melting of part of the core - albeit without consequences for the environment or people ...

The possibility of expanded plutonium production, necessary for the Soviet atomic project, was proved at the first Soviet research reactor with the unpretentious nomenclature name BR-1, launched in Obninsk in 1956. It was possible to obtain the data necessary for the development of a fast power reactor only on an older version of the BR-5, created in 1959. Later, in 1970, an experimental BOR-60 reactor was launched at NIIAR (Dimitrovgrad), which still provides the city with heat and electricity. Further, the technology was also tested at the world's first fast-neutron power reactor BN-350, which was launched in 1973 and was engaged in power generation and desalination of water in the steppes until its shutdown in the 1990s. However, the BN-350 was stopped not due to the exhaustion of its technical resource, but because of concerns about the quality of ensuring its operation after the collapse of the USSR.

In 1980, as of today, it is the world's only operating industrial fast neutron reactor. Today, a new generation BN-1200 reactor, intended for serial construction, is already at the technical design stage - its commissioning is scheduled for 2025. Also, by 2020, a 300 MW fast reactor with a lead-bismuth coolant is planned to be launched on the territory of the Siberian Chemical Combine in Seversk. - This technology has been tested for decades in the reactors of submarines and icebreakers.

In the late 1950s, Britain and France joined the leaders of the nuclear race with their projects. In 1986, a consortium of European countries connected the Superphenix reactor to the network, during the creation of which some solutions were borrowed earlier embodied in the Soviet BN-600, but in 1996 the project was closed without the right to resurrect. The fact is that mass hysteria was inflated around Superphenix due to the efforts of the mass media: the reactor under construction was associated primarily with the production of plutonium.

The turmoil inflated in the media field resulted in sixty-thousand protests, escalating into street riots, and a year after the physical launch, the nuclear power plant building was fired in five volleys through the Rhone from the Soviet RPG-7 anti-tank grenade launcher.

The authors of this celebration of life, fortunately, could not inflict significant damage to the station. But the project was soon canceled. However, in 2010, the French again return to the construction of a fast neutron reactor with a sodium coolant - the project is called "Astrid", the planned capacity is 600 MW. And although France relies on its own developments in its fast reactor program, it still mainly relies on Russian enrichment plants.

The Chinese are striving to catch up and overtake everyone in the world, including because India has bypassed them here, which, after numerous transfers, is going to carry out the physical launch of a demonstration fast reactor of its own design PFBR-500 this year. After its commissioning, India wants to start construction of a series of six commercial power units of 500 MW each and to build a nuclear fuel reprocessing plant on the same territory, using its own nuclear fuel thorium, of which they have a lot.

The Japanese, in turn, contrary to the expected reaction after the Fukushima accident, continue the revival of the Monzu fast reactor, which operated from 1994 to 1995. By the way, one should not be deceived about the Fukushima tragedy: nuclear power is generally characterized by cyclical development. After each accident (Three-Mile Island, Chernobyl, Fukushima), interest in nuclear power plants weakens slightly, but then the demand for electricity again dictates its categorical imperative - and now the next generations of reactors are put into operation, with new types of protective mechanisms.

In total, about 30 concepts of fast reactors have been developed in the world, some of which have been experimentally tested "in iron". But today only one country can boast of proven technologies and trouble-free operation of industrial fast reactors in its national portfolio - and that is Russia.

Complex engineering

The advantages of fast reactors are obvious, as well as the engineering complexity of their creation. The lack of the necessary technologies is one of the key reasons why fast reactors have not gained wider acceptance at the moment. As noted earlier, water, a neutron moderator, cannot be used in fast reactors; therefore, metals are used in a liquid state: from the most common sodium to lead-bismuth alloys. The use of a liquid metal coolant under conditions of many times more intense energy release than in traditional reactors poses another serious problem - materials science. All components of the reactor vessel and in-reactor systems must be made of corrosion-resistant special materials that can withstand 550 ° C typical of liquid sodium in a fast reactor.

The problem of selecting the right materials has created many challenges for the inexhaustible resourcefulness of domestic engineers. When one fuel assembly was twisted in the core of an operating reactor to reach it, French nuclear scientists invented a complicated and expensive way of "seeing" through a layer of liquid sodium. When the Russians faced the same problem, our engineers decided to elegantly use a simple video camera housed in a kind of diving bell - a pipe with argon blowing from above, which allowed operators to quickly and efficiently retrieve the spoiled fuel cells.

Of course, the engineering complexity of a fast reactor affects its cost, which at present - when fast reactors are more likely in the conceptual field - is significantly higher than that of thermal reactors. All processes for closing the nuclear fuel cycle are also quite expensive: the technologies are available, they have been worked out, tested and developed, but they have yet to be brought to the commercial level. Fortunately, for Russia, this is a matter of the next two or three decades.

Fast neutron soft power

Russia's indisputable technological superiority in closing the nuclear fuel cycle should obviously be strategically implemented on the world stage. Russia can assume the burden of leadership in creating such a global infrastructure that would ensure equal access for all interested states to nuclear energy, but at the same time would reliably guarantee compliance with the requirements of the nonproliferation regime. The plan for the implementation of this initiative provides for the following areas:

Creation of international uranium enrichment centers (IUEC), the first of which is located in Angarsk;

Formation of international centers for reprocessing and storage of spent nuclear fuel (not all the same to lick your lips at our open spaces);

Creation of international centers for the training of qualified personnel for nuclear power plants and joint research in the field of nuclear technologies protected from unauthorized proliferation.

As of today, the most developed part of the proposed program has become the point on the creation of the IUEC: such centers function as joint commercial enterprises that do not enjoy government support. The board of directors of such enterprises should include representatives of the authorities, employees of the nuclear fuel cycle companies and IAEA experts, and the latter will turn out to be consultants without the right to vote, whose goal will be to verify the operation of the center and certify its individual actions. Accordingly, non-nuclear countries will not be allowed to enrichment technologies, and this is a rather serious question.

Unfortunately, the rest of the provisions of the initiative to create a global infrastructure for nuclear energy did not receive substantive content. In this connection, a natural question arises: are there any guarantees that these versions of the political exploitation of technical potential will not turn out to be forgotten fantasies on paper?

To get out of this situation, to attract a wide range of developing countries interested in the peaceful use of nuclear energy, for the start of the program of international centers for the nuclear fuel cycle, it is necessary to fill these proposals with predictive, research and scientific and technical content.

Small and developing states involved in major research projects in the field of nuclear energy economics are able to see their specific benefits from participating in the implementation of these initiatives and understand what changes are needed in their national programs.

The recognized advanced level of fast reactor technology in Russia - the only country operating an industrial reactor of this type in combination with experience in nuclear fuel reprocessing - will allow Russia in the long term to claim the role of one of the leaders in the world nuclear energy.

The successful implementation of Russian proposals for the creation of a global nuclear infrastructure is an important factor for the future development of world energy, not to mention Russia's place in this development. The implementation of Russian proposals may over time not only ensure the safety of global nuclear energy and its almost endless fuel self-sufficiency, but also reshape the landscape of the electricity market as a whole: the threat of a shortage of all types of fossil fuels, including uranium, at a certain stage will become much closer and more real than it can seem.

In response to the growing prices for hydrocarbons in the world over the past twenty years, there has been an intensification of interest in alternative energy. However, there are a number of reasons to believe that the only sane alternative to traditional thermal generation can only be nuclear power. Very serious and thick books have been written about comparing the prospects of nuclear energy and renewable generation, which, in short, say that in the future, fast reactors will shine for us - and Russia's technological leadership.

The most widespread today are water-water and boiling thermal reactors. The SNF composition of different reactors is somewhat different. It depends, in particular, on burnout, but not only. In a typical VVER reactor with an electrical power of 1000 MW, using uranium fuel, 21 tons of spent nuclear fuel (SNF) with a volume of 11 m 3 (1/3 of the total fuel load) are generated annually. 1 ton of SNF freshly extracted from a VVER-type reactor contains 950-980 kg of uranium-235 and 238, 5-10 kg of plutonium, fission products (1.2-1.5 kg of cesium-137, 770 g of technetium-90, 500 g of strontium -90, 200 g of iodine-129, 12 - 15 g of samarium-151), minor actinides (500 g of neptunium-237, 120 - 350 g of americium-241 and 243, 60 g of curium-242 and 244), as well as in smaller the amount of radioisotopes of selenium, zirconium, palladium, tin and other elements. When using MOX fuel, the SNF will contain more americium and curium.

Fission products

During the first ten years, the SNF heat release after unloading drops by approximately two orders of magnitude and is mainly determined by fission products. The largest contribution to the activity of spent fuel with a three-year holding time is made by: 137 Cs + 137m Ba (24%), 144 Ce + 144 Pr (21%), 90 Sr + 90 Y (18%), 106 Ru + 106 Rh (16% ), 147 Pm (10%), 134 Cs (7%), the relative contribution of 85 Kr, 154 Eu, 155 Eu is approximately 1% of each isotope.

Short-lived fission products

Nuclide	T 1/2	Nuclide	T 1/2
85 Kr	10.8years	137 Cs	26.6 years
90 Sr	29 years	137m Ba	156 days
90 Y	2.6 days	144 Ce	284.91 days
106 Ru	371.8 days	144 Pr	17.28 m
106 Rh	30.07 s	147 Pm	2.6 years
134 Cs	2.3 years	154 Eu	8.8 years
		155 Eu	4.753 years

For several years after unloading, while spent fuel is stored in water-filled pools, the main risk is that the loss of cooling water can heat the fuel to a temperature high enough to ignite the zirconium alloy from which the fuel rods are made, resulting in to the release of volatile radioactive fission products.

Long-lived fission products

In the long term (10 4 -10 6 years), these products can be dangerous due to their greater mobility than actinides.

Actinides

Minor actinides include long-lived and relatively long-lived isotopes of neptunium (Np-237), americium (Am-241, Am-243), and curium (Cm-242, Cm-244, Cm-245).

Neptunium

Neptunium, which is mainly represented by the only isotope Np-237, is produced from the uranium isotope U-235 according to the following chain:

The scheme of its decay to the nearest long-lived daughter nucleus has the form

Np-237 (T 1/2 = 2.14 10 6 years; α) → Pa-233 (T 1/2 = 27 days; β) → U-233 (T 1/2 = 1.59 10 5 years; α)

Analyzing the dynamics of changes in the activities of nuclei in the decay chain, we can say that Np-237 and Pa-233 will be in secular equilibrium and their activities will be equal, and the activity of Pa-233 will be very small and can be ignored.

Radiation characteristics of Np-237 and Ra-233

C 0 - specific activity of the material per 1 kg of Np-237 (Ci / kg); Q is the decay energy (MeV);
E α - energy of α-particles (MeV); E β - average energy of β-particles (MeV);
E γ is the total energy of γ-quanta (keV); W - heat dissipation (W / kg).

Neptunium, which is predominantly represented by the single isotope Np-237, contributes significantly to long-term radiotoxicity due to its long half-life. However, Np-237 does not make a significant contribution to heat generation. Np-237 can be transmuted in both thermal and fast reactors.

Americium

The long-lived isotopes of americium produced in significant quantities in thermal reactors include the isotopes Am-241 and Am-243. The Am-242m isotope is produced in significantly smaller quantities, but its content in americium released from spent nuclear fuel can have a significant effect on the characteristics of neutron radiation of the material.
The isotopes of americium Am-241, Am-243 and isotopes of curium Cm-242, Cm-244 and Cm-245 are produced from the uranium isotope U-238 in the following chains:

Am-241
In spent nuclear fuel Am-241 is the dominant isotope of americium, although there are also Am-242, Am-242m and Am-243.
The scheme of decay of Am-241 to the nearest long-lived daughter nucleus has the form

Am-241 (T 1/2 = 4.32 10 2 years; α) → Np-237 (T 1/2 = 2.14 10 6 years; α)

Since T 1/2 (Am-241)<< T 1/2 (Np-237), то радиационные характеристики процесса определяются исключительно параметрами распада собственно Аm-241

Am-243
The scheme of decay of Am-243 to the nearest long-lived daughter nucleus has the form

Am-243 (T 1/2 = 7.38 10 3 years; α) → Np-239 (T 1/2 = 2.35 days; β) → Pu-239 (T 1/2 = 2.42 10 4 years; α)

Am-243 and Np-239 are in radiation equilibrium and their activities are equal.

Am-242m
Thermal reactors also produce the long-lived isomer Am-242m

Am-242m (T 1/2 = 1.52 10 2 years; γ) → Am-242 (T 1/2 = 16 hours; 82% β; 18% EZ *) →
→ Pu-242 (T 1/2 = 3.76 10 5 years; α) → Cm-242 (T 1/2 = 1.63 10 2 days; α) → Pu-238 (T 1/2 = 88 years; α )

The following radionuclides contribute to the radioactivity of material containing Am-242m:
Am-242m, Am-242, Cm-242

Radiation characteristics of Am-241, Am-243, Np-239, Am-242m, Am-242 and Cm-242

Isotope	T 1/2	C 0	Type of decay	Q	E α	E β	E γ	W
Am-241	4.32 10 2 years	3.44 · 10 3	α	5.64	5.48		29	1.11 10 2
Am-243	7.38 10 3 years	200	α	5.44	5.27	0	48	6.6
Np-239	2.35 days	200	β	0.72	0	0.118	175	6.6
Am-242m	1.52 10 2 years	9.75 · 10 3	γ	0.072	0	0	49	310
Am-242	16 hours	1.75 · 10 3 8 · 10 3	EZ β	0.75, 17.3% 0.66, 82.7%	0 0	0 0.16	18
Cm-242	1.63 10 2 days	8 · 10 3	α	6.2	6.1	0	1.8

Americium is the main contributor to the gamma activity and radiotoxicity of spent nuclear fuel approximately 500 years after unloading, when the contribution of fission products decreases by several orders of magnitude. All americium lends itself to transmutation in an intense neutron flux using capture and fission reactions.

Curium

Cm-242
The decay scheme for Cm-242 is:

Сm-242 (Т 1/2 = 163 days; α) → Pu-238 (Т 1/2 = 87.7 years; α) → U-234 (Т 1/2 = 2.46 10 5 years; α)

The activity of Cm-242 decreases rapidly, while the activity of Pu-238 increases and, rather quickly, in ≈ 3.4 years, the activities of Pu-238 and Cm-242 become equal, while the activity of Cm-242 decreases approximately 200 times compared to the initial level.

Radiation characteristics of Сm-242 and Pu-238

Cm-244
The decay scheme of Сm-244 is as follows:

Сm-244 (Т 1/2 = 18.1 years; α) → Pu-240 (Т 1/2 = 6.56 · 10 3 years; α).

Radiation characteristics of Сm-244

Cm-245
The scheme of Сm-245 decay is as follows:

Сm-245 (Т 1/2 = 8.5 10 3 years; α) → Pu-241 (Т 1/2 = 14.4 years; β) → Am-241 (Т 1/2 = 4.33 10 2 years; α) ...

At t >> T 1/2 (Pu-241), the activity of Pu-241 is in equilibrium with the activity of Cm-245.

Radiation characteristics of Cm-245 and Pu-241

Curium contributes significantly to gamma activity, neutron emission and radiotoxicity. Curium is poorly suited for transmutation, since the fission and capture cross sections of the main isotopes (Cm-242 and Cm-244) are rather small. Although Cm-242 has a very short half-life (163 days), it is constantly generated in irradiated fuel by decay
Am-242m (half-life 141 years).

Heat release and radiotoxicity of spent nuclear fuel

Rice. 3. Heat release of spent fuel from a light water reactor with a burnup of 50 GW · dn / ttm

In fig. 3 shows the heat release from the spent fuel of a light water reactor with a burnup of 50 GWd / ttm. Burnup is defined as the ratio of the generated thermal energy during the reactor run to the weight of the loaded fuel. After storage for about 40 years, only a few percent of the original radioactivity remains in the spent fuel. Heat dissipation drops rapidly during the first 200 years after discharge. Moreover, for the first 60 years, the decay of fission products makes the main contribution to heat release. The largest contribution is made by 137 Cs + 137 Ba and 90 Sr + 90 Y. Despite the fact that minor actinides are produced in reactors in relatively small quantities, they make a significant contribution to the heat release, neutron yield and radiotoxicity of spent nuclear fuel. After 60 years, actinides prevail in the amount of heat release. After 200 years, the heat release is almost entirely caused by the actinides - plutonium and americium. The slow decrease in heat release is due to the relatively long half-lives of 241 Am, 238 Pu, 239 Pu, and 240 Pu.
In fig. 4 shows how the dose rate of external radiation from SNF changes with time.

Rice. 4. Time dependence of the radiation dose rate from one ton of spent nuclear fuel after unloading from the reactor with a burnup of 38 GW ּ dn / t at a distance of 1 meter.

Approximately a year after fuel loading, when SNF is unloaded from the reactor, the dose rate from 1 ton is about 1000 Sv / h. This means that a lethal dose, about 5 Sv, is taken in about 20 seconds. The dose depends entirely on the contribution of gamma radiation. The radiation decreases with time, but the dose rate after 40 years, when the spent fuel must be placed in deep storage, is still high - 65 Sv / h. Therefore, when handling spent nuclear fuel, protective measures are required against external radiation, from unloading from the reactor to final disposal. Fig. 4 that the dose from neutron radiation is always much less than from gamma radiation, but neutron radiation decreases more slowly.
During the first few decades, radiotoxicity is mainly determined by fission products such as 90 Sn and 137 Cs and their decay products. After intermediate storage for about 40 years, only a few percent of the original radioactivity remains in the spent fuel. Over the course of several hundred years, most radionuclides decay, and the main contribution to radiotoxicity is made by long-lived actinides (plutonium and americium). The radiotoxicity of spent nuclear fuel will decrease to the level of uranium ore radiotoxicity in about 100,000 years.

Rice. 5. Time dependence of SNF radiotoxicity at burnup 60 GW ּ dn / t.

Views