Nuclear fuel cycle: Spent nuclear fuel. The third leg: SNF reprocessing in Russia How SNF reprocessing threatens the environmental situation

LJ user uralochka writes on her blog: I have always wanted to visit Mayak.
It's no joke, this place is one of the most knowledge-intensive enterprises in Russia, here
The first nuclear reactor in the USSR was launched in 1948, specialists from Mayak PA produced
plutonium charge for the first Soviet nuclear bomb. Once upon a time it was called Ozersk
Chelyabinsk-65, Chelyabinsk-40, since 1995 it became Ozersk. Here in Trekhgorny,
once Zlatoust-36, a city that is also closed, Ozersk was always called
“Sorokovka” was treated with respect and awe.

Now you can read about a lot in official sources, and even more in unofficial ones,
and there was a time when even the approximate location and name of these cities were kept in the strictest
secret. I remember how my grandfather Yakovlev Evgeniy Mikhailovich and I went fishing, and
local questions - where are we from, my grandfather always answered that from Yuryuzan (a neighboring town to Trekhgorny),
and at the entrance to the city there were no signs except the constant “brick”. Grandfather had one of
best friends, his name was Mitroshin Yuri Ivanovich, for some reason I called him nothing else throughout my childhood
like “Vanalize”, I don’t know why. I remember once I asked my grandmother why,
Vanalise, so bald, doesn't have a single hair? Grandmother, then, explained to me in a whisper,
that Yuri Ivanovich served in the “Sorokovka” and eliminated the consequences of a big accident in 1957,
received a large dose of radiation, ruined his health, and his hair no longer grows...

...And now, many years later, I, as a photojournalist, am going to photograph that same RT-1 plant for
agency "Photo ITAR-TASS". Time changes everything.

Ozersk is a restricted city, entry requires passes, my profile was being checked for more than a month and
Everything is ready, you can go. I was met by the press service at the checkpoint, unlike
Ours have a normal computerized system here, enter from any checkpoint, exit like this
from anyone. After that, we drove to the administrative building of the press service, where I left
I was advised to leave my car and my mobile phone, because on the territory of the plant with
Mobile communication devices are prohibited. No sooner said than done, let's go to RT-1. At the factory
We spent a long time at the checkpoint, somehow they didn’t let us through right away with all my photographic equipment, but here it is
It happened. We were given a stern man with a black holster on his belt and white clothes. We met
with the administration, they formed a whole team of guides for us and we moved into the ranks. pass.
Unfortunately, the external territory of the plant and any security systems must be photographed
strictly prohibited, so my camera was in my backpack all this time. This is the frame of me
I filmed it at the very end, this is where the “dirty” territory begins. The division is
really conditional, but it is observed very strictly, this is what allows you not to take it away
radioactive dirt throughout the area.

San. There are separate entrances, women from one entrance, men from the other. Me my companions
They showed me the locker, they said take everything off (absolutely everything), put on rubber flip-flops, close it
locker and move to that window over there. So I did. I'm standing completely naked, in one hand
me the key, into another backpack with a camera, and the woman from the window, which for some reason is located
too low, for my position he asks what my shoe size is. For a long time
I didn’t have to be embarrassed, I was promptly given something like underpants, a light shirt,
overalls and shoes. Everything is white, clean and very pleasant to the touch. Got dressed, attached to
I put a dosimeter tablet in my chest pocket and felt more confident. You can move out.
The guys immediately instructed me not to put the backpack on the floor, not to touch anything unnecessary,
photograph only what is allowed. Yes, no problem - I say, it’s too early for me to have a backpack
throw it away, and I don’t need secrets problems either. This is the place to put on and take off
dirty shoes. The center is clean, the edges are dirty. Conditional threshold of the plant territory.

We traveled around the plant territory on a small bus. External area without special
decoration, blocks of workshops connected by galleries for the passage of personnel and the transfer of chemicals through pipes.
On one side there is a large gallery for collecting clean air from the neighboring forest. This
made so that people in the workshops breathe clean outside air. RT-1 is only
one of the seven plants of the Mayak PA, its purpose is to receive and reprocess spent nuclear
fuel (SNF). This is the workshop where it all begins; containers with spent nuclear fuel arrive here.
On the right is a carriage with an open lid. Specialists unscrew the top screws with a special
equipment. After this, everyone is removed from this room, the large door is closed.
about half a meter thick (unfortunately, the regime demanded that photographs with it be deleted).
Further work is carried out using cranes that are controlled remotely via cameras. The taps are removed
covers and remove the assemblies with spent fuel.

The assemblies are transferred by cranes to these hatches. Pay attention to the crosses, they are drawn,
to make it easier to position the position of the tap. Under the hatches, the assemblies are immersed in
liquid - condensate (simply put into distilled water). After this assembly on
carts are moved to a nearby pool, which is a temporary warehouse.

I don’t know exactly what it’s called, but the essence is clear - a simple device so as not to
drag radioactive dust from one room to another.

On the left is the same door.

And this is the same adjacent room. Under the feet of the employees there is a swimming pool with a depth of 3.5 to 14
meters filled with condensate. ? You can also see two blocks from the Beloyarsk Nuclear Power Plant, their length is 14 meters.
They are called AMB - “Peaceful Large Atom”.

When you look between the metal plates, you see something like this. Under condensation
an assembly of fuel elements from a shipping reactor is visible.

But these assemblies just came from the nuclear power plant. When the lights were turned off, they glowed with a pale blue glow.
Very impressive. This is the Cherenkov glow, about the essence of it physical phenomenon You can read it on Wikipedia.

General view of the workshop.

Go ahead. Transitions between departments along corridors with dim yellow light. Enough underfoot
specific coating, rolled up at all corners. People in white. In general, I immediately went to “Black Mass”
I remembered))). By the way, about the coating, it’s a very reasonable solution, on the one hand it’s more convenient to wash,
nothing will get stuck anywhere, and most importantly, in case of any leak or accident, the dirty floor can be
easy to dismantle.

As they explained to me further operations with SNF are carried out in enclosed spaces in automatic mode.
The whole process was once controlled from these remote controls, but now everything happens from three terminals.
Each of them runs on its own autonomous server, all functions are duplicated. In case of refusal of all
terminals, the operator will be able to complete processes from the remote control.

Briefly about what is happening with spent nuclear fuel. The assemblies are disassembled, the filling is removed, sawn into
parts and placed in a solvent (nitric acid), after which the spent fuel is dissolved
undergoes a whole complex of chemical transformations, from which uranium, plutonium, and neptunium are extracted.
Insoluble parts that cannot be recycled are pressed and glazed. And stored on
the plant area is under constant surveillance. The output after all these processes is formed
ready-made assemblies are already “charged” with fresh fuel, which is produced here. Thus the Lighthouse
carries out a full cycle of working with nuclear fuel.

Department for work with plutonium.

Eight layers of 50 mm leaded glass protect the operator from active elements. Manipulator
connected exclusively by electrical connections, there are no “holes” connecting to the internal compartment.

We moved to the workshop that ships finished products.

The yellow container is intended for transportation of finished fuel assemblies. In the foreground are lids from containers.

The inside of the container is where fuel rods are apparently mounted.

The crane operator controls the crane from any place convenient for him.

On the sides are all-stainless steel containers. As they explained to me, there are only 16 of these in the world.

Spent nuclear fuel from power reactors The initial stage of the post-reactor stage of the nuclear fuel cycle is the same for open and closed nuclear fuel cycles.

It involves removing fuel rods with spent nuclear fuel from the reactor, storing it in an on-site pool (“wet” storage in underwater cooling pools) for several years and then transporting it to a reprocessing plant. In the open version of the nuclear fuel cycle, spent fuel is placed in specially equipped storage facilities (“dry” storage in an inert gas or air environment in containers or chambers), where it is kept for several decades, then processed into a form that prevents the theft of radionuclides and prepared for final disposal.

In the closed version of the nuclear fuel cycle, the spent fuel is supplied to a radiochemical plant, where it is processed to extract fissile nuclear materials.

Spent nuclear fuel (SNF) - special kind radioactive materials – raw materials for the radiochemical industry.

Irradiated fuel elements removed from the reactor after their exhaustion have significant accumulated activity. There are two types of spent nuclear fuel:

1) SNF from industrial reactors, which has a chemical form of both the fuel itself and its cladding, convenient for dissolution and subsequent processing;

2) Fuel rods for power reactors.

SNF from industrial reactors is reprocessed without fail, while SNF is not always reprocessed. Energy SNF is classified as high-level waste if it is not subjected to further processing, or as a valuable energy raw material if it is processed. In some countries (USA, Sweden, Canada, Spain, Finland), SNF is completely classified as radioactive waste (RAW). In England, France, Japan - to energy raw materials. In Russia, part of the spent fuel is considered radioactive waste, and part is sent for reprocessing to radiochemical plants (146).

Due to the fact that not all countries adhere to closed-loop tactics nuclear cycle, SNF in the world is constantly increasing. The practice of countries adhering to a closed uranium fuel cycle has shown that partial closure of the nuclear fuel cycle of light water reactors is unprofitable, even with a possible 3-4 times increase in the price of uranium in the next decades. Nevertheless, these countries are closing the nuclear fuel cycle of light water reactors, covering the costs by increasing electricity tariffs. On the contrary, the United States and some other countries refuse to reprocess spent nuclear fuel, keeping in mind the future final disposal of spent nuclear fuel, preferring its long-term storage, which turns out to be cheaper. However, it is expected that by the twenties the reprocessing of spent nuclear fuel in the world will increase.

The fuel assemblies with spent nuclear fuel removed from the core of a power reactor are stored in a cooling pool at a nuclear power plant for 5-10 years to reduce heat generation and decay of short-lived radionuclides. On the first day after its unloading from the reactor, 1 kg of spent nuclear fuel from a nuclear power plant contains from 26 to 180 thousand Ci of radioactivity. After a year, the activity of 1 kg of spent fuel decreases to 1 thousand Ci, after 30 years, to 0.26 thousand Ci. A year after removal, as a result of the decay of short-lived radionuclides, the activity of spent fuel is reduced by 11 - 12 times, and after 30 years - by 140 - 220 times and then slowly decreases over hundreds of years 9 (146).

If natural uranium was initially loaded into the reactor, then 0.2 - 0.3% 235U remains in the spent fuel. Re-enrichment of such uranium is not economically feasible, so it remains in the form of so-called waste uranium. The waste uranium can later be used as breeding material in fast neutron reactors. When low-enriched uranium is used to load nuclear reactors, spent fuel contains 1% 235U. Such uranium can be further enriched to its original content in nuclear fuel and returned to the nuclear fuel cycle. The reactivity of nuclear fuel can be restored by adding other fissile nuclides to it - 239Pu or 233U, i.e. secondary nuclear fuel. If 239Pu is added to depleted uranium in an amount equivalent to enriching the fuel with 235U, then a uranium-plutonium fuel cycle is implemented. Mixed uranium-plutonium fuel is used in both thermal and fast neutron reactors. Uranium-plutonium fuel ensures the fullest use of uranium resources and expanded reproduction of fissile material. For nuclear fuel regeneration technology, the characteristics of the fuel unloaded from the reactor are extremely important: chemical and radiochemical composition, content of fissile materials, activity level. These characteristics of nuclear fuel are determined by the power of the reactor, the burnup of the fuel in the reactor, the duration of the campaign, the reproduction rate of secondary fissile materials, the holding time of the fuel after unloading it from the reactor, and the type of reactor.

Spent nuclear fuel unloaded from reactors is transferred for reprocessing only after a certain period of time. This is due to the fact that among the fission products there are a large number of short-lived radionuclides, which determine a large share of the activity of the fuel discharged from the reactor. Therefore, freshly unloaded fuel is kept in special storage facilities for a time sufficient for the decay of the main amount of short-lived radionuclides. This greatly facilitates the organization of biological protection, reduces the radiation impact on chemical reagents and solvents during the reprocessing of treated nuclear fuel, and reduces the set of elements from which the main products must be purified. Thus, after two to three years of exposure, the activity of irradiated fuel is determined by long-lived fission products: Zr, Nb, Sr, Ce and other rare earth elements, Ru and α-active transuranium elements. 96% of spent nuclear fuel is uranium-235 and uranium-238, 1% is plutonium, 2-3% is radioactive fission fragments.

The spent fuel holding time is 3 years for light water reactors, 150 days for fast neutron reactors (155).

The total activity of fission products contained in 1 ton of VVER-1000 spent fuel after three years of aging in the spent fuel pool (SP) is 790,000 Ci.

When SNF is stored in an on-site storage facility, its activity monotonically decreases (by about an order of magnitude over 10 years). When activity drops to the standards that determine the safety of spent nuclear fuel transportation railway, it is removed from their storage facilities and moved either to long-term storage or to a fuel reprocessing plant. At the processing plant, fuel rod assemblies are reloaded from containers into the factory buffer storage pool using loading and unloading mechanisms. Here the assemblies are stored until they are sent for processing. After holding in the pool for a period selected at a given plant, the fuel assemblies are unloaded from storage and sent to the fuel preparation department for extraction for the operation of opening spent fuel rods.

Reprocessing of irradiated nuclear fuel is carried out with the aim of extracting fissile radionuclides from it (primarily 233U, 235U and 239Pu), purifying uranium from neutron-absorbing impurities, separating neptunium and some other transuranic elements, and obtaining isotopes for industrial, scientific or medical purposes. Nuclear fuel reprocessing refers to the reprocessing of fuel rods from power, scientific or transport reactors, as well as the reprocessing of breeder reactor blankets. Radiochemical reprocessing of spent fuel is the main stage of the closed version of the nuclear fuel cycle, and a mandatory stage in the production of weapons-grade plutonium (Fig. 35).

Reprocessing of fissile material irradiated with neutrons in nuclear reactor fuel is carried out to solve problems such as

Obtaining uranium and plutonium for the production of new fuel;

Obtaining fissile materials (uranium and plutonium) for the production of nuclear weapons;

Obtaining a variety of radioisotopes that are used in medicine, industry and science;

Rice. 35. Some stages of spent nuclear fuel reprocessing at Mayak PA. All operations are carried out using manipulators and chambers protected by a 6-layer lead glass (155).

Receiving income from other countries that are either interested in the first and second, or do not want to store large volumes of spent nuclear fuel;

Solving environmental problems associated with radioactive waste disposal.

In Russia, irradiated uranium from breeder reactors and fuel rods from VVER-440, BN and some ship engines are processed; Fuel rods of the main types of power reactors VVER-1000, RBMK (any type) are not recycled and are currently accumulated in special storage facilities.

Currently, the amount of spent fuel is constantly increasing and its regeneration is the main task of radiochemical technology for reprocessing spent fuel rods. During the reprocessing process, uranium and plutonium are separated and purified from radioactive fission products, including neutron-absorbing nuclides (neutron poisons), which, when fissile materials are reused, can prevent the development of a nuclear chain reaction in the reactor.

Radioactive fission products contain a large number of valuable radionuclides that can be used in low nuclear power(radioisotopic heat sources for thermoelectric power generators), as well as for the manufacture of sources of ionizing radiation. Transuranium elements are used, resulting from side reactions of uranium nuclei with neutrons. Radiochemical technology for reprocessing spent nuclear fuel must ensure the extraction of all nuclides useful from a practical point of view or of scientific interest (147 43).

The process of chemical reprocessing of spent fuel is associated with solving the problem of isolating from the biosphere a large amount of radionuclides generated as a result of the fission of uranium nuclei. This problem is one of the most serious and difficult to solve problems in the development of nuclear energy.

The first stage of radiochemical production includes fuel preparation, i.e. to free it from the structural parts of the assemblies and destroy the protective shells of the fuel rods. The next stage is associated with the transfer of nuclear fuel into the phase from which chemical processing will be carried out: into a solution, into a melt, into the gas phase. Conversion into solution is most often done by dissolving in nitric acid. In this case, uranium goes into the hexavalent state and forms a uranyl ion, UO 2 2+, and plutonium partially in the hexavalent state and into the tetravalent state, PuO 2 2+ and Pu 4+, respectively. Transfer to the gas phase is associated with the formation of volatile uranium and plutonium halides. After the transfer of nuclear materials, the corresponding phase involves a series of operations directly related to the isolation and purification of valuable components and the release of each of them in the form of a commercial product (Fig. 36).

Fig.36. General scheme for the circulation of uranium and plutonium in closed loop (156).

Reprocessing (reprocessing) of spent nuclear fuel involves the extraction of uranium, accumulated plutonium and fractions of fragmentation elements. 1 ton of spent fuel at the time of removal from the reactor contains 950-980 kg of 235U and 238U, 5.5-9.6 kg of Pu, as well as a small amount of α-emitters (neptunium, americium, curium, etc.), the activity of which can reach 26 thousand Ci per 1 kg of spent fuel. It is these elements that must be isolated, concentrated, purified and converted into the required chemical form during a closed nuclear fuel cycle.

The technological process of spent nuclear fuel reprocessing includes:

Mechanical fragmentation (cutting) of fuel assemblies and fuel rods in order to open the fuel material;

Dissolution;

Cleaning solutions of ballast impurities;

Extraction separation and purification of uranium, plutonium and other commercial nuclides;

Release of plutonium dioxide, neptunium dioxide, uranyl nitrate hexahydrate and uranium oxide;

Processing of solutions containing other radionuclides and their separation.

The technology for separating uranium and plutonium, separating them and purifying them from fission products is based on the process of extracting uranium and plutonium with tributyl phosphate. It is carried out on multi-stage continuous extractors. As a result, uranium and plutonium are purified from fission products millions of times. SNF reprocessing is associated with the formation of a small volume of solid and gaseous radioactive waste with an activity of about 0.22 Ci/year (maximum permissible release 0.9 Ci/year) and big amount liquid radioactive waste.

All construction materials of fuel rods are characterized by chemical resistance, and their dissolution poses a serious problem. In addition to fissile materials, fuel rods contain various storage devices and coatings consisting of stainless steel, zirconium, molybdenum, silicon, graphite, chromium, etc. When nuclear fuel is dissolved, these substances do not dissolve in nitric acid and create a large amount of suspensions and colloids in the resulting solution.

The listed features of fuel rods have necessitated the development of new methods for opening or dissolving shells, as well as clarification of nuclear fuel solutions before extraction processing.

The fuel burnup of plutonium production reactors differs significantly from the fuel burnup of power reactors. Therefore, materials with a much higher content of radioactive fragmentation elements and plutonium per 1 ton U are received for reprocessing. This leads to increased requirements for the purification processes of the resulting products and for ensuring nuclear safety during the reprocessing process. Difficulties arise due to the need to process and dispose of large amounts of liquid high-level waste.

Next, uranium, plutonium and neptunium are isolated, separated and purified in three extraction cycles. In the first cycle, uranium and plutonium are jointly purified from the bulk of fission products, and then uranium and plutonium are separated. In the second and third cycles, uranium and plutonium are further separately purified and concentrated. The resulting products - uranyl nitrate and plutonium nitrate - are placed in buffer tanks before being transferred to conversion units. Oxalic acid is added to the plutonium nitrate solution, the resulting oxalate suspension is filtered, and the precipitate is calcined.

Powdered plutonium oxide is sifted through a sieve and placed in containers. In this form, plutonium is stored before it enters the plant for the production of new fuel rods.

Separation of fuel rod cladding material from the fuel cladding is one of the most difficult tasks in the nuclear fuel regeneration process. Existing methods can be divided into two groups: opening methods with separation of the cladding and core materials of fuel rods and opening methods without separating the cladding materials from the core material. The first group involves removing the cladding of fuel rods and removing structural materials before dissolving the nuclear fuel. Water-chemical methods involve dissolving shell materials in solvents that do not affect the core materials.

The use of these methods is typical for the processing of fuel rods made from uranium metal in shells made of aluminum or magnesium and its alloys. Aluminum easily dissolves in caustic soda or nitric acid, and magnesium - in dilute solutions of sulfuric acid when heated. After dissolving the shell, the core is dissolved in nitric acid.

However, fuel rods of modern power reactors have shells made of corrosion-resistant, poorly soluble materials: zirconium, zirconium alloys with tin (zircal) or niobium, stainless steel. Selective dissolution of these materials is only possible in highly aggressive environments. Zirconium is dissolved in hydrofluoric acid, in its mixtures with oxalic or nitric acids or NH4F solution. Stainless steel shell - in boiling 4-6 M H 2 SO 4. The main disadvantage of the chemical method of removing shells is the formation of a large amount of highly saline liquid radioactive waste.

To reduce the volume of waste from the destruction of shells and obtain this waste immediately in a solid state, more suitable for long-term storage, processes are being developed for the destruction of shells under the influence of non-aqueous reagents at elevated temperatures (pyrochemical methods). The zirconium shell is removed with anhydrous hydrogen chloride in a fluidized bed of Al 2 O 3 at 350-800 o C. Zirconium is converted into volatile ZrC l4 and is separated from the core material by sublimation, and then hydrolyzed, forming solid zirconium dioxide. Pyrometallurgical methods are based on the direct melting of shells or their dissolution in melts of other metals. These methods exploit differences in the melting temperatures of the shell and core materials or differences in their solubility in other molten metals or salts.

Mechanical methods Shell removal involves several stages. First, the end parts of the fuel assembly are cut off and disassembled into bundles of fuel rods and individual fuel rods. Then the shells are mechanically removed separately from each fuel element.

Opening fuel rods can be carried out without separating the cladding materials from the core material.

When implementing water-chemical methods, the shell and core are dissolved in the same solvent to obtain a common solution. Co-dissolution is advisable when processing fuel with a high content of valuable components (235U and Pu) or when different types of fuel elements differing in size and configuration are processed at the same plant. In the case of pyrochemical methods, fuel rods are treated with gaseous reagents, which destroy not only the shell, but also the core.

A successful alternative to the methods of opening with simultaneous removal of the shell and methods of joint destruction of the shell and cores turned out to be the “cutting-leaching” method. The method is suitable for processing fuel rods in shells that are insoluble in nitric acid. Fuel rod assemblies are cut into small pieces, the exposed fuel rod core becomes accessible to chemical reagents and dissolves in nitric acid. Undissolved shells are washed from the remnants of the solution retained in them and removed in the form of scrap. Chopping fuel rods has certain advantages. The resulting waste - the remains of the shells - are in a solid state, i.e. there is no formation of liquid radioactive waste, as with chemical dissolution of the shell; there is no significant loss of valuable components, as during mechanical removal of shells, since sections of shells can be washed with a high degree of completeness; the design of cutting machines is simplified in comparison with the design of machines for mechanical removal of casings. The disadvantage of the cutting-leaching method is the complexity of the equipment for cutting fuel rods and the need for its remote maintenance. The possibility of replacing mechanical cutting methods with electrolytic and laser methods is currently being explored.

In spent fuel rods of high and medium burnup power reactors, large amounts of gaseous radioactive products accumulate, which represent a serious biological hazard: tritium, iodine and krypton. During the dissolution of nuclear fuel, they are mainly released and go with gas streams, but partially remain in solution, and are then distributed in a large number of products throughout the reprocessing chain. Tritium is especially dangerous, forming tritiated water NTO, which is then difficult to separate from ordinary water H2O. Therefore, at the stage of preparing fuel for dissolution, additional operations are introduced to free the fuel from the bulk of radioactive gases, concentrating them in small volumes of waste products. Pieces of oxide fuel are subjected to oxidative treatment with oxygen at a temperature of 450-470 o C. When the structure of the fuel lattice is rearranged due to the transition UO 2 -U 3 O 8, gaseous fission products - tritium, iodine, and noble gases - are released. Loosening of the fuel material during the release of gaseous products, as well as during the transition of uranium dioxide into nitrous oxide, helps to accelerate the subsequent dissolution of materials in nitric acid.

The choice of method for transferring nuclear fuel into solution depends on the chemical form of the fuel, the method of preliminary preparation of the fuel, and the need to ensure a certain productivity. Uranium metal is dissolved in 8-11M HNO 3, and uranium dioxide is dissolved in 6-8M HNO 3 at a temperature of 80-100 o C.

The destruction of the fuel composition upon dissolution leads to the release of all radioactive fission products. In this case, gaseous fission products enter the exhaust gas discharge system. The waste gases are cleaned before being released into the atmosphere.

Isolation and purification of target products

Uranium and plutonium, separated after the first extraction cycle, are further purified from fission products, neptunium, and each other to a level that meets the specifications of the nuclear fuel cycle and then converted into a commercial form.

Best results Further purification of uranium is achieved by combining different methods, such as extraction and ion exchange. However, on an industrial scale, it is more economical and technically simpler to use repeated extraction cycles with the same solvent - tributyl phosphate.

The number of extraction cycles and the depth of uranium purification are determined by the type and burnup of nuclear fuel supplied for reprocessing and the task of neptunium separation. To meet the technical specifications for the content of impurity α-emitters in uranium, the overall neptunium removal factor must be ≥500. After sorption purification, uranium is re-extracted into an aqueous solution, which is analyzed for purity, uranium content and degree of 235U enrichment.

The final stage of uranium refining is intended to convert it into uranium oxides - either by precipitation in the form of uranyl peroxide, uranyl oxalate, ammonium uranyl carbonate or ammonium uranate followed by calcination, or by direct thermal decomposition of uranyl nitrate hexahydrate.

After separation from the main mass of uranium, plutonium is subjected to further purification from fission products, uranium and other actinides to its own background for γ- and β-activity. The plants strive to produce plutonium dioxide as the final product, and then, in combination with chemical processing, to produce fuel rods, which avoids expensive transportation of plutonium, which requires special precautions especially when transporting solutions of plutonium nitrate. All stages of the technological process for purifying and concentrating plutonium require special reliability of nuclear safety systems, as well as the protection of personnel and the prevention of contamination. environment due to the toxicity of plutonium and high levels of α-radiation. When developing equipment, all factors that can cause criticality are taken into account: mass of fissile material, homogeneity, geometry, reflection of neutrons, moderation and absorption of neutrons, as well as the concentration of fissile material in this process, etc. The minimum critical mass of an aqueous solution of plutonium nitrate is 510 g (if there is a water reflector). Nuclear safety during operations in the plutonium branch is ensured by the special geometry of the devices (their diameter and volume) and the limitation of the concentration of plutonium in the solution, which is constantly monitored at certain points of the continuous process.

The technology for the final purification and concentration of plutonium is based on successive cycles of extraction or ion exchange and an additional refining operation of plutonium precipitation followed by its thermal conversion into dioxide.

Plutonium dioxide enters the conditioning unit, where it is calcined, crushed, sifted, batched and packaged.

For the production of mixed uranium-plutonium fuel, the method of chemical coprecipitation of uranium and plutonium is advisable, which makes it possible to achieve complete homogeneity of the fuel. This process does not require separation of uranium and plutonium during spent fuel reprocessing. In this case, mixed solutions are obtained by partial separation of uranium and plutonium by displacement stripping. In this way it is possible to obtain (U, Pu)O2 for light water nuclear reactors on thermal neutrons with a PuO2 content of 3%, as well as for fast neutron reactors with a PuO2 content of 20%.

The discussion about the feasibility of spent fuel regeneration is not only of a scientific, technical and economic nature, but also of a political nature, since the deployment of construction of regeneration plants poses a potential threat of proliferation nuclear weapons. The central problem is ensuring complete safety of production, i.e. ensuring guarantees of controlled use of plutonium and environmental safety. Therefore, they are now creating efficient systems control of the technological process of chemical reprocessing of nuclear fuel, providing the ability to determine the amount of fissile materials at any stage of the process. Proposals of so-called alternative technological processes, for example the CIVEX process, in which plutonium is not completely separated from uranium and fission products at any stage of the process, which significantly complicates the possibility of its use in explosive devices, also serve to ensure guarantees of the non-proliferation of nuclear weapons.

Civex - reproduction of nuclear fuel without releasing plutonium.

To improve the environmental friendliness of SNF reprocessing, non-aqueous technological processes are being developed, which are based on differences in the volatility of the components of the reprocessing system. The advantages of non-aqueous processes are their compactness, the absence of strong dilutions and the formation of large volumes of liquid radioactive waste, and the lesser influence of radiation decomposition processes. The generated waste is in the solid phase and takes up a significantly smaller volume.

Currently, a variant of organizing a nuclear power plant is being studied, in which not identical units (for example, three of the same type of thermal neutron units) are built at the station, but different types (for example, two thermal and one fast reactor). First, fuel enriched in 235U is burned in a thermal reactor (with the formation of plutonium), then the fuel is transferred to a fast reactor, in which 238U is processed using the resulting plutonium. After the end of the use cycle, the spent fuel is supplied to the radiochemical plant, which is located directly on the territory of the nuclear power plant. The plant does not engage in complete fuel reprocessing - it is limited to separating only uranium and plutonium from spent fuel (by distilling off hexafluoride fluorides of these elements). The separated uranium and plutonium are used for the production of new mixed fuel, and the remaining spent fuel goes either to a plant for separating useful radionuclides or for disposal.

The planet's population, as well as its need for energy, is only growing every year, along with the prices of gas and oil, the processing of which, by the way, has its sad and irreversible consequences for the ecology of the earth. And nuclear energy today does not have a worthy alternative, either in terms of profitability or the ability to meet global energy needs.

Despite the fact that such statements sound very abstract, in practice, the abandonment of nuclear energy will mean a sharp rise in price for such things as necessary for everyone, such as food, clothing, medicine, comfortable Appliances, education, medicine, the ability to move freely around the world and much more. In such a situation, the best solution is to focus efforts on making nuclear energy as safe and efficient as possible.

Not everyone knows this fact: fresh nuclear fuel does not pose any danger to humans. Before the widespread introduction of industrial automation, uranium dioxide fuel pellets were driven into assembly rods by hand. The radioactivity of fuel increases several million times after irradiation in a nuclear reactor. It is at this moment that it becomes dangerous to humans and the environment.

Like any production, nuclear power plants generate waste. At the same time, the amount of waste produced by nuclear power plants is significantly less compared to other industries, but due to its high danger to the environment, it requires special handling. And here it is necessary to clarify some confusion between the concepts of RW (radioactive waste) and SNF (spent nuclear fuel), which often arises in the media.

By Russian classification, SNF refers to spent fuel elements removed from the reactor. Let us trace the path along which natural uranium mined in mines is converted into spent nuclear fuel. As we know, natural uranium consists of the isotopes uranium-235 and uranium-238. Modern nuclear power plants operate on uranium - 235. But due to the low content of the 235 isotope (only 0.7%), for use as nuclear fuel, uranium extracted from the bowels of the earth must be enriched to a few percent. Uranium used in reactors is placed in fuel elements (fuel elements), from which fuel assemblies are assembled in the form of hexagonal rods. They are immersed in the reactor until a critical mass is reached. Before starting the reactor, the fuel rods contain 95% uranium-238 and 5% uranium-235. As a result of the operation of the reactor, fission products - radioactive isotopes - appear in place of uranium-235. The rods are removed, but as spent nuclear fuel.

SNF has rich resource potential. First, radioisotopes from spent fuel that can be chemically extracted have wide application for medical and scientific purposes. And not only for medical purposes - platinum group metals formed in a reactor during the fission of uranium are cheaper than the same metals obtained from ore. Secondly, the spent fuel contains uranium-238, which is considered worldwide as the main fuel element of future nuclear power plants. Thus, reprocessed spent nuclear fuel becomes not only the richest source for obtaining fresh nuclear fuel, but also solves ecological problems uranium deposits: there is no point in developing uranium mines, because already this moment Russia has accumulated 22 thousand tons of spent nuclear fuel. At the same time, the content of radioactive elements in spent fuel, which cannot be reprocessed and require reliable isolation from the environment, is only 3%. For reference: reprocessing 50 tons of spent nuclear fuel saves 1.6 billion cubic meters natural gas or 1.2 million tons of oil.

Radioactive waste (RAW) also contains radioisotopes. The difference is that it is not possible to extract them, or the costs of extracting them are not economically feasible. At the moment, depending on the type of radioactive waste, there are several ways to manage radioactive waste. The sequence of actions is as follows: first, the volume of radioactive waste is reduced. In this case, for solid radioactive waste, pressing or combustion is used, for liquid radioactive waste – coagulation and evaporation, processing through mechanical or ion-exchange filters. After treatment using special fabric or fiber filters, the volume of gaseous radioactive waste is reduced. The next stage is immobilization, that is, placing radioactive waste in a durable matrix of cement, bitumen, glass, ceramics or other materials that reduce the likelihood of radioactive waste being released into the environment. The resulting masses are placed in special containers and then stored. The final stage is the movement of containers with radioactive waste to the disposal site.

According to scientists, the most effective method for disposing of radioactive waste today is in stable geological formations of the earth’s crust. This method provides an effective insulating barrier for a period of tens of thousands to millions of years. Published in the electronic bulletin of the European Atomic Society, the results of joint research by the Subatech laboratory in France and the SCK-CEN research center in Belgium showed that the period during which blocks with nuclear waste can maintain their integrity exceeds 100 thousand years. The researchers came to this conclusion after making probabilistic estimates of the possible dissolution of buried nuclear waste from open and closed fuel cycles over various periods of time.

At the recent international scientific and practical conference “Safety, Efficiency and Economics of Nuclear Energy” held in Moscow, the pressing problems of spent nuclear fuel management were also discussed. In Russia, the storage and reprocessing of spent nuclear fuel is currently carried out by the Mayak production association (Ozersk, Chelyabinsk region) and the Mining and Chemical Combine (Zheleznogorsk, Krasnoyarsk region), which are part of the nuclear and radiation safety complex of the State Corporation Rosatom. Advisor to the State Corporation "Rosatom" I.V. Gusakov-Stanyukovich spoke about the departmental “Program for creating infrastructure and handling spent nuclear fuel for 2011-2020 and for the period until 2030.” According to him, today, of the 22,000 tons of spent fuel available, most of it is located at nuclear power plants. At the same time, the amount that is removed for storage during the year is less than what the nuclear power plant manages to produce during this time. And if spent fuel from those stations that use VVER-type reactors (pressurized water power reactor) is transported for storage at the Federal State Unitary Enterprise Mining Chemical Combine or for reprocessing at the Federal State Unitary Enterprise PA Mayak, then the main problem of the moment is the spent fuel of RBMK reactors (high-power channel reactor), the quantity of which is 12.5 thousand tons. The dry storage facility for RBMK spent fuel at the Mining and Chemical Combine recently began operating, and in the spring of 2012 the first train with spent fuel from the Leningrad NPP arrived there. In the future, conditioned SNF from Leningrad, Kursk and Smolensk NPPs will be sent to the Mining and Chemical Combine, and substandard SNF will be sent to PA Mayak.

The implementation of the program for creating infrastructure and handling spent nuclear fuel by 2018 will make it possible to increase the volume of annual removal of spent nuclear fuel from nuclear power plant sites, which will exceed the annual production of spent nuclear fuel by 1.5 times. And by 2030, all 100% of the spent fuel from RBMK-1000 and VVER-1000 reactors will be placed for long-term centralized storage at the MCC site, after which the main specialization of the MCC will be the production of MOX fuel. As for plans for spent fuel from VVER-440 and BN-600 reactors, as well as transport and research reactors, the processing of these spent fuel will be carried out at Mayak. An exception will be the Bilibino NPP, where it is impractical to transport spent fuel to centralized reprocessing facilities due to its geographical remoteness, so it will be buried on site.

Nuclear energy consists of a large number of enterprises for various purposes. The raw materials for this industry are mined from uranium mines. It is then delivered to fuel production plants.

The fuel is then transported to nuclear power plants, where it enters the reactor core. When nuclear fuel reaches the end of its useful life, it is subject to disposal. It is worth noting that hazardous waste appears not only after fuel reprocessing, but also at any stage - from uranium mining to work in the reactor.

Nuclear fuel

There are two types of fuel. The first is uranium mined in mines, respectively, natural origin. It contains raw materials that are capable of forming plutonium. The second is fuel that is created artificially (secondary).

Nuclear fuel is also divided according to its chemical composition: metallic, oxide, carbide, nitride and mixed.

Uranium mining and fuel production

A large share of uranium production comes from just a few countries: Russia, France, Australia, the USA, Canada and South Africa.

Uranium is the main element for fuel in nuclear power plants. To get into the reactor, it goes through several stages of processing. Most often, uranium deposits are located next to gold and copper, so its extraction is carried out with the extraction of precious metals.

During mining, human health is at great risk because uranium is a toxic material, and the gases that appear during its mining cause various forms of cancer. Although the ore itself contains a very small amount of uranium - from 0.1 to 1 percent. The population living near uranium mines is also at great risk.

Enriched uranium is the main fuel for nuclear power plants, but after its use a huge amount of radioactive waste remains. Despite all its dangers, uranium enrichment is an integral process of creating nuclear fuel.

IN natural form Uranium practically cannot be used anywhere. In order to be used, it must be enriched. Gas centrifuges are used for enrichment.

Enriched uranium is used not only in nuclear energy, but also in weapons production.

Transportation

At any stage of the fuel cycle there is transportation. It is carried out by all available means: by land, sea, air. This is a big risk and a big danger not only for the environment, but also for humans.

During the transportation of nuclear fuel or its elements, many accidents occur, resulting in the release of radioactive elements. This is one of the many reasons why it is considered unsafe.

Decommissioning of reactors

None of the reactors have been dismantled. Even the infamous Chernobyl The whole point is that, according to experts, the cost of dismantling is equal to, or even exceeds, the cost of building a new reactor. But no one can say exactly how much money will be needed: the cost was calculated based on the experience of dismantling small stations for research. Experts offer two options:

1. Place reactors and spent nuclear fuel in repositories.
2. Build sarcophagi over decommissioned reactors.

In the next ten years, about 350 reactors around the world will reach their end of life and must be taken out of service. But since the most suitable method in terms of safety and price has not been invented, this issue is still being resolved.

There are currently 436 reactors operating around the world. Of course, this is a big contribution to the energy system, but it is very unsafe. Research shows that in 15-20 years, nuclear power plants will be able to be replaced by stations that run on wind energy and solar panels.

Nuclear waste

A huge amount of nuclear waste is generated as a result of the activities of nuclear power plants. Reprocessing nuclear fuel also leaves behind hazardous waste. However, none of the countries found a solution to the problem.

Today, nuclear waste is kept in temporary storage facilities, in pools of water, or buried shallowly underground.

The safest method is storage in special storage facilities, but radiation leakage is also possible here, as with other methods.

In fact, nuclear waste has some value, but requires strict compliance with the rules for its storage. And this is the most pressing problem.

An important factor is the time during which the waste is hazardous. Each has its own decay period during which it is toxic.

Types of nuclear waste

During the operation of any nuclear power plant, its waste enters the environment. This is water for cooling turbines and gaseous waste.

Nuclear waste is divided into three categories:

1. Low level - clothing of nuclear power plant employees, laboratory equipment. Such waste can also come from medical institutions and scientific laboratories. They do not pose a great danger, but require compliance with safety measures.
2. Intermediate level - metal containers in which fuel is transported. Their radiation level is quite high, and those who are close to them must be protected.
3. The high level is spent nuclear fuel and its reprocessing products. The level of radioactivity is rapidly decreasing. High level waste is very small, about 3 percent, but it contains 95 percent of all radioactivity.

Removal, processing and disposal of waste from hazard classes 1 to 5

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In the 20th century, the non-stop search for an ideal energy source seemed to have ended. This source was the nuclei of atoms and the reactions occurring in them - the active development of nuclear weapons and the construction of nuclear power plants began all over the world.

But the planet quickly faced the problem of processing and destroying nuclear waste. Energy nuclear reactors carries a lot of dangers, just like the waste from this industry. Until now, there is no thoroughly developed processing technology, while the field itself is actively developing. Therefore, safety depends primarily on proper disposal.

Definition

Nuclear waste contains radioactive isotopes of certain chemical elements. In Russia, according to the definition given in Federal Law No. 170 “On the Use of Atomic Energy” (dated November 21, 1995), the further use of such waste is not provided for.

The main danger of materials is the emission of gigantic doses of radiation, which has a detrimental effect on a living organism. The consequences of radioactive exposure include genetic disorders, radiation sickness and death.

Classification map

The main source of nuclear materials in Russia is the nuclear energy sector and military developments. All nuclear waste has three degrees of radiation, familiar to many from physics courses:

• Alpha - radiating.
• Beta - emitting.
• Gamma - radiating.

The first are considered the most harmless, as they produce a non-hazardous level of radiation, unlike the other two. True, this does not prevent them from being included in the class of the most hazardous waste.


In general, the map of classifications of nuclear waste in Russia divides it into three types:

1. Solid nuclear debris. It includes a huge amount of materials Maintenance in the energy sector, personnel clothing, waste accumulated during work. Such waste is burned in furnaces, after which the ashes are mixed with a special cement mixture. It is poured into barrels, sealed and sent to storage. The burial is described in detail below.
2. Liquid. The operation of nuclear reactors is impossible without the use of technological solutions. In addition, this includes water that is used to treat special suits and wash workers. The liquids are thoroughly evaporated, and then burial occurs. Liquid waste is often recycled and used as fuel for nuclear reactors.
3. Elements of the design of reactors, transport and technical control equipment at the enterprise form a separate group. Their disposal is the most expensive. Today, there are two options: installing the sarcophagus or dismantling it with its partial decontamination and further sending it to storage for burial.

The map of nuclear waste in Russia also identifies low-level and high-level:

• Low-level waste - arises during the activities of medical institutions, institutes and research centers. Here radioactive substances are used to carry out chemical tests. The level of radiation emitted by these materials is very low. Proper disposal can turn hazardous waste into normal waste in about a few weeks, after which it can be disposed of as regular waste.
• High-level waste is spent reactor fuel and materials used in the military industry to develop nuclear weapons. The fuel at the stations consists of special rods containing a radioactive substance. The reactor operates for approximately 12 - 18 months, after which the fuel must be changed. The volume of waste is simply colossal. And this figure is growing in all countries developing the nuclear energy sector. Disposal of high-level waste must take into account all the nuances in order to avoid disaster for the environment and humans.

Recycling and disposal

At the moment, there are several methods for disposing of nuclear waste. All of them have their advantages and disadvantages, but no matter how you look at them, they do not allow you to completely get rid of the danger of radioactive exposure.

Burial

Waste disposal is the most promising disposal method, which is especially actively used in Russia. First, the process of vitrification or “vitrification” of the waste occurs. The spent substance is calcined, after which quartz is added to the mixture, and this “liquid glass” is poured into special cylindrical steel molds. The resulting glass material is resistant to water, which reduces the possibility of radioactive elements entering the environment.

The finished cylinders are brewed and washed thoroughly, getting rid of the slightest contamination. Next they are sent to storage for a very long time. long time. The storage facility is located in geologically stable areas so that the storage facility is not damaged.

Geological disposal is carried out at a depth of more than 300 meters in such a way that the waste does not require further maintenance for a long time.

Burning

Some nuclear materials, as mentioned above, are direct results of production, and a kind of by-product waste in the energy sector. These are materials that were exposed to irradiation during production: waste paper, wood, clothing, household waste.

All this is burned in specially designed furnaces that minimize the level of toxic substances into the atmosphere. The ash, among other wastes, is cemented.

Cementing

Disposal (one of the methods) of nuclear waste in Russia by cementing is one of the most common practices. The idea is to place irradiated materials and radioactive elements in special containers, which are then filled with a special solution. The composition of such a solution includes a whole cocktail of chemical elements.

As a result, it is practically unaffected external environment, which allows you to achieve an almost unlimited period. But it is worth making a reservation that such burial is possible only for the disposal of waste of medium hazard level.

Seal

A long-standing and fairly reliable practice aimed at disposal and reduction of waste volume. It is not used for the processing of basic fuel materials, but allows the processing of other wastes low level danger. This technology uses hydraulic and pneumatic presses with low pressure force.

Reuse

The use of radioactive material in the field of energy does not occur to its full extent due to the specific activity of these substances. Having spent its time, the waste still remains a potential source of energy for reactors.

In the modern world, and especially in Russia, the situation with energy resources is quite serious, and therefore reuse nuclear materials as fuel for reactors no longer seems improbable.

Today, there are methods that make it possible to use spent raw materials for energy applications. Radioisotopes contained in waste are used for food processing and as a “battery” to operate thermoelectric reactors.

But the technology is still in development, and an ideal processing method has not been found. However, the processing and destruction of nuclear waste can partially resolve the issue with such waste by using it as fuel for reactors.

Unfortunately, in Russia, such a method of getting rid of nuclear waste is practically not being developed.

Volumes

In Russia, throughout the world, the volume of nuclear waste sent for disposal amounts to tens of thousands of cubic meters annually. Every year, European storage facilities accept about 45 thousand cubic meters of waste, while in the United States only one landfill in the state of Nevada absorbs this volume.

Nuclear waste and work related to it abroad and in Russia are the activities of specialized enterprises equipped with high-quality technology and equipment. At enterprises, waste is exposed in various ways processing described above. As a result, it is possible to reduce the volume, reduce the level of danger, and even use some waste in the energy sector as fuel for nuclear reactors.

The peaceful atom has long proven that everything is not so simple. The energy sector is developing and will continue to develop. The same can be said about the military sphere. But if we sometimes turn a blind eye to the emission of other waste, improperly disposed nuclear waste can cause a total catastrophe for all of humanity. Therefore, this issue requires an early solution before it is too late.