Natural uranium consists of a mixture of three isotopes: Uranium-238 (99,28%), uranium-235 (0,7%) and uranium-234 (0,006%). Of these, only Uranium-235 can maintain a chain reaction in a nuclear reactor. Since its content in the natural uranium is insufficient for Russian reactors, a number of technological operations in the fuel cycle is aimed at rising the content of uranium-235 (this process is usually called enriching).
The nuclear reactor installations in Eastern Europe and former USSR operate on fuel produced from ceramic dioxide of uranium. For different types of reactors, the level of uranium-235 (the enrichment) varies from 2,4% to 26%. The level of enrichment differs from one type to another of a particular nuclear installation: VVER-1000 requires 4-5% enrichment; RBMK-1000 requires 2,4-2,6% enrichment; VVER-440 requires 3,6% enrichment; BN-600 reactor cores consist of fuel assemblies with different degrees of enrichment: 17%, 21% and 26%. Weapon-grade uranium, usable in nuclear warheads, is enriched to more than 90%.
Generation of spent nuclear fuel
The generation of spent nuclear fuel in the nuclear power plants is the following. Uranium pellets are encapsulated into fuel pins, which are collected in fuel assemblies, which are used in the reactor core of a nuclear power plant for 3-5 years. During this period of time, the uranium-235 burns out sustaining the chain reaction in the reactor.
The isotope uranium-238, the amount of which is significant in the enriched uranium, absorbs superfluous neutrons, allowing control of the chain reaction. In the course of this process, uranium-238 rapidly converts into plutonium-239 through neutron irradiation. Other, similar conversions happen to all the involved isotopes, including those which are the results of previous conversions, allthough at much slower speeds. In the end (after three years’ use), 100 kg of spent nuclear fuel from a VVER-1000 reactor will contain 740 g of long-lived plutonium isotopes (emitting alfa radiation), and some 4 kg of other long-lived trans-uranium radio nucleides.
The fuel assemblies removed from the reactor after 3 years of utilisation contain 26,000 Curie of activity for each kg. Taking into account the fact that the amount of fuel inside a VVER-1000 reactor is some 90 tons, the total activity will be approx. 780 million Curie (on removal of one third of the fuel). The removed fuel assemblies are stored in cool water ponds located on-site of the nuclear power plants, for some three years. Nuclear power plants outfitted with VVERs have a pond with free rack space for emergency transfer of the complete reactor core. The water ponds typically have a storage capacity of from 3 to 8 reactor cores, depending on the number of reactor installations. Through the first year of storage the activity in the spent fuel is reduced 12 times, while the full three years storage reduction is some 32 times.
On-site storage of spent nuclear fuel
Currently, as reported by the Russian State Nuclear Inspection (Gosatomnadzor), the general spent fuel storage situation at Russian nuclear power plants (NPPs) is quite unfavourable: Most of the on site storage facilities are filled to capacity, because shipments of fuel from RBMK-1000 reactors have been halted, and shipments from VVER-1000 and BN-1000 reactors are delayed by default. In connection with the RBMK reactors, some experts claim that the lack of onsite storage capacity may cause their decommissioning before the operational life-time expires.
The cooling water ponds for the four VVER-440 reactors at Kola power plant are filled to their capacity, containing some 2500 fuel asseblies. The same situation prevailes at the fourth reactor installation (VVER-440) of Novovoronezh power plant. This plant has three operational reactor installations (two VVER-440 and one VVER-1000). At both of these NPPs, the emergency water ponds are filled with regular fuel, thus disallowing removal of a reactor core in case of an accident.
The storage water pond at Kursk NPP (4 RBMK-1000 reactors) is filled to capacity; at Leningrad NPP the water pond capacity was increased in 1995 by reducing the distance between fuel assemblies, temporarily solving the storage problem. Today, the LNPP has stored some 22,000 spent fuel assemblies, and the revised storage pond capasity has been reached.
At Bilibino NPP, which operates four EGP-12 reactors, the storage capacity will be full in five years, while the plant has no resources to build an additional storage facility. At Beloyarsk NPP no decision has been taken on handling the spent fuel from two shut down reactor installations. Beloyarsk NPP is currently operating one BN-600 reactor, having shut down one AMB-100 and one AMB-200.
Currently there are some 7500 tons of spent fuel from RBMK reactors stored in nuclear power plants’ on site storage facilities, 1800 tons of VVER-1000 fuel assemblies (the annual generation of spent fuel for VVER-1000s is 135 tons) stored in the storage facility of Krasnoyarsk-26 (the total capacity of which equals 6000 tons). Some 1100 tons from VVER-1000 reactors are stored on site at four NPPs. At Mayak in Chelyabinsk-65 there are 465 tons of fuel from various types of reactors. The on site accumulation of spent fuel at research reactors continues to grow.
The current stock total of spent nuclear fuel from nuclear power plants in Russia as a hole, can be estimated as more than 10,000 tons, with a total activity of 5 billion Curie.
Handling of spent VVER reactors’ fuel
In, 1976 the spent fuel reprocessing plant RT-1 (Mayak) was put into operation in Siberia. The initial capacity of the plant was 400 tons of fuel a year. Currently, the plant reprocesses the fuel coming from VVERs (except VVER-1000), BN-600, BN-350 and some research reactors, as well as the spent fuel coming from the nuclear-powered submarines and ice-breakers. The products from the reprocessing are uranium as salt of uranil-nitrate (the enrichment of the U-235 is up to 2,5%) for reuse in fabrication of RBMK-1000 type reactor fuel; extraction of fuel plutonium as a plutonium dioxide; extraction of granulated powder for fabrication of MOX uranium-plutonium fuel (5-25% of plutonium) for use in fast breeder reactors. Due to the fact that there currently is no industrial application of fuel plutonium, the generated stocks are stored at Mayak. Recent estimations say there are currently some 30 tons of fuel plutonium.
In addition to spent fuel from Russian nuclear installations, fuel also comes from Ukraine, Hungary, Czhech republic, Slovene and Bulgaria. There were as well some unregular shipments of spent fuel from a Russian designed research reactor in Iraq.
The reprocessing in Mayak is very hazardous to the environment. According to the estimates, each ton of reprocessed spent fuel generates some 600,000 Curie of waste. As follows from the agreement between Mayak administration and Chelyabinsk county authorities, the RT-1 plant can annually reprocess 250 tons of spent nuclear fuel out of the 400 tons a year design capacity. This results in an annual generation of 150 million Curie of radioactive waste a year. However, Minatom claimed that in the year 1995 the plant handled far less than this. In 1996, it was expected to handle even less. Between 1991 and 1994 Mayak reprocessed approx. a quarter of the VVER-440 fuel sent there. Since March this year the operation of the reprocessing plant was suspended by the Russian State Nuclear Inspection.
VVER-1000 fuel handling
Fuel from VVER-1000 reactors is shipped to the storage facility in Krasnoyarsk-26. The fuel comes from three Russian nuclear power plants operating on this reactor type as, well as from four nuclear power plants in Ukraine and one in Bulgaria.
The reprocessing of VVER-1000 fuel was to be conducted at the RT-2 reprocessing plant in Krasnoyarsk-26. The plant would have an annual capacity of 1500 tons. But construction was stopped in 1990 due to the lack of proper funding. The only part of the reprocessing complex commissioned, is a storage facility for 6000 tons of VVER-1000 fuel. Currently, the facility is filled to 30% (approx. 1800 tons of fuel). The storage facility is expected to be filled to its capacity by the year 2015. The completion of RT-2 is questioned from economical and environmental points of view. The attempt of the Krasnoyarsk green movement to carry out a referendum against RT-2 was hampered by the county deputies council on April 18 this year. A complaint against the deputies’ decision was delivered to the county court. The court’s consideration of this complaint should be completed by the beginning of June this year.
RBMK fuel handling
The ways of handling RBMK-1000 fuel are not defined yet. The extractable content of U-235 isotopes is very low, while stocks of accumulated fuel plutonium, extractable from the spent RBMK fuel, is considerably large. Hence, reprocessing of this type of fuel can not bring any economical benefits, at least till the year 2010. The strategy for the time being is to deposit the fuel in deep geological formations, or reconsidering the economical calculations in the year 2010.
Currently, there are some 7500 tons of RBMK-1000 fuel with a total activity of 1.25 million Curie stored in on-site storage facilities at Leningrad, Kursk and Smolensk nuclear power plants. The annual generation of RBMK-1000 spent fuel is some 750 tons. It is expected that by the year 2005 the on-site storage facilities of the plants will be filled to capacity, and in case no solution is found by then, the plants will have to be shut down. The plants are currently working on increasing the storage capacity by reducing the distance between stored fuel assemblies in the storage rooms. This solution was in particular implemented at Leningrad nuclear power plant. Of course, this only buys some time – it is not a long term solution.
By 2010 Russia plans to shut down 24 of the 29 currently operational reactor installations. In the mean time, great amounts of spent nuclear fuel will have to be stored in a proper way.
Recently, two reactor installations of Beloyarsk nuclear power plant (AMB-100 and AMB- 200) and two reactor installations of Novovoronezh nuclear power plant (VVER-210 and VVER-365) were shut down. At Novovoronezh the spent fuel was removed from the reactors and stored in the onsite storage facility. On the first reactor installation at Beloyarsk all the fuel was taken out, while on the second installation there are still a few fuel assemblies left inside the reactor. In the onsite storage facility there are 4990 fuel assemblies. A part of the cladding is no longer tight, leading to contamination of the cooling water. Radioactivity in the water increased during the last three years by a factor of 1.6. The first reactor installation at Beloyarsk was taken out of operation in 1980, but the decommissioning is still not finished.
The closed cycle principle, which Russia is sticking to, has not justified itself, since the extracted fuel plutonium accumulates at the special storage facilities rather than being utilised. More over, the operation of Mayak reprocessing plant was suspended on March 21 by rule of the Gosatomnadzor. The time when the plant will restart is unclear both for the Mayak administration and Gosatomnadzor officials. No final solution has been suggested for the long term repository problem. And judging upon the reactor installation decommissioning experience of Beloyarsk and Novovoronezh nuclear power plants, the process of pulling out of operation 24 nuclear power plants by 2010 will constitute severe challenges and problems.
Nuclear Control magazine, no.28-29:97
Judith Perera, The Nuclear Industry in the Former Soviet Union: Transition from Crisis to Opportunity, FT Energy Publishing, vol.2, 1997
Inventory of radioactive waste and spent fuel at the Kola Peninsula region of north-west Russia, Europan Commission, DG: Environment, Nuclear Safety and Civil Protection, 1996