PRESENTATION. 1. Brief description of the IPPE

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1 PRESENTATION Liquidation of Legacy SNF at Russian Research Centers: Example of Institute for Physics and Power Engineering, Obninsk V.M. Mamaev, G.A. Miakishev, V.M. Skorkin, N.I. Stasyuk, SSC RF IPPE, Russia 1. Brief description of the IPPE The STATE SCIENTIFIC CENTER OF THE RUSSIAN FEDERATION INSTITUTE FOR PHYSICS AND POWER ENGINEERING named after A. I. Leypunsky (hereinafter IPPE) was founded in 1946 to solve scientific and technical issues related to nuclear power creation and development. The IPPE develops its scientific and technical activity in the following topic areas: - fast reactors with sodium coolant; - water-graphite reactors; - reactors with lead-bismuth coolant for transport and stationary use; - space nuclear power systems. Scientific studies are carried out in the field of nuclear physics, nuclear reactor physics, low-temperature plasma physics, nuclear pumped laser physics, behavior of materials under radiation, radiochemistry, core reactor materials and fuel elements technology, thermal physics, hydrodynamics, nuclear and radiation safety and other areas of nuclear science and technology. The following nuclear installations and sites have been created under the IPPE scientific supervision: - World s First Nuclear Power Plant; - BR-10, BОR-60, BN-350 and BN-600 reactors; - Two units of Beloyarsk NPP; - Bilibino NPP; - A number of transport and space nuclear power installations. At the IPPE there is a large-scale research and trial infrastructure that embraces several research reactors, critical facilities, charged particle accelerators, hot cells and storage facilities for fresh and spent nuclear fuel (SNF). 2. Some of IPPE nuclear facilities and their spent fuel characteristics The World s First NPP with the АМ reactor was put into operation on June 27th, Its rated thermal power was 30 MW and electric power was 5 MW. After operation for 5 years as a nuclear power plant, it started to be used as an experimental installation to test various types of fuel elements and structural materials, to develop and improve water chemistry modes. It was also used for production of radioisotopes. The reactor core consisted of 128 fuel subassemblies, with 4 fuel elements in each. In the initial stage, U-Mo alloy (ОМ-9) and low enrichment uranium carbide (UC) filled with molten magnesium in the inter-tube annular gap and then uranium dioxide (UO 2 ) were used as fuel. Reactor was shut down in 2002, the fuel was discharged and in 2008 it was transferred to the IPPE central spent fuel storage facility. In 1956, 100 kw BR-2 reactor with mercury coolant was put into operation. This facility demonstrated feasibility of fast neutron reactors application for energy generation. In 1958, the БР-2 reactor was retrofitted to 5 MW BR-5 reactor with sodium coolant. It was used to test and develop design approaches for their subsequent application in designing and construction of commercial fast neutron reactors. Fuel elements of various compositions were used, namely: plutonium dioxide (PuO 2 ), uranium dioxide (UO 2 ) and uranium carbide (UС). As a result, as high as 6-7 % fuel burnup was achieved, experience was gained in handling failed fuel elements and studies were made on the ingress of fission products to the coolant and primary gas plenum. Fuel element failure detection system based on delayed neutrons monitoring was developed.

2 Also, studies on safety and dynamics characteristics of the facility were carried out. A whole complex of nuclear, physical and material studies was performed. In 1973, BR-5 reactor was retrofitted. Now its capacity was increased to 10 MW, so this facility was renamed to BR-10. In this case fuel compositions were represented by plutonium dioxide (PuO 2 ), uranium dioxide (UO 2 ), uranium carbide (UС) and uranium nitride (UN). This reactor was used to study nuclear fuel and materials working capacity. Also it was used for isotopes production and neutron therapy. Many design approaches were elaborated and tested in this reactor with the aim to improve fast neutron reactor safety. The BR-10 reactor was shut down in 2002 as well, the fuel was discharged into the reactor cooling pond and then in a certain period of time it was gradually transferred to the central SNF storage facility. The last spent fuel subassembly was transferred in August, Transportable power plant TES-3 of 1.5 MW electric power was designed at the IPPE and during period it was in operational testing. Fuel elements for this reactor were made of uranium-aluminum alloy (UAl 3 +Si) with 36 wt.% concentration of U-235 (enrichment). Diameter of the fuel element was 12 mm, its fuel section length being 1 m. The amount of uranium in one fuel subassembly was about 1 kg. The average fuel burnup reached 3% value. The experience gained in designing and operating TES-3 turned out to be useful for the development of transportable and floating nuclear power plants. Seven power plants based on thermoelectric converter «Topaz» were tested on special test facility during period. Pre-flight tests of two standard plants were conducted on this facility. Electricity generating channels of «Topaz» reactor were designed and manufactured at the IPPE where their in-pile tests were conducted. Fuel elements were made of uranium dioxide with mass concentration (enrichment) of U-235 ranging from 21% to 90%. Fuel element diameter was 10 mm, and fuel section length was 300 mm. The amount of uranium in one fuel element was about 200 g, and the average fuel burnup was up to 0.4%. Studies on reactor materials and fuel compositions were carried out in the hot cells and heavy boxes of the IPPE. These cells and boxes are used for cutting and inspecting pilot and standard fuel elements, fuel subassemblies, ampoules, component parts and material specimens (including those from research reactors AM, BR-2, BR-5, BR-10 and BOR-60 and power reactors BN-350, BN-600, etc). 3. Handling of spent fuel and problems and technology of fuel storage at the IPPE Spent fuel from research reactors core was first put into the cooling ponds (all research reactors have these ponds) for 1.5 to 3 years, and then it was transported to the central storage facility. Spent fuel central storage facility qualified as dry facility and designed as an intermediate storage of spent fuel was put into operation in Life-support systems, such as power and water supply, special drainage, radiation control, fire and alarm signaling systems, ventilation, heating and emergency water pumping systems are located in the elevated part of the storage facility. There are bridge cranes of 20 and 5 tons loadcarrying capacity, reloading container and various equipment for spent fuel handling. In the underground section, spent fuel is kept in special cells. These cells are located in the heavy concrete slab forming square lattice with 800 mm spacing. Stainless steel casings of various length ( mm) are placed in this cells. Fuel elements are placed into these casings. Each cell is closed by a steel shielding plug and a cover with rubber sealing. Heavy concrete monolith slab, shielding plugs, sealed covers and underground basement provide attenuation of gamma radiation to permissible level both inside and outside the storage even with full loading. Spent fuel storage conditions (19 o C average temperature and about 60% humidity) are maintained constant. System of spent fuel accounting and control adopted at the IPPE allows getting all necessary information on the contents of each storage cell: 2

3 - certificates are drawn up on the most part (about 80%) of casings and fuel subassemblies indicating reactor type, manufacturer s number of the fuel subassembly, design description, dimensions, mass of nuclear material prior to their loading to the reactor and calculated mass of nuclear material after unloading, dates of loading and unloading of the reactor, fuel burnup, the number of casing, into which SNF is loaded, and the date of putting SNF to the storage facility; - spent fuel is transferred for storage in due order with filling-in of all necessary documentation; - names of the fuel subassemblies (or fuel elements), their number, certificates and transferring claim numbers, uranium or plutonium weights and loading dates are registered for each central storage cell; - after putting casing with spent fuel into the cell it is covered by the gastight plug, on which information is indicated about loading date and reactor type; - visual control of cell cover condition is carried out. Spent fuel physical inventory implies gamma field measurement above the cells; - concentrations of alpha- and beta-active aerosols and gamma dose rate are periodically measured in central storage facility. Problems related to spent fuel legacy at the IPPE are as follows: - During period, uranium burnup was calculated by various methods and, hence, all accounting data and characteristics of spent fuel have to be refined. - In 1985 and 1989, cells of AM reactor spent fuel storage facility were sealed. Casings from various cells were delivered to the hot laboratory, where fuel subassemblies were cut into elements and these elements were compactly packed into one casing. As a result of this operation uranium-molybdenum and uranium carbide fuel elements with 3% to 10% U-235 enrichment (which were taken from the fuel subassemblies with different fuel burn-up and energy production irradiated in the different core loadings) were found in the same casings. Besides, fuel elements in the sealed casings have no identification numbers and don t differ from each other (initially the identification numbers were indicated on the fuel subassemblies). - It is impossible to reliably determine condition of AM reactor fuel elements and their mechanical properties without additional examination. After all, fuel elements of AM reactor that entered central storage facility until 2006 were made of thin-wall stainless steel tubes. In the course of the long-term storage of spent fuel micro cracks are likely to appear in these tubes causing high sensitivity of ОМ-9 based fuel compositions to oxygen influence. - As a result of sealing of spent fuel subassemblies of BR reactor with high enrichment uranium after their cleaning from coolant (liquid sodium) fuel subassemblies with various fuel compositions (uranium dioxide, nitride and carbide) were in the same casing. Fuel subassemblies of BR reactor previously had identification numbers, however chemical and mechanical effects made many of them indiscernible. Some fuel subassemblies from BR plutonium core have not been cleaned from coolant (liquid sodium). - In 1980 and during period, fuel subassemblies of VM transport reactor (based on UO 2 +Al+Ni, UZr and UO 2 ) with various mass concentrations and U-235 enrichment varying from 21% to 90% were also sealed, these subassemblies being visually indiscernible. - In period, AM research reactor was operated in various experimental modes. There is no detailed information on the unloaded fuel burnup in the accounting data. Activity assay was undertaken as of The most part of spent fuel is not gas-tight, so it is necessary to handle this as failed fuel elements. - After long-term storage (in some cases up to 50 years) it is impossible to remove spent fuel without additional cutting. - Drawings of some types of fuel subassemblies have not survived. - Technology of sorting and certification of spent fuel should be worked out. Also it is necessary to manufacture related non-standard equipment. 3

4 4 - By now, spent fuel central storage facility is filled up to 99%. Decision about spent fuel shipment for reprocessing (first of all, SNF with standard fuel composition, i.e. uranium dioxide forming) could mitigate this situation at the IPPE. As regards uranium carbide and nitride and uranium alloys with molybdenum and other rare metals not included in the standard regeneration technologies, it is necessary either to develop technologies of their reprocessing or to arrange its shipment for the long-term dry storage in the federal storage facility. 4. Prospects and possibilities of spent fuel export from IPPE Based on the analysis of characteristics of available SNF, conditions of its storage and existing infrastructure of the IPPE, studies were made on various possible options of creation of ex-storage technological complex with special equipment for certification and preparation of spent fuel for shipment. This complex should provide safe handling of spent fuel, i.e. removal of the fuel from casings, fuel preparation, placing in canisters, loading into shipping package set (SPS) and putting SPS on a vehicle. One of the IPPE buildings appears suitable for its placing because there are appropriate technological premises and special load-lifting equipment. Preliminary analysis of refueling system has shown that spent fuel shipment from the IPPE in transport containers SPS-19 is an optimum approach, since it is yet impossible to use heavy containers (SPS-18, SPS-32 or SPS-108) unless approach lines of the IPPE are modified. Since overall dimensions of AM fuel elements (forming about 60% of the total spent fuel amount) are almost twofold as those permissible for SPS-19, it is necessary to cut them and put into the canisters before loading into SPS. It is also necessary to decrease the length of the other type fuel subassemblies, although by removing only their structural elements, but not fuel section. The bulk of spent fuel at the IPPE is not included in the nomenclature of fuel reprocessed on radiochemical plants (basically because of lack of technology). All types of spent fuel are considered below, as well as potential possibilities of its reprocessing, preparation work and cost estimates. Fuel based on UO 2 Fuel based on uranium dioxide (about 40% of total load fuel) with initial uranium-235 enrichment up to 90% from all types of the reactors is reprocessed by the standard technology. A distinctive feature appears only for the fuel filled up with molten magnesium in the annular gap between the tubes (AM reactor fuel). It is reprocessed by the standard technology by adding it in small amounts to the oxide fuel. Fuel based on UO 2 -Al-Ni There exists small amount of fuel with uranium dioxide dispersed in Al-Ni matrix. Now there is no reprocessing technology for such fuel. Fuel based on U-Mo Uranium-molybdenum alloy was used as fuel composition in the fuel subassemblies of AM reactor. In the cells of spent fuel storage facility there is about 40% of total load of a fuel in the form of ring fuel elements of 1700 mm length, 14 mm outer diameter and 9 mm inner diameter (all fuel elements of АМ reactor have different fuel compositions but the same geometrical parameters). Currently this fuel is not reprocessed however its regeneration technology is under development. Fuel on the basis of UN and UC Uranium nitride and uranium carbide were applied as fuel compositions for BR-5 and BR-10 reactors. Fuel subassemblies in the storage facility contain 3% of total load of a high enrichment fuel (90% of U-235) stored. Now its reprocessing is impossible due to the absence of technology.

5 Fuel based on UZr and U-Zr-Nb Now there is no technology of reprocessing of this fuel types. Corresponding R&D work should be performed. It should be taken into account that the quantity of this fuel to be reprocessed is insignificant. Fuel based on UBe There is about 5% of total load of UBe spent fuel in the storage facility. Development of technology of reprocessing of the fuel from test facility (prototype of nuclear submarine power plant) was carried out during period however it was not completed because of financing termination. It is still necessary to develop technology of handling radioactive waste resulting from reprocessing of this fuel composition. Fuel based on U-Al-Si Composition of uranium, silicon and aluminum was used as a fuel composition for subassemblies of transport reactors. There is over 1% of total load of this fuel stored. Fuel on the basis of U-Al-Si-AlZr There is about 1% of total load a fuel composition based on uranium, aluminum, silicon and aluminum zirconium stored. This fuel composition is not reprocessed now due to the lack of technology. 5 Fuel on the basis of PuO 2 Plutonium dioxide was used as a material of fuel composition for BR-10 reactor. There is about 1% of total load of this fuel stored. Reprocessing of this fuel composition is not possible due to the lack of technology. Fuel fragments (named as U different in the fuel nomenclature) There is about 1% of total load of fuel composition based on 90% enrichment uranium in the storage facility, its detailed composition should be specified. The initial measures on the fuel preparation for reprocessing are supposed to carry out at the IPPE. Upon completion of identification and classification procedures it is necessary to make postponed decision about the possibility of the fuel reprocessing. Fuel on the basis of Th and Np Sometimes fuel compositions based on thorium and neptunium were studied at the IPPE. There is small amount of fuel based on thorium and of neptunium in the storage facility. There is no reprocessing technology for these materials however thorium and neptunium are the end products of reprocessing cycle of spent nuclear fuel. It is possible to consider the process of extraction of these elements while adding this fuel composition to the other type of spent fuel. Corresponding R&D work should be carried out. In the scope of Federal Target Program Assurance of nuclear and radiation safety for 2008 and period till 2015 under the State contract signed in 2010, PROGRAM of work on preparation and export of spent fuel of various types from the territory of IPPE was developed. Also preliminary schedule of export stages and cost estimation for each case of spent fuel export were made indicating work nomenclature (SNF preparation, transportation to reprocessing plant and reprocessing). In particular, it is planned to involve a number of specialized enterprises of State Corporation "Rosatom" in this work. Preliminary estimated cost of all activities is about 5 billion RR including about 2.3 billion RR for preparation of spent fuel for shipment, about 300 million RR for transportation and about 2.4 billion RR for reprocessing. Totally 10 shipments of spent fuel are planned, including:

6 6-2 shipments in (350 million RR); - 5 shipments in (3.1 billion RR); - 3 shipments of spent fuel with the postponed decision in (1.8 billion RR). In August 2011 pilot shipment from the IPPE of spent fuel batch with fuel composition based on low-enrichment uranium dioxide (fuel subassemblies EK-10 (10%) and VM (6%), total weight ~ 200 kg) was prepared and carried out in the scope of fulfillment of the Program. This fuel was sent to PA Mayak for radiochemical reprocessing. The export volume was planned proceeding from the task to make the train fully loaded with 16 containers SPS-19 in order to avoid non-productive transport expenses. The whole batch of EK-10 fuel subassemblies available at the IPPE (27 pieces) was exported in 7 containers SPS-19, while 36 VM fuel subassemblies were transported in the other 9 containers SPS-19. For export preparations the following measures were made: - some cells of SNF central storage were inspected; - SNF batch was chosen and certified; - project of hot cell modification was prepared and coordinated; - related equipment was prepared and its adaptation and model tests were conducted; - canisters for the fuel subassemblies were designed and manufactured; - refueling route was worked out; - packing design and transportation scheme were certified; - technical work regulations were developed. Total cost of pilot shipment (preparation of spent fuel and infrastructure for its handling, transportation and reprocessing) is 76.4 million RR. 5. Conclusion Successful preparation of the first spent fuel batch and organization of pilot export to PA Mayak demonstrates feasibility of carrying out further exports and clearing IPPE from accumulated highly active nuclear materials. Experience gained in preparing pilot export has revealed a number of problems to be solved for realization of the second and subsequent shipments of higher activity fuel. For instance, taking into account need for SPS-19 containers, the frequency of shipments cannot be higher than twice a year, this expending period of export of all SNF to over 30 years. Fuel preparation could be carried out several times faster on condition of corresponding modification of shielding cell. The following possibilities are considered in the stage of feasibility study on the alternative options of refueling route: - restoration of the railway line at the IPPE and in the adjoining city territory; - updating equipment and systems for the use of higher capacity SPS; - modification of shielding cell and special communication for cutting spent fuel on the fuel section boundaries. Technology developed for pilot batch of low-enrichment spent fuel can be applied for high-enrichment fuel of BR-10.

PLUTONIUM UTILIZATION IN REACTOR FUEL

Second Moscow International Nonproliferation Conference PLUTONIUM UTILIZATION IN REACTOR FUEL A. Zrodnikov Director General State Scientific Center of the Russian Federation Institute for Physics and Power