Project 'Almaz' phase 1: Verification of spent fuel canning at fast breeder reactor BN 350

Full text: The 'Almaz' Project, consisting of two distinct phases, is implemented under a trilateral agreement between Kazakhstan, the USA and the IAEA. The purpose of the project is to pack all irradiated fuel and blanket assemblies of the BN-350 fast breeder reactor into purpose designed canisters which are then welded closed, each holding 6 normal assemblies or 4 abnormal assemblies and to transfer this material to long term dry storage facility. Under this Agreement the IAEA has the obligation to apply safeguards to the nuclear material during all phases of the Project. Phase 1 of the project, namely the discharge of all assemblies from the core, conditioning and stabilizing of all items and storing in baskets in the spent fuel pond, started in November 1998 and is was completed in June 2001. In total, 2788 items, consisting of 2537 normal fuel items and 251 abnormal fuel items were conditioned and canned into 478 canisters in 69 baskets. The safeguards approach during this project required the use of the latest technologies and the development of purpose designed NDA equipment and monitoring systems, supported by the US support programme in conjunction with Los Alamos National Laboratory. Such newly developed equipment can and will be applied in other facilities. Aside from the normal safeguards measures at such a facility, specific safeguards activities included the verification of all core discharges through item identification by underwater camera and verification of operator declared plutonium content by the use of a Spent Fuel Coincidence Counter (SFCC), designed and purpose built by Los Alamos National Laboratory. Non fuel items loaded to the reactor to replace the discharged assemblies were verified as such. SFCC exploits the unique feature of the fast breeder reactor spent fuel - the neutron emission is caused by plutonium isotopes only, thus making it possible to use a well established neutron coincidence counting techniques for quantitative plutonium measurements. SFCC is a collar type underwater counter containing 20 He3 tubes imbedded in polyethylene and shielded by 7 cm thickness lead ring to protect the tubes against spent fuel gamma radiation. The data are collected by a standard neutron coincidence electronics and INCC software. Because direct measurement of the plutonium isotopic of the spent fuel was not possible the relative plutonium isotopic abundance determination is based on the ANL validated BN-350 burn up chains code. Combination of MCNP modeling of various BN-350 assembly types with specially developed iterative software allowing to harmonize all multiplication correction algorithm parameters for estimation of the verified assembly plutonium content was validated through comprehensive calibration exercise at BN-350 with all types of fuel assemblies. Interactive measurement controlling (IPANIC) software performs all required calculations and guides the user through all measurement, evaluation and decision making (accepted/rejected) process. The partial defect acceptance criterion is formulated as Operator Declared - Inspector Measured plutonium amount difference shall not exceed 50% with 3 sigma confidence level. All stabilization and canning activities took place in a hot cell. Safeguards measures included the use of integrated digital surveillance and radiation monitoring systems designed specifically for this project by Los Alamos National Laboratory to the Agency's requirements. This system, the Multiple Instrument Measurement System (MIMS), which worked in both attended and unattended mode, enabled the Inspector to observe what was occurring at all stages and to verily nuclear material movements and their direction in the hot cell though the use of radiation monitoring graphs and triggered surveillance images. In October 2000, the final core assembly was discharged, and in November 2000 the Agency developed a specific procedure to verify the emptiness of the core of all nuclear material, by verification of several empty channels in the core. At all stages of the project, there have been tri-lateral meetings held, both high-level policy meetings, and technical meetings. Co-operation between all parties has been excellent, and the project has benefited from such timely meetings, were potential future problems were highlighted and solutions developed and implemented. (author)