No abstract
Shipping out the spent fuel of the research reactors at the Institute for reprocessing is examined. The spent fuel is characterized by a great diversity of structural characteristics of the fuel assemblies and fuel elements, fuel compositions, and the enrichment, burnup, and cool-down times of the fuel as well as the state of the components of the assemblies and the structural materials. A classification and quantitative indicators of the accumulated spent fuel from the standpoint of the modern state of its reprocessing technology and the requirements for delivery to the Mayak Industrial Association are presented. The structural features of the TKU-19 and -128 shipment containers are presented, and the loading of spent fuel assemblies into them for shipment to reprocessing is described. The plans and goals of further work on the removal of spent fuel from the Institute's territory are presented.Twelve research nuclear reactors, about 20 experimental critical and subcritical nuclear stands, hot materials science laboratories for performing research with irradiated nuclear fuel, and some other unique physical factilities have operated as part of the experimental base at the Russian Science Center Kurchatov Institute [1, 2]. As a result of many years of experimental operation of the reactor base, a substantial amount of spent nuclear fuel with total activity exceeding 10 16 Bq has accumulated in the course of various scientific programs. This high level of activity is what dictates the urgency of removing this fuel from the Institute's territory to reprocessing facilities.Storage Conditions, Characteristics, and Classification of Spent Fuel. The irradiated fuel is primarily in the form of spent fuel assemblies, fuel elements, and their fragments in research reactors which were disassembled at different times: RFT, IRT, Romashka, Enisei, VVR-2 and OR, MR operated in the final shutdown regime, and the IR-8 and rebuilt OR which are currently operating.After being off-loaded, the irradiated fuel was put into temporary storage sites at the Institute, which were built so that the reactors could meet their operational requirements and that the spent fuel is handled safely. The technical state of the storage sites meets the modern nuclear and radiation safety as well as physical protection requirements. Spent IR-8 fuel is located in a storage pond at the reactor site; IRT, RFT, and MR fuel is located in a centralized dry storage facility on the main site of the Institute; Romashka and Enisei fuel is located in a dry storage facility of complex "R" as well as on the main site; VVR-2 and OR fuel is located in storage ponds of a complex of research reactors and critical stands (Gazovyi Zavod complex) that is located on an auxiliary site at the Institute.
A program of decommissioning of MR research reactor in the Kurchatov institute started in 2008. The decommissioning work presumed a preliminary stage, which included: removal of spent fuel from near reactor storage; removal of spent fuel assemble of metal liquid loop channel from a core; identification, sorting and disposal of radioactive objects from gateway of the reactor; identification, sorting and disposal of radioactive objects from cells of HLRW storage of the Kurchatov institute for radwaste creating form the decommissioning of MR. All these works were performed by a remote controlled means with use of a remote identification methods of high radioactive objects. A distribution of activity along high radiated objects was measured by a collimated radiometer installed on the robot Brokk-90, a gamma image of the object was registered by gammavisor. Spectrum of gamma radiation was measured by a gamma locator and semiconductor detector system. For identification of a presence of uranium isotopes in the HLRW a technique, based on the registration of characteristic radiation of U, was developed. For fragmentation of high radiated objects was used a cold cutting technique and dust suppression system was applied for reduction of volume activity of aerosols in air. The management of HLRW was performed by remote controlled robots Brokk-180 and Brokk-330. They executed sorting, cutting and parking of high radiated part of contaminated equipment. The use of these techniques allowed to reduce individual and collective doses of personal performed the decommissioning. The average individual dose of the personnel was 1,9 mSv/year in 2011, and the collective dose is estimated by 0,0605 man×Sv/year. Use of the remote control machines enables reducing the number of working personal (20 men) and doses. X-ray spectrometric methods enable determination of a presence of the U in high radiated objects and special cans and separation of them for further spent fuel inspection. The sorting of radwaste enabled shipping of the LLRW and ILRW to special repositories and keeping of the HLRW for decay in the Kurchatov institute repository.
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