Safety of Pyroelectrochemical Reprocessing of Spent BOR-60 Fuel

Abstract

The results of an investigation of the safety of reprocessing 15.5 kg of spent BOR-60 fuel are presented. The absolute amounts of radioactive aerosols entering the ventilation system of the pyroelectrochemical setup during the reprocessing of spent fuel are determined. The transfer of radionuclides from fuel into aerosols is estimated. This makes it possible to obtain an expression for the expected inflow of radioactive substances from the setup, depending on the amount of materials handled in the technological scheme. The data presented on the possibility of obtaining large amounts of uranium and plutonium in the finished product when their content in the solid wastes is negligible are presented. Estimates are made of the irradiation of workers at all stages of the process.A demonstration experiment on reprocessing a large batch of spent BOR-60 nuclear fuel, performed at the Scientific-Research Institute of Nuclear Reactors in 2000-2002, became the first step in substantiating a closed nuclear fuel cycle for fast reactors on the basis of a nonwater technology for obtaining granular mixed uranium-plutonium fuel suitable for fabricating fuel elements with a vibrationally compacted kernel [1,2]. Together with technological studies, the safety of the process and of its individual stages was studied in detail in the experiment.The radioecological safety at the stages of preparation of spent BOR-60 fuel assemblies for pyroelectrochemical reprocessing was examined in [3,4]. In the present paper, the results of an investigation of the safety of the spent fuel reprocessing process itself, which is the most important stage of a closed fuel cycle, are presented.Characteristics of the Reprocessed Product. The initial product consisted of the spent fuel from six BOR-60 fuel assemblies which was separated from the cladding by the Wohl oxidation method: two fuel assemblies based on pelleted uranium fuel with burnup 10.5-11.9% h.a. and holding time 10.4-23.7 yr and four with vibrationally compacted mixed uranium-plutonium fuel (19% Pu) with burnup 9.5-11.6% h.a. and holding time 11.2-12.5 yr [4]. The total fuel mass subjected to the processing was 15.5 kg, the total specific activity of actinides in the fuel composition was 24.1 TBq/kg, and the specific activity of the fission products was 36.7 TBq/kg. Plutonium isotopes made the greatest contribution to the activity of the actinides (%): 241 Pu 80.2, 238 Pu 0.6, 239 Pu 0.6, 240 Pu 0.8, 241 Am 2.6; among fission products -137 Cs + 137m Ba 52.7, 90 Sr + 90 Y 41.3, 155 Eu 0.6, 125 Sb 0.3, 106 Ru + 106 Rh 0.1 [4].The composition of the initial product was determined using destructive methods of analysis and certified procedures (coulometry, mass spectrometry, spectrophotometry, and α, γ spectrometry), which are "standard," and certified equipment. The relative error in the measurements performed by any method did not exceed 10% [5].Description of the Process. The fuel was reprocessed on an experimental setup intended for studying the reprocessing of spent nuclear fuel by pyrochemi...