Evaluation of optimal amount of americium that should be extracted from spent nuclear fuel of the Brest-OD-300 reactor for transmutation to ensure radiological equivalence of radioactive waste and natural uranium

Closed fuel cycle with fast reactors makes reduction of radioactive waste (RW) more effective as compared with the open fuel cycle with thermal reactors. Quantitative parameters of radionuclides extraction from spent nuclear fuel (SNF) depend on the radiological equivalence of generated RW and initial mass of natural uranium used for nuclear fuel fabrication. The length of RW storage before the radiological equivalence is achieved should not be longer than 300 years. To meet the requirement is possible if americium (Am) is extracted from SNF and burnt in the fast reactor. The more Am is in the RW, the lower the cash outflow during SNF reprocessing is. However, in that case radiological equivalence will be achieved later and the expected cash outflow during subsequent controlled storage of RW will be higher. Hence, a decrease in total cash outflow during SNF reprocessing and subsequent storage of RW may be possible by optimizing the amount of Am in the RW. In this paper we consider the possibility to estimate optimal Am content in RW, at which the total cash outflow during extraction of Am from SNF and subsequent controlled storage of RW is minimal. This optimum depends on a method for estimating time for radiological equivalence achievement and the ratio between cash outflows during Am extraction and SNF storage, accounting for the discount rate of the latter. The length of time needed for achievement of the equivalence between RW and natural uranium is estimated by the time of achievement of equality between the lifetime attributable risks (LAR) from RW and natural uranium or equality between values of their committed effective doses. The optimum amount of Am in RW calculated on the basis of LARs estimates is considerably higher (1-2%) than the amount calculated on the basis of committed effective doses (0.5%), with that the total cash outflow calculated using LARs are 1.5 times lower than one calculated using committed effective doses. For making estimates more accurate further research using variety of actual data is needed.