Determination of the optimal plutonium fraction in transuranium discharged from pressured water reactor (PWR) spent fuel for a flat fission power generation in the force-free helical reactor (FFHR) along the transmutation period

Abstract

Transmutation of transuranium (TRU) discharged from PWR spent fuel and the possibility of a flat fission power (FFP) generation along the transmutation process have been investigated in the force-free helical reactor (FFHR), which is a demo relevant helical-type D-T fusion reactor, for an operation period (OP) of up to 10 years by 75% plant factor (η) under a neutron wall load (P) of 1.5 MW/m 2. For this purpose, the TRUs discharged from four different pressured water reactor (PWR) spent fuels have been selected as fuel, which include minor actinides (MAs) and plutonium isotopes, and in each spent fuel, the MA has been mixed with the plutonium by using various fractions. The MA–Pu mixture has been spherically prepared, and cladded with SiC to prevent the TRU nuclides from contacting coolant and the fission products from contaminating coolant. The mixture has been located in transmutation zone (TZ) of the FFHR to incinerate and/or transmute the TRU nuclides effectively, and helium has been used for the nuclear heat transfer in the TZ. The calculations have brought out that the fission power generation profiles are quasi-linear for the mixtures with small Pu fractions, in the range of 0–30%, along the transmutation period. The optimal Pu fraction in the mixture for the FFP generation has been determined individually for each mixture by applying interpolation method to the fission rate (R F) values obtained for the relevant mixture with various the Pu fractions along the transmutation period. In consequence of the calculations, the optimal Pu fractions are obtained as 18.94, 19.90, 18.10 and 11.85% for the fuel types A, B, C and D, respectively. In the mixture types A, B, C and D with their optimal Pu fractions, the R Fs are quasi-constant and about 0.84, 0.73, 0.94 and 0.79, respectively. At the end of operation period (EOP), the averages of effective half-lives of 237Np, 239Pu, 241Pu, 241Am and 243Am can decrease to 9.8, 9.4, 9.9 and 9.6 years in the mixture types A, B, C and D, respectively. The average net transmutation fractions (TFs) for the whole TRUs and MAs are about 31 and 52%, respectively.