Light and heavy water cooled hybrid reactors for rejuvenation of LWR spent fuels

Abstract

This study analyzes the rejuvenation performance and energy production of D–T driven hybrid blankets fueled by LWR spent fuel and cooled by heavy water (D 2O) and light water (H 2O). A fuel zone is placed between two cylindrical walls (first wall and second wall). The coolants through the fuel zone are circulated at an operation pressure of 70 bar. The fusion plasma chamber radius is 39.2 cm. The volume fractions selected for the fuel and coolant are 45.5% and 45.5%, respectively, corresponding to the ratio of coolant to fuel of 1:1. For the wall exposed by a first wall load of 1 MW/m 2 and the operation pressure of 70 bar, non-linear thermal-plastic analysis showed that the first and second wall thicknesses have to be 8 and 10 mm, respectively. LiH is the best tritium breeder material for the water cooled hybrid reactor. LiH provides sufficient tritium breeding with higher energy production. For sufficient tritium breeding, the number of fuel rows in the fuel zone are calculated as 13 and 17 for H 2O and D 2O, respectively. The reactor lifetime with the first wall load of 1 MW/m 2 is 4 years. After the operation period of 4 years, the displacement per atom and helium production in the first wall are 50 dpa and 480 ppm, respectively. After the rejuvenation process, the rejuvenated fuel from the hybrid blanket has a burn-up potential of ≈20,000 MWd/t for re-utilization in the LWRs. During the operation period, the tritium breeding ratio (TBR) is higher than unity (TBR>1) for all cases and throughout the operation period. The H 2O and D 2O fairly increase the rejuvenation performance and the energy production. Other positive results, the effects of fission products on neutronic performance of the hybrid reactor cooled by H 2O and D 2O, can be ignored. For the investigated cases, the suggested hybrid blankets are safe with respect to nuclear weapons. After the rejuvenation operation, the fuel remaining from the hybrid reactor has enough safety from the viewpoint of plutonium non-proliferation, since the isotropic percentage of 240Pu in the produced plutonium is higher than 20%. Furthermore, the calculated k eff values indicate that the considered hybrid reactor cannot reach critical conditions ( k eff=1) for all cases. Therefore, the sub-critical conditions, being the most important advantage ( k eff<1) of the hybrid reactors, are not spoiled by the strong moderation effect of water for the coolant/fuel ratio of 1:1.