Evolution of Actinides in ThO₂ Radial Blanket of Prototype Fast Breeder Reactor

Abstract

The third stage of India’s nuclear program envisages utilization of thorium through Th–U233 cycle in view of the better abundance and relative merits of thorium. For early introduction of Thorium into the nuclear energy system, several R&D programs have started to find the best possible route of thorium utilization. Toward this, efforts were made to assess the feasibility of Th–U cycle in a fast spectrum reactor like prototype fast breeder reactor (PFBR). The effect on core neutronic parameters and actinide evolution with the replacement of depleted UO₂ in the PFBR blanket SA with thorium oxide has been studied using 3D diffusion code FARCOB. Study shows that by the introduction of thorium blanket, core excess reactivity is coming down by ~535 pcm, and core breeding ratio is slightly lower than that with conventional oxide blanket. The distribution of region wise power production is slightly changed. Power from radial blanket is reduced from 3 to 2% while the core-1 power is increased from 49 to 50%. The estimated U²³³ production is 7.6, 11.5, and 14.1 kg/t with 180, 360, and 540 days of irradiation, respectively. In addition, U-232 production is also estimated using ORIGEN-2 code. The amount of U-232 per radial blanket SA is about 165 ppm at discharge burnup of 3500 GWd/t.