Preliminary analysis of thorium fuel cycle in a fast neutron spectrum reactor

In this thesis, the performance of the thorium fuel cycle in a fast neutron flux was examined. In particular, this work focused on the TRU legacy burning and breeding capabilities of two sodium-cooled type fast reactors. Namely, a modified version of the Advanced Recycling Reactor (ARR) and a heterogeneous core design, which has been proposed in this work. The ARR is a Toshiba-Westinghouse design, and was chosen due to the availability of the core design data. The heterogeneous design was addressed to improve the breeding capabilities of the ARR, in order to move toward a self-sustained Th-based fuel cycle. Simulations covered the entire life of the reactors, i.e. 60 EFPYs, cycle-by-cycle. To simulate the fuel cycle, basically procedure within the framework of the ERANOS code was developed to perform, burn-up, cooling, reprocessing, and fuel manufacturing for the next cycle. This procedure handles two different external feeds, the fertile feed and the fissile feed. The fertile feed may be thorium or depleted uranium, while the fissile feed is taken as legacy TRU. Cycle-by-cycle, the mass of the fertile and fissile feed which must be added for manufacturing the new fuel is estimated in order to have a keff equal to 1 at the end of the cycle. As a result, the whole reactor life can be simulated with one run of the procedure. Analysis of the ARR core is divided into two parts. First, the ARR core is loaded with metallic fuel, both U-based and Th-based, in order to compare the two fuel cycles and their TRU burning capabilities. Second, performance of Th-based fuel is studied for metallic, nitride (using either natural nitrogen viii or nitrogen enriched with 95 15 N a/o), and oxide fuels. Calculations have sim- ulated 60 Equivalent Full Power Years (EFPYs), spanning the entire reactor life. Additionally, a heterogeneous core design has been surveyed for exploring the transition phase from a Th/TRU core to a pure Th/U233 fuel cycle. To this aim, the first 60 EFPYs have been simulated where external fissile feed was legacy TRU, after which, the feed has been changed to in-bred uranium. External supply of uranium was necessary because the breeding gain is 0.8. The vector of uranium feed was taken from the average of the in-bred uranium vector within blankets and drivers. The fuel form chosen for this study is nitride fuel enriched with 95 15 N a/o. For this work, the TRU external feed comes from 10-yr cooled reprocessed LWR UOX fuel with 4.2 235 U w/o and 50 GWd/tHM discharge burnup.

In questa tesi ho svolto degli studi preliminari per lo studio delle performance del ciclo del torio in un reattore veloce proposto. Lo studio si e' concentrato sulla capacita' di bruciare transuranici e il breeding di U-233.