Fuel cycle optimization of pebble-bed reactors with medul fuel management using particle swarm algorithm

Pebble bed reactor (PBR) features, such as robust thermo-mechanical fuel design and on-line continuous fueling, facilitate wide range of fuel cycle alternatives. A range of fuel pebble types, containing different amounts of fertile or fissile fuel material, may be loaded into the reactor core. A wide range of fuel cycle options suggest to employ optimization algorithms for finding the fuel cycle design which yield the highest performance. The MEDUL fuel management scheme of PBR features recirculation of fuel pebbles several times through the core until reaching their target burnup. This fuel management scheme is characterized by efficient neutron economy since the rapid on-line pebble recirculation results in a low excess reactivity core. Moreover, the robust fuel pebble design permits the fuel pebble utilization up to very high burnup levels of 140000 MWD/THM or even higher. In this work, we have used the Particle Swarm Optimization (PSO) algorithm to optimize fuel utilization of PBMR400 reactor design, running MEDUL fuel management. Optimization was carried out also for cores with Th232 as a fertile material. Results show only a modest improvement in the natural uranium utilization (NUU) (~5%) with regard to reference designs. Investigation of thorium fuel cases showed that the use of highly enriched uranium (HEU) in combination with thorium results in the most favorable reactor performance in terms of uranium utilization. The results reveal that neutronic characteristics of the PBR running MEDUL fuel management are only marginally affected by specific fuel management choices