Analysis of actinide recycling in a Boiling Water Reactor using CASMO-4/SIMULATE-3

Final disposition of spent nuclear fuel in a permanent repository is still on debate; meanwhile the stockpile of depleted fuel is increasing. Actinide recycling has the potential to reduce that stockpile. This study analyzes the potential to burn actinide from depleted fuel in a thermal reactor without reducing the nominal electricity generation of the reactor and meeting all the safety constraints. The study takes an equilibrium cycle of a Boiling Water Reactor (BWR) as the reference cycle and then it proposes the design of an equivalent fuel assembly in which 4 fuel rods are replaced by minor actinide-bearing rods, the process ends when the equilibrium cycle is met. The new BWR fuel assembly design, that is called MA-c, has the goal to maximize the actinide recycling while introducing the lowest perturbation possible to the control and safety systems of the reactor. MA-c is successful, according to our analysis. The performance of the core is analyzed using MA-c and it is compared against the UO2 reference core, results show that both of these cores produce the same amount of energy for an 18-month cycle. The MA-c fuel assembly has a higher enrichment than the UO2 reference fuel assembly to compensate for the use of four MA-bearing rods, however all the fuel pins inside the MA-c fuel assembly have enrichments below 5 w/o of U-235. The MA-c core met all the safety BWR constraints without modifying any of the control systems. Results for a BWR with a nominal power of 2027 MWt show a reduction of 135.30 kg HM of minor actinide per 18-month operating cycle when the whole core is composed of “once-through” MA-c fuel assemblies. The use of this new BWR fuel assembly design can be used effectively for the reduction of minor actinide without the need of control systems modification in the reactor to meet safety limits and without affecting the energy production.