Evaluation of thorium-based fuels for 12-year operation of small modular BWR without refueling

The object of this study is an 870 MW small modular boiling water reactor (SMR-BWR) core that is expected to operate for 12 years without refueling. The main issue addressed is conventional BWR designs' limited fuel cycle duration, typically requiring refueling every 2–3 years. This short refueling period increases operational costs, leads to more extended maintenance downtimes, and generates larger volumes of spent fuel waste. This study examines the neutronic performance of thorium-based fuels, namely (Th-235U)O2 and (Th-233U)O2, and compares them with standard UO2 fuel in an SMR-BWR core configuration. The reactor core is a heterogeneous core consisting of 3 fuel zones. To control reactivity, a burnable poison in the form of B4C is also added to the fuel. Neutronic calculations are performed using the standard reactor analysis code (SRAC) system with the JENDL-4.0 nuclear data library. The SRAC code uses the PIJ module for fuel cell level calculations and the CITATION module for reactor core level calculations. The results show that (Th-233U)O2 offers the most stable Keff over a 12-year operating period, consistently remaining above the criticality threshold at all fuel volume fractions. In addition, this fuel type exhibits the most uniform power density distribution and the lowest PPF values, reducing the potential for thermal hotspots. (Th-233U)O2 fuel can achieve a burnup level of around 50,000 MW/ton, which aligns with SMR-BWR standards. UO2 and (Th-235U)O2 fuels show a more pronounced Keff decrease and less favorable power distribution characteristics. These findings underline the potential of (Th-233U)O2 as a promising candidate for long-cycle, continuous SMR-BWR applications without refueling