Comparison of the neutronic properties of the (Th-²³³U)O₂, (Th-²³³U)C, and (Th-²³³U)N fuels in small long-life PWR cores with 300, 400, and 500 MW_th of power

The neutronic characteristics of (Th-²³³U)O₂, (Th-²³³U)C, and (Th-²³³U)N have been compared in small long-life pressurized water reactors (PWRs). Neutronic calculations were carried out at 300 MW_th, 400 MW_th, and 500 MW_th with two cladding types: zircaloy-4 and ZIRLO (Zr low oxygen). They were performed using the Standard Reactor Analysis Code (SRAC) and JENDL-4.0 nuclide data, dividing the reactor core into three fuel zones with varying ²³³U enrichment levels, ranging from 3% to 9% and fluctuating by 1%, employing the PIJ module at the fuel cell level and the CITATION module at the reactor core level. In addition, ²³¹Pa was added as burnable poison (BP). The (Th-²³³U)N fuel demonstrated superior criticality compared to the other fuel types, as it consistently achieves critical conditions throughout the reactor’s operating cycle with excess reactivity <1.00% dk/k for several fuel configurations at the 300 MW_th and 400 MW_th power levels. Moreover, the (Th-²³³U)N and (Th-²³³U)C fuels exhibited similar and flatter power density distribution patterns compared to the (Th-²³³U)O₂ fuel. The power peaking factor (PPF) value was relatively higher for (Th-²³³U)O₂ fuel than the other two fuels. The (Th-²³³U)N fuel exhibited the most negative Doppler coefficient, followed by (Th-²³³U)C and (Th-²³³U)O₂ fuels. Analysis of burnup levels revealed that the (Th-²³³U)O₂ fuel achieved significantly higher burnup than the other two fuels.