Enhancing plutonium incineration in the thorium-based I2S-LWR design with loading pattern optimization

This paper presents an optimization of a thorium-plutonium fuel cycle, through a multi-batch reloading scheme, developed for the Integral Inherently Safe Light Water Reactor (I2S-LWR). The I2S-LWR is an advanced 2850 MWt integral pressurized water reactor with enhanced safety beyond that of Gen-III+ reactors. Its baseline fuel and cladding materials are U3Si2 and advanced FeCrAl steel, respectively. The advanced steel cladding can withstand longer exposure periods with significantly lower degradation rates compared to traditional Zr-based alloys. In principle, increasing the number of batches allows higher discharge burnups and thus deeper Pu and transuranic elements incineration to be achieved. Therefore, various refuelling strategies were considered in this study, namely 3-, 5- and 7.56-batch schemes. The Simulated Annealing optimization technique was applied for the different batch schemes to obtain the most favourable loading pattern with respect to cycle length performance. The results confirm that increasing the number of batches allows the discharge burnup to be increased by 20% (above 100 MWd/kg), which improves the Pu incineration performance. In addition, the increased number of batches improves the reactivity coefficients without violating the power peaking factors limits.