Thorium and fully ceramic microencapsulated TRISO fuel neutronics feasibility analysis in a gas cooled fast reactor: Enhancing transmutation of long-lived fission products

This study investigates the feasibility of using Fully Ceramic Microencapsulated (FCM) TRISO fuel and thorium fuel in gas-cooled fast reactor, focusing on enhancing the transmutation of long-lived fission products by performing neutronics analysis using the OpenMC Monte Carlo code. The implementation of FCM and modifications to the TRISO layer aim to decrease the moderation effect of the TRISO fuel and achieve a harder neutron spectrum. Four alternative FCM TRISO fuels were proposed by replacing the porous buffer, inner pyrolytic carbon, and outer pyrolytic carbon layers with SiC, ZrC, TiC, and Si₃N₄ in each case. For thorium fuel, two options were investigated-ThUC and ThPuC. The analysis of neutronics parameters revealed that all models achieved a harder neutron spectrum, with all FCM models displaying more harder neutron spectrum than others. This enhancement in neutron spectra and the robust safety of FCM came with a decrease in cycle length and a marginal increase in the power peaking factor due to a more non-uniform neutron flux. Nevertheless, the FCM models still achieved a satisfactory long core life and maintained power peaking factors within acceptable limits. In contrast, the thorium models, particularly ThUC, demonstrated a longer cycle length and an improved power peaking factor. To completely analyze the viability of all models a comprehensive reactivity parameters calculation was performed including reactivity swing, effective delayed neutron fraction, fuel temperature coefficient, power coefficient of reactivity, control rod worth, and shutdown margin. The findings revealed that all models achieved satisfactory results across all reactivity parameters. Notably, all FCM models exhibited improved power coefficient, control rod worth, and shutdown margin compared to the other models. This comprehensive neutronics analysis suggests that while all proposed models displayed satisfactory neutronics performance, the FCM models showed superior reactivity performance. Notably, the FCM model demonstrated significantly improved transmutation efficiency for four long-lived fission products: Nb-94, Pd-107, I-129, and Sm-151.