The neutronics effect of TRISO duplex fuel packing fractions and their comparison with homogeneous thorium‐uranium fuel

Abstract

To improve the performance of the thorium fuel, the duplex fuel potential for the micro-sized high-temperature reactor (HTR) using TRISO fuel has previously been investigated. The objective of this work is to expand on past research by delving deeper into several crucial components of the microheterogeneous thorium-uranium TRISO fuel compact. The MCNPX simulation was used to compare the neutronic performance of TRISO duplex fuel to that of homogeneous (Th,U)O2 fuel at various packing fractions and 235U enrichment. Variations in duplex fuel packing fraction and 235U enrichment were shown to have a significant effect on the neutronics of TRISO fuel. The fuel rod with 20% TRISO packing fraction has the highest kinf value at BOC, fastest burnup rate, fastest 235U depletion, and longest cycle length. As the packing fraction increases, these values however deteriorate in the opposite direction. Furthermore, the conversion ratio increases and the Doppler effect becomes stronger. The findings of evaluating duplex fuel rods at the fuel block level differed. The 40% packing fraction fuel block model achieves the lowest reactivity swing, the strongest Doppler effect, and the longest cycle length. As its packing fractions reduced to 30% and 20%, the values changed in the opposite direction. In comparison to the duplex fuel design, the homogenous TRISO fuel has a lower achievable discharged burnup and shorter cycle length. However, at the beginning of its cycle, it has a stronger doppler effect and lower pin power peaking. Despite the fact that the duplex's power peaking value drops with increasing burnup and becomes comparable to homogeneous fuel, these are some of the challenges and concerns that should be addressed in future research. Despite this, the overall result indicates that the duplex fuel design has promising potential for application in a micro-sized HTR.