A neutronic investigation of tristructural isotropic‐duplex fuel in a high‐temperature reactor prismatic seed‐and‐blanket fuel block configuration with reduced power peaking

Abstract

This paper presents the neutronic analysis of a tristructural isotropic (TRISO)-duplex fuel loaded into the high-temperature reactor (HTR) prismatic fuel block designs for a seed-and-blanket (S&B) reactor model. The selected fuel block design is the simplified model of a representative fuel configuration for the gas turbine–module helium reactor (GT-MHR) and high-temperature engineering test reactor (HTTR). The duplex fuel pellet comprises of UO2 as the seed and ThO2 as the blanket and uses the TRISO fuels. Monte Carlo N-particle extended (MCNPX) simulations were conducted to analyze the power and neutron flux distributions of the reference fuel block and that of the TRIOS-loaded duplex fuel designs. Standard neutronic parameters were computed, such as burnup-dependent infinite multiplication factors (kinf), average block spectrum, and fissile inventory. It was discovered that while the S&B model could attain the highest burnup and the longest cycle duration, its power peaking was more than threefolds than that of the reference model at the beginning of the cycle (BOC). The results also show that the “Duplex-2” model could reduce its power peaking by 24% through the integration of S&B arrangement with the duplex rods. It is noted that spatial distribution of the UO2 seed and 235U enrichment are the chief determining factors in the power optimization of the heterogeneous HTR prismatic fuel blocks loaded with thorium.