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

Summary 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.

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

“…Figure 11 depicts how the FTC becomes increasingly negative, which is advantageous, as the packing percentages of the TRISO fuels increase. The FTC range of the fuels with 40% packing fraction and 10 wt% 235 U/U is similar to that of the TRISO UO 2 fuel described in prior studies 10,14 . Using a higher uranium enrichment results in a weaker FTC value that is up to 20% and 24% less negative for the duplex and homogeneous fuel with a 40% packing fraction, respectively.…”

“…Fuel mass distribution heterogeneity exists at the fuel rod level as well as between fuel rods in duplex fuel blocks. Although previous studies have demonstrated that its power distribution is more stable than that of an SBU fuel block configuration, it is not as flat as the homogeneous fuel block 14 . The pin power peaking for duplex and homogeneous fuel blocks with different packing values is shown in Figure 15.…”

“…The plutonium building trends for duplex and homogeneous fuels, on the other hand, diverge, particularly at burnups greater than 10 GWd/MTHM. In comparison to the homogeneous fuel, the duplex fuel has a higher loss or lower net output of plutonium 10,14 . Furthermore, the 239 Pu trend in duplex fuel is substantially flattened after 10 GWd/MTHM particularly for fuels with lower packing fraction and lower enrichment.…”

“…The neutronics of the fuel rod model was also investigated at the fuel block level. The duplex rods function as blanket rods in an SBU design, as shown in Figure 5A 14 . The fuel block was composed of 75% duplex rods and 25% UO 2 rods.…”

“…The conceptual design of the TRISO duplex fuel compact has already been investigated in two related works 10,14 . The first was a rod level analysis that contrasted the TRISO duplex design to the UO 2 fuel compact.…”