Comparison of homogeneous and heterogeneous thorium fuel blocks with four drivers in advanced high temperature reactors

Abstract

Thorium is an attractive potential fuel owing to its abundance and unique thermal, neutronic, and chemical properties. One way to utilize thorium in block-type advanced high temperature reactors (AHTRs) is to homogenously mix the driver fuel (eg, U-233) with thorium in every fuel kernel of the tristructural-isotropic particles in a fuel block, which is the mixed oxide fuel (MOX) concept. Application of the seed and blanket (S&B) concept, that is, driver fuel in the seed region of a fuel block and thorium in the blanket region, is also another method to utilize thorium. To investigate the differences in the utilization of thorium using the MOX and S&B concepts in AHTRs, their multiplication factors (k ∞ ), discharge burnups, conversion ratios, and reactivity temperature coefficients are compared. The investigated drivers include U-233 (U3), weapons-grade uranium (WU), weapons-grade plutonium (WPu), and reactor-grade plutonium (RPu). The results demonstrate that the MOX block with plutonium drivers has a higher discharge burnup in comparison with the S&B block. When the heavy metal mass is 6 kg and the initial mass of the fissile materials is 0.65 kg per block, the MOX block achieves 27% higher discharge burnup than the S&B block with the RPu driver. In contrast, the S&B block achieves higher discharge burnup in the case of uranium drivers (U3 and WU). The MOX block achieves a higher conversion ratio for all the drivers. Furthermore, the MOX block achieves a stronger negative moderator temperature coefficient of reactivity than the S&B block for all the driver fuels.

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

“…The difference in fertile material loss between duplex and homogeneous fuels is minor, but the loss of 235 U and plutonium is substantially higher in duplex. As a result, the CR of a heterogeneous design, such as the duplex fuel, is lower than that of a homogeneous fuel 44 . Figure 10 compares CR values for duplex and homogeneous fuels with varied packing percentages and uranium enrichment for both duplex and homogeneous fuels.…”

“…As a result, the CR of a heterogeneous design, such as the duplex fuel, is lower than that of a homogeneous fuel. 44 Figure 10 compares CR values for duplex and homogeneous fuels with varied packing percentages and uranium enrichment for both duplex and homogeneous fuels. Furthermore, given the difference in CR value, it has been predicted that the higher the packing fraction value, the higher the CR value.…”

“…Homogeneous fuel has a greater CR because the fissile isotopes are distributed more uniformly. 44 The duplex fuel has a concentrated initial fissile distribution at the center, resulting in higher incineration of fissile, including bred plutonium, lowering the CR. Fuels with a packing fraction of 20% have CR values ranging from 0.45 to…”

A comparative analysis of the neutronic performance of thorium mixed with uranium or plutonium in a high‐temperature pebble‐bed reactor

“…As a result, the most practical option is to add the driver fuel with thorium into a TRISO particle known as mixed oxide (MOX) fuel. 22,23 Historically, the use of Th-232 as a fertile material in HTGRs has been commonly suggested as a potential way to increase the burnup of the fuel element or recycle the nuclear waste produced by reactors. The main HTGR model comes in a variety of fuel cycles, designs, and variants.…”

“…The fuel element in an HTGR reactor can be cylindrical, such as in the Dragon reactor 29 ; spherical, such as in the AVR, Xe-100, and HTR-PM reactors [30][31][32][33][34] ; or block-type, as is the case with the AHTR reactor. 22 According to the literature review, studies comparing the use of thorium-based fuel with various driver materials in HTGRs have often been conducted in prismatic block-type HTRs because of the flexible core that can support a wide range of fuel cycles. [35][36][37] Studies for PBR, on the other hand, have been conducted separately, and ThO 2 + UO 2 or ThO 2 + PuO 2 fuels have been widely used.…”