Abstract

Although η, the number of neutrons released per neutron absorbed in a ²³²Th-²³³U (thorium) fuel cycle, is greater than 2 in the thermal spectrum and therefore the possibility of breeding in a water-moderated reactor exists, it has been found difficult to achieve in practice. It is useful to relax the constraint for breeding and examine a thorium cycle for pressurized water reactors PWRs, denoted as PWR-Th, with the provision that the shortfall be made up by ²³³U bred in a PWR operating on a uranium fuel cycle, denoted as PWR-U, both of which utilize bimetallic thorium-zirconium alloy cladding as part of the fuel rod design. The number of complementary PWRs that could be sustainably operated on a thorium cycle was seen to critically depend on the moderator-to-fuel ratio (MF). Detailed cycle-by-cycle analysis shows that at the end of the first cycle, the sustainability ratio, namely, the ratio of sustainable PWR-Th reactors to PWR-U reactors, is 1.07 at an MF of 1.91, 1.4 at an MF of 1.43, and 4.45 at an MF of 0.954. The shortfall in ²³³U was found to decrease continually in subsequent cycles with the sustainability ratio increasing to 1.45, 2.01, and 28.3 at the respective MF values of 1.91, 1.43, and 0.954 by the 25th cycle. Although the sustainability ratio increases with lower MF, the achievable discharge exposure decreases necessitating larger material throughput in reprocessing. Detailed evaluations for fuel thermal, mechanical performance and nuclear reactivity feedback parameters require a further narrowing of potential design parameters based on holistic considerations arising from reprocessing. The PWR-Th reactors generate only trace amounts of transuranic (TRU) waste, and combined with a PWR-U design with bimetallic thorium cladding that generates only a fourth of the TRU waste compared to the standard all-UO₂ fuel cycle, a significant reduction in TRU waste is possible.

摘要

尽管 η（在²³² Th- ²³³ U（钍）燃料循环中吸收的每个中子释放的中子数）在热谱中大于 2，因此存在在水慢化反应堆中繁殖的可能性，但已经发现实践中难以实现。放宽对压水反应堆 PWR 的繁殖限制和检查钍循环是有用的，记为 PWR-Th，并规定缺口由²³³U 在以铀燃料循环运行的压水堆中培育，表示为 PWR-U，两者都利用双金属钍-锆合金包壳作为燃料棒设计的一部分。可以在钍循环中可持续运行的补充压水堆的数量被认为主要取决于减速剂燃料比 (MF)。详细的逐周期分析表明，在第一个周期结束时，可持续性比率，即可持续 PWR-Th 反应堆与 PWR-U 反应堆的比率，在 MF 为 1.91 时为 1.07，在 MF 为 1.4 时1.43 和 4.45，MF 为 0.954。短缺²³³发现 U 在随后的循环中不断降低，到第 25 个循环时，可持续性比率分别在 1.91、1.43 和 0.954 的 MF 值下增加到 1.45、2.01 和 28.3。尽管可持续性比率随着 MF 的降低而增加，但可实现的放电曝光量减少，因此需要更大的后处理材料吞吐量。对燃料热、机械性能和核反应性反馈参数的详细评估需要基于后处理产生的整体考虑进一步缩小潜在设计参数的范围。PWR-Th 反应堆仅产生痕量的超铀 (TRU) 废物，并结合带有双金属钍包层的 PWR-U 设计，与标准全 UO ₂相比，仅产生四分之一的 TRU 废物 燃料循环，TRU 废物的显着减少是可能的。