Potential of duplex fuel in prebreeder, breeder, and power reactor designs: tests and analyses (AWBA Development Program)

Abstract

and does not represent a f i n a l expression o f t h e opinion o f Westinghouse. When t h i s memorandum i s d i s t r i buted e x t e r n a l 1y , i t i s w i t h 'the express understanding t h a t Westinghouse makes no representation as t o completeness, accuracy, o r usabi 1 i t y o f i n f o r m a t i o n contained therein.

Review of the microheterogeneous thoria‐urania fuel for micro‐sized high temperature reactors

“…This was due to the fact that at the beginning of the cycle (BOC), relatively high fractional power exists in the seed region to enable high breeding, which adversely results in a significantly high UO 2 temperature. Without high power density and high enrichment in the seed region, it may take inefficiently long period of irradiation to sufficiently breed 233 U from 232 Th which in turn negatively affects the overall fuel economy 20‐23 . During thorium irradiation for breeding, either very high amount of seed is needed to ensure a single‐batch operation or the thorium needs to remain very long in the reactor core to endure multiple seed refueling cycles to enable sufficient 233 U breeding for the in‐situ burning 50‐52 .…”

“…This possibly ensures extended fuel burnup and increased breeding rate of 233 U from 232 Th 53,54 . Alternatively, innovative fuel design such as duplex fuel pellet could be used to extend ThO 2 burnup 11,14,17,23,47,54‐56 …”

“…The duplex pellet concept was introduced following the development of the seed‐and‐blanket configuration for thorium‐fueled PWR reactor. Initial design of the duplex pellet consists of an inner ThO 2 layer and an outer UO 2 layer, as shown in Figure 2A 23 . To extend the burnup and increase the CR value, the duplex pellet was later inversely arranged (Figure 2B), in which UO 2 and ThO 2 are positioned inside and outside, respectively 14 …”

“…There are two major challenges associated with the development of duplex pellet design: (a) rate of fission reactions in the UO 2 portion is double of the conventional pellets, making it more fragile, and (b) complexity of duplex pellet manufacturing 23 . The first issue is related to the imbalance in the power distribution due to the difference in fissile material mass distribution.…”

“…In‐situ 233 U burning in the uranium‐thorium cycle also results in high fuel utilization, especially in HTR, where the thorium portion is consumed effectively 14 . However, with the reduced enrichment of uranium, long and multiple cycles of thorium‐fuel irradiation is needed to produce sufficient amount of 233 U for commercial operation using the seed‐and‐blanket or the homogenous fuel 20‐23 . The use of duplex fuel is therefore suggested where it has the potential to offer a higher fuel discharge burnup, improve the power peaking and help solve the 233 U conversion issues 11,24 .…”