Symbiotic systems consisting of large-FBR and small water-cooled thorium reactors (WTR)

Small long life water-cooled thorium reactors (WTR; 30–300 MWth) have been investigated. For realizing thorium cycle of the reactors, a uranium–thorium mixture core is introduced to fast breeder reactors (FBR; 3000 MWth) to be a 233U producer. In the present study, two distinct metallic fuel pins, with natural uranium and thorium, are loaded into a large sodium-cooled FBR. The FBR itself is self-sustained by the plutonium produced in the uranium pins. Under the equilibrium burnup state, the FBR spent fuels are periodically discharged with a certain discharge rate and then separated. Some actinides are returned to the FBR core while 233U, which is discharged from the thorium pins, is utilized for the WTR fresh fuel. Fissile support capability is the main investigated parameter of the study. The system achieves higher support capability at higher burnup and lower power of the WTR, and shows that larger number of uranium pins is better for the FBR criticality while larger number of thorium pins and lower burnup give better support factor capability. For a symbiotic system consisting 3000 MWth FBR and 100 MWth WTRs, where discharged fuel burnup is 96 and 60 GWd/t for the FBR and WTRs, one FBR can support 5 WTRs.