Potential of a fusion-fission hybrid reactor using uranium for various coolants to breed fissile fuel for LWRs

Abstract

In this study, neutronic performances of the (D,T) driven hybrid blankets, fuelled with UC2 and UF4, are investigated under first wall load of 5 MW/m(2). The fissile fuel zone is considered to be cooled with three coolants: gas (He or CO2), flibe (Li2BeF4), and natural lithium. The behaviour of the UC2 and UF4 fuels are observed during 48 months for discrete time intervals of Delta t = 15 days and by a plant factor of 75%. At the end of the operation time, calculations have shown that Cumulative Fissile Fuel Enrichment (CFFE) values varied between 5 and 8.5% depending on the fuel and coolant type. The best enrichment performance is obtained in UF4 fuelled blanket with flibe coolant, followed by gas and natural lithium coolant. CFFE reaches maximum value (8.51%) in UF4 fuelled blanket (in row #1) and flibe coolant mode after 48 months. The lowest CFFE value (4.71%) is in UC2 fuelled blanket (in row #8) and natural lithium coolant at the end of the operation period. This enrichment would be sufficient for LWR reactor. At the beginning of the operation, tritium breeding ratio (TBR) values were 1.090, 1.3301 and 1.2489 in UC2 fuelled blanket and 1.0772, 1.2433 and 1.1533 in UF4 fuelled blanket for flibe, natural lithium and gas coolant, respectively. At the end of the operation, TBR reach 1.1820, 1.3983 and 1.3138 in UC2 fuelled blanket and 1.2041,1.3266 and 1.2407 in UF4 fuelled blanket for flibe, natural lithium and gas coolant, respectively. Nuclear quality of the plutonium increases linearly during the operation period. The isotopic percentage of Pu-240 is higher than 5% in UF4 and UC2 fuel with flibe coolant, so that the plutonium component in these modes can never reach a nuclear weapon grade quality during the operation period. This is very important factor for safeguarding. The isotopic percentage of Pu-240 is lower than 5% in UC2 fuel with gas and natural lithium coolant. In these modes, operation period must be increased to safeguarding.