Neutronic performance of CANDU reactor fuelling with ThC_2/~(233)UC_2

摘要

~(233)U isotope is used as a booster fissile fuel material in the form of mixed ThC_2/~(233)UC_2 fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup. Three different fuel compositions have been used: (1) 97% ThC_2+3% ~(233)UC_2, (2) 98% ThC_2+2% ~(233)UC_2 and (3) 99% ThC_2+l% ~(233)UC_2. The temporal variation of the criticality K_∞ and the burn-up values of the reactor have been calculated by full-power operation for a period of 20 years. The criticality starts by k_∞ = 1.541, 1.355 and 0.995 for modes of (1), (2) and (3) fuel compositions, respectively. A sharp decrease in the criticality has been observed in the first 2 years as a consequence of rapid ~(233)U burnout fuelling with (1) and (2) modes. The criticality becomes quasi-constant after the second year and remains above K_∞ 1.06 for 20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner. Very high burnup could be achieved with the same fuel materials (up to 500000 MWdayt~(-1)), provided that the fuel rod claddings would be replaced periodically (after every 50000 or 100000 MWdayt~(-1)). The reactor criticality will be sufficient for fuelling with (1) and (2) modes until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.