CANDU reactor as minor actinide/thorium burner with uniform power density in the fuel bundle

Abstract

A CANDU reactor fueled with a mixed fuel made of thoria (ThO2) and nuclear waste actinides has been investigated. The mixed fuel composition has been varied in radial direction to achieve a uniform power distribution and fuel burn-up in the fuel bundle. The best fuel compositions with respect to power flattening as well as long term reactivity have been found by mixing thoria with 14% minor actinides in form of MAO(2) in the central fuel bundle and with a radially decreasing MAO(2) content at discrete levels down to 2% at the periphery. Furthermore, as an alternative fuel composition, 5% UO2 has been added to the mixed fuel for the sake of a higher degree of nuclear safeguarding through denaturing the U-233 component with U-238. The temporal variation of the criticality k(infinity) and the burn-up values of the reactor have been calculated for a period of 10 years, operated at full power. The criticality starts at time zero near to k(infinity) = similar to 1.24 for both fuel compositions. A sharp decrease of the criticality has been observed during the first year as a consequence of rapid plutonium burnout in the actinide fuel. The criticality becomes quasi-constant after the 2nd year after sufficient U-233 is accumulated and remains close to k(infinity,end) = similar to 1.06 over similar to 10 years. Quasi-uniform power generation density has been realized in the fuel bundle throughout the reactor operation. Very high burn-up could be achieved with the same fuel material (up to 200,000 MW D/MT), provided that the fuel rod claddings would be replaced periodically. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically. (C) 2007 Elsevier Ltd. All rights reserved.