ANALYSIS OF A PU-TH FUEL CYCLE FOR THE REDUCTION OF THE PLUTONIUM STOCKPILES

摘要

In the present scenario of availability of excess plutonium, proliferation concern is a major problem. Therefore, there is a pressing need to find new and more secure methods to deal with excess plutonium and make it unusable for weapon purposes. Burning plutonium in a nuclear reactor for producing energy is a safe and rapid way to deal with fissile material. The candidate nuclear fuels, i.e. (U,Pu)O_2, (Th,Pu)O_2, inert matrix fuels and thorium-doped inert matrix fuels, were analysed with main emphasis to plutonium elimination capabilities, reactivity coefficients and proliferation resistance of the plutoniumbearing spent fuel. Inert matrix based fuels appear very convenient under any aspect: >93% of fissile plutonium and 74/85% of total reactor- /weapon-grade plutonium is burnt at end of fuel life; critical mass, neutron background and isotopic power of the plutonium mixture left in the spent fuel are significantly higher that those of fresh weapon-grade plutonium, thus discouraging its recovery for misuse. However, fuel technology is still to be developed and the value of reactivity coefficients allows only partial loadings. (Th,Pu)O_2 fuels show better plutonium disposition performances and worst spent fuel quality than those of (U,Pu)O_2; the total plutonium consumption is higher by a factor >2 and the fissile plutonium burnt fraction by a factor >1.6. Moreover, there exists experience, although limited to (Th,U)O_2, that indicates very good behaviour under both irradiation and waste conditions, so that they are likely to be suited for use in once-through cycles. The main disadvantage is the breeding of ~(233)U but the high gamma activity of the separated uranium mixture, coming mainly from ~(232)U, discourages this proliferation pathway.