Neutronic analysis of U-free inert matrix and thoria fuels for plutonium disposition in pressurised water reactors

摘要: Abstract Inserting reactor-grade (RG) or weapons-grade (WG) plutonium in uranium-free matrices and burning it light water reactors (LWRs) is an option gaining a wider consensus the nuclear community. The main results of our neutronic studies performed last few years on this subject are reported. Our attention was mainly concentrated two kinds matrices: inert matrix form calcia-stabilised zirconia, thoria. Both materials likely to exhibit excellent behaviour under irradiation (already demonstrated for thoria fuels) high chemical stability. Direct disposal spent fuel should be made feasible attractive. A preliminary analysis these U-free fuels, imposing constraint maintaining same assembly design cycle length standard enriched-uranium fuel. In particular (IMF) showed capability, but associated with unacceptable feedback coefficients. Therefore, whole IMF core unfeasible, only partial loading possible. solution then studied consists replacing ≈21% pins enriched-U subassembly pins. Detailed calculations were performed. crucial aspect choice suitable burnable poison, which has dampen power peaks different pin types without life penalisation. Among considered poisons, thin boron coating pellets resulted effective one. Preliminary cell detailed ones gave similar terms burnt fractions: 90% fissile 73% total when RG used. drawbacks limited capability lack in-pile technological validation. case Pu–Th that increasing plutonia content, decreasing pellet diameter all possible ways reach longer higher percentage plutonium. Attained values RG–Pu ⩾80% >60% plutonium, respectively. use proliferation concerns, while some concerns remain fuels because production 233U. This, however, can eliminated by small addition 238U. Long time radiotoxicity scarcely affected respect conventional MOX.