Advanced U–Np–Pu fuel to achieve long-life core in heavy water reactor

The objective of this paper is to look at the possibility of approaching the long-life core comparable with reactor life-time. The main issues are centered on U±Np±Pu fuel in a tight lattice design with heavy water as a coolant. It is found that in a hard neutron spectrum thus obtained, a large fraction of 238Pu produced by neutron capture in 237Np not only protects plutonium against uncontrolled proliferation, but substantially contributes in keeping criti- cality due to improved fissile properties (its capture-to-fission ratio drops below unit). Equili- brium fuel composition demonstrates excellent conversion properties that yield the burn-up value as high as 200 GWd/t at extremely small reactivity swings.