Neutronic analysis of pebble-bed cores with transuranics

At the brink of nuclear waste repository crises, viable alternatives for the long term radiotoxic wastes are seriously being considered worldwide. Minor actinides serve as one of these targeted wastes. Partitioning and transmutation in fission reactors is one possible incineration option and could potentially serve as a source of nuclear fuel required for sustainability of energy resources. The objective of this research was to evaluate the neutronic performance of the pebble-bed Very High Temperature Reactor (VHTR) configurations with various fuel loadings. The configuration adjustments and design sensitivity studies specifically targeted the achievability of spectral variations. The development of several realistic full-core 3D models and validation of all modeling techniques used was a major part of this research effort. In addition, investigating design sensitivities helped identify the parameters of primary interest. The full-core 3D models representing the prototype and large scale cores were created for use with SCALE 5.0 and SCALE 5.1 code systems. Initially the models required the external calculation of a Dancoff correction factor; however, the recent release of SCALE 5.1 encompassed inherent double heterogeneity modeling capabilities. The full core 3D models with multi-heterogeneity treatments are in agreement with available pebble-bed High Temperature Test Reactor data and were validated through benchmark studies. Analyses of configurations with various fuel loadings have indicated promising performance and safety characteristics. It was found that through small configuration adjustments, the pebble-bed design can be tweaked to produce desirable spectral shifts. The future operation of Generation IV nuclear energy systems would be greatly facilitated by the utilization of minor actinides as a fuel component. This would offer development of new fuel cycles, and support sustainability of a fuel source.