Some reactor physics effects related to recent trends in in-core fuel management

This paper examines some of the reactor physics aspects of recent in-core fuel management trends (higher burnups and longer fuel cycles) and describes related considerations and changes for Combustion Engineering (C-E) design methods. The following specific effects are discussed: effects related to higher enrichments which consider the use of enrichment zoning, the use of burnable absorbers in reloads, and the use of gadolinium to replace boron as a burnable absorber; effects related to higher burnup and the larger reactivity contrast between new and old fuel which consider potentially more non-uniform flux and burnup distributions within coarse mesh nodes, increased inter-nodal leakage influencing the performance of coarse mesh neutronics, and impact on the in-core instrumentation system