Incorporation of a New Spectral History Correction Method into Local Power Reconstruction for Nodal Methods

The spectral history problem encountered in reconstructing local homogeneous power distributions is investigated. Because of difficulties in most nodal codes concerning spectral interactions between neighboring assemblies when rebuilding the local power distribution, nodal codes assume a constant spectrum or do not properly consider local spectrum variations within an assembly. A simple, fuel-type-independent method is presented to eliminate the spectrum-induced errors from local homogeneous powers within an assembly over the entire burnup range. The method, which is generalized for its application to any fuel type in the entire assembly burnup domain, uses the proportional relationship between macroscopic cross sections and average spectral history indices. Verification results through embedded calculations and an actual core calculation show that local homogeneous power errors are reduced to the same magnitude as flux errors. The error reduction is conspicuous in the cases of mixed-oxide and highly poisoned fuel assemblies.