Principles and application of advanced nodal reactor analysis methods

The application of coarse-mesh methods to three-dimensional light-water-reactor burnup calculations requires additional methods which allow the description of heterogeneously structured fuel assemblies and non-uniformly depleted nodes. A three-dimensional nodal reactor analysis system is presented which is based on the equivalence theory and the burnup-corrected nodal expansion method. For each reactor state pin-wise power and burnup distributions can be computed for the heterogeneous assemblies throughout the entire core. The accuracy and efficiency of the methods used for reconstructing the local distributions from a converged two-group nodal reactor solution is exemplified by comparison to a six-group pin-by-pin transport theory solution for a model problem of a reactor with gadolinium poisoned fuel assemblies. A unique feature of the code system is the fact that the use of any full core or quarter core fine-mesh calculations is avoided and that there is no need for user normalizations or ad hoc adjustment. The experience with this design procedure is presented with respect to practical application and accuracy. (orig.)