Adjoint sensitivity analysis in nuclear reactor fuel behavior modeling

Abstract

A computer program, SCODE, has been developed for calculating sensitivities for EPRI's SPEAR-ALPHA nuclear fuel performance code FCODE-ALPHA. Eleven critical parameters are assessed for the effects of their independent variations on 33 basic variables in the FCODE-ALPHA model. The enormous wealth of sensitivities that result, consisting of 363 quantities per axial node per time step, are calculated following FCODE-ALPHA computations on each time step. SCODE is based on adjoint sensitivity analysis, which is an analytic technique, obviating the need for numerical differentiation via repeated code runs at varied parameter values. Evaluation of sensitivities is reduced to a problem in linear algebra and is handled by standard matrix manipulations. Compared with the customary numerical differentiation approach, SCODE offers advantages of significant runtime reduction, exactitude of results, and on-line computation of sensitivities.