Computation of Higher Eigenmodes Using Subspace Iteration Scheme and Its Application to Flux Mapping System of AHWR

Abstract

This paper presents the computation of fundamental and multiple higher eigenmodes of a reactor using subspace iteration scheme. This scheme generates a large set of dominant eigenmodes simultaneously instead of successive evaluation of higher eigenmodes. Using this set of eigenmodes and in-core detector measurements, a three-dimensional flux map of a reactor configuration can be estimated. In this paper, the subspace iteration (SSI) scheme is used to generate multiple higher eigenmodes simultaneously for conventional as well as modified flux mapping algorithms (FMAs). An improved modified flux synthesis method (IMFSM) has been proposed which uses few higher eigenmodes of the snapshot configuration generated from SSI to better estimate the three-dimensional flux distribution of a reactor. The performance of various flux mapping schemes has been studied for advanced heavy water reactor (AHWR) by varying the set of flux modes and the number of in-core detectors.