Simulation of Darlington Fuelling with SIMODEX, a Fuel Management Program Based on Modal Expansion Method

Abstract

The simulation of reactor operation using a three dimensional finite difference code such as SORO or FMDP/OHRFSP is quite expensive, even when fairly long time steps are used. There is a need for a fuel management tool which will give approximate power distributions at much lower cost.

Modal methods allow inexpensive calculation of flux distributions. In this method the flux distribution is approximated as the sum of a series of "modes". A fuel management program, SIMODEX, has been developed to use modal methods for the flux calculation.

The program has been validated by simulating a short period of burnup and fuelling of the Darlington A reactor both with SIMODEX and with the finite difference flux calculation (SIMULATE). Comparison of SIMODEX and SIMULATE after the first 10 day burn step gave excellent agreement.

Simulation of fuelling was continued using manual selection of channels up to 100 full power days. At this point another flux calculation was done with SIMULATE. Agreement at this point was not as good as at 10 days. Recomputing the modal matrices, however, improved the results.This paper develops the basic theory behind the method and outlines the results obtained to date from the Darlington fuelling study.