Implementation of the Sanchez-Pomraning Double Heterogeneity Treatment Method in DeCART

Abstract

The Sanchez-Pomraning method to resolve the double heterogeneity (DH) in the method of characteristics (MOC) transport calculation, which we call DH MOC, is implemented into the DeCART code for the application of the DeCART code to the gas cooled reactors involving particulate triso fuels. Since the DH MOC requires essentially no modification of the existing MOC calculation module other than providing the effective macroscopic cross section and the effective source constructed from the stochastic material properties and micro regional source, implementation is focused on the variable structure changes to incorporate micromaterials and the pre and post processing for the DH MOC calculation. The DH MOC solver is incorporated first in the shielded resonance cross section determination and then as in the normal MOC transport solution. As a prerequisite for the implementation of the DH MOC solver, a method to determine the volume to volume collision probabilities (CP) for a sphere is derived in detail. The verification of the CP routines and other code modifications are performed using various analytical solutions. The final verification of the DH MOC is performed by comparing the DeCART DH MOC results with the MCNP results obtained with an explicit representation of the particulate fuels. The effect of double heterogeneity on the resonance cross section and on the normal MOC transport calculation are assessed separately.