Effects of cross section sets and quadrature orders on neutron fluxes and on secondary 24Na activation rate of a pool type 500 MWe FBR

Abstract

In the early stages of shield design for the 500 MWe pool type Prototype Fast Breeder Reactor (PFBR), the DLC-37 coupled (100n, 21 γ) cross section set, extended to include data for the plutonium isotopes, only was used for the transport calculations. Several limitations were recognised in this set. Two new sets IGC-S2 (100n, 21 γ) and IGC-S3 (175n, 42 γ) have been created and validated at IGCAR, based on ENDF/B-VI (5). Comparison of the results of two-dimensional transport calculations using DLC-37, IGC-S2 and IGC-S3 is presented in this paper, for PFBR. Since the activation of secondary sodium in the Intermediate Heat Exchanger (IHX) depends significantly but differently on the axial and radial neutron fluxes leaking from the core, 2-D transport calculations with reasonable orders for the anisotropy and angular quadrature are necessary. The effects of anisotropy in the scattering cross sections and the S N order, on the shield parameters are studied with IGC-S2. It is found that 175-group calculations clearly predict the finer details of the neutron spectrum in the sodium pool and would facilitate more accurate shield design of PFBR.