A NEW CROSS-SECTION GENERATION MODEL IN THE FAST CODE SYSTEM AND ITS APPLICATION TO THE GEN-IV GAS-COOLED FAST REACTOR

摘要

The cross-section generation scheme employed in the 3D spatial kinetics, PARCS subroutines of the FAST code system being used and developed at the Paul Scherrer Institute (PSI) is currently based on the use of pre-processed region-wise macroscopic cross-sections for reference conditions, and their first order derivatives with respect to the state variables. In this study, this approach is compared for both steady-state and transient conditions to a more rigorous background cross-section, or sigma-zero (σ_0-) model accounting for interrelations between the various feedback effects. Thereby, use is made of the simulation of hypothetical unprotected overcooling and loss of flow transients for the Gen IV Gas-cooled Fast Reactor (GFR). As expected, for this kind of transients without strong interrelations of the feedback effects, reactivity and power evolutions indicate overall good agreement of the two methods, which systematically use ERANOS cross-sections and consistent delayed neutron data. In addition, the relative differences of steady-state values between the σ-_0-model and corresponding ERANOS calculations are rather small. These findings give a certain confidence in the correct implementation and suitability of the new methodology. After completion of these verifications, it is foreseen to make additional comparisons for control assembly fast movements or accidental ejections. As opposite to the cases investigated in this study, larger differences may then be expected.