Multi-scale analysis of an ATLAS-MSLB test using the coupled CUPID/MARS code

This study describes a multi-scale nuclear safety analysis method for a main steam line break accident, which focuses on the 3-dimensional approach for the coolant temperature in the reactor pressure vessel related to the re-criticality and/or pressurizer thermal shock. The direct coupled code, CUPID/MARS, where CUPID is a 3-dimensional two-phase flow analysis code and MARS is a 1-dimensional nuclear system analysis code, was validated against a main steam line break test in the ATLAS facilities, which are a 1/2 scale integral test loop for a Korean APR1400 PWR. The calculation indicates that the suggested 4-step method, which expands the previous 2-step method of steady-state and transient calculations of a 1-dimensional system code, is valid for analyzing a direct 1-D/3-D coupled safety analysis, and the 3-dimensional temperature distribution in the downcomer agrees with the measured result.