Evaluation of Three-Dimensional Initial Dynamics of the Decompression Wave at LB LOCA in the Advanced Supercritical Reactor ECC-SMART

Abstract The paper presents an adaptation of the modelling approach to initial dynamics during decompression for an advanced small modular supercritical reactor, which was previously developed and applied for the VVER-1000 reactors. The practice of performing such an assessment in one- and two-phase formulations indicates that three-dimensional assessment using CFD is more realistic than similar calculations using system codes (e.g. RELAP5). The main feature of modelling decompression from a supercritical state to a subcritical state is the complexity of the transition through critical pressure, where the medium can go both into the two-phase region and into superheated vapor/liquid. These features require the introduction of some abstract functions to be able to calculate a supercritical medium in a two-component approximation. The paper represents the assessment of dynamic forces during the initial dynamics of LB LOCA using a representative CFD model of a perspective supercritical reactor concept. The initial dynamic analysis is performed for the following conditions: hot zero power reactor state, break of the inlet piping with maximum reference pressure. The structural integrity analysis of some critical components based on preliminary (pre-conceptual) ECC-SMART SMR design is done using CFD results.