Analysis of Loss of Vacuum Accident at ITER using SOCRAT-V1/V2

Abstract

Since the end of the 1990s, work has been carried out on the creation of integrated computer programs that make it possible to simulate different scenarios of representative LOCA and LOVA at thermonuclear installations. Since many processes at thermonuclear installations and nuclear power plant reactors are similar integrated computer programs originally developed and used for NPP safety analysis are used as the basis for the calculation method. In Russia, the main volume of numerical analysis of severe accidents at NPPs with VVER reactors, accompanied by core damage, hydrogen release, and radioactive emissions into the environment, is performed using a certified integrated computer program SOCRAT. The article evaluates the applicability of SOCRAT in the phenomenological windows of beyond design basis accidents at thermonuclear installations, determined by thermohydraulic processes. Numerical analysis of the model problem LOVA accident in a simplified formulation demonstrated the fundamental possibility of using thermohydraulic models of SOCRAT and their stable operation under LOVA conditions. It has been found that the phenomenology of an accident is determined by choked and subsonic flow, convective heat transfer in the vacuum vessel, and flow reversal in a failed penetration line. The comparison of the results of calculations according to SOCRAT with calculations according to the MELCOR (version adapted to ITER condition) was performed, which showed good agreement in terms of the pressure dynamics in the vacuum vessel and bypass room during the accident and the air flow rate through the penetration line. Additionally, a sensitivity analysis was performed demonstrating the presence of a cliff-edge effect for parameters important to safety. The found monotonic correlations demonstrate consistency with analytical estimates, which provide additional confirmation of the adequacy of the models of the processes under consideration.