Benchmarking MAAP-CANDU V4.0.7b With Gothic 7.2B: Response of Containment Models to Flashing and Condensation

Abstract

Containment is the last line of defence in a reactor accident, preventing radioactive releases to the public, so well-modelled containment behaviour is important. MAAP-CANDU is an integrated severe accident simulation code of the CANDU Owners Group Industry Standard Toolset; it has model simplifications, limited nodalization and lumped-parameter containment models. GOTHIC is a generalized thermalhydraulic code, also part of the IST, used for more sophisticated containment modelling. Water + steam injections to a single containment node are modelled, with and without a heat sink, comparing MAAP-CANDU to GOTHIC (lumped containment models). For LOCA break conditions, both codes predict similar heat and mass transfer rates, with minor differences, when the GOTHIC flashing model is configured similar to that of MAAP-CANDU. However, when the recommended flashing model is used in GOTHIC, larger differences are observed, including lower pressures and vapour temperatures and higher steam concentrations in GOTHIC.