Validation of the MELCOR input model for a CANDU PHWR containment analysis by benchmarking against integrated leakage rate tests

Highlights: • CANDU 6 containment leakage rate tests were simulated with MELCOR. • An acceptable level of agreement was achieved with regard to the temperature and pressure. • Available data are limited when verifying the flow path and heat structure model. • An ILRT during the commissioning stage with elaborate test provisions was proposed. - Abstract: In an effort to overcome limitations when validating a code input model for the containment of a nuclear power plant, two integrated leakage rate tests (ILRTs) performed at a CANDU 6 plant were simulated with a MELCOR input model consisting of 51 control volumes. Leakages were assumed to occur at the volumes enclosed within the containment wall. The initial conditions were set to the measurements at the time when the atmosphere stabilization phase was started. The analysis was then carried out until the end of the main test phase. The analysis results show reasonable agreement with the measurements of temperature and vapor pressure, whereas they show deviations with regard to pressure and local temperatures in the middle and lower regions. In addition, a sensitivity analysis of the effects of the heat structure model and the manner by which thermodynamic variables can be lumped was carried out. This study revealed that the ILRT is useful for validating the containment input model. However, available data with which to verify the appropriateness of modeling flow paths and heat structures are limited. Based on the insights obtained, we suggest that an elaborate ILRT be carried out during the commissioning stage with more detailed test provisions and analysis methods to allow this specific application.