An assessment of RELAP5/Mod3.3 condensation model for high Reynolds number flows

Passive safety systems utilized in most of the advanced nuclear reactors comprise the condensation phenomenon to cope with the design basis accidents. The inhibiting effect of noncondensable gases on condensation is an extremely important phenomenon and several experimental research studies have been performed in recent years. This paper represents the result of an assessment of RELAP5/Mod3.3 for the condensation in the presence of a noncondensable gas phenomenon. The database covering the wide range of systems parameters such as mixture Reynolds number and air mass fraction has been benefitted and been extracted from the experimental work conducted at the Middle East Technical University (METU) to investigate the inhibiting effect of noncondensable gas on the condensation phenomenon. It is observed that RELAP5/Mod3.3 cannot evaluate the relationship between mixture Reynolds number and air accumulation at interface leading to underpredicted wall subcooling and overpredicted heat transfer coefficient with an unacceptable deviations. The mean deviations with respect to the experimental data are determined as 80% and 130% for wall subcooling and heat transfer coefficient, respectively. Relatively better agreement is achieved for heat flux with a maximum deviation of 50%. It is also found that RELAP5/Mod3.3 version of Colburn–Hougen method, which neglects the mixture side resistance, does not work for high mixture Reynolds number condensation due to markedly increasing mixture side thermal resistance.