Water evaporation over sump surface in nuclear containment studies: CFD and LP codes validation on TOSQAN tests

•Simulations of evaporative TOSQAN sump tests are performed.•These tests are under air–steam gas conditions with addition of He, CO2 and SF6.•ASTEC-CPA LP and TONUS-CFD codes with UDF for sump model are used.•Validation of sump models of both codes show good results.•The code–experiment differences are attributed to turbulent gas mixing modeling. During the course of a severe accident in a Nuclear Power Plant, water can be collected in the sump containment through steam condensation on walls and spray systems activation. The objective of this paper is to present code validation on evaporative sump tests performed on TOSQAN facility. The ASTEC-CPA code is used as a lumped-parameter code and specific user-defined-functions are developed for the TONUS-CFD code. The seven tests are air–steam tests, as well as tests with other non-condensable gases (He, CO2 and SF6) under steady and transient conditions (two depressurization tests). The results show a good agreement between codes and experiments, indicating a good behavior of the sump models in both codes. The sump model developed as User-Defined Functions (UDF) for TONUS is considered as well validated and is ‘ready-to-use’ for all CFD codes in which such UDF can be added. The remaining discrepancies between codes and experiments are caused by turbulent transport and gas mixing, especially in the presence of non-condensable gases other than air, so that code validation on this important topic for hydrogen safety analysis is still recommended.