Application of thermal hydraulic and severe accident code SOCRAT/V2 to bottom water reflood experiment PARAMETER-SF4

Abstract

Abstract The PARAMETER-SF4 test conditions simulated a severe LOCA (loss of coolant accident) NPP (nuclear power plant) sequence in which the overheated core up to 1700–2300 K would be reflooded from the bottom on ECCS (emergency core cooling system) recovery. The test was successfully conducted at the NPO “LUTCH”, Podolsk, Russia, on July 21, 2009, and was the fourth of four experiments in the series PARAMETER-SF. The PARAMETER facility of NPO “LUTCH”, Podolsk, is designed for studies of VVER fuel assembly behavior under conditions simulating design basis, beyond design basis and severe accidents. After the maximum cladding temperature of about 1900 K had been reached in the bundle during PARAMETER-SF4 test, bottom flooding was initiated. The thermal hydraulic and SFD (severe fuel damage) best-estimate computer modeling code SOCRAT/V2 was used for the calculation of PARAMETER-SF4 experiment. The important feature of PARAMETER-SF4 was the air ingress phase during which air was supplied to the working section of experimental installation. It is known that zirconium oxidation in the air proceeds in a different way in comparison to oxidation in the steam. Thermal hydraulics in PARAMETER-SF4 experiment played a very important role and its adequate modeling is important for the thermal analysis. The results obtained by SOCRAT/V2 were compared with experimental data concerning different aspects of the air ingress phase and thermal hydraulic behavior during the reflood. The temperature experimental data were found to be in a good agreement with calculated results. It is indicative of the adequacy of modeling the complicated thermal hydraulic behavior in the PARAMETER-SF4 test.