Validating the VAPEX-M Module as Part of the SOCRAT Code against Experimental Data on Corium-to-Water Interaction

In the framework of a nuclear power plant safety analysis, it is necessary to analyze postulated beyond-design basis accidents with nuclear fuel melting. One of possible tools for carrying out such analyses is numerical simulation by means of special software (computer codes). According to the legal regulatory acts of the Russian Federation in the field of atomic energy use, the software tools supposed to be used for these purposes shall be certified, the codes shall be verified, and the built-in models shall be validated. The SOCRAT severe accident best-estimate computer code can be used for numerically analyzing severe accidents involving nuclear fuel melting in the reactors of VVER-based NPPs from the initiating event onset to the release of fission products. In the late stage of the postulated severe accident with core damage, the process of molten fuel-to-coolant interaction may take place. For analyzing the core melt-to-water interaction, the VAPEX-M module has been incorporated into the SOCRAT code. In the framework of the SOCRAT code development process, the code modules undergo changes, which entails the need to perform additional validation of the built-in modules. The validation base of the VAPEX-M module as part of the SOCRAT-V1/V2 severe accident computer code has been extended. The validation process was performed using the data from open sources containing a description of the experimental data on interaction between molten metals and water in the FARO and KROTOS test facilities. The FARO L-31 and KROTOS K-45 experiments were simulated, and the computation errors were estimated by using mean absolute deviation. For the FARO L-31 experiment, the pressure, water temperature, and quenching energy were calculated. The deviations of calculated parameters from the experimental values were 2.5; 7.5, and 3.1%, respectively. For the KROTOS K-45 experiment, the melt jet leading edge pressure and coordinate (the leading particle coordinate) were calculated. The deviation of the calculation results from the experimental values were 8.6 and 17.3%, respectively. A conclusion has been drawn based on the analysis performed that the VAPEX-M module as part of the SOCRAT-V1/V2 severe accident best-estimate computer code is able to predict a qualitative pattern of the melt-to-water interaction with a sufficiently good quantitative coincidence of the main physical parameters