Fuel-coolant interactions in combined stratified and melt jet configurations

A vapour explosion is a possible threatening consequence of a fuel-coolant interaction. This phenomenon can occur during a severe accident in a nuclear power plant, when the molten reactor core may come in contact with the coolant. Our recent research raised an important uncertainty regarding vapour explosion assessment. Past research was devoted to either melt jet configuration, where the melt jet penetrates into the deep pool of coolant, or stratified configuration, where the melt is spread below the coolant. However, an intertwined configuration can be a realistic condition. Combined stratified and melt jet configuration will be studied within the proposed project that has following two objectives: 1) First objective of the proposed research is to combine modelling of melt and coolant mixing in both configurations prior to vapour explosion, which largely defines the amount of melt, participating in the vapour explosion. At first, the vapour explosion experiments in combined stratified and melt jet configurations will be analysed to improve the understanding of fuel-coolant interaction phenomena. Secondly, the fuel-coolant interaction computational code will be upgraded, making it possible to simulate the fuel-coolant interaction in combined stratified and melt jet configuration. The modelling approach will be validated on the available experimental results, simulating both, the premixing and the explosion phase. 2) Second objective is to expand the research to the reactor conditions. Simulations of mixing and vapour explosion in reactor conditions will demonstrate the applicability of the developed model and estimate the expected pressure loads, which is of high importance in nuclear safety. To the best of our knowledge, the results obtained in the frame of the proposed project will present original contribution in understanding of fuel-coolant interaction. Typically in nuclear safety, the vapour explosions are mostly analysed in the melt jet-coolant pool geometry. In the stratified melt-coolant configuration, the recent experiments unexpectedly resulted in strong spontaneous vapour explosions, which was analysed as a part of our previous research. The proposed project will present the first attempt to understand and model the fuel-coolant interaction in combined stratified and melt jet configuration. Within the project, the pressure loads during vapour explosions in such combined configuration will be assessed, including in reactor conditions.