Computational Modeling of Systems with Low Heat Fluxes

Resumo

The results of computational modeling of experiments with heating of a water-filled and dewatered system are reported. The aim of the experiments was to test the computational methods used to analyze accidents in RBMK spent fuel storage, which is an example of a system with low heat fluxes. The calculations were performed using the RELAP5 code and a model specially developed for analyzing such experiments. It is shown that the RELAP5 code with the Reflood option gives acceptable results, but for lack of a description of surface evaporation in the code water level reduction in the calculations starts with a delay (after water boils) and occurs faster than in the experiment. When surface evaporation is taken into account by means of Balter’s empirical relation, the time dependence of the water level coincides with the experimental dependence. The variation of temperature at the control points of the heater is also close to the experiment. The heating of a dewatered system is described well by both models. Heat transfer by radiation from the heater to the vessel walls and into the ambient environment plays the main role.