Application of multi-dimensional sodium fire analysis code AQUA-SF to severe accident (Benchmark analysis of upward spray combustion experiment)

Abstract

Sodium fire is one of risk factors for containment failure in a sodium-cooled fast reactor in case of sodium spray from the top of a reactor vessel due to a power excursion during a severe accident. Modifications of multi-dimensional sodium fire analysis code AQUA-SF have been carried out so as to investigate the sodium fire under the severe accident condition inside a reactor containment. The GGDH (Generalized Gradient Diffusion Hypothesis) turbulence model and a radiation model for sodium droplets were newly implemented to the AQUA-SF code. A validation study has been conducted through a benchmark analysis of an upward spray combustion experiment. This paper describes detailed influencing factors in the benchmark analysis. Reasonable temperature distribution is obtained in turbulence analyses although a laminar analysis shows an upward high temperature jet which was not observed in the experiment. The temperature distributions are almost the same between the analyses with the previous and GGDH turbulence models because there is no significant difference in the balance of production and dissipation of turbulence energy between them. The radiation model for sodium droplet increases heat transfer to structure and hence gas temperature and pressure decrease. Consequently, it has been confirmed that the experimental results is simulated reasonably by the newly introduced models in the AQUA-SF code. This means the improved AQUA-SF code is applicable for investigation of sodium fire under the severe accident condition. In addition, because the improved models on turbulence and radiation are applicable for various sodium fire events, general validity for various cases would be confirmed by additional validation activities.