METHODOLOGY DEVELOPMENT FOR EXPLOSION HAZARD EVALUATION IN HYDROGEN PRODUCTION SYSTEM USING HIGH TEMPERATURE GAS-COOLED REACTOR

High temperature gas-cooled reactor (HTGR) is expected to use nuclear heat to wide range of industrial applications such as hydrogen production due to its high temperature heat supply capability and inherent safe characteristics. One of the key technologies is a safety evaluation method which can simulate an impact of explosion hazards occurred in the hydrogen production plant to safety functions in the nuclear plant because HTGR hydrogen production system contains large amount of combustible gases such as hydrogen. A computational fluid dynamics code FLACS has been sufficiently validated for dispersion and explosion of combustible gases such as hydrogen and methane gas worldwide, however, only few attempts have been made for validation of analysis in closed area with small space. A leak of combustible gases to the piping in HTGR hydrogen production system may occur in case of abnormal condition in hydrogen production plant and therefore an explosion in the piping should be considered. Two experiments on combustible gas explosion in piping are selected to compare with calculated results obtained by FLACS code. One is the deflagration of natural gas in a simple closed system consisting of two spherical vessels of different sizes and a thin straight piping (Experiment 1), and the other is the deflagration of mixture of hydrogen and methane gas in an opened complex piping including multiple branches (Experiment 2). The comparison of calculated and experimental results showed good agreement for maximum pressure and temperature in Experiment 1. In Experiment 2, the maximum pressure and flame spread velocity in a section of straight piping from the ignition point to the first branch also agreed well in calculated and experimental results.