Abstract
This paper presents the hydrogen risk analysis of a large Pressurized Water Reactor (PWR) undergoing a severe accident using the HYDRAGON code. The code has been developed by the Department of Engineering Physics, Tsinghua University, as a hydrogen risk analysis software specialized for containment building of nuclear reactor power plants. The chemical interaction between zirconium cladding of the fuel rods and overheated coolant may release hydrogen when severe accidents occur in PWRs. The hydrogen mixed with air existing in containment may jeopardize the integrity of containment building if the flammable mixture explodes. In order to mitigate the hydrogen risk, many nuclear power plants install the Passive Autocatalytic Recombiners (PARs) that allow hydrogen and oxygen react chemically at low temperature without any sights of flame. Recombiners remove hydrogen and thereby prevent explosions. This work simulated the gas diffusion behaviors during the accident in the containment of a large PWR. The simulations obtained spatial concentration distribution of various gas species including hydrogen, oxygen, steam and nitrogen and several key parameters that are required to complete hydrogen burning and explosion investigation. Sensitivity analyses of recombiners’ quantity and positions and hydrogen discharge intensity provides the reference for hydrogen mitigation measure design in the containment. The results demonstrate that the number of recombiners rather than positions has stronger influences on hydrogen mitigation. Since the installation position reflects less sensitivity, the recombiners could be arranged as higher as possible if necessary.
