Analysis Of Hydrogen Risk Mitigation Measures In DayaBay Nuclear Power Plant

Nuclear power plants (NPPs) are increasingly becoming a viable alternate en-ergy source. The safety concerns regarding NPPs have largely been alleviated, thanks to rigorous designing and safety-focused attitude of the nuclear industry. Huge efforts are being undertaken on the international level to improve the design, instrumentation and control of the NPPs in order to further improve the efficiency and safety of NPPs. Despite all the precautions, there are still multiple ways a catastrophic accident may unravel. One such accident scenario is considered in this study. A Loss of Coolant Accident (LOCA) may result in hydrogen buildup inside the containment. If the buildup is not countered, the gas mixture inside the containment may become flammable, thus paving way for a detonation under the right conditions. Such a detonation would put the integrity of the entire contain-ment in question. A strong enough detonation will destroy the containment, and thus the last safety barrier may fail, leaking radioactive debris to the environment.This study assumes a SBLOCA accident in the Daya Bay nuclear power plant in steam generator 1 compartment. GASFLOW software is used for modeling and simulation. The distribution of hydrogen is monitored in two different cases: (i) With mitigation measures, and (ii) Without mitigation measures. The behav-ior of key parameters, such as temperature, pressure, volumetric composition of gas mixture, flame acceleration risk, etc. is also monitored in the simulations. Results show that the recombiners try to neutralize hydrogen risk but the hydro-gen production rate is much larger than the recombination rate. The analysis of results suggest that:(1) When mitigation measures are not enabled, the flame acceleration factor (σ) in SG1 compartment exceeds value of ’1’ which may lead to turbulent combustion. When mitigation measures are enabled, the maximum value of a in SG1 compartment stays lower than ’1’ in the entire simulation period; (2) As far as pressure is concerned, we can see that in the case when mitigation measures are enabled, a flame is initiated by igniters at 730 sec. This results in a steady rise in pressure in both the SG1 compartment and the top of containment from 730 sec onwards. But the maximum pressure in both regions is well within the design limits of DayaBay containment; (3) The volume fraction of hydrogen in SG1 compartment and top of the containment is very small when mitigation measures are enabled as compared to the case when mitigation measures are dis-abled. To conclude, we can say that hydrogen recombiners and igniters are very useful and effective in avoiding large scale hydrogen buildup and explosion, thus ensuring the integrity of containment, and preventing the leakage of radioactive material to the environment.