Study On Hydrogen Removal System For Severe Accident In Containment Of Qinshan Phase Ⅲ

As all the fuel canning, calandria tube and presseure tube of heavy water reactor aremade of zirconium alloy, since zirconium-steam reaction and molten core concreteinteraction in sever accidents, large amounts of hydrogen is procured, then the hydrogen isreleased into the containment and mixed with atmosphere, and a flammable mixtureformed in containment is likely to cause deflagration or explosion which can generate highthermal and pressure, and the containment integrity could be damaged by them, sohydrogen control measures must be adopted to prevent the deflagration or explosion whichcan destroy the integrity of the containment.This thesis chooses CANDU-6heavy water reactor of QINSHAN Phase Ⅲ asresearch subject, the existing hydrogen removal system that is comprised of44igniters hasbeen conducted Qualitative analysis, the results show that the existing hydrogen removalsystem is effective only to the hydrogen control requirements of design basic accidents.Therefore, the hydrogen control objective for the severe accidents is made according to therequirements of the latest laws, and three typical severe accidents are chosen for the severeaccidents analysis based on one-level probabilistic safety analysis (PSA) and foreignexperience, three typical severe accidents are comprised of total loss of class Ⅳ poweraccident, feeder stagnation break accident and large loss of coolant accident.Secondly, the lumped-parameters program MELCOR is utilized to model thecontainment and analyze the hydrogen distribution and average concentration while thecontainment without hydrogen removal system. The result indicates that there isdeflagration or explosion risk under all those three typical severe accident conditions.According to the analysis results in combination with the practical situation of the site, anew hydrogen removal system is designed, it installs18passive automatic recombiners(PARs) inside the containment to eliminate hydrogen under accident conditions. Then thePARs module of MELCOR program is utilized to analyze the effect of hydrogen removalsystem, the results turn out that the uniform distribution of hydrogen concentration is notexceed10vol.%under all those three typical accident conditions, the hydrogen removalsystem is able to fulfill the hydrogen control requirements and acceptance criteria of hydrogen removal system under severe accident conditions.Last of all, by performing performance testing of PARs’ catalyze board and the wholemachine, it shows that the precious metal coating of catalyze board is excellent, thecombining power of catalyst and substrate is enough, the performance of eliminatinghydrogen is very stable, PARs’ start and stop threshold and the hydrogen removal rate aresatisfied the design requirements and the hydrogen removal requirements inside thecontainment under severe accident conditions.By systematically studying on the hydrogen removal system for QINSHAN Phase Ⅲunder severe accident conditions, it provides a powerful guarantee for QINSHAN PhaseⅢ to alleviate severe accidents, and also provides engineering experience and referentialsignificance for nuclear stations in service or under construction.