Study On Hydrogen Risk And Management For Large-Power Advanced Passive PWR

Hydrogen risk in the containment,as a major threat to the containment integrity,has drawn extensive attention especially after the Fukushima accident.Since hydrogen risk is particularly depend on the plant design,a specific effectiveness assessment of hydrogen risk control is necessary for the Large-power Advanced Passive Pressurized Water Reactor(LAPPWR)which is now under design and construction in China.The reactor model is established and analyzed with the integral accident analysis code for hydrogen risk and control analysis.The interaction between hydrogen risk and the severe accident mitigation strategies is discussed.And also,the hydrogen risk of the spent fuel compartment induced by containment venting is analyzed.Finally all analysis is added up to optimize the hydrogen risk control strategies of the LAPPWR.Main research work and conclusion are listed below:(1)The analysis model of LAPPWR is built with integral accident analysis code including Reactor Cooling System(RCS)as well as the containment.The upper compartment is divided for seven nodes;comparison analysis shows that,the multiple node model can provide a better simulation of the steam/air mixture in the containment.The reliability of the model is demonstrated through steady-status analysis,as well as similarity analysis comparison of key parameters and phenomenon with AP600 & AP1000.Since buoyance is a main factor influence of hydrogen distribution,the buoyant convection model is developed in the integral code and compared with 3D CFD analysis.Research shows that the integral code can predict the stratification of the hydrogen in the upper compartment and agree with the CFD prediction.(2)Representative accident sequences are selected considering contribution for core damage frequency(CDF)as well as the hydrogen generation rate and the release location to analyze the hydrogen distribution in the containment.After that,the effectiveness of the hydrogen control system is evaluated base on source term analysis.It is concluded that with the hydrogen control system of the LAPPWR,hydrogen risk in the containment can mitigated effectively.Meanwhile,the hydrogen mitigation effectiveness with PAR only is analyzed to optimize the Hydrogen recombination subsystem.Result shows that increasing the number of PAR can improve the capability of nuclear power plant dealing with hydrogen risk.(3)Negative impact on hydrogen risk caused by the containment outer spray system is studied.Computational Aid(CA)for containment hydrogen flammability is developed for LAPPWR Severe Accident Management Guideline(SAMG),to support the follow-up study on containment hydrogen risk.With this,the influence of the passive containment cooling system(PCCS)flow rate is discussed on the hydrogen risk control.Research shows that by reducing the PCCS flowrate to 50%,the containment pressure can be controlled,in the meantime the containment stays being inerted.Based on this,quantitative suggestions are made to optimize severe accident management strategy by mitigating the hydrogen risk through containment pressure control,to find a mutual way for a conflicting situation when implementing containment cooling strategy and mitigation hydrogen risk at the same time.This can provide technical support for decision-making of the technical support center(TSC)and improve the operability of the SAMG.(4)Fire protect containment spray system(FPCS)can work as a backup system for severe accident mitigation according to SAMG of Advanced Passive PWR.Reference to the FPCS of AP1000,its effectiveness and negative impact is evaluated when implementing sever accident mitigation for LAPPWR with design parameters from AP1000.Besides,considering hydrogen risk,a minimum flow rate is suggested through analysis for actuating FPCS to mitigate severe accident,which can allow FPCS to depressurize the containment for a short time without causing hydrogen risk in the containment as a negative impact under some extreme conditions.(5)Hydrogen risk in the spent fuel pool compartment becomes a matter of concern after the Fukushima accident.As a severe accident management strategy,one of the containment venting paths is to vent the containment through the normal residual heat removal system(RNS)to the spent fuel compartment,which will cause hydrogen build up in it.Therefore,the spent fuel pool compartment model is built and analyzed with integral accident analysis code couple with the containment analysis.Hydrogen risk in the spent fuel pool compartment is evaluated conbining with containment venting.Result shows that there will not be significate hydrogen built up with the hydrogen control system available in the containment.However,if the hydrogen control system is not available,venting into the the spent fuel pool compartment will cause a certain level of hydrogen risk there.Besides,suggestions are made for containment venting strategy considering hydrogen risk in spent fuel pool compartment.