Hydrogen Risk Reducing Technology In Small Modular Reactor

At the beginning of the 21 st century,the National Atomic Energy Agency defined the reactor which power less than 300 MWe as Small Modular Reactor(SMR).Small Modular Reactor has a short construction period and a small initial inve stment,and can be modularized.During severe accident in SMR,the chemical reaction between Zircoloy and steam generates hydrogen which could be released to the containment through the RCS.Hydrogen deflagration or detonation produces both high thermal and pressure loads on the containment,which may threaten the integrity of the containment and result in the release of large quantity of radioactive materials into the environment and the public.It is of paramount importance to control and manage hydrogen risk,in order to eliminate large scale detonation for protecting the containment integrity.Ignitors and PARs are applied to reduce the hydrogen risk.With the development of small modular light water reactor,the hydrogen risk reducing technology can not be ignored.Firstly,special safety facilities of SMR are investigated and studied,and a serious accident analysis program model for SMR is established.The accident of LOCK,hydrogen source,Source term,and other thermodynamic parameters is studied.Then,by analyzing the international mature hydrogen control scheme and comparing the advantages and disadvantages of hydrogen igniter,hydrogen recombiner,mixing,inerting and vacuuming,a reasonable and feasible hydrogen control scheme for SMR is proposed.The combination of Pre-inerting and hydrogen recombination was used to control the hydrogen risk.According to this scheme,the corresponding hydrogen control system is designed.On the basis of this,the capacity of hydrogen control system is calculated and calculated.Studies have shown that a small reactor requires 3698 kg of nitrogen to complete pre-inerting.Taking into account the decomposition of water under the accident,the inert atmosphere will be destroyed,PAR capacity of the hydrogen recombination system was calculated,it has long-term elimination of radiation decomposition of hydrogen and oxygen.Finally,the effectiveness of the hydrogen control system is analyzed by using the GASFLOW program.The results show that the volume fraction of hydrogen in the containment dome is higher than that in the other parts of the containment during the calculation.Because of the small size and tight internal structure,hydrogen accumulates in the narrow channel,which increases the hydrogen concentration in the local channel.Inerting reduces the concentration of oxygen in the containment and effectively controls the possibility of flame acceleration and blasting transitio n in high hydrogen concentration regions.The effect of hydrogen recombination on the hydrogen concentration is limited.