Abstract: The containment filtered venting system（CFVS）is used to depressurize the containment by venting the containment atmosphere under severe accident conditions.The steam of vent atmosphere will condensate across the CFVS’s pipe and vessel,which will lead the concentration rise of H₂ and O₂,and the possible hydrogen combustion or explosion.In order to evaluate the hydrogen risk in the containment filtered venting system of HPR1000,the reactor and containment model and the detailed CFVS model were established.The typical severe accident sequences were selected to calculate the process of CFVS opening and the mixed gases entering CFVS with their concentrations changing after accident occurred,and the hydrogen risk in CFVS was judged according to the Shapiro diagram of the gases composition in it.It calculated the concentrations variation of different containment atmosphere composition after entering the CFVS under the cavity injection cooling system（CIS）available or failed conditions.The calculation showed that the hydrogen in the mixture gases was mostly recombined under the former condition,as well as the oxygen in the mixture gases was depleted by the recombination reaction under the latter condition at the CFVS opening time,so combustion or explosion would not occur under both conditions.The calculation also analyzed the effects of two mitigation measures,i.e.hydrogen recombiners arranged in containment and the nitrogen covering the CFVS.The results showed that without the mitigation measures,the gases composition in CFVS enter the combustion or detonation zone in Shapiro diagram.The research indicated that the risk of hydrogen detonation will not occur in the CFVS of HPR1000,which had the above two mitigation measures applied.