Fragility Analysis And Probabilistic Safety Assessment Of Nuclear Containment Structure Considering Statistical Uncertainty

As one of the largest source of the clean energy,nuclear power is favored by countries all over the world due to its high energy and less waste,and it is also the orientation of the present and future development of clear energy.Ensuring nuclear safety has always been the first priority for the development of nuclear energy.As the final barrier in nuclear power plant,nuclear containment structure plays an important role in ensuring nuclear safety.Since then,the importance of the nuclear containment structure has been further recognized.In addition to considering the performance of nuclear containment structure under the design basis conditions,more attention should be paid to performance of nuclear containment structure beyond the design basis conditions.Due to the fact that the mechanical behavior of nuclear containment structure under beyond design basis conditions is complex and has great uncertainty.Probabilistic methods(especially Monte Carlo method),namely fragility analysis(FA)and probabilistic safety assessment(PSA),are widely used to evaluate the performance of nuclear containment structures under beyond design basis conditions at home and abroad.At present,most nuclear power plants in operation and under construction in China use prestressed concrete containment structure.Due to the high cost for finite element analysis of prestressed concrete containment structure,sample size obtained by Monte Carlo method is small,and there are statistical uncertainties in fragility analysis and probabilistic safety assessment,Therefore,fragility analysis and probabilistic safety assessment of prestressed concrete containment structure under beyond design basis conditions considering statistical uncertainty is an important aspect of probabilistic performance evaluation of the nuclear containment structure,but few relevant studies on this topic have been carried out recently,Therefore this study focus on this topic.Main research works and conclusions of this study are as following:(1)Uncertainties in fragility analysis and probabilistic safety assessment of prestressed concrete containment structures are classified.Three types of uncertainties in probabilistic analysis of nuclear containment structure are analyzed,with emphasis on statistical uncertainty.Based on internationally renowned nuclear research and design institute predicted finite element results of 1:4 prestressed concrete containment structure model,which organized by Sandia Laboratory,factors affecting the modeling uncertainty in finite element analysis of nuclear containment structure and their influence on the finite element analysis results of the nuclear containment structure are analyzed.(2)Methods for fragility analysis and probabilistic safety assessment of the nuclear containment structure under beyond design basis internal pressure and ground motions considering statistical uncertainty is proposed.Aiming at the time-consuming characteristics of finite element calculation,the limited number of Monte Carlo simulations and the obvious statistical uncertainty phenomenon in fragility analysis of containment structure,interval estimation method and non-interval estimation method of nuclear containment structure considering statistical uncertainty are proposed.On this basis,method for probabilistic safety assessment of nuclear containment structure considering statistical uncertainty is proposed.(3)Finite element model of prestressed concrete containment structure of a nuclear power plant is established,and changes for the performance of the nuclear containment structure under different internal pressure levels are analyzed;using the fragility analysis method of nuclear containment structure under beyond design basis internal pressure considering statistical uncertainty proposed in Chapter 3,two-sided confidence interval and one-sided confidence interval for fragility curve of nuclear containment structure under beyond design basis internal pressure is obtained.On this basis,expression of the relationship between the confidence level for fragility analysis results of nuclear containment structure under beyond design basis internal pressure and the number of simulations is proposed,and this expression can be used to determine the minimum number of FE simulations required for the fragility analysis of nuclear containment structure under beyond design basis internal pressure with specified accuracy.Finally,probabilistic safety performance of the nuclear containment structure under beyond design basis internal pressure is evaluated.(4)Finite element model of prestressed concrete nuclear containment structure is established,roof drift,tensile damage and cracking state evolution of the nuclear containment structure under different peak ground motion acceleration are analyzed.Using the seismic fragility analysis method of nuclear containment structure under beyond design basis ground motion considering statistical uncertainty given in Chapter 3,two-sided confidence interval and one-sided confidence interval for seismic fragility curve of nuclear containment structure is provided.On this basis,expression of the relationship between the confidence level for fragility analysis results of nuclear containment structure under beyond design basis ground motion and the number of ground motion records is proposed,and this expression can be used to determine the minimum sample size of the ground motion records required for the fragility analysis of nuclear containment structure under beyond design basis ground motion with specified accuracy.Combined with seismic hazard curve for the site of the nuclear power plant,seismic risk of nuclear containment structure corresponding to different performance levels is evaluated.