Verification And Optimization Of The Evaluation Method Of Nuclear Graphite Failure Probability

The fast neutron irradiation and high temperature environment inside the molten salt reactor will cause changes in the size,elastic modulus,and thermal expansion coefficient parameters of nuclear graphite,which may cause damage and fracture of nuclear graphite components,affecting the safe operation of the reactor.Therefore,in the process of reactor design,scientific methods must be used to evaluate the failure probability of nuclear graphite components under different loads.The current evaluation method for ultra-fine nuclear graphite in molten salt reactor is ModifiedASME standard proposed by the American Society of Mechanical Engineers based on ASME standard.However,the Modified-ASME standard has not been verified by experiments,and its applicability to ultra-fine nuclear graphite is unknown.In this paper,the Modified-ASME standard was verified and optimized by relevant experiments.First of all,the four-point bending experimental data of T-220 ultrafine nuclear graphite were selected as the verification benchmark,and the finite element model of the four-point bending experiment was established by ABAQUS software.The 50%failure probability prediction method and the full-scale prediction method were used to verify the Modified-ASME standard.The results show that the Modified-ASME standard is more suitable for the evaluation of ultra-fine nuclear graphite than the ASME standard,but the error between the calculation results of the Modified-ASME standard and the experimental results is more than 20%.Unable to meet the requirements of reactor engineering design(error within 18%),further optimization is required.Secondly,in order to find a direction for the optimization method of the ModifiedASME standard,this paper conducted a numerical study on the Modified-ASME standard from the aspects of unit type,mesh density,grouping conditions and Weibull parameters.It is found that the Weibull parameter and the stress gradient in the grouping condition have obvious effects on the calculation results.Finally,according to the results of numerical study,the limiting strength S0 and characteristic strength Sc of Weibull parameters were selected as the correction parameters,and the Modified-ASME standard was optimized by using parameter optimization method and Brazilian disk experimental data.The optimization results show that the error between the calculation results of Modified-ASME standard after optimization and the experiment is less than 10%,which can meet the requirements of engineering design.