Study On Fatigue Analyses Incorporating The Effects Of Lwr Coolant Environment

Nuclear safety class 1 components shall be designed in accordance with the requirements of Section III of the ASME Code to ensure the structural integrity of the reactor coolant pressure boundary.Fatigue analysis is one of the important aspects of the evaluation.RG 1.207 issued by the US Nuclear Regulatory Commission requires to take into account the impact of the LWR coolant environment on fatigue in the engineering design of new nuclear power plants,and National Nuclear Safety Administration also put forward requirements to the demonstration of coolant environmental impact on fatigue in the safety review of the third generation nuclear power plant construction.At present,the fatigue analysis of nuclear safety class 1 components of nuclear power plants under construction and operation has not considered the effect of coolant environment on fatigue.Therefore,it is necessary to carry out the study on the fatigue analyses incorporating the effects of the coolant environment on the engineering design.In this paper,fatigue analyses incorporating the effects of coolant environments were carried out for a nuclear safety class 1 pressure vessel nozzle with the reactor coolant system design transients.The analyses were in accordance with the specifications of Section III of ASME BPVC and the requirements of RG 1.207 and NUREG/CR-6909.The results show that the applying of environmental fatigue correction factors to the fatigue evaluation results based on ASME code is feasible in engineering design,and the results of the fatigue analysis of the nozzle are significantly increased after considering the effect of the coolant environment,which in some cases may lead to over-conservative design.It is need to carry out a large amount of data processing to calculate the environmental fatigue correction factors in the modified rate approach.For the components with large design margin,the conservative factors can be used directly in the calculation.In this paper,the fatigue evaluation results with the design fatigue curves in ASME Code are compared with the results with the new curves provided by the NNUREG/CR-6909.The results show that the new design fatigue curves are conservative.In the fatigue analyses incorporating the effect of coolant environment,the complex load conditions of the engineering design are simulated,and the engineering application of the requirements of RG 1.207 guideline and the calculation method of the environmental fatigue coefficient are studied.The impacts of the coolant environment on the design of the pressure boundary components are validated by the study.The accumulated practical experience on the fatigue analyses incorporating the effect of coolant environment are helpful to meet the requirements of RG 1.207 in engineering design and laid a good foundation for the further application and improvement of the calculation method of the environmental fatigue coefficient.