A Study on Creep-Fatigue Evaluation of Nuclear Cladded Components by ASME-III Division 5

In this paper, a study on creep-fatigue evaluation on the cladded nuclear component subjecting to low pressure and high temperature services is carried out. To do this, the codes and standards presented by ASME-III Division 5 are reviewed, and a detailed evaluation procedure is presented step by step for practical applications. As an example of practical design application, a molten salt reactor vessel with a cladding thickness of 10% of the base material thickness is designed and four representative operation cycle types are established. The stress cycle types based on finite element stress analysis are determined from the operation cycle types having coolant temperature and pressure time history loads, and results of the creep-fatigue evaluation are described step by step according to the evaluation procedure. From the result of the creep-fatigue evaluation, it is found that the creep-fatigue evaluation for reactors such as molten salt reactor, sodium-cooled reactor, and so on, which are operated at low pressure and high temperature, is dominated by thermal loads. In this study, the effects of the cladding material and the thermal stresses on the creep-fatigue evaluation are investigated. In addition, as one of the design options to reduce the thermal stresses, the thickness of the exampled vessel is reduced, and the calculated creep-fatigue values are compared with the acceptance creep-fatigue envelope criteria of the ASME-III Division 5.