Advanced creep-fatigue evaluation rule for fast breeder reactor components: generalization of elastic follow-up model Original Research Article

High temperature operative conditions of fast breeder reactors (FBRs) cause plastic and creep deformations of structures, which lead to the magnification of the creep-fatigue damage of the materials. To take these effects into account, a structural design code for the Japanese prototype FBR “Monju” has adopted an elastic follow-up model. The elastic follow-up model shows a potential for expressing both the plastic and creep behaviors of structures. However, this model has weaknesses which mean that it cannot be used to treat material properties quantitatively and also cannot be adaptive to the existence of stress redistributions. Consequently, we have generalized the elastic follow-up model, by introducing the following concepts: (1) an elastic follow-up model using a power law, for the purpose of the quantitative evaluation of material properties; (2) combined elastic follow-up models, for consideration of stress redistributions; (3) an equivalent elastic follow-up model of Neuberʹs rule. By applying the generalized elastic follow-up model to structural discontinuity portions, we proposed an advanced creep-fatigue evaluation rule based on elastic analysis. The proposed method is verified through structural strength tests and inelastic finite element calculations. As a result, the design stresses are raised significantly compared with those of the structural design code for “Monju”.