Assessment of the structural design criteria to prevent ratcheting damage for fusion component design

Abstract

This paper focuses on the structural design criteria (3Sm, Bree Diagram and Efficiency Index Diagram) to prevent ratcheting damage for fusion component design, which includes conservative comparison of shakedown / ratcheting evaluation criteria and the elastic / elastoplastic analysis of first wall. The results show that: 3Sm rule is over conservative for low primary stress component while is less conservative than Bree Diagram for high primary stress (~ yield stress Sy) component. The conservatism between Efficiency Index Diagram and Bree Diagram is different with the specific structural primary stress. According to the elastic and elastoplastic analysis of the first wall, the 3Sm rule is too conservative, which may decrease the economy of the first wall. However, common Bree Diagram and Efficiency Index Diagram in nuclear pressure vessel design criteria (ASME BPVC III, SDC-IC and RCC-MRx) cannot effectively ensure the safety of the first wall. The mainly reason is that the mechanical characteristics of high thermal membrane stress in the first wall is different with fission pressure vessels. The modified Bree Diagram in ASME BPVC VIII, considering the impacts of thermal membrane stress on ratcheting, meet with the nonlinear result and is more reasonable. As a result, considering economy and conservatism of the first wall, it is suggested that Bree Diagram of ASME BPVC VIII is the most suitable shakedown / ratcheting assessment rule in the design of first wall though ASME BPVC III is more commonly used for nuclear pressure vessels.