Acceptance criteria for the mechanical integrity of clad/base metal interface for high temperature nuclear reactor cladded components

The existing Class A metallic materials qualified in the ASME Section III, Division 5 rules for high temperature nuclear reactors do not have optimal corrosion resistance for some reactor coolants such as liquid lead, lead/bismuth eutectic, and molten salts which is a major constraint on long life designs. A near term solution to this limitation is the use of cladded components - overlay the Class A materials with a thin layer of some corrosion resistant material. However, this necessitates the development of a design method for cladded components without requiring long-term testing of clad materials in order to support the near-term deployment of these advanced reactor systems. In two other PVP papers [PVP2020-21469, PVP2020-21493], the development of such design method along with a complete set of design rules and clad selection criteria are presented. However, the developed design rules and clad selection criteria are based on a priori assumption of perfect bonding between the clad and base materials. In practice the clad/base debonding may occur before the end of the design life of the component. Therefore, this paper focuses on developing a general acceptance test for checking whether the mechanical integrity of the clad/ base metal interface will be retained till the end of the design life. This work proposes to perform temperature cycling tests on cladded buttons of 12.7 mm diameter and a few mm thickness. A simple analytical expression is provided to determine the temperature range for the temperature cycling tests so that the clad/base interface shear stress intensity at the edge of the cladded button mimics the maximum interface shear stress intensity experienced by the component during the design transients. The paper also provides a method to determine the clad/base interfacial shear stress from finite element structural analysis of components.