Simplified Criteria With Reduced Testing Effort for Selecting Clad Materials for High Temperature Reactor Structural Components

Abstract

Abstract Current Class A materials qualified in the ASME Section III, Division 5 rules for high temperature nuclear service do not have optimal resistant to salt corrosion in fluoride salt-cooled high temperature reactor and molten fluoride salt reactor. This limitation can be overcome by using cladded components — overlay the Class A materials with a thin layer of some non-qualified corrosion resistant material. However, there are currently no ASME design rules for cladded components to guard against creep-fatigue failure and ratcheting strain accumulation in elevated temperature nuclear service. Therefore, design methods along with a complete set of design rules for cladded components were developed in [PVP2020-21469]. In order to support the near-term deployment of these advanced reactor systems, the underlying goal of the new design rules was to avoid relying on long-term test data of the clad materials. New design rules for two types of clad materials fulfill this requirement. They are soft clad materials that creep much faster and hard clad materials that creep much slower than the Class A base materials. This necessitates the development of criteria for selecting clad materials which fall into either the hard or soft category. A previous work [PVP2020-21493] developed such clad selection criteria for a Class A metallic alloy — Type 316H stainless steel. These criteria require comparing the minimum creep rate between the clad and base materials at different stresses and temperatures and therefore need some short term creep test data to develop a minimum creep rate model for the prospective clad materials. To reduce the creep testing effort for the clad materials this work develops a new set of clad selection criteria — requiring creep tests at a single condition or no test at all; thus it is much simpler to execute. Sample finite element analyses of a representative high temperature reactor vessel are performed to verify the clad selection criteria.