Novel Concepts for Damage-Resistant Alloys in Next Generation Nuclear Power Systems Phase II Annual Report

Abstract

The discovery of a damage resistant alloy based on Hf solute additions is the highlight of the Phase II research. The damage resistance is supported by characterization of damage microstructures, measurement of radiation-induced grain boundary compositions and measurements of cracking in irradiated 316SS alloys with oversize solute additions. The addition of Hf reduced the impact of radiation for two processed conditions, a standard condition and a modified (optimized) condition. Pt additions reduced the impact of radiation on grain boundary segregation but did not reduce the impact on damage development or cracking. Because cracking susceptibility is associated with several material characteristics, separate effect experiments exploring strength effects using nonirradiated SSs were conducted. These crack growth tests suggest that irradiation strength by itself can promote environmental cracking. The novel concept of using oversized solutes to promote catalyzed defect recombination is a major thrust of this Nuclear Energy Research Initiative. The successful demonstration of damage resistance in the modified Hf-doped alloy demonstrates promise in the concept for developing damage resistant alloys for future generation nuclear reactors. Differences between irradiation responses for Hf-doped and Pt-doped alloys suggest that the influence of the oversized elements depends on chemical reactivity in addition to solute size. Elimination of void formation to a dose of 50 dpa is a significant improvement in material performance. Strength effects on environmental cracking susceptibility were elucidated using cold-work variation in nonirradiated stainless steels. These results indicate that suppression of RIS alone will not assure that an alloy will be resistant to cracking.