The Probabilistic Nature of Environmental Cracking in Candidate Waste Package Materials

Abstract

The objective of this research is to determine the effects of material condition and applied stress on environmental cracking in candidate waste package materials for the Yucca Mountain Project. Time-to-failure experiments were performed on smooth bar tensile specimens in a hot, concentrated, mixed-salt solution chosen to simulate concentrated Yucca Mountain water. Smooth tensile specimens were individually loaded by the internal pressure of a 55-liter autoclave, where the applied stress varied with the individual specimen gauge cross section. The effects of material, applied stress, welding, surface finish, shot peening, cold work, crevicing, and aging treatment were investigated for Alloy 22, Titanium Grade 7, and 316NG stainless steel. Testing of multiple specimens allowed statistical differences among material conditions to be determined. Sensitized 304SS specimens were included in the test matrix to provide benchmark data. Microstructural effects on time-to-failure were studied for Alloy 22, where heat treatments designed to produce topologically close-packed phases (TCP) and long-range ordering (LRO) were investigated. This research complements high-resolution crack-growth-rate experiments performed in a parallel research project.