Publications

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Metal hydrides can store hydrogen isotopes with high volumetric density. In metal tritides, tritium beta decay can result in accumulation of helium within the solid, in some cases exceeding 10 at.% helium after only 4 years of aging. Helium is insoluble in most materials, but often does not readily escape, and instead coalesces to form nanoscale bubbles when helium concentrations are near 1 at.%. Blistering or spallation often occurs at higher concentrations. Radioactive particles shed during this process present a potential safety hazard. This study investigates the effects of high helium concentrations on erbium deuteride (ErD₂), a non-radioactive surrogate material for erbium tritide (ErT₂). To simulate tritium decay in the surrogate, high doses of 120 keV helium ions were implanted into ErD₂ films at room temperature. Scanning and transmission electron microscopy indicated spherical helium bubble formation at a critical concentration of 1.5 at.% and bubble linkage leading to nanoscale crack formation at a concentration of 7.5 at.%. Additionally, crack propagation occurred through the nanocrack region, resulting in spallation extending from the implantation peak to the surface. Electron energy loss spectroscopy was utilized to confirm the presence of high-pressure helium in the nanocracks, suggesting that helium gas plays a predominant role in deformation. This work improves the overall understanding of helium behavior in ErD₂ by using modern characterization techniques to determine: the critical helium concentration required for bubble formation, the material failure mechanism at high concentration, and the nanoscale mechanisms responsible for material failure in helium implanted ErD₂.

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This report documents work done at the Sandia Ion Beam Laboratory to develop a capability to produce 14 Me neutrons at levels sufficient for testing radiation effects on electronic materials and components. The work was primarily enabled by a laboratory directed research and development (LDRD) project. The main elements of the work were to optimize target lifetime, test a new thin- film target design concept to reduce tritium usage, design and construct a new target chamber and beamline optimized for high-flux tests, and conduct tests of effects on electronic devices and components. These tasks were all successfully completed. The improvements in target performance and target chamber design have increased the flux and fluence of 14 MV neutrons available at the test location by several orders of magnitude. The outcome of the project is that a new capability for testing radiation-effects on electronic components from 14 MeV neutrons is now available at Sandia National Laboratories. This capability has already been extensively used for many qualification and component evaluation and development tests.

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Understanding the stability of the zircaloy-4 liner, which is used in the Tritium- Producing Burnable Absorber Rod, is important for predicting the maximium reasonable life time and failure mechanisms of this essential component for tritium production. In this year-long study, a combination of in-situ ion irradiation transmission electron microscopy and thermal desorption measurements were used to explore the structural stability of Zr-4 as a function of sequential and concurrent displacement damage, helium implantation, and molecular deuterium implantation at the temperature of interest for reactor operation. Under the limited conditions explored, the liner alloy appeared to be relatively stable based on the direct TEM observation of the microstructure.