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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Retention of radionuclides in sol–gel surrogate nuclear explosive debris

Sol–gel vitrification can be used to rapidly produce solid, vitreous materials to support nuclear forensics research. Here, this work investigates three sol–gel synthetic approaches’ ability to retain fission products within the glass as a function of drying temperature. Eight of the ten fission products studied were quantitatively retained (less than 5% losses) at temperatures up to 600 °C for glasses prepared using an acidic catalyst and at temperatures up to 300 °C for glasses prepared using a basic catalyst. Both systems show partial loss of ruthenium and complete loss of iodine at temperatures above 300 and 100 °C, respectively.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Revisiting Wagner’s Criteria to Predict Establishment and Retention of Alumina Scales on Ternary NiCrAl Alloys

Despite the advent of numerical modeling approaches and high-performance computing infrastructure, the design and development of corrosion-resistant high temperature alloys (> 500 °C) continue to be largely empirical and typically involve extensive experimentation. This is mainly due to the lack of a single unified physics-based model that can address the impact of multiple competing factors such as time, environment, alloy composition, microstructure, and geometry. The classical Wagner’s criteria have been foundational to estimate the minimum concentrations required of an oxide-forming element to establish and sustain a protective oxide scale. However, the formulation is primarily limited to lower-order alloy systems (binary alloys) and ignores the time dependence of subsurface compositional changes in the alloy. The lack of key data on the temperature and composition dependence of the solubility and transport of oxidants in multicomponent-multiphase alloys further exacerbates the problem. In the present work, a few of these limitations were addressed using a flux-based approach (FLAP) which tracks the spatiotemporal evolution of the fundamental flux balance between oxygen and the oxide-forming elements to enable the prediction of the formation of an external alumina scale in ternary NiCrAl alloys. In conclusion, the modeling results were validated with the literature findings and additional experimental work conducted in the present work.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cs retention and diffusion in C-S-H at different Ca/Si ratio

Cement and concrete are commonly used in the construction of repository sites for radioactive wastes. The correct isolation of those contaminants requires good adsorption and low diffusion rates. Both parameters are highly affected by many factors, such as pH, temperature or composition. The large variability of experimental conditions and formulations makes it extraordinarily difficult to tackle the influence of each of them independently in experimental samples. To this effect, molecular dynamics simulations have been employed in this study to investigate the role of the composition in the capacity to retain Cs and diffusivity of these ions in calcium silicate hydrate (C-S-H) gel pores. The results indicate that the adsorption of Cs ions is worsened at high Ca/Si ratios due to a lower interaction of the cations with the C-S-H surface, while hydrophilicity of the C-S-H nanopore rises, resulting in higher long-range ordering and lower diffusion coefficients of Cs ions.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of carbonation on the retention of heavy metals in chemically activated BOF slag pastes

Basic Oxygen Furnace slag contains heavy metals, including vanadium, chromium and molybdenum. The leachability of these elements determines the industrial applicability of slag-based building products. This study investigates the post‑carbonation leaching of heavy metals from activated BOF slag pastes with the focus on the activator dosage and type (sodium and potassium citrate). Results reveal that the high degree of brownmillerite hydration boosts the leachability of heavy metals as its hydration product- hydrogarnet is less stable upon carbonation. With two leaching procedures, it is demonstrated that the carbonation resistance of pastes becomes the main attribute in preventing the leaching of heavy metals. It can be enhanced by optimising the activator dosage to facilitate the hydration of C{sub 2}S and consequent structural densification.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A potential emerging issue concerning repair welding of out-of-core PWR components involving tritium exposure and 3 He retention

This paper identifies a potential but previously unrecognized risk of helium-induced embrittlement and cracking during repair welding of out-of-core pressurized water reactor (PWR) components exposed to tritium-contaminated coolant. While previous weldability concerns centered on 4 He accumulation in neutron-irradiated alloys located within the in-core or near-core regions, new measurements show that 3 He generated by tritium decay can accumulate in out-of-core components. Because hydrogen isotopes readily diffuse to grain boundaries and become trapped there, significant 3 He generation at grain boundaries may lead to cracking during weld repairs. Initial data from far-below-core PWR flux thimble tubes confirm the presence of 3 He levels above known cracking thresholds for repair welds. In conclusion, these findings indicate that out-of-core regions should be considered when defining safe weld repair windows in reactors operating for 60–100 years.

Extended PWR lifetimes↗