Tritium Aging Effects Research Articles

Simulated Aging of Metal Tritides by Ball Milling Induced Gas Incorporation

The study of tritium aging effects on materials requires a significant time commitment as a consequence of its 12.3-year half-life, making developmental studies prohibitively difficult and expensive. However, detailed knowledge of long-term aging effects is critical to the development of structural and storage materials for future fusion reactor technologies. As a result, multiple approaches to simulated aging effects have been investigated. We report a method of simulated tritium aging achieved though the incorporation of trapped gases via high-energy ball milling of LaNi4.25Al0.75 alloy storage material. Experimental results verify the presence of trapped gases by a combination of temperature programmed desorption and LECO chemical analysis. Following gas incorporation, we find that many of the degraded hydrogen sorption properties found in aged storage materials are reproduced by the ball milled powders.

Tritium Aging Effects on Fracture Toughness of Stainless Steel Weldments

The long-term embrittlement effects of tritium and decay helium on the structural properties of stainless steels have been studied for years at Savannah River National Laboratory (Savannah River) to provide required data for establishing safe operating conditions and the lifetimes of the pressure vessels used to contain tritium gas. In this study, the fracture toughness properties of the longest-aged tritium-precharged stainless steel base metals and weldments tested at Savannah River were measured and compared to earlier results. The fracture toughness values were the lowest recorded here for tritium-exposed stainless steel. As-forged and as-welded specimens were thermally precharged with tritium gas at 34.5 MPa and 623 K, then aged for up to 17 years to build in decay helium prior to testing. American Society for Testing and Materials J-integral fracture mechanics analyses, transmission electron microscopy (TEM), and small-angle neutron scattering (SANS) examinations were conducted to characterize the effects of tritium and its radioactive decay product 3He. Results show that the fracture toughness values were reduced to less than 2% to 4% of the as-forged values for specimens with more than 1300 atomic parts per million helium from tritium decay. The trend of decreasing fracture toughness values with increasing helium content was consistent with earlier observations, and the data show that Type 304L stainless steel is more resistant to tritium-induced cracking than Type 21-6-9 stainless steel at similar decay helium levels. The fracture toughness properties of long-aged weldments were also affected, but the reductions were not as severe over time because the weldments did not retain as much tritium as did the base metals. TEM observations were used to characterize the effects of decay helium bubbles on the deformation substructures, but nanometer-sized helium bubbles were not easily resolved because of high dislocation densities within the forged microstructures. SANS results are presented that suggest the technique can provide information on decay helium bubble size, spacing, and distribution in these steels.

Tritium aging effects on separation factors in palladium-hydrogen system

Abstract The separation factors of the palladium-hydrogen system were experimentally measured at different temperatures ranging from 248 to 303 K after aging for up to 3.5 years by tritium. The results showed a remarkable hydrogen isotope effect in the aged palladium-hydrogen system compared to the raw system. The hydrogen-deuterium separation factor of the palladium-hydrogen system aged by tritium was correlated to temperature and hydrogen/deuterium ratio in the solid phase of palladium hydride.

Thermal Enhancement Cartridge Heater Modified (Tech Mod) Tritium Hydride Bed Development Part I – Design and Fabrication

The Savannah River Site (SRS) tritium facilities have used 1st generation (Gen1) LaNi4.25Al0.75 (LANA0.75) metal hydride storage beds for tritium absorption, storage, and desorption. The Gen1 design utilizes hot and cold nitrogen supplies to thermally cycle these beds. Second and 3rd generation (Gen2 and Gen3) storage bed designs include heat conducting foam and divider plates to spatially fix the hydride within the bed. For thermal cycling, the Gen2 and Gen 3 beds utilize internal electric heaters and glovebox atmosphere flow over the bed inside the bed external jacket for cooling.The currently installed Gen1 beds require replacement due to tritium aging effects on the LANA0.75 material, and cannot be replaced with Gen2 or Gen3 beds due to different designs of these beds. At the end of service life, Gen1 bed desorption efficiencies are limited by the upper temperature of hot nitrogen supply. To increase end-of-life desorption efficiency, the Gen1 bed design was modified, and a Thermal Enhancement Cartridge Heater Modified (TECH Mod) bed was developed. Internal electric cartridge heaters in the new design to improve end-of-life desorption, and also permit in-bed tritium accountability (IBA) calibration measurements to be made without the use of process tritium. Additional enhancements implemented into the TECH Mod design are also discussed.

Tritium aging effects on hydrogen permeation through Pd8.5Y0.19Ru alloy membrane

Palladium alloy membranes have been widely used as permeator to produce pure tritium from gas mixture or tritiated impurities in tritium technology related to fusion reactor. But long term continuous operation will lead to accumulation of 3He in alloy, resulting in tritium aging effects. In this work, the changes in protium/deuterium permeation characteristics of Pd8.5Y0.19Ru (at.%) alloy membrane with 3He concentration of 0.042 (He/M) induced by tritium decay was investigated. In the temperature range 573 K–723 K the permeability of the aged membrane decrease seriously, and the permeation separation factor for H–D mixture increase somewhat.

Aging effects in uranium tritide

The aging behaviors of uranium tritide, such as the release of helium-3, changes of equilibrium desorption isotherms, and tritium heels, have been investigated. It is suggested that part of 3He from decay should be retained in the aged uranium tritide. The plateau of P– C– T curve is still wide and flat, and the change of the equilibrium plateau pressure is inconspicuous. Significant tritium heel is not observed in present works, so it can be neglected. The reduction of the reversible storage capacity is very little. In conclusion, the tritium aging effects in uranium tritide are slight, and uranium can be used as an effective material for long-term storage of tritium.

Tritium aging effects in LaNi4.25Al0.75

Tritium desorption isotherms and helium release properties are reported for three different LaNi4.25Al0.75 samples having seen 11.5 and 13 years of tritium exposure, and are compared to earlier data from similar samples with less exposure. The isotherms show a complete loss of the typical plateau structure, and a decreasing absorption capacity. However, the capacity loss is not due to further increase in heel content. Helium breakout is show to occur in one sample when the T content became low.

Thermodynamic characterization of new palladium alloy tritides

The decay of tritium in a metal tritide generates 3He in the lattice which tends to degrade the performance of the material over time. It is desired to develop a material which minimizes the tritium aging effects and may be tailored to a particular tritium processing application. Pd alloys with Ni and Co have been investigated, as Pd tritide is known to be resistant to tritium aging effects and alloying provides a means for adjusting the plateau pressure of the metal tritide. Sets of tritium desorption isotherms were acquired at temperatures between 273 and 338 K over the pressure range of 1–900 kPa. The thermodynamic parameters of ΔHandΔS for the β-α phase transition of the metal tritides were determined across the plateau regions of the pressure-composition-temperature curves. The average values of ΔH (kJ mol−1 T−1) and ΔS (J K−1 mol−1 T−1) were found to be 15.8 and 50.1 for Pd(2.8 wt.%)Ni, 13.7 and 50.3 for Pd(5.2 wt.%)Ni, 15.9 and 51.3 for Pd(2.8 wt.%)Co, and 13.6 and 51.8 for Pd(5.2 wt.%)Co, respectively.

Tritium Aging Effects in Zirconium-Cobalt

he effects of tritium aging on ZrCo have been characterized to determine the suitability of ZrCo as a long term tritium storage medium. Four 1 gram ZrCo storage beds were aged for three years with varying amounts of tritium. Equilibrium tritium pressures were found to increase by approximately threefold at a given temperature and composition in the range of 100–300°C. At 25°C, the pressure increase is predicted to be twenty-fold. Tritium aged ZrCo retains the majority of decay 3He within the bulk. As this 3He concentration increases, the rate of helium release increases. Longer term tritium aging may result in a 3He release rate equal to its production rate from tritium decay. In such a case, the pressure within a sealed storage bed would steadily increase. These tritium aging effects indicate that practical ZrCo storage bed design should include conservative design pressure specifications, to safely contain the maximum possible 3He pressure.