Tritium Aging Effects in Some Pd - Cr, Ni, and Co Alloys

Tritium decays to ³He, and when this decay occurs inside a metal tritide, the ³He is largely retained in the material’s bulk. This impacts the subsequent behavior of the hydrogen isotope absorption and desorption, altering the materials thermodynamic characteristics. Chemical substitution can form alternative miscible hydridable metal alloys over some concentration ranges with modified thermodynamic properties. This allows the ‘tuning’ of metal hydride characteristics to expand the inventory of available materials for use, potentially allowing a closer match to desired performance characteristics. It is important to quantify tritium aging effects in order to predict the long term, in-process behavior of metal hydride materials. The Savannah River National Laboratory has been interested in elucidating the impact of tritium exposure on the behavior of hydrideable metals and metal alloys. Pd alloy foils of nominal 5 and 9 at% Cr, Ni, and Co, were loaded with tritium, and stored for ~1 year in static storage. One sample (Pd-4.8 at% Ni) was subsequently stored for an additional ~3 years. Isotherms were determined following storage periods to study the tritium induced changes caused by tritium decay. Typical effects such as plateau pressure depression and heel formation were noted. The materials proved to be unusually sensitive to the isotherm determination process and decay effects were partially reversed, or “healed”. The Pd-4.8wt%Ni sample was removed from its storage unit, whereupon it was found to have turned into powder, and further studied with additional techniques elsewhere.