Alpha spectrum profiling of plutonium in leached simulated high-level radioactive waste-glass

Low-geometry x-ray spectra from 239Pu and 237Np, incorporated into simulated high-level radioactive waste-glass, were transformed into depth distributions for these elements. Changes in the depth profiles were observed for a series of static leachings in 750C water. Radiochemical assay of the leach solutions revealed that little neptunium or plutonium was leached, and that the amount leached was independent of leaching time. The depth profiles of the leached specimens showed that there was selective leaching of nonradioactive components of the glass, concentrating the remaining neptunium and plutonium in a broad zone near (but not at) the glass surface. Eventual redeposition of nonradioactive material onto the glass surface inhibited further leaching. Since the depth profiles exhibit uniform concentrations of plutonium and neptunium in undisturbed simulated waste-glass, the depth of attack by the solution can be inferred by departures from the uniform concentrations. A different mechanism was observed in leaching the simulated waste-glass by room temperature 0.03 M NaHCO3. There was no evidence for selective leaching or invasion of the glass by the leaching solution. There was, however, a steady buildup of plutonium (but not neptunium) upon the surface of the glass. 4 figures, 3 tables