Release of volatile carbon compounds from nuclear waste packages. Release from Zircaloy

This is a doctoral thesis that primarily investigates the release of C-14 compounds from zircaloy to a noble gas atmosphere at various temperatures. The results show that this process requires the presence of reactive gases like oxygen, e.g., in the atmosphere surrounding the metal. The oxygen in the carrier gas reacts with the carbon that diffuses to the metal surface and thus forms volatile carbon compounds, mainly CO2, whose share in overall release rises from 80% at 200deg C to up to 92% at temperaturs of about 600deg C. The other volatile products formed presumably consist of CO. The experimental measurements revealed at 600deg C a release of C-14 inventory of 80%, which reduces to 50% at 500deg C, 25% at 400deg C, and only 1.5% at 200deg C, measurements done over an experimental period of four months. With drawing all oxygen from the carrier gas reduces the C-14 release to non-detectable values. The study also investigates the depth distribution of Xe-135 in zircaloy. A surface layer of about 10 μm of a metal specimen is doped with xenon, which proves to be rather immobile at temperatures below 500deg C, and only at 700deg C starts to move towards the metal surface. (orig./MM)