Lokalisation, Freisetzung, Speziesbestimmung von C-14 und H-3 in Reaktorgraphit

Worldwide over 250 000 tons of neutron irradiated graphite from nuclear reactors were temporarily retained in interim storage facilities. Concept for the management or final disposal for contaminated nuclear graphite remains an issue worldwide. In Germany it is anticipated that major part of contaminated graphite will be disposed in an underground repository (i.e. KONRAD), which requires radioactive wastes to be classified according to the waste acceptance requirements for KONRAD. This implies that reliable information about chemical behavior of contaminated material is available. Despite the extensive studies on nuclear graphite data on radionuclide behavior in graphite are rather scarse and assorted, which makes classification of graphite wastes questionable. Major part of contamination in nuclear graphite is comprised of 14C and 3H, mobile radionuclides which pose potential threat of bioincorporation unless safely isolated. In order to develop potential strategy for graphite waste management, the mechanisms of 3H and 14C release was studied using irradiated graphite from German AVR. In particular, the work is dealing with speciation of 14C and 3H both in the solid-phase as well as in gaseous or aqueous phases. Complementary examination of 14C release in gaseous and aqueous phases revealed the fractions of rather complex composition of 14C-containing organic compounds, e.g. alkanes and formic acid. Virgin graphite was -irradiated in different gas atmospheres. After irradiation different functional groups were found on the surface of irradiated graphite. They are assumed to be theresult of corrosion of graphite surface exposed to oxidizing conditions. For qualitative and quantitative description of irradiated graphite surface functionality X-ray-Photoelectron-Spectroscopy (XPS) and water uptake-experiments were applie