Spectroscopic Investigation of Actinides (U, Np) and Zr in Nuclear Glasses

English Abstract:

Vitrification of high-level radioactive waste in borosilicate glasses is currently used on an industrial scale in several countries. The fundamental properties of the waste forms are their chemical and mechanical durability against the forcing conditions represented by chemical alteration or internal/external irradiation. The waste immobilized in glass is composed of over 30 different nuclear fission and activation products, as well as minor actinides. The oxidation state and local coordination of long-lived radionuclides are important parameters during glass elaboration but also help model the actinide behavior during glass alteration or irradiation. We will present a short overview of the local structure around actinides and Zr in the inactive analog of the French nuclear glass SON68. X-Ray absorption spectroscopy has been used to probe the local environment around uranium and neptunium in these glasses. The surrounding of Zr, a waste directly inherited from zircalloy claddings, has been also investigated for comparison in these glasses. Together with UV-visible spectroscopy used to get information on the different oxidation states of U in glasses, our spectroscopic data show that these elements occur in glasses in a peculiar surrounding, with significant differences with those encountered in crystalline compounds, as well as in the alteration gels. Element speciation is then an important parameter to follow the evolution of structural properties during long–term aging of nuclear glasses.