SPENT FUEL CHARACTERISTICS DISPOSAL CONSIDERATIONS

摘要

Spent fuel characterization has shown that the original single phase uranium dioxide becomes a polyphase assemblage during irradiation. The elements of particular interest in assessment of the performance of a high level radioactive waste repository over long time scales are the actinides, especially Pu and U, Tc, Cs, I, and Sr if it can be used as an indicator of matrix degradation rate. Characterization of spent fuel has shown that some of the Cs and I in fuels segregates to the grain boundaries and/or the pellet/cladding gap during reactor operation and is available for rapid release as soon as the fuel is contacted by water. The amount of the rapid release fraction increases with bumup and with linear power at which the fuel is run. Thus, CANDU spent fuel has a high instant release fraction even though it has a low burnup. Tc is located in a 5-metal alloy phase in spent fuels.