Direct Investigations of the Immobilization of Radionuclides in the Alteration Phases of Spent Nuclear Fuel

In a moist oxidizing environment, such as in the proposed geological repository at Yucca Mountain, rapid alteration rates are expected for spent nuclear fuel. Laboratory simulations and studies of natural analogues demonstrate that the dominant alteration products of spent fuel under repository conditions will be uranyl phases. There is an inadequate database concerning the effects of the alteration products on the release of radionuclides, but this information is essential to provide a radionuclide-release estimate. It is likely that many of the radionuclides contained in the spent fuel will be incorporated into the uranyl phases that form during alteration, potentially with a profound impact on the future mobility of radionuclides in the repository. Our objective is to develop a theoretically founded and experimentally verified understanding of the incorporation of radionuclides into uranyl phases under repository conditions. The research will permit a more realistic estimate of the release rates of the radionuclides from the near-field environment