ECN publication
Immobilisatie van langlevende splijtingsproducten: een literatuurstudie
Published by: Publication date:
ECN NUC 1998
ECN report number: Document type:
ECN-C--97-095 ECN publication
Number of pages: Full text:
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With present nuclear facilities, the transmutation of long-lived fissionproducts Cs-135, Tc-99 and 1-129 into short-lived, harmless isotopes does not seem to be efficient. Therefore, appropriate solutions for the ultimate disposal of these geochemical mobile radionuclides should be developed. At present, the high-level liquid waste stream that results from the commercial reprocessing of spent fuel is vitrified using borosilicate glass. This high-level waste stream includes most fission products, minor actinides (Am, Np, Cm) as well as traces of U and Pu. However, under conditions of constant water-renewal in the disposal facility the long-term stability of borosilicate glass cannot be guaranteed over the lifetime of Cs-135 and Tc-99. Alternatively, the use of synthetic mineral assemblages such as, e.g., SYNROC, for the immobilization of spent fuel high-level waste stream is under study in various countries. For most geological conditions, this material seems to have better corrosion resistance as compared to borosilicate glass with (much) better leaching characteristics of the radionuclides. In addition, natural analogues studies can be used to assess the performance of SYNROC assemblages on a geological timescale, including the effect of radiation damage on long-term stability and leaching characteristics of the mineral assemblages. At present, with commercial reprocessing of spent fuel I-129 is disposed of via controlled discharges into the ocean in accordance with official regulations. For this reason, little effort has been given for the immobilization of I-129. In order to further reduce the long-term radiological hazards involved with geological disposal of high-level radioactive waste it is interesting to study the selective immobilization of individual radionuclides, most importantly Cs-135, Tc-99 and I-129. It is anticipated that selective immobilization gives better opportunities to prevent these radionuclides from entering the biosphere on the long term. This report summarizes the state-of-the-art in the selective immobilization of long-lived fission products and actinides. The role of natural analogue studies in assessing the performance of the waste form under actual disposal conditions on geological time scale is also discussed. 100 refs.

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