LONG-TERM STABILITY OF SPENT NUCLEAR-FUEL WASTE PACKAGES IN GORLEBEN SALT REPOSITORY ENVIRONMENTS

The results are summarized of 15 yr of German research on spent fuel w ith respect to its suitability as a waste form disposed of in a reposi tory located in the Gorleben salt dome. Within the multibarrier system for longterm isolation of high-level waste (HLW), the innermost engin eered barrier ''canistered spent fuel'' contributes essentially to iso lating radionuclides from the biosphere ifa salt brine were to came in to contact with the waste form. A large fraction of the radionuclide c ontents of the reacted fuel mass would become reimmobilized within sec ondary alteration products and on container corrosion products, but in evitably a certain nuclide-specific fraction would be released into th e aqueous geochemical environment. The corrosion resistance of the fue l and the radionuclide mobility are nor inherent material properties b ut also depend on geological disposal conditions, packing concepts, an d radioactive decay, fn particular; the availability of oxidants is cr itical, controlling spent fuel alteration rates and alteration product s as well as radionuclide solubilities. Spent fuel is at least as suit able for final disposal as is HLW glass.