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    Alligator Rivers analogue project final report volume 14 radionuclide transport
    (Australian Nuclear Science and Technology Organisation, 1992) Golian, C; Lever, DA; Baker, AJ; Bennett, DG; Brandberg, F; Connell, LD; Kimura, H; Lindgren, M; Murakami, T; Ohnuki, T; Pers, K; Read, D; Skagius, K; Snelling, A
    The Koongarra orebody and its associated dispersion fan are examined as a geological analogue for the transport of radionuclides from waste repositories. The aim is to build a consistent picture of the transport that has been taking place in the orebody and the important processes controlling the retardation of uranium series isotopes and to test models of radionuclide transport. A particularly distinctive feature of the Koongarra system is the strong seasonal dependence of the groundwater flow. However, the Koongarra system is similar to a radioactive waste disposal system in that mobilization of uranium is taking place as a result of the infiltration of groundwaters that are in gross chemical disequilibrium with the mineralogy of the primary ore body. There are considerable differences between the Koongarra uranium orebody and a radioactive waste repository, particularly a deep waste repository. The Koongarra system is shallow, affected by seasonal hydrogeological changes as well as climatic variations on a longer timescale and transport is taking place in a zone of active weathering. Some of these features make the Koongarra system harder to characterise than a deep repository. However, there are nevertheless many analogies between the processes occurring at Koongarra and those occurring around a deep or shallow waste repository. The difficulties encountered because of the heterogeneity of the Koongarra weathered zone mirror those to be addressed in assessing radionuclide transport in repository systems. The 234U/238U activity ratios in rock samples from the dispersion fan decrease in the direction of groundwater transport, whereas in many other systems it has been reported that 234U is preferentially mobile relative to 238U (Osmond and Cowart, 1982; Osmond et al., 1983). As most uranium resides in the rock rather than in the groundwater, the net recoil flux of uranium daughter radionuclides is usually from the rock to the groundwater, thus leading to (234U/238U)r less than one. Other models explain the observations by invoking the presence of a phase in which 234Th is irreversibly fixed.