99Tc, Pb and Ru Migration Around the Oklo Natural Fission Reactors
The generally favored method for disposal of commercially generated radioactive wastes is deep geologic burial (1). Existing information supports the belief that appropriate geologic media in conjunction with engineered barriers will be adequate to isolate the waste from the biosphere (1). Because of the long half-lives of many of the radionuclides, the required periods of isolation are much longer than recorded human history, therefore evaluation of the reliability of particular geologic media to isolate the waste must rely heavily upon analytic models of radionuclide transport in geologic environments. Studies of element migration in natural systems can yield important constraints for such analytic transport models. Of particular value are the remains of naturally occurring fission reactors found at the Oklo uranium mine in Gabon, Africa. The uranium rich zones began to undergo sustained nuclear fission 2×109 years ago and remained critical for several hundred thousand yqs (2). Approximately 10 tons of fission products and 4 tons of Pu were generated. Hence, Oklo provides a unique opportunity to study movement of fission-produced materials which have resided in a geologic media for times greater than those of concern in the storage of radioactive wastes (3,4). Such studies will be valuable in evaluating transport models and can provide information regarding chemical and physical conditions, time scales, and processes operative in the movement of elements from a well-characterized reactor waste source.
KeywordsRadioactive Waste Fission Product Geologic Medium Spontaneous Fission Basal Conglomerate
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