NEAR-SURFACE DISPOSAL OF URANIUM - AN UNRESOLVED ISSUE

At the present time, two different approaches are taken in defining ac ceptable near-surface disposals of uranium in low-level radioactive wa ste. For civilian waste, the waste classification system developed by the Nuclear Regulatory Commission (NRC) in 10 CFR Part 61 does not inc lude limits on concentrations of uranium. Therefore, in principle, ura nium in any concentrations is generally acceptable for near-surface di sposal, provided the performance objective for protection of off-site members of the public is met. For defense waste, Order 5820.2A of the Department of Energy (DOE) includes dose limits for protection of inad vertent intruders, principally a limit on effective dose equivalent of 100 mrem per year for continuous exposures, rather than limits on con centrations of radionuclides as in the NRC's waste classification syst em. Since the DOE Order does not specify a time limit for protecting i nadvertent intruders, the eventual buildup of uranium decay products c ould result in doses to inadvertent intruders in excess of 100 mrem pe r year for concentrations of uranium comparable to the average backgro und concentration in surface soil of about 1 pCi/g. Therefore, near-su rface disposal of uranium at DOE low-level waste disposal sites essent ially could be precluded. As an alternative to the current NRC and DOE approaches, this paper discusses analyses which suggest that a concen tration limit for uranium of at least 0.2-2 nCi/g, depending on the is otopic composition, would provide reasonable protection of inadvertent intruders. However, such a concentration limit can be supported only with some or all of the following conditions: (1) protection of inadve rtent intruders were required only for 10(4) years after disposal; (2) doses to inadvertent intruders from exposure to radon were excluded; and (3) concentrations of uranium in disposal facilities were signific antly reduced over long time periods by mobilization and transport int o the environment. The first two conditions would require changes in c urrent DOE regulatory policies.