Typical Uranium Mill Tailings

Current environmental standards for uranium mill tailings (EPA, 1983) permit surface disposal of these wastes with appropriate engineered controls. The controls include use of a cap that typically 

In this analysis, it was conservatively assumed that an individual could enter a disposal site and remove a portion of the protective surface cover (about 200 m2) and expose on-site workers to the tailings.19 It was further assumed that such an unlikely scenario would occur only once in an individual s lifetime, and that exposure would occur over a period of 1,000 h. Exposure pathways considered in this analysis involve external exposure, inhalation of outdoor radon and its short-lived decay products, inhalation of particulates, and ingestion of waste. The activity concentrations of 226Ra and its decay products in the waste were conservatively assumed to be 37 Bq g 1, a 

Based on the assumptions described above, the risk calculated using the RESRAD code (Yu etal., 1993) and EPA slope factors (HEAST, 1991 1995) is a probability of cancer incidence of about 7 X 10 4. The assumed acceptable risk for low-hazard waste is 10 3 (see Table 7.1), resulting in a risk index of 0.7. Hence, domestic uranium mill tailings could be classified as low-hazard waste acceptable for licensed near-surface disposal under conditions of perpetual institutional control over disposal sites. 

An alternate analysis was performed using dose as a surrogate for risk. Using the same assumptions given above and the RESRAD code, the dose to an intruder was estimated to be 15 mSv. Assuming an allowable dose of 20 mSv (see Table 7.1), the risk index was estimated to be 0.8. Therefore, as expected, either approach yields about the same result. 

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