DOE Low-Level Radioactive Waste

The risk index normally is determined by computing the risk or by using dose as a surrogate for risk. In the example in Section 7.1.3.1, the calculated dose associated with intrusion into the waste is divided by the assumed maximum allowable dose to estimate the risk index. In the example in Section 7.1.3.2, limits on acceptable concentrations are developed as surrogates for the allowable risk. The concentrations in the waste are then divided by these allowable concentrations to determine the risk index. The same approach is used in the example in Section 7.1.3.3, except the allowable concentrations are lower because a less protective disposal option is evaluated. The consequences of alternative assumptions about intrusion scenarios on classification of the Hanford waste are considered in Section 7.1.3.4. 

1 Classification by Calculation of Total Dose. Exposure pathways considered in this analysis involve external exposure, ingestion of waste materials, and inhalation. Doses were estimated 

For the purposes of this example, it was assumed that the waste was placed 4 m deep and covered with a cap and soil that was at least 3 m thick. As a consequence, the assumed scenario was an onsite drilling event. The dose analysis assumes a two-fold volume increase (50 percent dilution) of the drill tailings by uncontaminated material. The mixture of waste and uncontaminated cover material is spread on the surface of the site, and individuals working in the area are exposed to the tailings for 1,000 h. The thickness of the layer of contaminated drill tailings is assumed to be about 5 cm and the area to be about 3.3 m2. Using dose as a surrogate for risk, analysis of this scenario yields a dose of0.002 mSv from all radionuclides. Since the assumed allowable dose is 20 mSv (see Table 7.1), the risk index would be 0.002/20 = 10 4, which is well below the value of unity, and the waste would be classified as low-hazard. 

2 Classification Using Pre-Established Limiting Concentrations. Another approach to classifying the Hanford low-level waste 

18The RESRAD code was used to illustrate implementation of the proposed waste classification system. NCRP did not evaluate the code or its underlying assumptions and database, and its use should not be construed to constitute endorsement. 

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Duguid, J.O., "Assessment of DOE low-level radioactive waste solid disposal storage activity", Battelle Columbus Laboratory, BMI-1984, 1977. 

L.R. Dole and H.A. Friedman, Radiolytic gas generation from cement-based waste hosts for DOE low-level radioactive wastes, Report No. CONF-860605-14 (Oak Ridge National Laboratory, 1986). 

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