Comparative cancer risk assessment of radionuclides and hazardous material in support of mixed waste disposal

Abstract

In the 1980s, the United States began assessing the risk associated with the disposal of assessment mixed wastes, which are hazardous materials that have become radioactively contaminated. The majority of mixed waste generated by commercial nuclear power plants is considered low-level waste. Even though the volume of mixed waste generated is small, the toxicity of the hazardous chemical portion of the waste can remain well beyond the period that the radioactive portion is considered dangerous to the public. Hazardous waste treatment prior to disposal is commonly performed but can be very costly because of the small volumes and specific needs of the mixed wastes generated. This research assessed the cumulative health risk, radiological plus hazardous chemical risk, of mixed waste disposal without treatment of the hazardous portion of the waste and determined the maximum allowable concentration of each contaminant by using the generic guidelines. Given that low-level radioactive waste disposal facilities are designed to contain the waste for 300 years, this assessment was conducted to determine whether the untreated hazardous portion of mixed waste would be sufficiently isolated to protect humans and the environment. Currently available software and models for risk assessment evaluate only one of the wastes, either radioactive or chemically hazardous without assessing the combined effect of radioactive and hazardous chemical waste. In this research, a new simplified model was developed to assess the risk of the contaminants released from the disposal facility into the groundwater over a 1000-year period. The U.S. Idaho National Laboratory’s GWSCREEN model was used as a reference to develop a new simplified model. This research found that the risk of radioactive components contributes to the total risk of mixed waste mostly for over 100 years, and the hazardous components contributes to the total mixed waste after 100 years, proving that hazardous chemical waste also contributes to the total cancer risk. Besides that, the generic guideline is provided to determine the maximum allowable concentration in the facility. It uses generic analysis and inventory limit as a method to assess the mixed waste. The concentration ratio is needed to do the inventory limit.