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Decision Support for Low-Level Waste DisposalThe U.S. Nuclear Regulatory Commission (NRC) uses performance assessment to support decisionmaking regarding low-level waste (LLW) disposal in a variety of applications, including the following examples described on this page:
Concentration Averaging To Classify LLW for Near-Surface DisposalThe regulatory requirements for licensing a land disposal facility (10 CFR Part 61) establish a system for classifying radioactive waste for near-surface disposal, based on the concentrations of specific radionuclides that the waste contains. In particular, 10 CFR 61.55(a)(8) allows the concentration of a radionuclide to be determined indirectly, or averaged over the volume of the waste, or weight of the waste, provided that the concentration is expressed in nanocuries per gram. Performance assessment was used to establish the Branch Technical Position (BTP) on Concentration Averaging and Encapsulation for use in classifying LLW for commercial disposal, and is currently used to provide guidance for exceptions to the BTP. Through modeling, the NRC staff can evaluate how the degree of homogeneity in concentration contributes to protecting the general public and inadvertent intruders at near-surface disposal sites. The NRC staff has accepted intentional mixing of radionuclides, in past cases where similar waste streams from different sources have been mixed to meet a disposal facility's waste acceptance criteria, provided that the mixing did not change the waste classification (determined according to 10 CFR Part 61). Intentional blending is the mixing of higher and lower concentrations into a homogenous final waste form. It is not the blending of clean or untainted material with contaminated material. Additionally, the NRC staff has completed a regulatory analysis of intentional mixing of contaminated soil, in the course of its rulemaking activities related to the License Termination Rule (LTR). The results of that analysis are documented in the staff's related Commission paper (SECY-04-0035), and the Commission's approval of this type of intentional mixing is described in the corresponding Staff Requirements Memorandum (SRM). That SRM tasked the staff with developing guidance regarding consideration of intentional mixing of contaminated soil, on a case-by-case basis, for meeting the requirements of the LTR. It also instructed the staff to include intentional mixing in revised guidance to address options for restricted release, site disposal, and realistic land use scenarios to be developed as recommended in SECY-03-0069. The staff published this guidance in revisions to NUREG-1757, “Consolidated Decommissioning Guidance,” which the NRC issued in September 2006. On that basis, performance assessment tools are applied in developing guidance on intentional mixing of contaminated soil. In addition, the NRC staff has developed a tool to risk-inform concentration estimates for waste incidental to reprocessing, based on site conditions that were not considered in developing 10 CFR Part 61. Guidance regarding the use of this tool for concentration averaging is available in NUREG-1854; however, this guidance does not supersede the Branch Technical Position (BTP) on Concentration Averaging and Encapsulation.
Evaluation of Proposed Alternative LLW Disposal ProceduresWithin the NRC's "Standards for Protection Against Radiation," 10 CFR 20.2002 is a general provision that allows licensees or applicants to obtain approval of alternative LLW disposal procedures. If approved, these alternatives allow disposal of what is frequently referred to as “low-activity” waste (LAW) in a facility other than a LLW disposal facility licensed under 10 CFR Part 61. Although the United States has no official legal definition for the term, the National Research Council (NRC) of the National Academies has defined LAW as including all types of conventional low-level radioactive waste produced by generators in the nuclear fuel cycle, discrete sources, slightly contaminated solid materials, uranium and thorium ore processing wastes, and wastes containing technologically enhanced naturally occurring radioactive materials (TENORM). Thus, LAW is considered to be radioactive waste that may contain radionuclides in concentrations that are sufficiently small to allow the radionuclides to be managed in ways that do not require all of the radiation protection measures that are needed to manage materials with higher activity levels. In practice, 10 CFR 20.2002 is most often used for disposal of radioactive waste in hazardous or solid waste landfills, which are permitted under the Resource Conservation and Recovery Act. However, it can also be used for any type of disposal not already defined in the regulations, such as disposal on a licensee's site or offsite on private property. To be approved, an application for approval of alternative LLW disposal procedures must demonstrate that doses will be maintained “as low as reasonably achievable” (ALARA) and within the dose limits set forth in 10 CFR Part 20. In addition, as a part of an application for LLW disposal under 10 CFR 20.2002, the NRC ensures public and environmental safety by evaluating the proposed activities and estimating the potential doses associated with transportation, waste handing, and disposal by burial. Toward that end, each application must include all of the following information:
As part of its evaluation of a 10 CFR 20.2002 application, the NRC's technical staff reviews the performance assessment submitted by the licensee or applicant. The purpose of this review is to determine whether the proposed procedures meet the NRC’s alternative disposal guideline of contributing a dose of no more than “a few millirem per year” to any member of the public. Although the limits in 10 CFR Part 20 specify that the total effective dose equivalent to individual members of the public from the licensed operation must not exceed 0.1 rem (1 mSv) in a year, the “few millirem per year” approach toward alternative disposal is consistent with the Commission's guidance documented in SECY-06-0056. Specifically, the NRC's technical staff reviews the ground-water monitoring plans, technical reports, or computer codes used to determine the dose impacts attributable to the disposal, as appropriate. In doing so, the staff employs a risk-informed approach by focusing on those aspects of the review that are expected to have the greatest impact on the results. The staff also ensures that the source term description, scenarios evaluated, parameters, and conceptual and mathematical models used are appropriate for the proposed alternative disposal method. In addition, the staff uses sensitivity analysis to help make certain that the estimated dose from the disposal will be within “a few millirem per year” to all possible human receptors. Finally, the staff documents the results of its review, usually in the form of a safety evaluation report (SER). Acceptability of individual licensee approaches depends on the proposed alternative method of disposal. More detailed information regarding the NRC’s dose assessment criteria can be found in NUREG-1757, Vol. 2, “Consolidated Decommissioning Guidance: Characterization, Survey, and Determination of Radiological Criteria.” Related Information
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