The Use of Collective Dose for Optimization of a Low-Level Waste Site Closure Cover

Low-level radioactive waste management regulations require that releases to the environment be as low as reasonably achievable. Collective dose's use in quantitative cost benefit analysis is well accepted for optimization of operational radiation safety, but seldom applied to routine environmental releases. One concern is that collective dose for large areas and long time periods may obscure the spatial and temporal distribution of risk and the magnitude of individual doses. Use of collective dose for optimization also requires that the decision maker justify subjective inputs including truncation limits for the summation of collective dose in space and time, a monetary value for collective dose, and a discount rate for future health detriment. In this study, a probabilistic collective dose model is developed and used to optimize the closure of the Area 5 Radioactive Waste Management Site (RWMS) on the Nevada Test Site. Collective dose's shortcomings are addressed by preparing a dose matrix that disaggregates the collective dose in space and time and by reporting individual doses for exposed subgroups. Important subjective inputs are assigned discrete values reflecting differing opinions, and the consequence of the differences on the final decision is described. The resulting optimization process remains subjective, but clearly identifies subjective inputs, the values selected, and their impact on the decision. For the Area 5 RWMS, the value of the collective dose is small compared to closure cover cost options over a broad range of subjective values for the spatial and temporal limits for truncation of collective dose, monetary value of collective dose, and discount rates for future dose. The collective dose matrix and individual doses indicate that the societal and individual risks are greatest for future residents within the disposal site boundary, suggesting that options deterring intrusion have the greatest potential for cost-effectiveness. The cost of various closure options far exceeds the value of the collective dose averted, indicating that there are few opportunities for cost-effective improvements when closures meet the low dose constraints in waste management regulations.