Evaluating the Probabilistic Land-Use Scenarios in the Radiological Dose Assessment for License Termination

A recent trend in establishing regulatory policy regarding environmental cleanup has been the adoption of a risk-informed decision approach. This approach places an emphasis on the development of a defensible technical basis upon which cleanup decisions can be understood and accepted by stakeholders. The process has been exemplified by the U.S. Nuclear Regulatory Commission's (NRC's) approach to implement its License Termination Rule in Title 10, Part 20, Subpart E of the Code of Federal Regulations (10 CFR 20, Subpart E), for which probabilistic radiological dose assessment has been a key technical element for demonstrating compliance. Further guidance including NUREG-1757 and its supplemental document are also prepared for this purpose. The approach also entails extensive data collection to cover the range of parameter variability, along with interpretations of the probabilistic dose results and demonstration of compliance. One major remaining issue, however, involves the future use of the land following cleanup. Land use is a key factor that may profoundly influence dose assessment, which in turn will affect the level of cleanup and therefore the associated costs. Despite this, incorporation of land-use considerations into the current probabilistic dose assessment approach has not actually been performed in the regulatory process. In order tomore » address the issue, a study was initiated to evaluate the potential influence of land use on dose analysis, to understand the possible ramifications in cleanup decision-making. A probabilistic distribution based on land use was developed as input into the probabilistic RESRAD analysis for the demonstration of this approach.. This results in an understanding of the characteristics of dose distributions as exhibited by various land-use scenarios. By factoring in the probability distribution of land-use scenarios, the potential 'levels of conservatism' can be explicitly defined and evaluated. The results allow the quantification of the potential influence of land-use scenario assumptions on the dose and the variations in the results by type of radionuclide as well as by regional land-use patterns. Further improvement of the study can be utilized to support the NRC's goal in achieving 'realistic conservatism' in its license termination activities. (authors)« less