Dose assessment for reentry or reoccupancy and recovery of urban areas contaminated by a radiological dispersal device: the need for a consensus approach

Abstract

Should an attack occur in an urban area with a Radiological Dispersal Device (RDD), guidance is available on the acceptable total dose equivalent for reentering the contaminated zone, and there is an accepted methodology for plume projection in the model used by the Federal Radiological Monitoring and Assessment Center (FRMAC). After initial characterization of the impact of the plume caused by an RDD, there will be considerable pressure from the public to allow them to return and quickly collect their belongings, and, eventually, to reoccupy residences and to reopen businesses. The FRMAC procedures principally deal with early and intermediate phase dose assessment, but do include late phase assessment procedures. However, the late phase assessments do not include complex geometries, such as the internal structure of buildings. This paper identifies areas where more specificity is needed to rapidly provide assessments to health officials and senior decision-makers. In this regard, there is no national consensus method to calculate projected dose inside buildings after an RDD event that addresses selecting the exposure pathways, scenarios, key parameters, etc. Therefore, to demonstrate an approach that exemplifies some of the technical and policy issues, which are unresolved, four exposure scenarios (residential, industrial, public park, park worker) were evaluated to determine the level of contamination that would deliver a dose equivalent of 10 mSv in the first year, excluding exposure during the first 4 d (emergency phase). In addition, the retrieval of personal belongings was simulated by assessing a 1-h exposure for the residential and industrial scenarios. RESRAD-BUILD was used to calculate the surface concentration of 60Co, 90Sr, 137Cs, 192Ir, 226Ra, 238Pu, 241Am, and 252Cf that would lead to a 10 mSv reference dose for these exposure periods. These example studies are intended to provide insights and guidance on how a municipal health agency can begin to develop a response plan, and to understand how the assessment process will determine the dose impacts resulting from an RDD event. The model's predictions heavily depend on the choice of the model's parameters; for several key ones, there are large uncertainties about their appropriate values. To avoid having to make hasty decisions during an emergency after an RDD attack, this analysis demonstrates that a detailed protocol for calculating dose should be developed prospectively so that decision-makers already are fully familiar with the process and its ensuing products.