11 Regulatory Characterization and Risk Analysis Modeling
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Performing site and facility characterisation assessments is often complex Chapter 10 presented the needs for a facility undergoing decommissioning. As discussed in Chapter 7, a key aspect to risk assessment is the evaluation of radiological exposures to hypothetic My maximum exposed individuals.. Computer-based tools have been developed to help address these challenges. This chapter specifically discusses three computer-based aids developed by government agencies for the conduct of decommissioning, namely RESRAD, DandD, and Compass, together with MARSSIM, and the adaptive characterization approach they support. RESRAD and DandD are used to conservatively calculate exposures to the maximum exposed individual through multiple pathways, based on measured values of residual radioactive contamination, These two codes are the primary dose modeling approaches considered acceptable by the NRC and DOE. Compass is a code used to automate some processes from the MARSSIM characterization protocols.
The MARSSIM methodology provides information on planning, conducting, evaluating, and documenting the final status radiological surveys of building surface and surface soils for demonstrating compliance with dose- or risk-based regulations or standards. MARSSIM is a multi-agency consensus document that was developed collaboratively by four federal agencies having authority and control over radioactive materials: the Department of Defense (DOD), the DOE, the EPA, and the NRC. The manual was originally issued in December 1997 as NUREG-1575 (NRC 1997a) and then as NUREG 1575, Rev.1 (NRC 2000a) in August 2000 to incorporate comments received on the 1997 version. Errata and modifications that were included in Revision 1 are shown on page xxviii of that document. In general, the two versions are quite similar; the former is part of the documentation of completed projects and the latter is used for future and on-going projects.
This chapter also addresses two approaches to characterization in decommissioning, MARSSIM is widely used to optimize a characterization program while helping ensure statistical validity of the results. The program is focused toward field radiological characterization. The second approach is an adaptive sampling and analysis program that has been demonstrated to improve cost and time performance objectives for characterization (DOE 2001c).