Comparison of CAP88 PC Ver. 3.0 and MAXDOSE dose assessment models involving co-located stack releases at the Savannah River site.

The Savannah River National Laboratory's Environmental Dosimetry Group performs dosimetry assessments for Savannah River Site (SRS) radionuclide air emissions utilizing the Clean Air Act Assessment Package-1988 (CAP88) code (CAP88 PC Ver. 3.0) and the MAXDOSE-SR Ver. 2011 code, which is an SRS-specific version of the Nuclear Regulatory Commission's MAXIGASP code. CAP88 PC and MAXDOSE-SR are used at SRS for demonstrating compliance with Environmental Protection Agency dose standards for radionuclide emissions to the atmosphere and Department of Energy Order 458.1 dose standards, respectively. During a routine comparison of these two assessment models, it was discovered that CAP88 PC Ver. 3.0 was not producing the expected results when using multiple co-located stacks in a single run. Specifically, if the stack heights are considered separately, the results for several radionuclides (but not all) differ from the combined run [i.e., 1 + 2 does not equal (1+2)]. Additionally, when two or more stack heights are considered in a run, the results depend on the order of the selected stack heights. For example, for a two stack-height run of 0 meter and 61 m input produces different results from a 61 m and 0 m input run. This study presents a comparison of CAP88 PC Ver. 3.0 and MAXDOSE-SR Ver. 2011 based on SRS input data and on two-stack release scenarios. The selected radionuclides for this study included gases/vapors (H, C, Kr, and I) and particulates (Sr, Cs, Pu, and Am) commonly encountered at SRS.