Modeling filtered building effluent stack sampling points for qualification criteria

Proposed construction of or changes to a radiological effluent stack must meet the mixing criteria at the sampled stack location required by the standards ANSI/HPS N13.1–2011 and ISO 2889. For more than a decade, three-dimensional computational fluid dynamics (CFD) models of such stacks have been used to assist in characterizing the sample location suitability. When inadequate mixing in the stack at the sampling location has been identified, additional modeling was used. Testing results have confirmed the CFD model predictions with similar values in both scale model and full-scale stack tests. Simulations of a stack scheduled for modifications can evaluate mixing at the limits of operation, recommend modifications, and indicate if the retrofitted stack passes criteria for baseline operating conditions. This work demonstrates CFD modeling is an effective design tool and should be considered to facilitate qualification of a stack sampling location to meet standards.