4th International Technical Meeting on Small Reactors - 2016 Nov. 02-04

Presented at:
4th International Technical Meeting on Small Reactors
2016 Nov. 02-04
Ottawa, ON Canada
Session Title:
Parallel Session C – Licensing

S. Talabi (Pittsburgh Technical / Carnegie Mellon University)


Current United States Nuclear Regulatory Commission (NRC) Emergency Planning Zone (EPZ) sizing for large LWR plants provides a 10-mile radius for inhalation pathways and a 50-mile radius for ingestion pathways. Due to the fact that Small Modular Reactors (SMRs) have a lower risk profile due to size, different source terms, and several mitigating design features, it is necessary to determine the appropriate appropriate EPZ size based on the specific risk profile for SMRs. A project has recently been concluded that provides the technical basis for a Scalable SMR-Specific EPZ. The project addressed the following issues: • Advances in Modelling Techniques since 1978 Assessment: o Significant advances in analytical techniques including computational fluid dynamics and stochastic methods (e.g. Monte Carlo sampling with software) o Overly conservative assumption of plume straight line trajectory can now be more accurately evaluated • Pseudo-quantitative Approach used in 1978 Assessment: o The selection of a 10-mile radius was determined based on an examination of the curves that showed the dose “decrease sharply within 10 miles and to decrease slowly at greater distances”. o Hence, the determination of the 10-mile radius was subjectively determined based on subject-matter experts’ review of the data. o The lack of a quantitatively determined basis for the 10-mile radius makes it challenging to draw inferences for the SMR. • Improved and Updated Meteorological Data since 1978 Assessment • Conservative approach for current plants shows that up to 30 percent of the plants in the sample exceed the EPA’s Protective Action Guide limits: o By improving the analysis and reducing the overly conservative assumptions, the level of confidence associated with the risk of exceedance for large plants would be improved beyond 70 percent as documented in NUREG 0396.

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