Document: NRC Regulatory Guide
Document ID: c406a126-ec51-4b8a-aafa-6fd4c7a7e7b9
Document Type: regulatory_guide
Title: Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1411/ML14114A674.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.111
CFR Part: 
CFR Title: 

Content:
early address related terminology (e.g., a well- defined rainy season, grazing and growing seasons), the possible use of seasonal as opposed to, or in addition to, annual data sets, whether and how to select and use data from hourly precipitation measurement stations over the 50-mile radius modeling domain, and the possible need for different deposition rates by precipitation type. Issues and items specific to model provisions and modeling assumptions include, but are not limited to: deciding whether other regulatory dispersion models (e.g., U.S. Environmental Protection Agency codes) or certain algorithms from those codes might be acceptable substitutes or alternative approaches for the XOQDOQ dispersion model; need for improvements in building wake entrainment and enhanced dispersion effects; accounting for plume dispersion and transport direction under calm wind conditions; the handling of potential recirculation effects on dispersion due to terrain; need to re-affirm the methodology used to account for diffusion due to mixed mode releases; guidance on handling routine releases not exhausted in a vertical (upward) direction; and a need to reconcile or justify different definitions between RG 1.111 and RG 1.145 for what constitutes an elevated (or stack) release. Issues and items requiring input from other internal stakeholders (e.g., health physics Staff) include, but are not limited to: determining whether to retain the 2.26- and 8.0-day radioactive decay removal mechanism for short-lived noble gases and iodines given much shorter plume travel times out to 50 miles even under low wind speed conditions; handling of dispersion calculations for intermediate (purge) releases and any implications of basing such analyses on hourly data rather than annual average conditions; and determining whether deposition over large bodies of water represents a potentially significant dose pathway and, if so, methodologies and data needs for handling such scenarios. Issues and