Document: NUREG-0800
Document ID: 4e1c316a-99c2-4fd3-9d9b-323791bd85f8
Document Type: srp
Title: SHORT-TERM ATMOSPHERIC DISPERSION ESTIMATES FOR ACCIDENT
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0707/ML070730398.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.3.4
CFR Part: 
CFR Title: 

Content:
effluent into the wake of plant structures is usually allowed for ground-level releases. Dispersion models used for radiological control room χ/Q estimates will be compared against ARCON96, which is described in Regulatory Guide 1.194. Most accidental releases can be considered as continuous releases (i.e., on the order of several minutes or more). However, some releases such as from steam line breaks or of hazardous materials may be considered as instantaneous (puffs). The general Gaussian diffusion model for continuous releases is used to evaluate releases on the order of several minutes or more. For puff releases, either instantaneous point-source Gaussian diffusion equations with a correction for initial source volume (Ref. 22) or hemispheric cloud configuration assumptions with the cloud traveling slowly downwind (e.g., at approximately 1 m/sec) can be used. Although the model implemented in ARCON96 is a general code for assessing atmospheric dispersion in building wakes under a wide range of situations, there may be atmospheric dispersion scenarios and source-receptor geometries for which the model would be inappropriate, e.g., control room outside air intakes located close to the base of tall elevated stacks, extremely short duration releases, or receptor distances shorter than about 10 meters. Section C.3.2.2 of Regulatory Guide 1.194 discusses an appropriate procedure for generating χ/Q values for those situations where the control room intake is located close to the base of a tall elevated stack. Extremely short duration (puff) releases can be modeled using the criteria discussed in the previous paragraph of this SRP section. Facility design and operation should attempt to maintain some minimal distance of separation (e.g., more than 10 meters) between postulated sources and control room receptors. However, if the distance to the receptor is less than about 10 meters, the ARCON96 code should not be used to assess χ/Q values. An acceptable alternative