Document: NRC Regulatory Guide
Document ID: 5cdd8024-5f0a-4a1b-8e14-1026125c5667
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Pressurized Water Reactor Radioactive Gas Storage Tank Failure (Rev. 0)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0833/ML083300020.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.24
CFR Part: 
CFR Title: 

Content:
orage system damage, they should be considered even though the radiological consequences of such an accident would be mitigated by the high wind speed required to generate such missiles. C. REGULATORY POSITION 1. The assumptions related to the release of radioactive gases from the postulated failure of a gaseous waste storage tank are: a. The reactor has been operating at full power with one percent defective fuel and a shutdown to cold condition has been conducted near the end of an equilibrium core cycle. As soon as possible after shutdown, all noble gases have been removed from the primary cooling system and transferred to the gas decay tank that is assumed to fail. b. The maximum content of the decay tank assumed to fail should be used for the purpose of computing the noble gas inventory in the tank. Radiological decay may be taken into account in the computation only for the minimum time period required to transfer the gases from the primary system to the decay tank. c. The failure is assumed to occur immediately upon completion of the waste gas transfer, releasing the entire contents of the tank to the building. The assumption of the release of the noble gas inventory from only a single tank is based on the premise that all gas decay tanks will be isolated from each other whenever they are in use. d. All of the noble gases are assumed to leak out of the building at ground level over a two hour time period. 2. The atmospheric diffusion assumptions for ground level releases are: a. The basic equation for atmospheric diffusion from a ground level point source is: z y u 1 Q / σ σ π = χ Where: χ = the short term average centerline value of the ground level concentration (curies/m3) Q = amount of material released (curies/sec) u = windspeed (meters/sec) σy = the horizontal standard deviation of the plume (meters) [ See Figure V-I, Page 48, Nuclear Safety, June 1961, Volume 2, Number 4, “Use of Routine Meteorological Observations for Estimating Atmospheric