Document: NRC Regulatory Guide
Document ID: bd0ffb9e-22f8-46a4-ab36-f5cffd435ed7
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Boiling Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739601.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.3
CFR Part: 
CFR Title: 

Content:
e surrounding reactor building atmosphere and should then be assumed to be released as an elevated plume for those facilities with stacks. ' f. No credit should be given for retention of iodine in the suppression pool. 2. Acceptable assumptions for atmospheric diffusion and dose conversion are: a. Elevated releases should be considered to be at a height equal to no more than the actual stack height. Certain site dependent conditions may exist, such as surrounding elevated topography or nearby structures which will have the effect of reducing the actual stack height. The degree of stack height reduction should be evaluated on an individual case basis. Also, special meteorological and geographical conditions may exist which can contribute to greater ground level concentrations in the immediate neighborhood of a stack. For example, fumigation should always be assumed to occur; however, the length of time that a fumigation condition exists is strongly dependent on geographical and seasonal factors and should be evaluated on a case-by-case basis.4 (See Figures IA through 1D for atmospheric diffusion factors for an elevated release with fumigation.) b. No correction should be made for depletion of the effluent plume of radioactive iodine due to deposition on the ground, or for the radiological decay of iodine in transit. c. For the first 8 hours, the breathing rate of persons offsite should be assumed to be 3.47x 104 cubic meters per second. From 8 to 24 hours following the accident, the breathing rate should be assumed to be 1.75 x 10"4 cubic meters per second. After that until the end of the accident, the rate should be assumed to be 2.32 x 10-4 cubic meters per second. (These values were 1The effect on containment leakage under accident conditions of1 features provided to reduce the leakage of radioactive materials from the containment will be evaluated on an individual case basis. "2 In some cases, credit for mixing will be allowed; however, the amount of credit