Document: NRC Regulatory Guide
Document ID: 14983af3-17d8-4f7b-866e-8d603a0f811c
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Loss of Coolant Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739614.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.4
CFR Part: 
CFR Title: 

Content:
sumed to be large compared to the distance that the gamma rays and beta particles travel. "Such a cloud would be considered an infinite cloud for a receptor at the center because any additional [gamma and] beta emitting material beyond the cloud dimensions would not alter the flux of [gamma rays and] beta particles to the receptor" (Meteorology and Atomic Energy, Section 7.4.1.1 -editorial additions made so that gamma and beta emitting material could be considered). Under these conditions the rate of energy absorption per unit volume is equal to the rate of energy released per unit volume. For an infinite uniform cloud containing X curies of beta radioactivity per cubic meter the beta dose in air at the cloud center is: SD4 = 0.457 fEX The effect on containment leakage under accident conditions of features provided to reduce the leakage of radioactive materials from the containment will be evaluated on an individual case basis. The surface body dose rate from beta emitters in the infinite cloud can be approximated as being one-half this amount (i.e., PD-1 = 0.23 Eox). For gamma emitting material the dose rate in air at the cloud center is: ^/DL = 0.507 E&x From a semi-infinite cloud, the gamma dose rate in air is: 7D = 0.25EYx Where 0 , = beta dose rate from an infinite cloudi(rad/sec) DI= gamma dose rate from an infinite cloud (rad/sec) E3 average beta energy per disintegration (Mev/dis) EF" = average gamma energy per disintegration (Mev/dis) X = concentration of beta or gamma emitting isotope in the cloud (curie/m 3) f. The following specific 'assumptions are acceptable with respect to the radioactive cloud dose calculations: (1) The dose at any distance from the reactor should be calculated based on the maximum concentration in the plume at that distance taking into account specific meteorological, topographical, and other characteristics which may affect the maximum plume concentration. These site related characteristics must be evaluated on an individual case