Document: NRC Regulatory Guide
Document ID: 0cfc3978-32da-4370-9f31-8a3547d82846
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Fuel Handling Accident in the Fuel Handling and Storage Facility for Boiling and Pressurized Water Reactors (Rev. 0)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0833/ML083300022.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.25
CFR Part: 
CFR Title: 

Content:
lt Inhalation Thyroid Dose Conversion Factors IODINE ISOTOPE CONVERSION FACTOR (R) (RADS/CURIE INHALED) 131 1.48 × 106 132 5.35 × 104 133 4.0 × 105 134 2.5 × 104 135 1.24 × 105 b. The assumptions relative to external whole body dose approximations are: (1) The receptor is located at a point on or beyond the site boundary where the maximum ground level concentration is expected to occur. (2) External whole body doses are calculated using “Infinite Cloud” assumptions, i.e., the dimensions of the cloud are assumed to be large compared to the distances that the gamma rays and beta particles travel. The dose at any distance from the reactor is calculated based on the maximum ground level concentration at that distance. For an infinite uniform cloud containing χ curies of beta radioactivity per cubic meter, the beta dose rate in air at the cloud center is:11 χ E 457 .0 D β β = ′∞ Where : ∞′ D β = beta dose rate from an infinite cloud (rad/sec) β E = average beta energy per disintegration (MeV/dis) χ = concentration of beta or gamma emitting isotope in the cloud (curie/m3) Because of the limited range of beta particles in tissue, the surface body dose rate from beta emitters in the infinite cloud can be approximated as being one-half this amount or: χ E 23 .0 D β β = ′∞ For gamma emitting material the dose rate in tissue at the cloud center is: χ E 507 .0 D γ γ = ′∞ 11 Meteorology and Atomic Energy–1968, Chapter 7. RG-1.25, Page 8 Where : ∞′ D γ = gamma dose rate from an infinite cloud (rad/sec) γ E = average gamma energy per disintegration (MeV/dis) However, because of the presence of the ground, the receptor is assumed to be exposed to only one-half of the cloud (semi-infinite) and the equation becomes: χ E 25 .0 D γ γ = ′ Thus, the total beta or gamma dose to an individual located at the center of the cloud path may be approximated as: ψ E 25 .0 D or ψ E 23 .0 D γ γ β β = = ∞ Where ψ is the concentration time