Document: NRC Regulatory Guide
Document ID: 4d46a966-d280-43da-9b03-8b0abe7b29ce
Document Type: regulatory_guide
Title: Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2120/ML21204A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.183
CFR Part: 
CFR Title: 

Content:
by this guide, provided that such values remain relevant to the particular accident, release characteristics that affect plume rise, its release points, and receptor locations. Licensees should ensure that any previously approved values remain accurate and do not include any misapplication of a methodology or calculational errors in the identified values. RG 1.145, “Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants,” issued November 1982 (Ref. 37), and the paper by Murphy and Campe (Ref. 34) document methodologies used in the past for determining χ/Q values. RG 1.145 and RG 1.194, “Atmospheric Relative Concentrations for Control Room Radiological Habitability Assessments at Nuclear Power Plants,” issued June 2003 (Ref. 38), should be used if the FSAR χ/Q values are to be revised or if values are to be determined for new release points or receptor distances or release characteristics that affect plume rise. In addition to calculating control room χ/Q values, the modeling methodology outlined in RG 1.194 may be modified to estimate offsite χ/Q values at offsite boundaries out to distances of 1,200 m if using the procedures consistent with the Regulatory Positions in Part C of RG 1.145. EAB χ/Q values are determined for the limiting 2-hour period within a 30-day period following the start of the radioactivity release. Control room χ/Q values are generally determined for initial averaging periods of 0–2 hours and 2–8 hours, and the LPZ χ/Q values are generally determined for an initial averaging period of 0–8 hours. The control room and LPZ χ/Q values are also generally determined for averaging periods of 8–24 hours, 24–96 hours, and 96–720 hours. The source term defined in TID-14844 assumes that the entire source term is instantaneously released into the containment atmosphere. Therefore, the maximum release rate coincides with the most conservative 0–2 hour χ/Q value. In contrast, the