Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
rom the plant shown in Table 2. 1.1 Exemption Criteria for Stationary Sources Chemicals stored or situated at distances greater than 5 miles from the plant need not be considered because, if a release occurs at such a distance, atmospheric dispersion will dilute and disperse the incoming plume to such a degree that either toxic limits will never be reached or there would be sufficient time for the control room operators to take appropriate action. In addition, small quantities (i.e., less than 10 kg) for laboratory use in the plant can be exempt. In addition, the maximum allowable inventory in a single container should be stored at specified distances beyond 0.1 km from the CR (e.g., its fresh air inlet) and varies according to the distance and the CR type, as specified by CR air change per hour (ACH) rates in Table 2. If there are several chemical containers, the evaluation normally considers only the failure of the largest container unless the containers are interconnected in such a manner that failure of a single container could cause a release from several containers. 1.2 Screening Criteria for Mobile Source Chemicals For the chemicals in Table 1, known or projected to be present in either stationary form or in mobile form by rail, water, or road routes within an 8 km radius of a nuclear power plant, a CR habitability evaluation may be considered based on both Table 1 and Table 2 screening values. The Table 2 variables were established under Category F Pasquill stability class2 and at a fixed 50-mg/m3 concentration value. They are adjustable parameters needed for determining the total quantity (i.e., the minimum chemical’s weight) of the mobile sources and the seven tiers of incremental distance described in Table 2. The first column of Table 2 contains radii between 0.3 and 5 miles from the CR, and the three columns to the right list the calculated weights for three ACH values. 2. “Pasquill stability class” is a meteorological classification method for