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:
s against the types of accidental releases discussed in Section 3.2 above, the plant design should include features to: (1) provide capability to detect such releases; (2) isolate the CR if there is a release; (3) make the CR sufficiently leak tight; and (4) provide equipment and procedures for ensuring that the CR operators have access to breathable air, proper PPE, or both. Provisions that are adequate for the large, instantaneous release should also provide protection against the low-leakage-rate release. Section 3.4 provides the guidance related to making the CR sufficiently leak tight. The implementation of chemical safety and protection measures may be excluded if the detailed evaluation of CR habitability shows that the highest concentration predicted in the CR is below the IDLH value. Otherwise, licensees may select and implement specific protection measures based on the design features of their facilities. DG-1387, Page 12 4.1 Detection System The detection system should be able to detect and signal a concentration level that is significantly lower than the IDLH value, for example, a concentration level of 5 ppm for chlorine with an IDLH value of 10 ppm. The detection system should be qualified for all expected environments, including severe environments. The system should also be designated as seismic Category I and be qualified as such in accordance with the guidance in the second paragraph of Section 4.2 to address this issue. The installation of the detectors should ensure that they are protected from adverse temperature effects. The manufacturer’s guideline for maintenance, testing, and calibration, as well as adjustment to such guideline made by licensees, are acceptable provided they follow sound engineering practices and are compatible with the proposed application. If neither toxic information nor detection instruments are available, human detection, such as unpleasant smell, burning odor, irritated eyes, and choking, may be useful as a warning