Document: NRC Regulatory Guide
Document ID: 30181e34-3bc1-46b8-8de9-ef073c34bc13
Document Type: regulatory_guide
Title: Bypassed and Inoperable Status Indication for Nuclear Power Plant Safety Systems + HISTORY - HISTORY 10/2008 – DG-1205 , Proposed Revision 1 (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0821/ML082140114.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.47
CFR Part: 
CFR Title: 

Content:
ld affect a safety system. The decision to grant such permission should be based on knowledge of the operating status of the safety systems, the extent to which the activity will affect those systems, and whether that effect is permissible within the provisions of the license. Experience at operating plants, however, suggests that when the measures used to indicate inoperable status consist solely of administrative procedures, the operator is not always fully aware of the ramifications of each bypassed or inoperable component. Automatic indication display of any bypass or inoperability in a safety system supplements administrative procedures and aids the operator. Clause 5.16 of IEEE Std 338-1987 states that “indication should be provided in the control room if a portion of the safety system is inoperable or bypassed. Systems that are frequently placed in bypass or inoperative condition for the purposes of testing should have automatic indication.” Digital computer-based I&C systems make extensive use of self-testing. Digital computer-based I&C systems are more prone to different kinds of failures than traditional analog systems. Self-testing and watchdog timers should reduce the time to detect and identify failures. Computer self-testing is most effective at detecting random hardware failures. A bypass and inoperable status indication system should include a capability of assuring its operable status during normal plant operation to the extent that the indicating and annunciating function can be verified. However, the bypass and inoperable status indication system should be designed to avoid erroneous bypass indications. If the use of self-testing in digital computer-based I&C systems causes a protective action of some part of a safety system to be bypassed or deliberately rendered inoperative, then this fact should be automatically indicated in the control room. With regards to surveillance testing, if the protective action of some part of a protection or