Document: NUREG-0800
Document ID: 11a2be5f-50e6-47c7-beee-25b5049ab4bb
Document Type: srp
Title: REACTOR TRIP SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350474.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.2
CFR Part: 
CFR Title: 

Content:
e properly isolated to ensure that no credible failure at the output of an isolation device shall prevent the associated protective channel from meeting performance requirements." Examples of credible failures at the output of isolation devices are provided in Paragraph 4.7.2. b. Physical Independence To assure physical independence, the design bases governing the physical separation of redundant equipment including sensors, racks, panels, and control boards are evaluated in accordance with Repu- latory Guide 1.75, "Physical Independence of Electric Systems. This regulatory guide sets forth guidelines for the physical separa- tion of circuits and electrical equipment that is included In the RTS. This review should determine whether the RTS is located in seismic Category I structures. In certain designs, RTS sensors may be located in non-seismic Category I structures such as the turbine building. For these special cases, the reviewer must assure that the most reasonable installation of sensors and circuits is provided in regard to physical protection against damage from a seismic event. Further guidance is provided by Branch Technical Position ICSB 15. c. Single Failure Criterion To assess the RTS acceptability with regard to the single failure criterion, IEEE Std 379 and Regulatory Guide 1.53 are used. Again, as was the case for redundancy requirements, review for compliance with the single failure criterion may be reduced to an analysis in which it is determined that the system can perform all protective functions concurrent with failure of any sensor, logic circuitry and components that meet the single failure criterion. IEEE Std 279, paragraph 4.2, provides an additional example of single failure criterion application. With regard to power requirements, the RTS is required to assure that no failure of a power supply will result in maintaining power to the system such that the protective function (trip) of the RTS is 7.2-5 Rev. 2 - July 1981 negated (fail-safe