Document: NUREG-0800
Document ID: 949ca18d-b0e4-4b54-9ca9-fdb657988111
Document Type: srp
Title: Revision 5 - March 2007
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0706/ML070660170.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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Content:
be provided for the containment isolation function. For plants with digital-computer-based ESFAS, signal diversity can be confirmed by review of the licensee/applicant's diversity and defense-in-depth analysis. Reopening of isolation valves should be performed on a valve-by-valve or line-by-line basis, provided that electrical independence and the single-failure criterion for the ESFAS functions continue to be satisfied. Ganged reopening of containment isolation valves is not acceptable. Regulatory Guide 1.105, "Setpoints for Safety-Related Instrumentation," and SRP BTP 7-12 provide guidance on establishing and maintaining instrument setpoints. For isolation of nonessential containment penetrations, however, the trip setpoint should be established by adding measurement error terms to the highest pressure value expected during normal plant operations, rather than subtracting error terms from an accident analysis analytical limit. The setpoint should also be shown to be low enough to assure protection system functions are actuated before analytical limits are reached. The pressure setpoint selected should be far enough above the maximum observed, or expected, pressure inside containment during normal operation so that inadvertent containment isolation does not occur during normal operation from instrument drift or fluctuations due to the accuracy of the pressure sensor. The containment pressure history during normal operation should be used as a basis for arriving at an appropriate minimum pressure setpoint for initiating containment isolation. Applicants for new licenses should use pressure history data from similar plants that have operated for more than one year, if possible, to arrive at a minimum containment setpoint pressure. Containment purge lines and other penetrations that provide a path to the environment should be isolated on a high radiation signal as one of the diverse isolation functions. The review of these design provisions to address 10 CFR