Document: NUREG-0800
Document ID: 6c5a07e2-91cf-49ae-a450-62551ed6bcef
Document Type: srp
Title: CONTAINMENT ISOLATION SYSTEM
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052340703.pdf
Revision Date: 2023-06
Chapter: 6
Section ID: 6.2.4
CFR Part: 
CFR Title: 

Content:
ic isolation valves should take the posi- tion that provides greater safety. The position of an isolation valve for normal and shutdown plant operating conditions and postaccident condi- tions.depends on the fluid system function. If a fluid system does not have a postaccident function, the isolation valves in the lines should be automatically closed. For engineered safety features or.engineered safety feature-related systems, isolation valves in the lines may remain open or be opened. The position of an isolation valve in the event of power failure to the valve operator should be the "safe" position. Normally this position would be the postaccident valve position. For lines equipped with motor-operated valves, a loss of actuating power will leave the affected valve in the "as is" position, which may be the open position; however, redundant isolation barriers assure that the isolation function for the line is satisfied. All power operated isolation valves should have position indication in the main control room. 6.2.4-5 Rev. 2 - July 1981 k. To improve the reliability of the isolation function, which is addressed in General Design Criterion 54, Item II.E.4.2 of NUREG-0737 and NUREG-0718 requires that the containment setpoint pressure that initiates containment isolation for nonessential penetrations be reduced to the minimum value compatible with normal operating conditions. 1. There should be diversity in the parameters sensed for the initiation of containment isolation to satisfy the requirement of General Design Cri- terion 54 for reliable isolation capability. m. To improve the reliability of the isolation function, which is addressed in General Design Criterion 54, system lines which provide an open path from the containment to the environs (e.g., purge and vent lines which are addressed in Item II.E.4.2 of NUREG-0737'and NUREG-0718) should be equipped with radiation monitors that are capable of isolating these lines upon a high radiation signal. A high