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:
n prevent isolation of the con- tainment. This is accomplished by reviewing the containment isolation provisions for each line penetrating the containment to determine that two isolation bar- riers in series are provided, and in conjunction with the PSB by reviewing the power sources to the valve operators. The CSB reviews the information in the SAR justifying containment isolation provisions which differ from the explicit requirements of General Design Criteria 55, 56, and 57. The CSB judges the acceptability of these contain- ment isolation provisions based on a comparison with the acceptance criteria given in subsection II of this SRP section. The CSB reviews the position of isolation valves for normal and shutdown plant operating conditions, postaccident conditions, and valve operator power failure conditions as listed in the SAR. The position of an isolation valve for each of the above conditions depends on the system function. In general, power- operated valves in fluid systems which do not have a postaccident safety function (nonessential systems, as defined in Regulatory Guide 1.141) should close automatically. In the event of power failure to a valve operator, the valve position should be the position of greater safety, which is normally the postaccident position. However, special cases may arise and these will be considered on an individual basis in determining the acceptability-of the pre- scribed valve positions. The CSB also ascertains from the SAR that all power-operated isolation valves have position indication capability in the main control room. The CSB reviews the signals obtained from the plant protection system to initiate containment isolation. In general, there should be a diversity of parameters sensed; e.g., abnormal conditions in the reactor coolant system, the secondary coolant system, and the containment, which generate containment isolation sig- nals. Since plant designs differ in this regard and many different combinations of signals