Document: NRC Regulatory Guide
Document ID: c458fb43-5ee6-4e14-a33d-808ec974115a
Document Type: regulatory_guide
Title: Instrument Lines Penetrating Primary Reactor Containment + HISTORY - HISTORY 09/2009 – DG-1225 , Proposed Revision 1 Prior to the issuance of Revision 1, RG 1.11 was entitled "Instrument Lines Penetrating Primary Reactor Containment (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0909/ML090970530.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.11
CFR Part: 
CFR Title: 

Content:
an instrument line failure during normal operation being substantially below the guidelines of 10 CFR Part 100, “Reactor Site Criteria” (Ref. 2) and GDC 19, “Control Room.” The rate of coolant loss from an instrument line rupture outside containment can be reduced by including flow restrictions, such as orifices, in the instrument line. These flow restrictions should be sized to reduce the potential rate of coolant loss to the extent practical without adversely affecting the capability of the connected instruments to perform their functions. In particular, the response time of connected instruments must remain acceptable, and the potential for obstruction of the flow restrictions must be kept very low. It is also desirable that instrument line flow restrictions be located as close as practical to where the instrument line connects to the reactor coolant system to reduce potential blowdown inside of the primary containment. If the conditions presented in the two preceding paragraphs are satisfied, a single automatically operated isolation valve (i.e., no dependence on operator actions) or one that an operator can manually operate from a remote location (e.g. in the control room or in another appropriate location) can provide acceptable capability for isolating instrument lines that penetrate the primary reactor containment. A DG-1225, Page 3 self-actuated excess-flow check valve is acceptable as an automatically operated valve if it has the other features needed for this service. It is desirable that the isolation valve be located outside containment for greater accessibility. Power-operated isolation valves that provide a safety function in both the open and closed position would likely afford greater safety if designed to remain “as is” (usually open) if power is lost. Not having an isolation valve inside containment makes it even more important that there be a high degree of assurance that the instrument line from the containment out to and including