Document: NRC Regulatory Guide
Document ID: cf1737d6-2a8a-4765-aaf5-f5f2a617ef91
Document Type: regulatory_guide
Title: Design of Main Steam Isolation Valve Leakage Control Systems for Boiling Water Reactor Nuclear Power Plants
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740263.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.96
CFR Part: 
CFR Title: 

Content:
ected by the subject leakage. The long-term dose in the low population zone, however, is affected for uncontrolled Isolation valve leakage rates typical of current technical specification values. Thus the staff has concluded that a fully automatic quick-acting leakage control system Is not required to meet the system objectives. A manually initiated leakage control system capable of being actuated within about 20 minutes of an accident requiring .use of the system would be accept able. It should be noted that any leakage from the stem packing of the outboard isolation valve would contribute to the 2-hour dose, since in most designs such leakage would escape to the turbine building and the environ ment via the steam tunnel. Reduction and control of steam packing leakage or other direct leakage to the steam tunnel from the outboard isolation valve should be a design objective of the leakage control system or of other systems provided for this purpose. C. REGULATORY POSITION The isolation function of the main steam isolation valves in boiling water reactor plants should be supple mented by a leakage control system (LCS). An accept able approach for such a leakage control system is provided by the following design basis: 1. The leakage control system and any necessary subsystems, including the source of any sealing fluid if a fluid seal type of system is used, should be designed in accordance with Seismic Category I and Quality Group B requirements, with the exception of any portion of LCS piping that connects to main steam system piping between inner and outer containment isolation valves of the main steam system for either single- or dual-barrier containment structures. Such piping, up to and including the first isolation valve in the LCS piping, should be designed in accordance with Seismic Category I and Quality Group A requirements supplemented by Appen dix A of this guide. 2. The LCS (and any necessary subsystems) should be capable of performing its safety