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:
current BWR plants are provided with dual quick-closing isolation valves. These valves function to *Lines indicate substantive changes from previous Issue. isolate the reactor system in the event of a break in a steam-line outside the primary containment, a design basis LOCA, or other events requiring containment isolation. In the case of a steam line break, the isolation valves would terminate the blowdown of reactor coolant in sufficient time to prevent an uncontrolled release of radioactivity from the reactor vessel to the environment. In the case of a LOCA, the valves would isolate the reactor from the environment and prevent the direct release of fission. products from the containment. The valves are part of the reactor coolant pressure boundary. As such, they are Quality Group A compo nents and their integrity must be maintained by strict inservice inspection and testing requirements. However, operating experience has indicated that degradation has occasionally occurred in the leak-tightness of main steam isolation valves, and the specified low leakage require ments have not always been maintained. The staff has considered the need to provide addi tional features to ensure the low-leakage characteristics of the main steam isolation valves in the event of a postulated design-basis loss-of-coolant accident.1 The use of a leakage control system would reduce direct untreated leakage from the isolation valves when isola tion of the primary system and the containment is required. The results of staff analyses have indicated that calculated doses resulting from the maximum leakage lln its letters on the construction permit reviews of the Duane Arnold and Shoreham plants (December 18, 1969) and the James A. FitzPatrick plant (January 27, 1970), the Advisory Committee on Reactor Safeguards noted that additional features to control main steam Isolation valve leakage should be considered. USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission.