Resolution of Generic Safety Issues: Issue 16: BWR Main Steam Isolation Valve Leakage Control Systems ( NUREG-0933, Main Report with Supplements 1–34 )
This issue involves a potential deficiency in the ability to control leakage past the main steam isolation valves (MSIV) in BWR plants. Requirements for MSIV leakage control systems outlined in Regulatory Guide 1.9621 were developed as a result of the excessive MSIV leakage experience at operating plants. For events in which steam line isolation is required, MSIVs are designed to prevent the uncontrolled release of radioactivity from the reactor vessel or containment building to the environment. The leakage control system will prevent the direct release of untreated leakage past the MSIVs when isolation of the reactor system and the containment is required. Initial operating experience with leakage control systems suggests that they are prone to failures as stated in NUREG-0705.44
Item C-8, "Main Steam Line leakage Control Systems," also deals with the design and operability of MSIV leakage control systems. Since both of these issues are identical in scope, Issue 16 has been combined with Item C-8, which is prioritized in Section 2 of this report.