Gas accumulation
Gas accumulation in safety related nuclear power plant systems has been known to cause water hammer, gas binding in pumps, and inadvertent relief valve actuation that may damage pumps, valves, piping, and supports and may lead to loss of system operability. SRP Sections 5.4.7, 6.3 and 6.5.2 do not provide sufficient guidance to ensure that the gas accumulation concerns raised in GL 2008-01 are adequately addressed in applications for certified designs or COLs filed under 10 CFR Part 52.
History
Instances of gas accumulation in safety related systems have occurred since the beginning of commercial nuclear power plant operation. The NRC has issued a number of Information Notices and Generic Letters (GL) on the subject. In January 2008, the NRC staff issued GL 2008-01 to comprehensively address gas accumulation issues in operating reactors. Prior to that, in March 2007, the NRC revised SRP Sections 5.4.7, "Residual Heat Removal System," 6.3, "Emergency Core Cooling System," and 6.5.2, "Containment Spray System." The SRP revisions included limited mention of gas accumulation concerns but did not include specific concerns to the extent covered in GL 2008-01. These include sources of gas, gas accumulation locations, determination of gas quantities, water hammer and acceptable gas quantity, pump operation and acceptable gas quantity and control of gas. In reviewing the current applications for certified designs and combined licenses (COL) filed under Title 10 of the Code of Federal Regulations, Part 52 (10 CFR Part 52), the NRC staff finds that the March 2007 SRP staff guidance does not provide sufficient guidance to adequately evaluate applicants’ treatment of gas accumulation issues as above.
Rationale
The NRC staff finds the current guidance insufficient to review certified design and COL applicants’ treatment of the gas accumulation concerns raised in GL 2008-01. In order to ensure compliance with Appendix A and Appendix B to 10 CFR Part 50, the following areas have been identified as needing additional guidance:
- Potential Gas Accumulation Locations & Intrusion Mechanisms
- Pipe and Instrumentation Drawing (P&ID) and Isometric Drawing Confirmation
- Surveillance and Venting Procedures
See also