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UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 30, 1989 Information Notice No. 89-55: DEGRADATION OF CONTAINMENT ISOLATION CAPABILITY BY A HIGH-ENERGY LINE BREAK Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice is being provided to alert addressees to the potential for a high-energy line break (HELB) inside containment causing the failure of piping in a closed system thereby negating one containment isolation barrier and leaving the plant with only a single containment isolation valve to miti- gate potential radiological releases. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: Millstone Unit 1 is a boiling-water reactor with a Mark I containment. The original design basis for isolation of the reactor building closed cooling water (RBCCW) system required a single barrier outside containment. That is, one check valve was provided in the inlet line to containment while a single remote, manually operated block valve was provided in the return line from containment. Recently the licensee postulated a scenario in which a recirculation line failure (a HELB) inside containment could cause loss of the RBCCW system integrity. To maintain containment integrity, both RBCCW system isolation valves would have to close; therefore, a single failure of either of these valves would result in the loss of containment integrity. With failure of an RBCCW isolation valve to close, it would be possible for the containment atmosphere to displace water in the RBCCW piping and ultimately vent to the reactor building. Thus, an unanalyzed condition existed which involved poten- tial degraded containment integrity caused by HELBs. 8906260403 . IN 89-55 June 30, 1989 Page 2 of 2 Discussion: The RBCCW system was originally considered to be a closed system inside con- tainment and, therefore, part of the containment isolation provisions. That is, the closed system was a supplement to the single isolation valve provided in both the inlet piping and the outlet piping. (Note that the configuration of a single check valve outside containment in the inlet line of the RBCCW system was licensed prior to the formal issuance of the General Design Criteria for Nuclear Power Plants, Appendix A to 10 CFR Part 50 (GDC) and it does not meet the current implementation of General Design Criterion 57 "Closed System Isolation Valves.") The original safety evaluation did not consider that dynamic effects of HELBs could impact RBCCW system isolation integrity. As a result, the RBCCW system is more properly viewed as a system open to the containment atmosphere under the postulated accident scenario. As such, the applicable regulatory requirements are given by GDC 56 "Primary Containment Isolation" and TMI Action Plan Item II.E.4.2, "Containment Isola- tion Dependability". It is important that licensees recognize the need to assure adequate protection of systems within containment from pipe whip and jet impingement effects of HELBs when containment integrity must be maintained during and after a postulated accident consistent with the single failure criterion. No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the technical contact listed below or the Regional Administrator of the appropriate regional office. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contact: J. Carter, NRR (301) 492-1194 Attachment: List of Recently Issued NRC Information Notices . Attachment IN 89-55 June 30, 1989 Page 1 of 1 LIST OF RECENTLY ISSUED NRC INFORMATION NOTICES _____________________________________________________________________________ Information Date of Notice No._____Subject_______________________Issuance_______Issued to________ 89-54 Potential Overpressurization 6/23/89 All holders of OLs of the Component Cooling or CPs for nuclear Water System power reactors. 89-53 Rupture of Extraction 6/13/89 All holders of OLs Steam Line on High or CPs for nuclear Pressure Turbine power reactors. 88-46, Licensee Report of 6/8/89 All holders of OLs Supp. 3 Defective Refurbished or CPs for nuclear Circuit Breakers power reactors. 89-52 Potential Fire Damper 6/8/89 All holders of OLs Operational Problems or CPs for nuclear power reactors. 89-51 Potential Loss of Required 5/31/89 All holders of OLs Shutdown Margin During or CPs for nuclear Refueling Operations power reactors. 88-88, Degradation of Westinghouse 5/31/89 All holders of OLs Supp. 1 ARD Relays or CPs for nuclear power reactors. 89-50 Inadequate Emergency 5/30/89 All holders of OLs Diesel Generator Fuel or CPs for nuclear Supply power reactors. 89-49 Failure to Close Service 5/22/89 All holders of OLs Water Cross-Connect or CPs for nuclear Isolation Valves power reactors. 89-48 Design Deficiency in the 5/22/89 All holders of OLs Turbine-Driven Auxiliary or CPs for nuclear Feedwater Pump Cooling power reactors. Water System 89-47 Potential Problems With 5/18/89 All holders of OLs Worn or Distorted Hose or CPs for nuclear Clamps on Self-Contained power reactors and Breathing Apparatus fuel facilities. _____________________________________________________________________________ OL = Operating License CP = Construction Permit ..
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