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Information Notice No. 89-53: Rupture of Extraction Steam Line on High Pressure Turbine
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 13, 1989 Information Notice No. 89-53: RUPTURE OF EXTRACTION STEAM LINE ON HIGH PRESSURE TURBINE Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice is being provided to alert addressees to a potential generic problem involving erosion in carbon steel piping in secondary plant systems. 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: On April 18, 1989, a reactor trip from 100 percent power on high pressurizer pressure occurred at Arkansas Nuclear One, Unit 2 (ANO-2) as a result of a main turbine trip. The turbine tripped when steam escaping from a ruptured high pressure steam extraction line caused a spurious actuation of the electrical hydraulic control system's solenoid operated trip valve. The pipe rupture occurred about 3 inches below the weld which joins a 12-foot section of straight 14-inch diameter pipe to a second-stage extraction nozzle on the high pressure turbine. The pipe wall at the rupture was worn to a thickness of about 1/32-inch (nominal wall thickness is about 3/8 inches). The 180 degree "fishmouth" rupture was about 3 inches wide. This straight run of 14-inch diameter pipe terminates at an elbow. This elbow was replaced during the last outage because of erosion induced wall thinning. The elbow degradation was discovered as a result of the licensee's secondary system surveillance program for wall thinning. However, the recently failed pipe and those of similar geometries were not included in the surveillance samples. In addition, the degraded condition of the pipe was not detected during replacement of the elbow. 8906070273 . IN 89-53 June 13, 1989 Page 2 of 2 Discussion: The high pressure turbine at ANO-2 has two 14-inch second-stage extraction steam lines. Ultrasonic testing of the second 14-inch second-stage extraction steam line identified similar wall thinning conditions. The piping for both extraction steam lines has been replaced. The root cause assessment of this erosion phenomenon has not been finalized. The licensee currently believes that the flow turbulence necessary to induce erosion was likely set up by the geometry of the nozzle-to-pipe connection. The outside diameters of the nozzle and pipe were essentially equal; however, the thickness of the nozzle wall was greater than the thickness of the pipe wall. This resulted in a mismatch between the inside diameter of the nozzle and the inside diameter of the pipe. The expansion of the steam as it exited the nozzle is postulated to have caused the accelerated erosion of the pipe. NRC Information Notice 89-01 "Valve Body Erosion," dated January 4, 1989, and NRC Information Notice 88-17, "Summary of Responses to NRC Bulletin 87-01, 'Thinning of Pipe Walls in Nuclear Power Plants'," dated April 22, 1988, provide additional discussion on erosion of piping systems. 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: L. Gilbert, Region IV (817) 860-8156 Attachment: List of Recently Issued NRC Information Notices . Attachment 1 IN 89-53 June 13, 1989 Page 1 of 1 LIST OF RECENTLY ISSUED NRC INFORMATION NOTICES _____________________________________________________________________________ Information Date of Notice No._____Subject_______________________Issuance_______Issued to________ 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. 89-46 Confidentiality of 5/11/89 All holders of Exercise Scenarios licenses for fuel cycle facilities and byproduct material licensees having an approved emergency response plan. _____________________________________________________________________________ OL = Operating License CP = Construction Permit ..
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