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Information Notice No. 89-15: Second Reactor Coolant Pump Shaft Failure at Crystal River
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 February 16, 1989 INFORMATION NOTICE NO. 89-15: SECOND REACTOR COOLANT PUMP SHAFT FAILURE AT CRYSTAL RIVER Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: This information notice is being provided to alert addressees to indications of potential sudden failure of a reactor coolant pump (RCP) shaft. It is expected that recipients will review the information for applicability to their facil-ities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC require-ments; therefore, no specific action or written response is required. Description of Circumstances: On January 18, 1989, the Crystal River Unit 3 plant experienced a loop "A" low coolant flow alarm and an automatic power runback from 75 percent of full power to 64 percent of full power. Operators noted a drop in the "A" reactor coolant pump motor current from 90 percent to 25 percent. A preliminary review of the vibration and other coastdown data suggests that the pump shaft and the impeller have decoupled. This may be due either to fracture of the shaft itself or to failure of the cap screws and drive pins which hold the impeller to the shaft. The root cause of the failure will be more fully known when the pump is disassembled. The pump was manufactured by Byron Jackson. Both the low flow alarm and motor current decreases were also symptomatic of the previous pump shaft failure in 1986.* During the 1986 event, pump vibration remained high after the shaft break, indicating interference to motor spin at the fracture interface, and after the pump was tripped, the pump motor rotation stopped within a few seconds. The licensee believes that the lack of pump vi-bration and the longer post trip motor coastdown after the recent pump failure indicate a lack of interference at the fracture interface. ___________________________ *The 1986 failure is described in Information Notice 86-19, "Reactor Coolant Pump Shaft Failure at Crystal River." 8902100265 . IN 89-15 February 16, 1989 Page 2 of 3 Following the 1986 pump shaft failure, the licensee replaced the shafts in all four coolant pumps. Two of the reactor coolant pumps received new shafts of a different material (Alloy A-479 XM-19) and a different design. The new design did not contain the groove that was determined to be the crack initiation location for the 1986 fracture. One pump was fitted with a new shaft of the same material as that of the shaft that failed (Alloy A-286), but the licensee believes the new shaft did not contain a groove. The "A" pump was fitted with a new shaft of the same design and material as that of the shaft that had failed previously. In addition, following the 1986 failure, the licensee refurbished and improved the vibration monitoring equipment on each coolant pump and located vibration monitor alarms on the main control panel. The reactor coolant pump vibration is continuously monitored by the Bently-Nevada Dynamic Data Manager System. This system monitors the motor casing accelerometer inputs along with the pump shaft proximity probes (X & Y, Keyphasor) on all four reactor coolant pumps. Increased vibration on the "A" RCP was noted in November 1988. A review of the vibration monitoring data revealed a loss of rotor stiffness. The vibration monitor vendor (Bently-Nevada) believed that the pump shaft had cracked. The licensee examined the "A" RCP shaft with ultrasonic testing equipment and concluded that the shaft had not cracked. Cracks in the lower motor housing support were identified and corrected. After repair of the lower motor housing support, the licensee reported normal pump vibration. However, pump vibrations of varying magnitudes were again noted shortly thereafter. The ultimate objective of the vibration monitoring system is to correlate the vibration data with crack growth and to provide an early warning such that a shaft break can be avoided. The program depends on an early detection of shifts in steady state values of maximum shaft displacement, first and second harmonics and corresponding phase angles. Since shifts in the second harmonic and its phase angle are sensitive indicators of changes in shaft stiffness and crack growth, particular attention to these parameters is important. Additional RCP shaft failures are discussed in Information Notice 85-03, "Separation of Primary Reactor Coolant Pump Shaft and Impeller," and its supplement. . IN 89-15 February 16, 1989 Page 3 of 3 No specific action or written response is required by this information notice. If you have any questions about this matter, please contact one of the technical contacts 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 Contacts: Jai Rajan, NRR (301) 492-0917 Walton Jensen, NRR (301) 492-1190 Attachment: List of Recently Issued NRC Information Notices . Attachment IN 89-15 February 16, 1989 Page 1 of 1 LIST OF RECENTLY ISSUED NRC INFORMATION NOTICES _____________________________________________________________________________ Information Date of Notice No._____Subject_______________________Issuance_______Issued to________ 89-14 Inadequate Dedication 2/16/89 All holders of OLs Process for Commercial- or CPs for nuclear Grade Components Which power reactors. Could Lead to Common Mode Failure of a Safety System 89-13 Alternative Waste Management 2/8/89 All holders of NRC Procedures in Case of Denial specific licenses. of Access to Low-Level Waste Disposal Sites 89-12 Dose Calibrator Quality 2/9/89 All NRC medical Control licensees. 89-11 Failure of DC Motor-Operated 2/2/89 All holders of OLs Valves to Develop Rated or CPs for nuclear Torque Because of Improper power reactors. Cable Sizing 89-10 Undetected Installation 1/27/89 All holders of OLs Errors In Main Steam Line or CPs for BWRs. Pipe Tunnel Differential Temperature-Sensing Elements at Boiling Water Reactors. 89-09 Credit for Control Rods 1/26/89 All holders of OLs Without Scram Capability or CPs for test and in the Calculation of the research reactors. Shutdown Margin 89-08 Pump Damage Caused by 1/26/89 All holders of OLs Low-Flow Operation or CPs for nuclear power reactors. 89-07 Failures of Small-Diameter 1/25/89 All holders of OLs Tubing in Control Air, Fuel or CPs for nuclear Oil, and Lube Oil Systems power reactors. Which Render Emergency Diesel Generators Inoperable _____________________________________________________________________________ OL = Operating License CP = Construction Permit ..
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