United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-15: Second Reactor Coolant Pump Shaft Failure at Crystal River

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                February 16, 1989

                              CRYSTAL RIVER


All holders of operating licenses or construction permits for nuclear power


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."

.                                                            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 

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 

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 

.                                                            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 
Page Last Reviewed/Updated Friday, May 22, 2015