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
..
Page Last Reviewed/Updated Tuesday, March 09, 2021