Information Notice No.80-07 – Pump Shaft Fatigue Cracking
SSINS No.: 6870
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
February 29, 1980
Information Notice No. 80-07
PUMP SHAFT FATIGUE CRACKING
On October 9, 1979, the Tennessee Valley Authority (TVA) reported to NRC
that low-stress high-cycle fatigue cracks had been found in two
non-safety-related feedwater pumps at their Browns Ferry BWR facility. One
pump had been operated for approximately 20,000 hours and the other for
approximately 28,000 hours. TVA indicated that excessive vibration had been
experienced prior to detection of the cracks by ultrasonic and visual
inspection. TVA also reported that catastrophic failure had been
experienced with a boiler feed pump at their Paradise fossil unit. The TVA
failed pump shafts were of type 414 stainless steel. TVA plans to replace
the shafts with a type 17-4ph stainless steel.
A number of centrifugal charging/safety injection pump shaft failures have
been reported since 1977. The pumps of interest are the dual purpose
centrifugal pumps which are utilized for a normal charging function and in
the safeguard moce are aligned for high pressure borated coolant injection.
These pumps were procured by Westinghouse from the Pacific Pump Division of
Dresser Industries. The pump shaft material was supplied to Pacific Pump by
the Carpenter Technology Corporation.
Westinghouse and Pacific Pump have been conducting an on-going investigative
program since 1977 to resolve the shaft failure problem. Results from the
program suggested that the causes of the shaft failures could be related to
shaft material deficiencies, design and/or abnormal operation of the
Forty centrifugal charging/safety injection pump shafts fabricated from four
heats of A276 type 414 stainless steel bar were air cooled and tempered at
1000 F. The above stated heat treating practice resulted in shafts with low
toughness (Charpy "V" notch energies - Longitudinal 6-10 ft-lbs, transverse
Corrective actions taken to reduce the incidence of charging pump/safety
injection pump failure have included:
1. Replacement of the type 414 low toughness stainless steel material.
Replacement material for the charging pump shafts is type 414 stainless
steel, oil quenched and tempered at 1150-1200 F. Some of the air
cooled shafts have been re-tempered at 1150 F.
Information Notice No. 80-07 February 29, 1980
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2. Design modifications to the shaft to reduce stress raisers. The
modifications included increasing the fillet radius in the split ring
groove, increasing the thread root in the locknut section of the shaft
and the use of formed cutting tools during fabrication.
3. A review of the operating history of the dual purpose centrifugal pumps
indicated abnormal operation to be a potentially significant
contributor to the early failure of the pump shafts. Abnormal
operation includes any condition that results in partial or complete
loss of fluid in the pump or continued operation under high vibration
conditions caused by misalignment or other installation problems.
Westinghouse Nuclear Service Division's Technical Bulletins 77-9, 78-1
Rev. 1 and 79-6 provide guidance for monitoring of and limits for pump
vibration as well as guidance for pump operation and maintenance.
Ten additional Safety Injection Pumps manufactured by Pacific Pump were
identified as having shafts with the same material and heat treatment as the
failed charging/safety injection pump shafts. These ten additional pumps
are of a different design and provide for medium pressure boron injection in
the safeguard mode but do not function in normal operation.
Licensees are encouraged to review the materials utilized for and the design
of shafts in safety-related pumps and non-safety-related pumps which could
affect safety-related system performance. Particular attention should be
paid to abnormal operating conditions which could include high stress in the
pump shafts, susceptibility of materials to crack initiation and growth, and
the presence of stress raisers.
This Information Notice is provided as an early notification of a possibly
significant matter that is still under review by the NRC staff. It is
expected that recipients will review the information for possible
applicability to their facility. No specific action or response is
requested at this time. If you have any questions regarding this matter,
please contact the Director of the appropriate NRC Regional Office.
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