United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No.80-07 – Pump Shaft Fatigue Cracking

                                                            SSINS No.:  6870
                                                            Accession No.: 
                                                            7912190675 

                                UNITED STATES
                        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 
centrifugal pumps. 

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 
2-3 ft-lbs) 

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. 

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Information Notice No. 80-07                            February 29, 1980 
                                                           Page 2 of 2 

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.

Page Last Reviewed/Updated Tuesday, November 12, 2013