Information Notice 1994-76, Recent Failures of Charging/Safety Injection Pump Shafts: Difference between revisions
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{{#Wiki_filter:4 UNITED STATES | {{#Wiki_filter:4 UNITED STATES | ||
COMMISSION | NUCLEAR REGULATORY COMMISSION | ||
OFFICE OF NUCLEAR REACTOR REGULATION | |||
NOTICE 94-76: RECENT FAILURES OF CHARGING/SAFETY | WASHINGTON, D.C. 20555 October 26, 1994 NRC INFORMATION NOTICE 94-76: RECENT FAILURES OF CHARGING/SAFETY INJECTION | ||
PUMP SHAFTS | |||
==Addressees== | ==Addressees== | ||
All holders of operating | All holders of operating licenses or construction permits for pressurized | ||
licenses or construction | |||
permits for pressurized | |||
water rekctors. | water rekctors. | ||
==Purpose== | ==Purpose== | ||
The U.S. Nuclear Regulatory | The U.S. Nuclear Regulatory Commission (NRC) is issuing this information | ||
notice (IN)to alert addressees to recent failures of charging/safety | |||
injection pump shafts at facilities designed by the Westinghouse Electric | |||
Corporation (Westinghouse). It is expected that recipients will review the | |||
information for applicability to their facilities and consider actions, as | |||
appropriate, to avoid similar problems. However, suggestions contained in | |||
this information notice are not NRC requirements; therefore, no specific | |||
action or written response is required. | |||
Background 4 At Westinghouse-designed facilities, charging/safety injection pumps have | |||
4 ction flow to the reactor coolant | |||
three funct ons: (1) to deliver seal iri | |||
pumps, (2) .o eliver makeup water flcv ) the reactor coolant system, and | |||
and | (3) to deliver high head safety injection and recirculation flow to the | ||
reactor coolant system during and after a loss-of-coolant accident. During | |||
normal operation, one of two, or in some cases, one of three pumps is always | |||
in | in operation to deliver seal injection and makeup water flow. The loss of an | ||
inservice charging/safety injection pump creates a condition that may | |||
challenge reactor coolant pump seal integrity and, if makeup water flow is not | |||
restored in a timely manner, can result in a loss of coolant inventory. | |||
injection | On February 29, 1980, the NRC issued IN 80-07, "Pump Shaft Fatigue Cracking," | ||
to alert recipients to failures of charging/safety injection pump shafts that | |||
occurred during the 1970s. All of the charging/safety injection pump shafts | |||
addressed in that notice were procured by Westinghouse from the Pacific Pump | |||
Division of Dresser Industries (now Ingersoll-Dresser Pump Co). Actions taken | |||
at that time to correct the problem included design modifications, changes in | |||
the heat treatment of the shaft material, and the use of formed cutting tools | |||
during fabrication. Also, abnormal operation of the pumps such as operation | |||
with a partial or complete loss of fluid or with high vibration present was | |||
found to be a significant contributor to the shaft failures. The Westinghouse | |||
Nuclear Service Division issued Technical Bulletins TB-77-", TB-78-1, and | |||
TB-79-6, to provide guidance on vibration monitoring, operation and | |||
maintenance of the pumps, and allowable vibration amplitude limits. | |||
9410200153 4 gfokC 4 On P4R C AI 0+ic4V | |||
Iae | |||
vJ | |||
IN 94-76 October 26, 1994 Recent events indicate that failures of charging/safety injection pump shafts | |||
continue to be a problem. | |||
==Description of Circumstances== | |||
===Sequoyah Unit 1=== | |||
On February 18, 1991, plant operators for Sequoyah Unit 1 received indications | |||
pump | of decreasing flow and increasing motor current on charging pump IB-B. When | ||
efforts to restore full flow failed, they declared the pump inoperable and | |||
began shutting down the reactor as required by plant technical specifications. | |||
Charging pump lB-B had been in operation for several months and had shown no | |||
of the | previous signs of degradation. The licensee disassembled the pump, found | ||
heavy wear on the impeller shoulders and the balance drum, and found a | |||
280-degree crack in the shaft near the 11th stage impeller. Westinghouse | |||
analyzed the shaft and determined that the crack had been in the shaft for | |||
several months (possibly years) and that the rotating element was of the | |||
to | improved type referred to in IN 80-07. The licensee replaced +he rotating | ||
element and, after testing the pump successfully, returned the pump to | |||
service. [Licensee Event Report (LER) 50-327/91-003] | |||
Callaway | |||
On February 2, 1992, the Union Electric Company Callaway Plant was at power | |||
and charging pump B was in service to support operations. Plant operators | |||
and | received indications of zero flow in the charging header and at the reactor | ||
coolant pump seal. The operators placed charging pump A iA service to restore | |||
normal flow, and pump B tripped. Plant personnel inspected pump B and found | |||
that the shaft had sheared on the outboard end between the balance drum lock | |||
nut an, balance drum mating area. le licensee documented the failure in | |||
Suggestion Occurrence Solution 92-10 and replaced the failed shaft. | |||
Shearon Harris | |||
On March 18, 1993, operators at the Shearon Harris plant received indications | |||
of | of a shaft failure on charging/safety injection pump B. The indications were | ||
high motor current, low charging flow, and low pump discharge pressure. The | |||
operators secured pump B from service and placed pump A in service. Plant | |||
personnel uncoupled the pump from the motor and found that the pump shaft had | |||
sheared under the balancing drum lock nut. This was the same location as in | |||
three failures that occurred in the 1970s. (LER 50-400/93-005) | |||
===D.C. Cook Unit 2=== | |||
In July 1993, at D.C. Cook Unit 2, a charging pump failed a surveillance test | |||
when it could not deliver the required 454 liters [120 gallons] per minute. | |||
The rotating element in that pump had been installed in 1987. The licensee | |||
disassembled the pump and found a 10 centimeter [4 inch!, 180 degree | |||
circumferential crack through the number 9 impeller shaft keyway. Smaller | |||
cracks were found in two other impeller keyway areas. (LER 50-316/93-006) | |||
IN 94-76 October 26, 1994 Braidwood Unit 1 and Sequoyah Unit 2 The NRC staff has received information on two other recent failures of | |||
charging/safety injection pump shafts: (1) on September 15, 1993, at the | |||
Braidwood Nuclear Station Unit 1 (Braidwood), a charging/safety injection pump | |||
shaft sheared between the 10th and 11th stage impellers, and (2) on | |||
February 7, 1994, at Sequoyah Unit 2, a charging\safety injection pump shaft | |||
failed, resulting in a reactor shutdown as required by plant technical | |||
specifications. The licensee for Braidwood replaced the pump shaft and | |||
documented the failure on Problem Investigation Report 456-200-93-03600. The | |||
licensee for Sequoyah reported that the affected pump had not exhibited any | |||
indication of degradation before the shaft failure and that, similar to many | |||
of the other shaft failures, the shaft had failed near the location of the | |||
balancipng drum lock nut. (LER 50-328/94-002) | |||
Discussion | |||
Charging/safety injection pumps are important for normal plant operation and | |||
for core cooling during accidents such as a small break loss-of-coolant | |||
accident. Fcr most of the failure events described above, determination of | |||
of | the root cause of the failure was inconclusive. However, the operational | ||
histories of many of the failed shafts showed that they had been operated with | |||
void formation, gas entrainment, or other abnormal conditions within a few | |||
years of the failure. Operation of the pumps under these conditions may have | |||
caused or contributed to the later failure of the shafts. Avoiding operation | |||
of charging pumps under abnormal conditions and maintaining vibration levels | |||
within manufacturer recommendations may increase pump reliability. To | |||
increase the benefit of predictive maintenance programs, Wbstinghouse | |||
recommends that pump vibrations be monitored at least monthly; preferably, every two weeks. This is more frequent than is required by Section XI of the | |||
ASME B iler and Pressure Vessel Code. V'stinghouse will provide recommended | |||
vibration limits upon request. | |||
in | Industry experience in detecting shaft failures in pumps such as the reactor | ||
the pump | coolant pump and the recirculation pump is relevant to monitoring programs of | ||
charging/safety injection pumps because the precursors to shaft failure are | |||
similar. For those pumps, monitoring phase angles as well as monitoring | |||
vibration amplitude is considered to be important in detecting shaft | |||
degradation. These data are routinely trended by some licensees for detection | |||
of impending shaft failures. | |||
A description of the analyses and conclusions for some of the above events | |||
follows: | |||
Westinghouse evaluated seven possible root causes for the shaft failure at | |||
Callaway, including material defects, design flaws, errors in fabrication or | |||
processing, assembly or installation defects, off-design or unintended service | |||
conditions, maintenance deficiencies, and improper operation. Westinghouse | |||
concluded that the shaft failure was most likely the result of a 1986 event in | |||
pump | which the pump had experienced a loss of suction water flow for approximately | ||
seven minutes. The loss of suction flow increased the vapor-to-liquid ratio | |||
in the pump and caused a dynamic imbalance. Events of this type could cause | |||
K>~ | |||
IN 94-76 October 26, 1994 immediate pump failure or cause cyclic fatigue damage that could lead to | |||
premature shaft failure at a later date. | |||
A gas entrainment event that occurred on August 20, 1990, was determined to be | |||
the probable cause of the shaft failure at Sequoyah Unit 2. Problems caused | |||
by gas entrainment are discussed in NRC Information Notice 88-23, "Potential | |||
of | for Gas Binding of High-Pressure Safety Injection Pumps During a Design Basis | ||
Accident," and its supplements. | |||
Westinghouse considers an operational phenomenon, such as gas entrainment, may | |||
have led to the shaft failure at Shearon Harris, although the licensee found | |||
no evidence of gas pockets in the charging system. In May 1991 (two years | |||
before-the shaft failure), the licensee reported to the NRC that the charging | |||
system had been in a degraded condition during the previous operating cycle. | |||
and | An NRC Special Inspection Team reviewed the event and determined that several | ||
water hammer events could have occurred in the system as a result of | |||
weaknesses in the design of the alternate minimum flow system. The NRC issued | |||
IN 92-61, "Loss of High Head Safety Injection," and its supplement regarding | |||
that event. Another concern at Shearon Harris was the fact that the A and B | |||
charging/safety injection pumps are alternated at approximately 2-week | |||
intervals. Therefore, each pump is started about 25 to 30 times each year. | |||
of | Westinghouse believes the high number of starts also could contribute to early | ||
shaft failure. Problems associated with excessive pump starts include galled | |||
wear rings, increased vibration, and decreased pump performance. However, Westinghouse concluded that the available data were insufficient to directly | |||
link the failure of the shaft to the high number of pump starts. | |||
Although Westinghouse could not conclusively determine the root cause of the | |||
shaft failure at Shearon Harris, West 'nghouse made recommendations which could | |||
help pre-ent or detect impendine shaf fa;lures. Westinghou- suggested that | |||
the liceasee conduct a detailed review, of the possibility that gas could | |||
become entrained in the charging pump suction piping and the cross connczts to | |||
other systems. Westinghouse also recommended that, when the rotating element | |||
of the pump is replaced, consideration be given to installing the latest shaft | |||
design which has an improved one-piece balance drum lock nut. Westinghouse | |||
included recommendations for vibration monitoring in Westinghouse Technical | |||
Bulletin TB-79-6. Westinghouse has not specified a limitation on the number | |||
that pump | of pump starts but recommends that pump starts be minimized to maintain pump | ||
reliability. | |||
In addition to the industry actions described above, Westinghouse and the | |||
Westinghouse Owners Group (WOG) are implementing a program to address these | |||
pump shaft failures. The program includes: (1) a survey of WOG member | |||
utilities for pump service operating history data, (2) a pump design review, and (3) a shaft material enhancement evaluation. The program is intended to | |||
in | identify any weaknesses in design, maintenance, or operation of the pumps in | ||
shaft | order to improve shaft reliability. | ||
I S :. . | |||
. I | |||
IN 94-76 October 26, 1994 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
the technical contact listed below or the appropriate Office of Nuclear | |||
Reactor Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Project Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, RII | |||
(919) 362-0601 Attachment: | |||
List of Recently Issued NRC Information Notices | |||
daret4s C' | |||
Attachment | |||
IN 94-76 October 26, 1994 LIST OF RECENTLY ISSUED | |||
NRC INFORMATION NOTICES | |||
===Information Date of=== | |||
Notice No. Subject Issuance Issued to | |||
93-60, Reporting Fuel Cycle 10/20/94 All 10 CFR Part 70 | |||
Supp. 1 and Materials Events to fuel cycle licensees. | |||
the NRC Operations Center | |||
94-75 Minimum Temperature 10/14/94 All holders of OLs or CPs | |||
for Criticality pressurized-water reactors | |||
(PWRs). | |||
94-74 Facility Management 10/13/94 All U.S. Nuclear Regulatory | |||
Responsibilities for Commission Medical | |||
Purchased or Contracted Licensees. | |||
Services for Radiation | |||
Therapy Programs | |||
94-73 Clarification of Critical- 10/12/94 All fuel fabrication | |||
ity Reporting Criteria facilities. | |||
94-72 Increased Control Rod 10/05/94 All'holders of OLs or CPs | |||
Drop Time from Crud for pressurized water | |||
Buildup reactors | |||
94-71 Degradation of Scram 10/04/94 All holders of OLs or CPs | |||
Solenoid Pilot Valve for boiling water reactors | |||
Pressure and Exhaust (BWRs). | |||
Diaphragms | |||
94-70 Issues Associated with Use 09/29/94 All U.S. Nuclear Regulatory | |||
of Strontium-89 and Other Commission Medical | |||
Beta Emitting Radiopharma- Licensees. | |||
ceuticals | |||
94-69 Potential Inadequacies 09/28/94 All holders of OLs or CPs | |||
in the Prediction of Torque for nuclear power reactors. | |||
Requirements for and Torque | |||
of | Output of Motor-Operated | ||
Butterfly Valves | |||
94-68 Safety-Related Equip- 09/27/94 All holders of OLs or CPs | |||
ment Failures Caused by For nuclear power reactors. | |||
Faulted Indicating Lamps | |||
OL = Operating License | |||
= | CP = Construction Permit | ||
: . . I | |||
IN 94-76 October 26, 1994 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Original signed by | |||
Brian K. Grimes | |||
Brian K. Grimes, Director | |||
Division of Project Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, RII | |||
(919) 362-0601 Attachment: | |||
List of Recently Issued NRC Information Notices | |||
** See previous concurrence | |||
Mamn dated Mav 27 1994 OFFICE REGION II REGION II REGION II | |||
NAME DRoberts* JRJohnson** BBoger* | |||
DATE 08/18/94 05/27/94 08/19/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR | |||
NAME JRajan* RWessman* BWSheron* | |||
nATF | |||
Wu.-t L*, .I - | |||
fl/19194 I *- | |||
1 08/26/94 | |||
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08/30/94 | |||
- , X | |||
OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D | |||
: . | NAME JMain* JBirmingham* ELDoolittle* | ||
DATE 07/20/94 08/17/94 09/08/94 10t{/94 OFFICIAL DOCUMENT1 NAME: V4-/0. IN | |||
IN 94-xx | |||
If | October xx, 1994 This information notice requires no specific action or written response. If | ||
about the information | you have any questions about the information in this notice, please contact | ||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Operating Reactor Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, R11 | |||
(919) 362-0601 Attachment: | |||
===List of Recently Issued NRC Information Notices=== | |||
* See previous concurrence | |||
** Memo dated May 27 1994 OFFICE REGION II REGION II REGION II | |||
NAME DRoberts* JRJohnson** BBoger* | |||
DATE , 08/18/94 [05/27/94 j08/19/94 OFFICE [ EMEB:DE C/EMEB:DE ID/DE:NRR | |||
C/OGCB:DORS:NRR | NAME JRajan* RWessman* I BWSheron* | ||
DATE 08/22/94 08/26/94 08/30/94 OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR | |||
NAME JMain* JBirmingham* ELDoolittle* BKGrimes | |||
ELDoolittle* | |||
DATE | |||
vo | |||
, 07/20/94 | |||
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108/17/94 | |||
-.-. | |||
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, 09/08/94 1 10/ /94 A | |||
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IN 94-xx | |||
October xx, 1994 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Operating Reactor Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, RII | |||
(919) 362-0601 Attachment: | |||
===List of Recently Issued NRC Information Notices=== | |||
* See previous concurrence | |||
** Memo dated May 27 1994 OFFICE REGION II lREGION II REGION II | |||
NAME DRoberts* JRJohnson** BBoger* | |||
DATE 08/18/94 05/27/94 08/19/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR | |||
NAME JRajan* RWessman* BWSheron* | |||
DATE | |||
- , , | |||
08/22/94 | |||
, ,-,, | |||
08/26/94 | |||
* | |||
08/30/94 | |||
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OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR | |||
NAME JMain* JBirmingham* ELDoolittle* BKGrimes | |||
DATE ,07/20/94 [08/17/94 109/08/94 110/ /94 U-ILIAL DULUMLNI NAM: U:\FUMF 1N.JLU | |||
IN 94-xx | |||
September xx, 1994 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Operating Reactor Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, RII | |||
(919) 362-0601 Attachment: | |||
List of Recently Issued NRC Information Notices | |||
* See previous concurrence | |||
** MPm= dated May 27. 1994 OFFICE REGION II REGION II REGION II | |||
NAME DRoberts* JRJohnson** BBoger* | |||
DATE 108/18/94 ,05/27/94 08/25/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR | |||
NAME JRajan* RWessman* BWSheron& | |||
nATC | |||
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08/22/Q9 | |||
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OFFICE TECHED:RPB OGCB:DORS:NRR C B:DORS:NRR D/DORS:NRR | |||
NAME JMain* JBirmingham*l Ek6V2 ittle BKGrimes | |||
DATE 107/20/94 - | |||
- 108/17/94 - | |||
- - .-- - - | |||
j P'Z' 94 08/ /94 ' | |||
08/ | OF-FICIAL DOCUMEN NAME: b:\FUMr IN.VLb | ||
. r | |||
IN 94-xx | |||
September xx, 1994 This information notice requires no specific action or written response. If | |||
you have any questions about the information in this notice, please contact | |||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Operating Reactor Support | |||
Office of Nuclear Reactor Regulation | |||
Technical contact: D. Roberts, R11 | |||
(919) 362-0601 Attachment: | |||
List of Recently Issued NRC Information Notices | |||
* See previous concurrence | |||
** Memo dated May 27 1994 OFFICE | |||
NAME | |||
DATE | |||
I | |||
l | |||
REGION II | |||
DRoberts* | |||
08/18/94 REGION I1 JRJohnson** | |||
[05/27/94 REGION II | |||
BBoger* | |||
J08/19/94 OFFICE EMEB:DE C/EMEB:DE IDI iD IIRR | |||
NAME JRajan* RWessman* IB S on | |||
.t | |||
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D/DORS:NRR | DATE 08/22/94 08/26/94 08/S6/94 OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR | ||
NAME JMain* JBirmingham* | NAME JMain* JBirmingham* ELDoolittle BKGrimes | ||
ELDoolittle | |||
DATE 07/20/94 08/17/94 08/ /94 08/ /94 sors~arvral~I.- Plte ^. nstl ti. of ^ | |||
Plte ^. nstl ti. of ^UMtILIAL UUUUMtNI NAML: b: \FUMr 1N.ULV | UMtILIAL UUUUMtNI NAML: b: \FUMr 1N.ULV | ||
IN 94-xx | IN 94-xx | ||
notice requires no specific action or written response. | August xx, 1994 This information notice requires no specific action or written response. If | ||
you have any questions about the information in this notice, please contact | |||
technical contact listed below or the appropriate Office of Nuclear Reactor | |||
Regulation (NRR) project manager. | |||
Brian K. Grimes, Director | |||
Division of Operating Reactor Support | |||
Office of Nuclear Reactor Regulation | |||
contact: D. Roberts, RII | Technical contact: D. Roberts, RII | ||
(919) 362-0601 Attachment: | |||
* | ===List of Recently Issued NRC Information Notices=== | ||
* See previous concurrence | |||
** Memo dated May 27 1994 __41 OFFICE REGION II REGION II lEMED( C/EME l D/DE:NRR | |||
NAME DRoberts JRJohnson** JRajw" RWes ke rBWSheron | |||
D/DORS:NRR | DATE 08/ /94 05/27/94 08/,/94 9 | ||
089f4/94 08/ /94 OFFICE 1 TECHED:RPB JOGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR | |||
NAME l JMain* JBimnghim* | NAME l JMain* JBimnghim* It ELDoolittle BKGrimes | ||
It ELDoolittle | |||
DATE l 07/20/94 l 08/17/94 08/ /94 08/ /94 OFFICIAL DOCUMENT NAME: G:\PUMPIN.JLB}} | |||
{{Information notice-Nav}} | {{Information notice-Nav}} |
Latest revision as of 04:29, 24 November 2019
4 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 October 26, 1994 NRC INFORMATION NOTICE 94-76: RECENT FAILURES OF CHARGING/SAFETY INJECTION
PUMP SHAFTS
Addressees
All holders of operating licenses or construction permits for pressurized
water rekctors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice (IN)to alert addressees to recent failures of charging/safety
injection pump shafts at facilities designed by the Westinghouse Electric
Corporation (Westinghouse). It is expected that recipients will review the
information for applicability to their facilities and consider actions, as
appropriate, to avoid similar problems. However, suggestions contained in
this information notice are not NRC requirements; therefore, no specific
action or written response is required.
Background 4 At Westinghouse-designed facilities, charging/safety injection pumps have
4 ction flow to the reactor coolant
three funct ons: (1) to deliver seal iri
pumps, (2) .o eliver makeup water flcv ) the reactor coolant system, and
(3) to deliver high head safety injection and recirculation flow to the
reactor coolant system during and after a loss-of-coolant accident. During
normal operation, one of two, or in some cases, one of three pumps is always
in operation to deliver seal injection and makeup water flow. The loss of an
inservice charging/safety injection pump creates a condition that may
challenge reactor coolant pump seal integrity and, if makeup water flow is not
restored in a timely manner, can result in a loss of coolant inventory.
On February 29, 1980, the NRC issued IN 80-07, "Pump Shaft Fatigue Cracking,"
to alert recipients to failures of charging/safety injection pump shafts that
occurred during the 1970s. All of the charging/safety injection pump shafts
addressed in that notice were procured by Westinghouse from the Pacific Pump
Division of Dresser Industries (now Ingersoll-Dresser Pump Co). Actions taken
at that time to correct the problem included design modifications, changes in
the heat treatment of the shaft material, and the use of formed cutting tools
during fabrication. Also, abnormal operation of the pumps such as operation
with a partial or complete loss of fluid or with high vibration present was
found to be a significant contributor to the shaft failures. The Westinghouse
Nuclear Service Division issued Technical Bulletins TB-77-", TB-78-1, and
TB-79-6, to provide guidance on vibration monitoring, operation and
maintenance of the pumps, and allowable vibration amplitude limits.
9410200153 4 gfokC 4 On P4R C AI 0+ic4V
Iae
vJ
IN 94-76 October 26, 1994 Recent events indicate that failures of charging/safety injection pump shafts
continue to be a problem.
Description of Circumstances
Sequoyah Unit 1
On February 18, 1991, plant operators for Sequoyah Unit 1 received indications
of decreasing flow and increasing motor current on charging pump IB-B. When
efforts to restore full flow failed, they declared the pump inoperable and
began shutting down the reactor as required by plant technical specifications.
Charging pump lB-B had been in operation for several months and had shown no
previous signs of degradation. The licensee disassembled the pump, found
heavy wear on the impeller shoulders and the balance drum, and found a
280-degree crack in the shaft near the 11th stage impeller. Westinghouse
analyzed the shaft and determined that the crack had been in the shaft for
several months (possibly years) and that the rotating element was of the
improved type referred to in IN 80-07. The licensee replaced +he rotating
element and, after testing the pump successfully, returned the pump to
service. [Licensee Event Report (LER) 50-327/91-003]
Callaway
On February 2, 1992, the Union Electric Company Callaway Plant was at power
and charging pump B was in service to support operations. Plant operators
received indications of zero flow in the charging header and at the reactor
coolant pump seal. The operators placed charging pump A iA service to restore
normal flow, and pump B tripped. Plant personnel inspected pump B and found
that the shaft had sheared on the outboard end between the balance drum lock
nut an, balance drum mating area. le licensee documented the failure in
Suggestion Occurrence Solution 92-10 and replaced the failed shaft.
Shearon Harris
On March 18, 1993, operators at the Shearon Harris plant received indications
of a shaft failure on charging/safety injection pump B. The indications were
high motor current, low charging flow, and low pump discharge pressure. The
operators secured pump B from service and placed pump A in service. Plant
personnel uncoupled the pump from the motor and found that the pump shaft had
sheared under the balancing drum lock nut. This was the same location as in
three failures that occurred in the 1970s. (LER 50-400/93-005)
D.C. Cook Unit 2
In July 1993, at D.C. Cook Unit 2, a charging pump failed a surveillance test
when it could not deliver the required 454 liters [120 gallons] per minute.
The rotating element in that pump had been installed in 1987. The licensee
disassembled the pump and found a 10 centimeter [4 inch!, 180 degree
circumferential crack through the number 9 impeller shaft keyway. Smaller
cracks were found in two other impeller keyway areas. (LER 50-316/93-006)
IN 94-76 October 26, 1994 Braidwood Unit 1 and Sequoyah Unit 2 The NRC staff has received information on two other recent failures of
charging/safety injection pump shafts: (1) on September 15, 1993, at the
Braidwood Nuclear Station Unit 1 (Braidwood), a charging/safety injection pump
shaft sheared between the 10th and 11th stage impellers, and (2) on
February 7, 1994, at Sequoyah Unit 2, a charging\safety injection pump shaft
failed, resulting in a reactor shutdown as required by plant technical
specifications. The licensee for Braidwood replaced the pump shaft and
documented the failure on Problem Investigation Report 456-200-93-03600. The
licensee for Sequoyah reported that the affected pump had not exhibited any
indication of degradation before the shaft failure and that, similar to many
of the other shaft failures, the shaft had failed near the location of the
balancipng drum lock nut. (LER 50-328/94-002)
Discussion
Charging/safety injection pumps are important for normal plant operation and
for core cooling during accidents such as a small break loss-of-coolant
accident. Fcr most of the failure events described above, determination of
the root cause of the failure was inconclusive. However, the operational
histories of many of the failed shafts showed that they had been operated with
void formation, gas entrainment, or other abnormal conditions within a few
years of the failure. Operation of the pumps under these conditions may have
caused or contributed to the later failure of the shafts. Avoiding operation
of charging pumps under abnormal conditions and maintaining vibration levels
within manufacturer recommendations may increase pump reliability. To
increase the benefit of predictive maintenance programs, Wbstinghouse
recommends that pump vibrations be monitored at least monthly; preferably, every two weeks. This is more frequent than is required by Section XI of the
ASME B iler and Pressure Vessel Code. V'stinghouse will provide recommended
vibration limits upon request.
Industry experience in detecting shaft failures in pumps such as the reactor
coolant pump and the recirculation pump is relevant to monitoring programs of
charging/safety injection pumps because the precursors to shaft failure are
similar. For those pumps, monitoring phase angles as well as monitoring
vibration amplitude is considered to be important in detecting shaft
degradation. These data are routinely trended by some licensees for detection
of impending shaft failures.
A description of the analyses and conclusions for some of the above events
follows:
Westinghouse evaluated seven possible root causes for the shaft failure at
Callaway, including material defects, design flaws, errors in fabrication or
processing, assembly or installation defects, off-design or unintended service
conditions, maintenance deficiencies, and improper operation. Westinghouse
concluded that the shaft failure was most likely the result of a 1986 event in
which the pump had experienced a loss of suction water flow for approximately
seven minutes. The loss of suction flow increased the vapor-to-liquid ratio
in the pump and caused a dynamic imbalance. Events of this type could cause
K>~
IN 94-76 October 26, 1994 immediate pump failure or cause cyclic fatigue damage that could lead to
premature shaft failure at a later date.
A gas entrainment event that occurred on August 20, 1990, was determined to be
the probable cause of the shaft failure at Sequoyah Unit 2. Problems caused
by gas entrainment are discussed in NRC Information Notice 88-23, "Potential
for Gas Binding of High-Pressure Safety Injection Pumps During a Design Basis
Accident," and its supplements.
Westinghouse considers an operational phenomenon, such as gas entrainment, may
have led to the shaft failure at Shearon Harris, although the licensee found
no evidence of gas pockets in the charging system. In May 1991 (two years
before-the shaft failure), the licensee reported to the NRC that the charging
system had been in a degraded condition during the previous operating cycle.
An NRC Special Inspection Team reviewed the event and determined that several
water hammer events could have occurred in the system as a result of
weaknesses in the design of the alternate minimum flow system. The NRC issued
IN 92-61, "Loss of High Head Safety Injection," and its supplement regarding
that event. Another concern at Shearon Harris was the fact that the A and B
charging/safety injection pumps are alternated at approximately 2-week
intervals. Therefore, each pump is started about 25 to 30 times each year.
Westinghouse believes the high number of starts also could contribute to early
shaft failure. Problems associated with excessive pump starts include galled
wear rings, increased vibration, and decreased pump performance. However, Westinghouse concluded that the available data were insufficient to directly
link the failure of the shaft to the high number of pump starts.
Although Westinghouse could not conclusively determine the root cause of the
shaft failure at Shearon Harris, West 'nghouse made recommendations which could
help pre-ent or detect impendine shaf fa;lures. Westinghou- suggested that
the liceasee conduct a detailed review, of the possibility that gas could
become entrained in the charging pump suction piping and the cross connczts to
other systems. Westinghouse also recommended that, when the rotating element
of the pump is replaced, consideration be given to installing the latest shaft
design which has an improved one-piece balance drum lock nut. Westinghouse
included recommendations for vibration monitoring in Westinghouse Technical
Bulletin TB-79-6. Westinghouse has not specified a limitation on the number
of pump starts but recommends that pump starts be minimized to maintain pump
reliability.
In addition to the industry actions described above, Westinghouse and the
Westinghouse Owners Group (WOG) are implementing a program to address these
pump shaft failures. The program includes: (1) a survey of WOG member
utilities for pump service operating history data, (2) a pump design review, and (3) a shaft material enhancement evaluation. The program is intended to
identify any weaknesses in design, maintenance, or operation of the pumps in
order to improve shaft reliability.
I S :. .
. I
IN 94-76 October 26, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Project Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, RII
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
daret4s C'
Attachment
IN 94-76 October 26, 1994 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information Date of
Notice No. Subject Issuance Issued to
93-60, Reporting Fuel Cycle 10/20/94 All 10 CFR Part 70
Supp. 1 and Materials Events to fuel cycle licensees.
the NRC Operations Center
94-75 Minimum Temperature 10/14/94 All holders of OLs or CPs
for Criticality pressurized-water reactors
(PWRs).
94-74 Facility Management 10/13/94 All U.S. Nuclear Regulatory
Responsibilities for Commission Medical
Purchased or Contracted Licensees.
Services for Radiation
Therapy Programs
94-73 Clarification of Critical- 10/12/94 All fuel fabrication
ity Reporting Criteria facilities.
94-72 Increased Control Rod 10/05/94 All'holders of OLs or CPs
Drop Time from Crud for pressurized water
Buildup reactors
94-71 Degradation of Scram 10/04/94 All holders of OLs or CPs
Solenoid Pilot Valve for boiling water reactors
Pressure and Exhaust (BWRs).
94-70 Issues Associated with Use 09/29/94 All U.S. Nuclear Regulatory
of Strontium-89 and Other Commission Medical
Beta Emitting Radiopharma- Licensees.
ceuticals
94-69 Potential Inadequacies 09/28/94 All holders of OLs or CPs
in the Prediction of Torque for nuclear power reactors.
Requirements for and Torque
Output of Motor-Operated
Butterfly Valves
94-68 Safety-Related Equip- 09/27/94 All holders of OLs or CPs
ment Failures Caused by For nuclear power reactors.
Faulted Indicating Lamps
OL = Operating License
CP = Construction Permit
- . . I
IN 94-76 October 26, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Original signed by
Brian K. Grimes
Brian K. Grimes, Director
Division of Project Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, RII
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
Mamn dated Mav 27 1994 OFFICE REGION II REGION II REGION II
NAME DRoberts* JRJohnson** BBoger*
DATE 08/18/94 05/27/94 08/19/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR
NAME JRajan* RWessman* BWSheron*
nATF
Wu.-t L*, .I -
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1 08/26/94
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08/30/94
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OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D
NAME JMain* JBirmingham* ELDoolittle*
DATE 07/20/94 08/17/94 09/08/94 10t{/94 OFFICIAL DOCUMENT1 NAME: V4-/0. IN
IN 94-xx
October xx, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, R11
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
- Memo dated May 27 1994 OFFICE REGION II REGION II REGION II
NAME DRoberts* JRJohnson** BBoger*
DATE , 08/18/94 [05/27/94 j08/19/94 OFFICE [ EMEB:DE C/EMEB:DE ID/DE:NRR
NAME JRajan* RWessman* I BWSheron*
DATE 08/22/94 08/26/94 08/30/94 OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR
NAME JMain* JBirmingham* ELDoolittle* BKGrimes
DATE
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, 07/20/94
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108/17/94
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, 09/08/94 1 10/ /94 A
UV ILIAL UULUMtNl NAMt: U:\UMF 14N.JLU
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IN 94-xx
October xx, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, RII
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
- Memo dated May 27 1994 OFFICE REGION II lREGION II REGION II
NAME DRoberts* JRJohnson** BBoger*
DATE 08/18/94 05/27/94 08/19/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR
NAME JRajan* RWessman* BWSheron*
DATE
- , ,
08/22/94
, ,-,,
08/26/94
08/30/94
_,
OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR
NAME JMain* JBirmingham* ELDoolittle* BKGrimes
DATE ,07/20/94 [08/17/94 109/08/94 110/ /94 U-ILIAL DULUMLNI NAM: U:\FUMF 1N.JLU
IN 94-xx
September xx, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, RII
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
- MPm= dated May 27. 1994 OFFICE REGION II REGION II REGION II
NAME DRoberts* JRJohnson** BBoger*
DATE 108/18/94 ,05/27/94 08/25/94 OFFICE EMEB:DE C/EMEB:DE D/DE:NRR
NAME JRajan* RWessman* BWSheron&
nATC
ulIL. I
08/22/Q9
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nR/26/94 08/2_ v/94
.
OFFICE TECHED:RPB OGCB:DORS:NRR C B:DORS:NRR D/DORS:NRR
NAME JMain* JBirmingham*l Ek6V2 ittle BKGrimes
DATE 107/20/94 -
- 108/17/94 -
- - .-- - -
j P'Z' 94 08/ /94 '
OF-FICIAL DOCUMEN NAME: b:\FUMr IN.VLb
. r
IN 94-xx
September xx, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, R11
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
- Memo dated May 27 1994 OFFICE
NAME
DATE
I
l
REGION II
DRoberts*
08/18/94 REGION I1 JRJohnson**
[05/27/94 REGION II
BBoger*
J08/19/94 OFFICE EMEB:DE C/EMEB:DE IDI iD IIRR
NAME JRajan* RWessman* IB S on
.t
W
DATE 08/22/94 08/26/94 08/S6/94 OFFICE TECHED:RPB OGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR
NAME JMain* JBirmingham* ELDoolittle BKGrimes
DATE 07/20/94 08/17/94 08/ /94 08/ /94 sors~arvral~I.- Plte ^. nstl ti. of ^
UMtILIAL UUUUMtNI NAML: b: \FUMr 1N.ULV
IN 94-xx
August xx, 1994 This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
technical contact listed below or the appropriate Office of Nuclear Reactor
Regulation (NRR) project manager.
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: D. Roberts, RII
(919) 362-0601 Attachment:
List of Recently Issued NRC Information Notices
- See previous concurrence
- Memo dated May 27 1994 __41 OFFICE REGION II REGION II lEMED( C/EME l D/DE:NRR
NAME DRoberts JRJohnson** JRajw" RWes ke rBWSheron
DATE 08/ /94 05/27/94 08/,/94 9
089f4/94 08/ /94 OFFICE 1 TECHED:RPB JOGCB:DORS:NRR C/OGCB:DORS:NRR D/DORS:NRR
NAME l JMain* JBimnghim* It ELDoolittle BKGrimes
DATE l 07/20/94 l 08/17/94 08/ /94 08/ /94 OFFICIAL DOCUMENT NAME: G:\PUMPIN.JLB