Information Notice 1994-76, Recent Failures of Charging/Safety Injection Pump Shafts

Recent Failures of Charging/Safety Injection Pump Shafts

ML031060430
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	10/26/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-076, NUDOCS 9410200153
Download: ML031060430 (12)

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

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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).

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

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*

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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

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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

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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&

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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

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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

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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