Information Notice 1994-45, Potential Common-Mode Failure Mechanism for Large Vertical Pumps

Potential Common-Mode Failure Mechanism for Large Vertical Pumps

ML031070008
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, 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, 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, Crane
Issue date:	06/17/1994
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
IN-94-045, NUDOCS 9406130197
Download: ML031070008 (9)

V

UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.

20555

June 17, 1994

NRC INFORMATION NOTICE 94-45: POTENTIAL COMMON-MODE FAILURE MECHANISM FOR

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information

notice to alert addressees to a potential common-mode failure mechanism for

large vertical pumps. 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.

Description of Circumstances

On March 3, 1994, while performing vibration tests on standby service water

pump

B," Grand Gulf personnel noted that vibration levels at all monitored

points were higher than the reference values. Additional testing exhibited a

rapidly degrading trend in pump vibration performance. The pump was declared

inoperable and disassembled for inspection.

The pump is a two-stage vertical line shaft pump with the pump impellers

coupled to the pump motor via a segmented vertical line shaft, approximately

18 meters [60 feet] long (see Figure 1).

Six couplings (see Figure 2) are

used to connect the shaft segments.

The pumps are located in large cooling

towers that contain water which is chemically treated to reduce biofouling.

The pumps are run weekly for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to permit addition and circulation of

the chemicals.

Disassembly showed extensive corrosion of the carbon steel bolts and

lockwashers used in the pump shaft coupling assemblies.

Some lockwashers were

missing and were assumed to have corroded away completely. The corrosion

allowed each retainer to move away from its contact surface on the sleeve.

This allowed the gaps between the pump shaft sections to increase. This

process increased the effective shaft length which reduced the clearance

between the pump impellers and the bottom of the bowls.

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IN 94-45 June 17, 1994 Inspection of pump "B" revealed that the impellers had milled into the pump

bowls, extensively damaging the impellers and the bowls. The licensee

estimated that more than 2.54 cm [1 inch] of material had been worn away from

the impellers and bowls.

Subsequent disassembly and inspection of the "A"

standby service water pump also showed corrosion of the coupling fasteners, but there was only minor damage to the impellers and bowls.

The standby service water pumps are tested in accordance with the licensee's

inservice testing program. Neither pump indicated any degradation in

developed head, flow, or vibration during quarterly inservice testing

performed previously. Vibration measurements are taken near the motor bearing

housing because the pump bearings are submerged. Vibration measurements taken

at this location may not identify this type of failure mechanism until

significant damage has occurred. In addition, the motor did not indicate any

increase in running current during testing.

Discussion

This style of coupling is used by several manufacturers of vertical line shaft

pumps. The event at Grand Gulf indicates that current testing of vertical

line shaft pump hydraulic and mechanical performance may not identify, before

damage occurs, interference between the pump impellers and bowls caused by a

change in shaft length. Current manufacturer's recommendations do not require

"as-found" measurements of pump lift to be taken and evaluated whenever the

pump is uncoupled from the motor. The licensee of the Grand Gulf Station has

now added this inspection to its inservice testing program.

In addition, after the pumps were rebuilt subsequent to this event, measurements of

as-found total float between the impellers and the bowls were taken by the

licensee. The measurements were taken by lifting the shaft until the upper

part of the impeller contacted the bowl, then measuring the change when the

impeller was lowered and allowed to rest on the bottom of the bowl. This

measurement was taken after the pump was installed, and is to be used to

evaluate measurements taken during the service life of the pump.

Dissimilar materials used in the coupling assembly may have contributed to

this event.

The retainer bolts and lockwashers were made of carbon steel; the

pump shafts and remaining coupling components were made of stainless steel.

IN 94-45 June 17, 1994 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

rian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts: Rudolph H. Bernhard, RII

(601) 437-4620

Joseph Colaccino, NRR

(301) 504-2753 Attachments:

1. Figure 1, Grand Gulf Standby Service Water Pump

2. Figure 2, Standby Service Water Pump Coupling

3. List of Recently Issued NRC Information Notices

Attachment 1

IN 94-45 June 17, 1994 r/

PUMP MOTOR

ELEV 134' -8"

- KEED COUPUNG

max Water Lt".

EL. 82'-V

Attachment 2

IN 94-45

June 17, 1994

Page 1 of I

PUMP SHAFT

CAPSCREW

LOCKWASHER

RETAINER

SPLIT RING

SLEEVE-

Figure 2 Standby Service Water Pump Coupling (Typical of 6)

Attachment 3

IN 94-45

June 17, 1994 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information

Date of

Notice No.

Subject

Issuance

Issued to

94-44

94-43

94-42

94-41

94-40

94-39

94-38

Main Steam Isolation

Valve Failure to Close

on Demand because of

Inadequate Maintenance

and Testing

Determination of Primary- to-Secondary Steam

Generator Leak Rate

Cracking in the Lower

Region of the Core

Shroud in Boiling-Water

Reactors

Problems with General

Electric Type CR124

Overload Relay Ambient

Compensation

Failure of a Rod Control

Cluster Assembly to Fully

Insert Following a Reactor

Trip at Braidwood Unit 2

Identified Problems in

Gamma Stereotactic

Radiosurgery

Results of a Special NRC

Inspection at Dresden

Nuclear Power Station

Unit 1 Following a Rupture

of Service Water Inside

Containment

Misadministration Caused

by a Bent Interstitial

Needle during Brachy- therapy Procedure

06/16/94

06/10/94

06/07/94

06/07/94

05/26/94

05/31/94

05/27/94

05/27/94

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for pressurized water

reactors.

All holders of OLs or CPs

for boiling-water reactors

(BWRs).

All holders of OLs or CPs

for nuclear power reactors.

All holders of OLs or CPs

for pressurized-water

reactors (PWRs).

All U.S. Nuclear Regulatory

Commission Teletherapy

Medical Licensees.

All holders of OLs or CPs

for NPRs and all fuel cycle

and materials licensees

authorized to possess spent

fuel.

All U.S. Nuclear Regulatory

Commission Medical Licensees

authorized to us brachy- therapy sources in high-,

medium-, and pulsed-dose- rate remote afterloaders.

94-37 OL = Operating License

CP = Construction Permit

IN 94-45 June 17, 1994 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

one of the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

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Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

Rudolph H. Bernhard, RII

(601) 437-4620

Joseph Colaccino, NRR

(301) 504-2753 Attachments:

1. Figure 1, Grand Gulf Standby Service Water Pump

2. Figure 2, Standby Service Water Pump Coupling

3. List of Recently Issued NRC Information Notices

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Nuclear Reactor Regulation (NRR) project manager.

Brian K. Grimes, Director

Division of Operating Reactor Support

Office of Nuclear Reactor Regulation

Technical contacts:

Rudolph H. Bernhard, RII

(601) 437-4620

Joseph Colaccino, NRR

(301) 504-2753 Attachments:

1. Figure 1, Grand Gulf Standby Service Water Pump

2. Figure 2, Standby Service Water Pump Coupling

3. List of Recently Issued NRC Information Notices

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one of the technical contacts 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 contacts:

Rudolph H. Bernhard, RII

(601) 437-4620

Joseph Colaccino, NRR

(301) 504-2753 Attachments:

1. Figure 1, Grand Gulf Standby Service Water Pump

2. Figure 2, Pump Coupling

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