Information Notice 1986-39, Failures of RHR Pump Motors and Pump Internals

Failures of RHR Pump Motors and Pump Internals

ML031250031
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, 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, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, 05000115, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	05/20/1986
From:	Jordan E NRC/IE
To:
References
IN-86-039, NUDOCS 8605150473
Download: ML031250031 (5)

SSINS No.: 6835 IN 86-39 UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF INSPECTION

AND ENFORCEMENT

Washington, DC 20555 May 20, 1986 IE INFORMATION

NOTICE NO. 86-39: FAILURES OF RHR PUMP MOTORS AND PUMP INTERNALS

Addressees

All nuclear power reactor facilities

holding an operating

license (OL) or a construction

permit (CP).

Purpose

This notice is provided to alert licensees

to serious damage which has occurred at a licensed nuclear power plant to residual heat removal (RHR) pumps manufac-tured by Bingham-Willamette

with motors supplied by General Electric.

The damage identified

at the Philadelphia

Electric Co. (PECO), Peach Bottom facility involved failure of motor bearings and/or failure of pump impeller wear rings.It is expected that recipients

will review this notice for applicability

to their facilities

and consider actions, if appropriate, to preclude a similar problem occurring

at their facilities.

However, suggestions

contained

in this notice do not constitute

requirements;

therefore, no specific action or written response is required.Description

of Circumstances:

On November 2, 1985, during core reload of PECO's Peach Bottom Unit 3, a fire occurred in the 3C RHR pump motor which totally engulfed the motor and rendered the pump inoperable.

A lower guide bearing high temperature

alarm had been received for 3 days prior to the pump failure, but this warning of potential pump failure went unnoticed

by personnel

because of the large number of other alarms that were received during the shutdown.

The motor, a 2000 HP GE verti-cal induction

model 5K6348XC29, and pump, a Bingham-Willamette

single stage centrifugal

model 18x24x28 CVIC (Figure 1), were uncoupled, disassembled

and inspected

for damage. Results of the inspection

identified

that the motor lower guide bearing was destroyed, the rotor bars were gouged and scorched, and the stator windings were burned and gouged. The pump internals

were found to have sustained

internal damage. Specifically, the lower impeller wear ring (Figure 1) was separated

from the impeller and fused to the casing wear ring.No other wear surfaces indicated

wear or damage. On November 16, 1985, while replacing

the lower pump casing gasket on the 3A RHR pump, PECO personnel discovered

that the lower pump impeller wear ring was separated

from the impeller and cracked in three places. Subsequent

inspections

of the remaining two unit 3 RHR pumps and two unit 2 pumps (2A and 2C) revealed similar wear ring failures in three of the pumps inspected.

8605150473 IN 86-39 May 20, 1986 On December 22, 1985, after several overcurrent

alarms with pump 20 from Unit 2, PECO inspected

this pump and discovered

the lower pump impeller wear ring separated

and cracked, a 6-inch piece of wear ring missing, and the impeller vanes damaged. Not all failures noted above were as severe as the ones identified

on pumps 3C and 2D. However, the similarity

was evident.The RHR pump impeller wear rings are press fit to the impeller and attached with eight dowel pins. The wear rings provide a wearing surface on the pump impeller.

The wear rings are 410 stainless

steel, A 182 grade F6 with a Rockwell C hardness of 33 to 39. Metallurgical

examinations

of the wear ring fracture surfaces indicate the presence of intergranular

stress corrosion cracking (IGSCC). PECO has classified

the wear ring failures as IGSCC. On November 26, 1985, PECO made an INPO Network notification

regarding

these RHR pump failures.

PECO has repaired all affected pumps by replacement

of damaged motors and pump internals.

Tennessee

Valley Authority's

Browns Ferry Units 1, 2, and 3 utilize the identical

pumps for RHR service. Similar motor and pump impeller wear ring failures have occurred at these facilities, but not to the extent identified

at Peach Bottom. Pumps of similar design, but different

size, are utilized for core spray service both at Peach Bottom and Browns Ferry.However, these pumps use the "integral" impeller wear ring design, i.e., extended impeller part replaces separate wear ring and forms a single unit, and therefore

are not susceptible

to the type of wear ring failure previously

described.

Discussion:

These multiple events are of concern because of the potential

for common-mode failures of all pumps in the same system. At Peach Bottom, six of eight pumps inspected

exhibited

degraded pump impeller wear rings and internals.

These flaws could lead to pump hydraulic

degradation

and, under the worst conditions, complete pump failure. The motor guide bearing failures are signi-ficant because they could cause failure of the pump motors and pump internal damage.The full extent to which this type of pump may be used in safety-related

services at other facilities

is not known with complete certainty.

According to information

ascertained

from Bingham-Williamette

records and confirmed

by contact with affected sites, other plants utilizing

this type of pump in the RHR system include the following:

Cooper, Pilgrim 1, and Vermont Yankee.The exact cause of the pump internal failures has not been fully determined, except that there is evidence that IGSCC has contributed

to the impeller wear ring failures.

Operating

pumps with inadequate

flow and lubrication, whereby high internal temperatures

develop, is also a likely contributor, e.g., pump cavitation.

PECO is continuing

to pursue root causes and wear ring redesigns to prevent such occurrences

in the future.

IN 86-39 May 20, 1986 No specific action or written response is required by this information

notice.If you have any questions

regarding

this matter, please contact the Regional Administrator

of the appropriate

NRC regional office or the technical

contact listed below.r Jordan, Director Division of Emergency

Preparedness

and Engineering

Response Office of Inspection

and Enforcement

Technical

Contact: Ronald M. Young (301) 492-8985 Attachments:

1. Figure 1 -Typical CVIC RHR Pump Sectional

Assembly 2. List of Recently Issued IE Information

Notices

Attachment

1 IN 86-39 May 20, 1986 Casing Wear Ring Lower Impeller Wear Ring FIGURE 1 -Typical CVIC RHR Pump Sectional

Assembly

Attachment

2 IN 86-39 May 20, 1986 LIST OF RECENTLY ISSUED IE INFORMATION

NOTICES Information

Date of Notice No. Subject Issue Issued to 86-38 86-37 86-36 86-35 86-34 Deficient

Operator Actions 5/20/86 Following

Dual Function Valve Failures Degradation

Of Station 5/16/86 Batteries Change In NRC Practice 5/16/86 Regarding

Issuance Of Confirming

Letters To Principal

Contractors

Fire In Compressible

Material 5/15/86 At Dresden Unit 3 Improper Assembly, Material 5/13/86 Selection, And Test Of Valves And Their Actuators Information

For Licensee 5/6/86 Regarding

The Chernobyl Nuclear Plant Accident Request For Collection

Of 5/2/86 Licensee Radioactivity

Measurements

Attributed

To The Chernobyl

Nuclear Plant Accident Unauthorized

Transfer and 5/6/86 Loss of Control of Industrial

Nuclear Gauges Design Limitations

of 4/29/86 Gaseous Effluent Monitoring

Systems All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or CP Fuel cycle licensees and Priority 1 material licensees All power reactor facilities

holding an OL or CP All power reactor facilities

holding an OL or a CP All power reactor facilities

holding an OL or a CP 86-33 86-32 86-31 86-30 OL = Operating

License CP = Construction

Permit