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

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 Deficient Operator Actions 5/20/86 All power reactor

Following Dual Function Valve facilities holding

Failures an OL or CP

86-37 Degradation Of Station 5/16/86 All power reactor

Batteries facilities holding

an OL or CP

86-36 Change In NRC Practice 5/16/86 All power reactor

Regarding Issuance Of facilities holding

Confirming Letters To an OL or CP

Principal Contractors

86-35 Fire In Compressible Material 5/15/86 All power reactor

At Dresden Unit 3 facilities holding

an OL or CP

86-34 Improper Assembly, Material 5/13/86 All power reactor

Selection, And Test Of Valves facilities holding

And Their Actuators an OL or CP

86-33 Information For Licensee 5/6/86 Fuel cycle licensees

Regarding The Chernobyl and Priority 1 material

Nuclear Plant Accident licensees

86-32 Request For Collection Of 5/2/86 All power reactor

Licensee Radioactivity facilities holding

Measurements Attributed To an OL or CP

The Chernobyl Nuclear Plant

Accident

86-31 Unauthorized Transfer and 5/6/86 All power reactor

Loss of Control of facilities holding

Industrial Nuclear Gauges an OL or a CP

86-30 Design Limitations of 4/29/86 All power reactor

Gaseous Effluent Monitoring facilities holding

Systems an OL or a CP

OL = Operating License

CP = Construction Permit