ML19210A198

Abnormal Occurrence 50-289/75-14:on 750523,motor Shaft to B Decay Heat River Water Pump Sheared After Coupling.Damaged Pump Removed & Redundant Sys Took Over.Caused by Fatigue Failure & Possible Misalignment Between Motor & Shaft

ML19210A198
Person / Time
Site:	Three Mile Island
Issue date:	06/06/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1126, NUDOCS 7910240918
Download: ML19210A198 (5)

Text

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CONTROL NO: 6261 FILE: I!; CIDE"r REPC2T FILE I

FROM: Metropolitan Edison DATE OF DOC DATE REC'D LTR TWX RPT OTHER Readin;;, Ib R C Arnold 6-6-75 6-9-75 XX ORIG CC OTHER SENT AEC PDR XXXX TO: Director, invision of Rea.: tor Licensing 1 signed SENT LOCAL PDR X'CCCC CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

xxXXX 1 50-269 DESCRIPTION: ENCLOSURES:

Ltr concerns abnor::al occurrence mport No. Ao 50-269/75-14 on 5-23-75, the in- '

operative decay heat river water pump DR-P-13 - .

threaten to cause an Engineered Safeguards -

feature or system to to incapable of perform-in.; its intended:: function.. .

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PCST CFFICE BOX 542 READING, PENNSYLVANI A 19603 TELEPHONE 215 - 929-3601 June 6, 1975 e6%Q, -g GQL 1126 ,

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Director  ;-

Division of Reactor Licensing 1

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JUNS 1975 > 7 U. S . Nuclear Regulatory Commission '7 " 5 T *'

Washington, D.C. 20555 7).y [_ .~ '

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Dear Sir:

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Operating License DPR-50 Dockat No. 50-289 In accordance with Technical Specifications for the Ihree Mile Island Nuclear Station Unit 1 we are reporting the following abnormal occurrence:

(1) Report Number: A0 50-289 / 75-14 (2a) Report Date: June 6,1975

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(2b) Occurrence Date: May 23, 1975 (3) Facility : Three Mile Island Nuclear Station Unit 1 (TMI-1) ,

(4) Identification of Occurrence:

Title:

Inoperatf e Decay Heat River Water Pump DR-P-1B Type: An abnormal occurrence as defined by the Technical Specifications , paragraph 1.8d, in that the inoperative decay heat river water pump DR-P-1B threatened to cause an Engineered Safeguards feature or system to be in-capable of performing its intended function.

(3) Conditions Prior to Occurrence:

The reactor was in routine start-up with major plant parameters as follows:

Power: Core: 207.

Elec: 113 MW (Gross) 1 141 L 6

RC Flow: 136 x 10 lb/hr c^' .

- - v _.

RC Pressure: 2146 psig RC Temp: 579 F PRZR Level: 228 in.

PRZR Temp: 647 F (6) Description of Occurrence:

At 1400 on May 23, while running the B Decay Heat River Water Pump (DR-P-1B) during normal surveillance testing, the motor shaf t sheared above the coupling. The DR-P-1B pump was immediately removed f rom service and the redundant pump DR-P-1A was tested to verify operability.

On May 25, the reactor was placed in cold shutdown in accordance with the requirements of Technical Specifications 3.3.1 and 3.3.2.

(7) Designation of Apparent Cause of Occurrence:

Af ter extensive investigation, our analysis has sh<>wn that the cause of the shaft failure was rotating bending fatigue. Contributing factors are felt to be

a. mechanica design in that the upper pump bearing was found to have exces sive clearance due to pump shaf t vibration and ec centricity

b. installatioq in that there war possible misalignment between motor and shaft

c. material in that there is some evidence of a fatigue f ailure as a result of a. , b . , and d.

d. structural design in that hydraulic forces due to pump startup appear to have contributed.

Upon inspection of the DR-P-1A discharge check valve it was discovered that the hinge pin was missing and that the disc was lying on the bottom of the valve. It is possible that the resulting impact force, with the disc creating sudden flow restriction, created forces which were reflected back to the motor shaft. In addition, a crack was observed in the motor endbell.

Further investigations are continuing as described below.

(8) Analysis of Occurrence:

It is believed that the f ailure of DP-P-1B did not represent a threat to the health and safety of the publi in that only one decay heat river water pump is necessary to supply sufficient emergency cooling water in the event of a loss-of-coolant accident and the redundant DR-P-1A decay heat river water pump was verified as operable.

1476 210

(9) Corrective Action:

Immediate corrective action was taken to return the DR-P-13 pump motor to the vendor for repair and replacement of the shaft and motor endbell. As a complet; pump inspection indicated excessive wear on the upper pump shaf t bearing closest to the coupling, all nine pump shaf t bearings were replaced. Although eight bearings were found to be a.:ceptable it was deemed prudent to replace them at the time the pump was disassembled.

A complete examination and repair of the f ailed discharge check valve took place under the direction of a vendor representative.

The pump discharge strainer was disassembled and inspected with no signs of wear or damage.

Upon reassembly, a complete electrical check was performed on the motor as well as a functional test on the pump after acceptable motor checkout.

Cracks vere observed in the concrete foundation of DR-P-1B. A base plate ' hold-down" clamp was installed to assure the DR-P-1B baseplate is anchared in such a manner as to assure meeting the original seismic design criteria.

When DR-P-1B was declared operable, DR-P-1A was removed f rom service for inspection of the discharge check valve. As a small crack on one rib of the endbell was found, the endbell of the motor was replaced.

It should be noted that all other river water pumps, motors, and foundations were examined for similar problems. ill river water pump motor endbells were magnafluxed to determine if further cracks exist.

It was discovered that nuclear services river water pump NR-P-1A had a cracked endbell and that some cracks exist in the foundation NR-P-1A on a baseplate. The endbell will be replaced upon receipt of a replace-ment. The adequacy of the pump baseplate with regard to its intended seismic criteria was further assured by incorporating the same modification as inco rporated on DR-P-1B.

Long term corrective actions are being taken as follows. Anti-thrust restraints for the twelve river water pumps will be installed. These restraints will connect and secure the pump assembly to the screen house east wall.

Repairs will be made to replace the cracked endbell for NR-P-LA upon receipt of a replacement. When cracked endbell has been replaced, the pump will be declared operable.

Tae Plant Operations Review Committee and the S tation Superintendent reviewea and gave their approval of these actions. A pump surveillance program will be instituted and performed on a routine basis until a definite conclusion can be drawn regarding this shaft f ailure . De tails of the program are available at the TMI-l site.

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(10) Failure Data:

Previous Failures:

None Equipment Identification:

Manuf acturer - Westinghouse Type and Frame - 445 TBH HP - 200 Frequency - 60 Hz, 3 r aase Volts - 460 RPM - 1180 Amps - 230 Sincerely, l

R. C. rnold Vice President RCA: RSB : tas cc: Office of Inspection and Enforcement U. S . Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 File: 20.1.1 / 7.7.3.5.1 3476 ?I2 -

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