05000206/LER-1981-007, Forwards LER 81-007/01T-0.Detailed Event Analysis Encl

Forwards LER 81-007/01T-0.Detailed Event Analysis Encl

ML20004F156
Person / Time
Site:	San Onofre
Issue date:	06/01/1981
From:	Haynes J SOUTHERN CALIFORNIA EDISON CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20004F157	List: 05000206/LER-1981-007, Forwards LER 81-007/01T-0.Detailed Event Analysis Encl 05000206/LER-1981-007-01, /01T-0:on 810515,pump to Motor Coupling Failed During Qualification Testing of RHR Pump Motors.Caused by Corrosive Effects of Environ & Unnatural Stresses to Coupling Due to Test Setup.Couplings Will Be Replaced
References
NUDOCS 8106160566
Download: ML20004F156 (2)

LER-1981-007, Forwards LER 81-007/01T-0.Detailed Event Analysis Encl

Event date:
Report date:
2061981007R00 - NRC Website

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Attention: Mr. R. H. Engelken, Director

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DOCKET NO. 50-206 SAN ONOFRE - UNIT 1

Dear Sir:

By letter dated May 18, 1981, we provideo written, prompt notification of a reportable occurrence involving the Residual Heat Removal (RHR) Pumps. This letter provides the two week followup report and the licensee event report (LER No.81-007) in accordance with Specification 6.9.2.a of the San Onofre Unit 1 Techn1 cal Specifications!

The RHR pumps are located inside containment and are part of the Residual Heat Removal System. They are utilized during normal operation to bring the reactor from a hot shutdown condition to a cold shutdown.

In the event of a MSLB or FWLB, these pumps would be operated to bring the reactor to a cold shutdown and maintain it in that condition.

If the MSLB or FWLB were to occur inside conteinment, the RHR pumps would be required to operate in the post-accident environment which includes submergence.

i The original RHR pumps ware Pacific Pumps with a Westinghouse motor. As a result of an environmental qualification a,

s documented in Amendment 30 to the San Onofre Unit 1 Final Safety Analysa, it was identified that the RHR pump motors were not capable of operating in the post-accident environment.

It was indicated that the motors would be replaced with qualified motors.

During the 1976-1977 extended outage, the Westinghouse motors were replaced with Louis-Allis Motors. At this same time, the pump to motor couplings were also replaced with Bendix couplings.

In conjunction with this replacement, a qualification test program was begun at Wyle Labs to demonstrate the qualificatioli of the Louis-Allis motors. Continued safe l

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Mr. R. H. Engelken, Director June 1, 1981 operation of San Onofre Unit I during the qualification testing program was based on the existence of an alternate means for cooldown of the core in the event the RHR pumps failed to operate. This alternate means for cooldown was reflected in the NRC's Safety Evaluation provided by letter dated July 18, 1975.

In the course of the testing program, several test load to motor couplings failed. The last coupling, a Bendix coupling provided by Pacific Pumps, which failed during the test, was similar in design to those installed at San Onofre Unit 1.

This coupling was sent to Bendix for analysis of the failure mechenism. The results of that analysis indicated the failure was due to corrosion fatigue. The coating of the test coupling was not capable of protecting it from corrosive attack.

In addition, it was evident that the Wyle test setup performed in such a manner that high cyclic stresses were also experienced by the test coupling.

The test coupling and the coupling installed at Unit 1 are constructed of the same material, a 4340 carbon steel. The difference in the design of the couplings is the length of a small diameter tube which connects the two flexible disks of the cotpling. The tube is one inch long in the test coupling and 4.5 inches long in the Unit 1 couplings. The two flexible disks are attached to the pump shaft and the motor shaft. The coatings on the test coupling and the Unit 1 couplings are different. Bendix has suggested that the coating on the Unit 1 couplings would last longer; however, no supporting data is available. The stresses experienced by the test coupling in the test setup cannot*be quantified.

It is concluded that the stresses were probably in excess of the coupling's design limit.

It is expected, however, that similar stresses would be much lower at Unit 1.

Based on the information on the test coupling, neither Bendix nor Pacific Pumps could conclude that the Unit I couplings would function without failure in the post-accident environment. Our review of the Bendix analysis and the information available leads to the conclusion that replacement of the Unit 1 couplings is warranted. The couplings will be replaced with a Rexnord coupling. This coupling is of a different design and is fabricated of materials capable of withstanding the post-accident environment. These new couplings will be installed during the current outage prior to startup of Unit 1.

If you have any questions regarding this matter, please let me know.

Very truly yours, l

i Enclosure cc: Director, Office of Management and Informaticn Program Control (2) l

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