ML20148T434

Discusses Failures of Bergen-Paterson Snubbers During 1978 Snubber Test program.W/54 tested,10 Failed in Same Mode: Entrapped Spring Damaging Seat Surfaces.Engineer Hypothesizes That Failures Due to Abusive Handling

ML20148T434
Person / Time
Site:	Rancho Seco
Issue date:	11/30/1978
From:	Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 7812050116
Download: ML20148T434 (2)

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$~SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT O f 6201,S Street, Box 15830, Sacramento, California 95813; (916) 452-3211 .

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'I 5 7 N'ovember 30, 1978 i

Director of Nuclear. Reactor Regulation ATTN: Mr. Robert Wi Reid, Chief  ?

Operating Reactors, Branch No. 4 U. S.. Nuclear Regulatory Commission Washington, D. C. 20555 Docket No. 50-312 .

Rancho Seco Nuclear Generating l' Station, Unit No. 1~

Dear Mr. Reid:

Preliminary'to this letter, R. Colombo and J. Field from my staff

. contacted Mr. J. Zwetzig, our Section Chief, on November 29, 1978. Mr. Zwetzig asked for a written statement explaini.ng the. circumstances under which an nppropriate determination can be made to' provide the District.with a letter

.of concurrence. l

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The Snubber Test Program for the 1978 refueling outage was started 7 with a representative. sample of.10 snubbers as called for in the Rancho Seco Unit No. 1 Technical Specifications. 'There was one~ failure in the first  !

samp. ling. The failed unit was a Bergen-Paterson snubber. A second group of 10 snubbers was selected and tested. There were three failures'in this group.

All of the failures were Bergen-Paterson units. Only Bergen-Paterson units  ;

were. selected in the succeeding groups of 10. With 54' units tested, 10 failures have occurred. Nine of these Bergen-Paterson-snubbers failed in ,

the same mode. The spring is entrapped between the poppet and seat on the  !

retraction side of the valve block damaging'the seat surfaces. ,

f The responsible engineer, having reviewed these failures,' hypothesizes that these nine failures have been caused by abusive handling during reinstal-lation after the 1977 test program. The engineer states that he discovered that then t.hese units were being reinstalled after the 1977 test program, the shaft end of Bergen-Paterson units were being' slammed against floors and walls in order to shorten them for reinstallation. All units were reset to their proper' length in the test stand after testing; however, the spring loaded accumulator.In Bergen-Paterson units causes the units to grow if not installed soon after setting. When the engineer found that the. units were being mishandled, he stopped that procedure and selected some units for retest. No failures were found in this sampling, so no further action was taken. He now believes that the failures presently observed are a result of'the mishandling in 1977. .The ,

single failure of the reaaining Bergen-Paterson unit was a broken piston ring r and this isolated case has not been observed on any of the subsequent inspections. j Of the 281TT Grinnell units subject to testing, five have- been tested and have performed satisfactorily, y

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. Mr. Robert W. Reid Page 2 November 30, 1978 The District believes that within the requirements of Technical ,

Specification 4.14.4, this situation is clearly defined as isolated to Bergen-Paterson snubbers. Within this specification, a letter is required from NRC concurring that additional inspections of ITT Grinnell units are not necessary. The reply is required prior to completion of reactor building; work which is scheduled for December 9, 1978.

Respectfu ly submitted,_

J. J. Mattimoe .

j Assistance General Manager and Chief Engineer JMM:RWC: jim cs: Region V Maggled ,

Sent ,

11/30/78

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