ML20151X835

PNO-77-165:as of 770921,approx 675 Tubes Were Examined in C SG & Results Indicated That as Many as 100 Tubes in SG Might Have to Be Removed from Svc Due to Thinning of Tube Wall in Area Where Old anti-vibration Bars Left in Place

ML20151X835
Person / Time
Site:	Prairie Island, San Onofre
Issue date:	09/22/1977
From:	Klingler G, Nolan F, Sniezek J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
To:
References
PNO-77-165, NUDOCS 9809170270
Download: ML20151X835 (2)

Text

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JPMi4y }l7f PRELIMINARY NOTIFICATION ~

September 22, 1977 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-77-165

_This preliminary notification constitutes EARLY notice of an event of  !

POSSIBLE safety or public interest significance. The information '

presented is as initially received without verification or evaluation  !

and is basically all that is known by IE staff on this date.

Facility: Southern California Edison Company .

San Onofre (Docket No. 50-206)

Subject:

STEAM GENERATOR TUBE ELL THINNING This preliminary notification is issued for information only.

The San Onofre reactor commenced what was planned to be an approximate one week maintenance outage on September 8, 1977. One of the activities planned was the examination (including eddy current inspection) of the tubes in the station's three steam generators.

The licensee had previously comm!tted to examination of the steam generator tubes by April 1978, following modifications (principally the installation of newly designed anti-vibration bars to correct previously experienced tube wear) to the steam generators during the extended refueling and plant 6 modification outage of October 1976 through April 1977. Whereas complete /

examination of the steam generators had previously been scheduled by the #

licensee for April 1978, a partial examination was undertaken during the--

g current outage. .

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Ci The licensee has kept the Region V (San Francisco) Office of Inspection and-Enforcement and the Office of NRR informed by telephone of the inspection 2 results. As of September 21, approximately 675 tubes had been examined in the "C" steam generator, and the results indicate that as many as '100 tubes in this steam generator might have to be removed from service (by plugging),

because of thinning of the tube wall in the area where the old anti-vibration bars (AVB) were left in place. Approximately 1140 tubes have been examined in the "B" steam generator. The examination results indicate the potential for having to plug as many as 100 tubes in this steam generator because of wear in the AVB area. Inspection of the "A" steam generator is in progress. ._

There are approximately 3800 tubes in each of the three steam generators at San Onofre. Prior to the current outage, a total of 180 tubes (51 in steam generator A, 29 in B, and~100 in C) had been plugged in the more than 10 years operation of the plant. Approximately 30% of these resulted from wear in the AVB area. The results of current inspections strongly suggest that the modified AVB's installed during the 1976-77 outage have not been successful in correcting tube wear in the area of the "old" AVB's. -

CONTINUED

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1 9809170270 770922 PDR I&E PNO-77-165

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PDR r

Page 2 September 22, 1977

.l. .,' I Continued PN0-77-165

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The licensee is currently evaluating actions to correct this problem. The  ;

San Onofre plant is expected to remain shut down at least through the end i of Septenber. The licensee has committed to obtaining NRC review and t* approval of its plans for resolution of this problem prior to resuming operation. The Office of NRR has lead responsibility within NRC.for this determination. .

i The licensee has made information regarding the current outage available to

_ the news media as a routine practice. The steam generator problems have not, however, been highlighted.

The Region V office will examine details of this occurrence by on-site inspection prior to the plant returning to power operation.

The Region V office was initially informed of tnis occurrence by the Plant Superintendent by telephone at aoproximately 1:00 p.m. on September 16, 1977.

The information is current as of 4:30 p.m. on September 21, 1977.

Contact:

GKlin'gler, IE x28019 FNolan, IE x28019 JSniezek, IE x28019 Distribution: Transmitted H St L' o ' ;

Chairman Hendrie Commissioner Bradford ,

, Commissioner Kennedy S. J. Chilk, SECY C. C. Kammerer, CA Commissioner Gilinsky (For Distributio,n.).

• Transmitted: MNBB "Lj o.S~ P Bldg 2l 0 I L. V. Gossick, E00 E.,yolgenau[IE.$/

E. G. Case, NRR Region ~E(( L'/

S. H. Hanauer, ED0 J. J. Fouchard, PA SS B1dg 1* / / (MAIL) l W. G. Mcdonald, MIPC C. V. Smith', NMSS R. J. McTiernan, OIA R. G. Ryan,.0SP R. Minogue, SD H. K. Shapar, ELD T

f PRELIMINARY NOTIFICATION'  !

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