ML19254E874

Summary of 791012 Meeting W/Util Re Steam Generator Tube Rupture on 791002

ML19254E874
Person / Time
Site:	Prairie Island
Issue date:	10/22/1979
From:	Grotenhuis M Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
TAC-12237, NUDOCS 7911020477
Download: ML19254E874 (19)

Text

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NUCLEAR REGULATORY COMMISSION

.C WASHINGTON, D. C. 20555 g&.' \\%, 'u //

s OCTCBER 2 3 1979 Docket No. 50-282 LICENSEE: Northern States Power Company (NSP)

FACILITY: Prairie Island Nuclear Generating Plant Unit No.1

SUMMARY

OF MEETING HELD ON OCTOBER 12, 1979 TO DISCUSS THE STEAM GENERATOR TUBE RUPTURE OF OCTOBER 2,1979 On October 12, 1979, representatives of NSP met with the staff to present the details of the steam generator tube rupture; cause, inspections perfonned, remedial actions, and plans to return to power, etc. Attendees are listed in attachment 1.

The NSP presentation was opened oy G. Neils who presented the introductory remarts and the outline of the NSP presentation (see attachment 2 for outline and copies of visual aids employed).

The sequence of events was outlined and the cause of the tube rupture was explored with diagrams and pictures. The cause and data presented was, essentially as was indicated in phone conversations, namely that a spring (or springs) were introduced into the steam generator, became fixed by the flow blocking device and by virture of the constant vibration eroded three tubes, one to the point of causing the tube to rupture, one to 65% degradation and another to 20% (see copy of phone conversations dated October 9 and 10,1979, attachment 3). A fourth tube and the support plate were marked but had no signs of being eroded.

At the meeting, the licensee indicated that the size of the tube rupture was approximately 1-1/2 inches vertically and 1/2 inch across with a leak rate at the time of rupture on the order of approxiinately 380-390 gpm.

After the discussions were concluded and all questions were answered, the staff had a caucus to determine what requirements there would be for NSP to meet prior to Unit I returning to power operation. The staff concluded that the following requirements would be necessary:

1.

In regard to corrective measures applied to the ruptured tube, NSP must either:

a.

plug six tubes (a total of twelve plugs including the corresponding cold leg tubes); the ruptured tube, the 65% degraded tube and the four other tubes bounding the ruptured tube, or 1248 341 7911020 4-77

Meeting Summary for

'CTuBER i 2 1979 Prairie Island Unit 1 ~

b.

plug two tubes (a total of four plugs, including the corresponding cold leg tubes); the ruptured tube first having been stiffened to prevent it from breaking loose and causing further damage to surrounding tubes.

In addition, the ruptured and damaged tubes must be inspected at the next refueling shutdown and the results reported to the NRC.

A careful consideration of occupational exposures should be factored into the above choice.

2.

Documentation of the infomation presented at this meeting must be made prior to restart of Prairie Island Unit 1.

3.

Coolant technical specifications as given by the Standard Technical Specifications must be submitted to the NRC in thirty days.

In the interim period, but to be in effect before the startup of Prairie Island Unit 1, interim procedures shall be in effect for the reactor coolant and secondary coolant activity limiting conditions of operation.

4.

Three copies of the pertinent pictures taken during the inspections which show the location of the springs, eroded and ruptured tubes, etc.

Marshall Grotenhuis, Project Manager Operating Reactors Branch #1, D0R Attachments:

As Stated cc: w/ attachments See next page 1248 342

i Meeting Summary for ON 2o %'

Prairie Island 1 ~

Docket Files NRC POR Local PDR ORB 1 Reading NRR Reading H. Denton E. Case D. Eiserhut G. Zech B. Grimes W. Gammill-L. Shao J. Miller R. Vollner T. J. Carter A. Schwencer D. Ziemann P. Check G. Lainas D. Davis B. Grines T. Ippolito R. Reid V. Noonan D. Crutchfield G. Knighton D. Brinknan Project Manager OELD OISE (3)

C. Parrish/P. Kreutzer ACRS (16)

NRC Participants J._ Buchanan TERA' (C1$see Short Service List 1243 343

LIST OF ATTENDEES M. Grotenhuis haC DDR W. Hazelton NRC 00R V. S. Noonan NRC D0R E. L. Jordan NRC IE B. D. Liaw NRC D0R Jack Strosnider NRC D0R Jai Rajan NRC DSS D. C. Marburger Westinghouse H. VonHollon Westinghouse C. W. Hirst Westinghouse R. E. Carter Westinghoase E. Watzl NSP B. Turovlin NRC DSS W. Pasedag NRC 00R G. H. Neils NSP L. O. Mayer NSP D. Lindsey NSP P. J. Krumpos NSP M. Sellman NSP A. Schwencer NRC 00R R. Tedesco NRC 00R E. Murphy NRC D0R D. G. Eisenhut NRC 00R 1.243 344

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P.et No. 50-232 t'E"CU*CU:' FCR : Darrell G. Eisenhut, Acting Director Division of Operating Reactors FRC'i:

A. Schwencer, Chief Operating Reactors Branch #1, 00R Vince Noonan, Chief Engineering Branch, DDR

SUBJECT:

PHONE CONVERSATION WITH B. D. LIAW ON OCTOBER 9, 1979 AND WITH L. O. MAYER AND G. NEILS ON OCTOBER 10, 1979 REGARDING PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNIT NO.1 STEAM GENERATOR TUBE RUPTURE October 9,1979 Phone Report from B. D. Liaw. NRC at the Prairie Island Site On October 2,1979 about 3:30 pm EDT, Prairie Island Nuclear Generating Plant Unit No. I experienced primary to secondary steam generator tube l eak. The reactor was brought to cold shutdown in a routine nanner with the plant emergency procedures for such an event. Subsequent inspection revealed that the steam generator tube in row 4 column 1 had a rupture about 3 inches above the tube sheet. The rupture was about 2 inches long and about 3/8 inch wide, of the type commonly referred to as a " fish-mouth." The steam generator tubes in adjacent positions (row 3 colunn 1 and row 2 column 1) were thinned about 65% and 20%, respectively, at about the same height above the tube sheet. A steel spring about 6 inches long, about 1 inch in diameter and made of wire about 3/16 inch in diameter was found wedged between the tube sheet and a flow blocking device in the region of the degraded tubes (the flow blocking cevice diverts flow away from the open tube lane and into the tube bundle). The spring is a likely cause of the tube degradation. The spring is believed tc be from the inside of a suction hose used for sludge lancing. Sludge i2. cing has been performed as a part of a nunber of steam generator ins;sctions. EdQ current inscection consisted of an additional 12' of the stea gene-star tres 'n : tem gen 2ratcr A ll) anc til of the stean gene-aco-t;bes in row

1. ~ i s ',' de: al l the tubes ?dj::e-t to the degra:Ed tutes, tubes on the

.eH -"ery a# tre tune Nndle, whicr includes all the tubes in the "hard" s:::s, anc 3 ar.d:

e nie of tubes in the center of the tute bundle. At

'es:: P of the :;tes in ster gensator E (12) ei' i al so be insrected. ?00R OR GlEL 1243 357

s Darrell G. Eisenhut :.;T.IE;,: 73 Results of the inspection in steam generator A indicate no additional tubes that had wall thinning, although a small nu-ber of tubes had indications of 1 to 2 nil " dents" in the "12 o' clock" wedge region of the 7th tube support plate. The data from this inspecticn will be co pared to previous inspection data. The damaged tubes will be removed for further stud; if practicable. Current plans are to plug the ruptured tube, the degraded tubes and all adjacent to those tubes. A meeting will be held with the licensee to discuss the detailed results of the inspection prior to closing the steam generators. October 10, 1979 Reoort from Northern States Power A subsequent phone report on October 10, 1979 from L. O. Mayer and G. Neil s, NSP, to M. Grotenhuis and B. D. Liaw, t'RC, was made to update the NRC information ac follows: Further viewing indicates that the steel spring nay be 10 inches lone and lodged under the flow biccking device. It is postulated that the sprinc may have been in that location when the flow blocking device was installed in the spring oi 1976. Further details regarding the hoses used for sludge lancing indicate that the currently used hose is in a semi-rigid wall plastic hose. The previously used hose was a rubber hose with a wire spring imbedded. The earliest version used was a rubber hose with a steel spring inserted to prevent collapse. Further details of these hoses are being sought by NSP. G. Neils requested that the proposed October 12, 1979 8:00 am meeting in Bethesda be a firm date. The only item that may not be entirely clear at that time is the final disposition of the damaged tubes. NSP has Westinghouse making a preparation to remove the tubes and they will continue as long as that route is. practicable. At the tine of the meeting on October 12, 1979, all remaining details are ex:ected to be resolved and ready for presentation to NRC. All inspection of steam generatcr A (11) has been completed (12:30 cm Octcber 10, 1979). 303 DRBINM !243 358

Pogg gggg ~ C arrell G. Eisenhut - .:i; . c-0 cedures are being prepared for the removal cf the fl:.. blocking dev':e c: t".e spring. !!SP is preparing pictures and data to. support the ren :: ion c' oteration of Prairie Island Unit 1. 'f j 5

a. / :':

'llisin ' i d ' / Vince Noonan, Chief A. Schwsrcer, Chief 0:erating o.eactors Branch #1 Engineering Eranch Division of Operating Reactors Division of Operating Reactors cc: H. Denton W. Gammill L. Shao V. Noonan A. Schwencer M. Grotenhuis J. Strosnider B. D. Liaw S. Hanauer 1248 359 9 .}}