ML19318C720

Responds to NRC 800401 Request for Info Re Potential Failure of Once Through Steam Generator Auxiliary Feedwater Sleeve/ Collar Welds.Probable Cause & Failure Mode of Weld Cracking Not Yet Determined

ML19318C720
Person / Time
Site:	Arkansas Nuclear
Issue date:	06/05/1980
From:	Trimble D ARKANSAS POWER & LIGHT CO.
To:	Madsen G NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
1-060-01, 1-60-1, NUDOCS 8007020210
Download: ML19318C720 (3)

Text

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, T/C ARKANSAS POWER & LIGHT COMPANY POST OFFCE BOX 551 LITTLE ROCK. ARKANSAS 72203 (50'1371-4000 June 5, 1980 1-060-01 Mr. G. L. Madsen, Chief Reactor Operaticns & Nuclear Support Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Crive, Suite 1000 Arlington, Texos 76011

Subject:

Arkansas Nuclear One ~ Unit 1 Docket No. 50 - 313 License No. DPR-51 OTSG Auxiliary Feedwa w r !azzie Thermal Sleeve / Collar Welc Attachments (File: 1510)

Gentlemen:

By letter dated April 1,1980 you requested that Arkansas Power and Light provide you with certain information relative to the potential failure of 0TSG Auxiliary feedwater thermal sleeve / collar a-tachment welds. As you noted in your letter, cracking in the subject kelds has been observed at Oconee Uiiit 1 and the requested information was previously transmitted to AP&L by B&W.

The requested information is provided below.

1. Design / environmental conditions leading tc possible degradation of subject weld integrity. Identification of probable failure mode.

Reply:

The probable cause and failure mode of the subject weld cracking has not yet been determined. One of the affected AFW nozzle sleeves from Oconee Unit 1 is presently being metallurgically ]

examined at B&W's Lynchburg Research Center in order to define the cause of the weld attachment cracking.  ;

I s007020 1V ueueen uoate sour- uritiries svsre..

n o Mr. G. L. Mads:n 1-060-01

2. Interim actions taken.

Reply:

Magnetic particle examinations have been performed on all AFW nozzle thermal sleeve / collar attachment welds at ANO-1. These in-spections revealed no indications of weld cracking. However, as a conservative measure, a design modification recommended by B&W was installed in all AFW nozzles. This design modification restrains any axial movement of the AFW nozzle sleeve in the uMikely event that it becomes separated from its collar.

3. Possible long-term modifications.

Reply:

The need for long-term modifications will be evaluated pending the results of the investigations described in the reply to item 1 above. We have no plans for further modifications at this time.

4. Safety consequences.

Reply:

B&W has performed an evaluation of the potential consequences of 5 seaaration of the AFW nozzle thermal sleeves from their retaining collars during plant operation. The results of this evaluation are discussed below.

If the AFW nozzle thermal sleeve becomes separated from its collar, it can be postulated to back into the external piping elbow such that the four inch pipe may not penetrate the OTSG tube bundle wrap-per (shroud). B&W has performed a dimensional evaluation to de-termine the extent of possible lack of penetration of the thermal sleeve nozzle into the shroud. B&W has concluded that the resulting seaaration does not significantly affect the ability of the AFW sys-tea to deliver required flow to the tube bundle.

When the AFW system is used for long-term maintenance of a water level in the steam generator, AFW flow will be continually varied by the control system. As demand decreases and AFW flow decreases, increasing amounts of water could potentially spill into the steam annulus because of.the low velocity of the flow. Potential conse quences include; filling the steam annulus with water and subseque nt steam line water hammer resulting from " burping" steam through the steam lines, increases in steam line deadweight, local areas of high thennal stress in the steam annulus, and carryover of steam-water mixture to the secondary system. A detailed evaluation of these events has not been performed. The potential for these events at ANO-1 is precluded by the design modification discussed under item  ;

2 above.

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.,.. Mr. G.'L. Madstn . 1-060-01 The potential for physical contact of the thermal sleeve with OTSG tubes has also been evaluated. .During AFW operations there is a small net force on the sleeve in the direction of the tut; bundle. However, during normal operation the net force on the sleeve tends to move it away from the tube bundle. The eddy-current test histories of Oconee-I tubes located oppo-site the AFW nozzles have been reviewed and no indications of tube damage from thermal sleeve contact were found. The design modification discussed above precludes such damage at ANO-1.

Very truly yours, h a c. C M David C. Trimble DCT:DRH:ms i

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