ML20129B993

Forwards Summary Rept of Preliminary Ultrasonic Exams On...Steam Generators & Pressurizer, Summary of Repair Methodology of Ultrasonic Testing Indications In...Steam Generator Shell Welds & Metallurgical Investigation..

ML20129B993
Person / Time
Site:	Byron
Issue date:	05/24/1985
From:	Ainger K COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20129B995	List: ML20129B993 ML20129C016 ML20129C048 ML20129C079
References
NUDOCS 8506050380
Download: ML20129B993 (3)

Text

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Commonwealth Edison On3 Fast Nationri Plaza. Chicago, lihnois

' Addr:ss R: ply to: Post Ofhce Box 767

, , Chicago. Illinois 60690 May 24, 1985 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regu~1ation U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Byron Generating St'ation, Unit 2 Preservice Inspection NRC Docket No. 50-455

Reference:

(a): March 15, 1985 letter from T.R. Tramm to H.R. Denton

Dear Mr. Denton:

This letter provides additional information regarding the preliminary preservice inspection examinations of the Byron Unit 2 steam generators and pressurizer.

Based on our evaluation of the condition of these components, we plan to repair three Unit 2 steam generator weld s areas which contain indications unacceptable to ASME Code Section XI. We will also remove two core samples from other Unit 2 steam generator welds for metallurgical analysis. The results of this analysis will be used to disposition other weld reflectors identified in these components.

Reference (a) described the results of the preliminary ultrasonic (UT) examinations performed on the Byron Unit 2 steam generators and pressurizer. Preliminary conclusions were presented regarding the condition of the Unit 2 components based on the UT data recorded by EBASCO Services, Inc. and the Westinghouse metallurgical analysis of Byron Unit 1 steam generator weld samples. When correction factors are applied to the Unit 2 examination data to account ror ultrasonic oversizing, only five of the reported forty-five weld indications are unacceptable. Based on this information, only these five indications warrant repair. A more detailed summary of the data evaluation is provided in Attachment I.

areas.

We originally planned to repair three of the five weld defect We also proposed to extract metal samples from these three locations for destructive testing and metallurgical analysis. These areas are in the upper and lower welds of cone. The other two unacceptable indications, located in the welds near the steam generator transition the tubesheet, were to be evaluated by fracture mechanics analysis.

However, subsequent review of the steam generator design shows the welds near the tubesheet to be most favorable for extracting metal samples.

Consequently, we now plan to remove two 2.5 inch diameter plug samples from the tubesheet welds and install cover plates. No welding will be required in this procedure. The three indications near the transition cone will be removed by " controlled" grinding to minimize the f size of the excavations. If weld repair is required, we will use r '

procedures similar to those for the repair of the Byron Unit I steam generators. However, these Unit 2 procedures will be written in accordance with the requirements of ASME Code Section III. The Unit I

' lf rcpair methodoloov is nrovided in Attar.hment II.

8506050300 850524 gDR ADOCK 05 y 45

H.R. Denton May-24,'1985 2.-

The-metallurgical. analysis:of the two Unit 2 core samples will b 'be-performedLto determine if the nature of the weld-reflectors in the

' Unit 2-components is the~same as those in-Unit I components. Analysis.of c theLUnit I core' samples. demonstrated that the indications were oversized

.by aLfactor ofL6.5 for the through-wall depth dimension and by a factor of.2.5 for length. ~The Unit 1 metallurgical report is provided as

' Attachment III. -If'the Unit 2 analysis demonstrates that similar-e oversizing of,the reflectors has occurred, we feel that additional

-repairsaare unnecessary.

In an' attempt to determine the cause of the weld indications, 1 thel fabrication history and the original shop weld radiographs of the steam. generators have been reviewed. Details of this. review including fabrication materials and weld details are provided in Attachment IV.

Based on this~ review and-the UT examination data we believe that the

-indications are very small slag-induced discontinuities in the weld metal

! near the-inside diameter surfaces.- The formation of these discontinuities most likely occurred during fabrication when these weld areas were back gouged and rewelded after removing the backup bar.

The original construction radiographs show slag inclusion-type '

L Ldefects of' sizes varying from 1/4 to 3/8 inches. Commonwealth Edison ,

l personnel. performed ultrasonic examinations to more accurately size the  !

~

defects and this showed the defects to be smaller in the through-wall L

depth' dimension than those reported by EBASCO. This information supports cur belief that the UT-examination performed and reported in accordance

.with the. requirements of ASME Code Section XI exaggerates the sizes of the defects.

l l

Core sampling and weld repair-is currently scheduled to begin

-on June 3,.1985. The metallurgical analysis will be performed immediately after the samples are extracted. The results of the analysis are expected to be available by June 17, 1985 and will be submitted for '

your. review.

Please direct questions concerning this matter to this office.

One signed original and fifteen copies of this. letter and the u attachments are provided for NRC review.  ;

Very truly yours, i

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• 1 l j

2 i K.A. Ainger

! Nuclear Licensing Administrator Attachments O

g e

9 I

6 ATTACHMENT I j