ML19323G175

Nondestructive Exam of Prairie Island 2 Steam Generator Tubing.

ML19323G175
Person / Time
Site:	Prairie Island
Issue date:	04/25/1980
From:	Klien A WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML19323G170	List: ML19323G169 ML19323G172 ML19323G175 ML19323G177 ML19323G178
References
SG-80-04-030, SG-80-4-30, TAC-12657, NUDOCS 8005300499
Download: ML19323G175 (14)

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Attachment A

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Docket No. 50-306 LER R0-80-03

% 5/23/80 SG-80-04-030 NON-DESTRUCTIVE FXAMINATION OF PRAIRIE ISLAND 2 STEAM GENERATOR TUBING .'

i A. V. Klein Materials Technology Westinghouse Nuclear Technology Division April 25, 1980 Introduction Recent eddy current examinations of Prairie Island Unit 2 steam generator tubes have revealed indications in a number of tubes as summarized below. The affected tubes werc located primarily in the periphery of the bundle and the indications were located at the first and second tube support intersections on the cold leg side. The statistics are as follows:

Steam Generator 21 Steam Generator 22 No. of peripheral tubes inspected: 642 1026 No. of tubes with Indications at 1st TSP 31 40 No. of tubes with Indications at 2nd TSP 7 57 The Indications ranged from less than 20% wall thickness to one at approximately 75%, with the majority in the less than 20% category. The indications were Interpreted as some form of OD wall loss, located in the center of the support plate intersection, but no more definitive information could be obtained from the eddy current signals.

To determine the actual cause of the indications, a representative tube, R34C79 of S/G 22 was removed on Janu:ry 27, 1980, for detailed non-destructive and

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destructive examination. This document describes the tube removal and presents 1 the results of the non-destructive examination performed by Westinghouse. The results of the destructive evaluation are reported separately in Vestinghouse Research Report 80-5D9-PRARI-RI, " Examination of Prairie Island 2 Inconel Alley 600 Steam Generator Tube," R. G. Aspden, dated March 10, 1980.

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cxhibited wall loss, the next four intersections had slight discolorations and possibly local deposits and the seventh exhibited sh7tiow circumferential striations. All other areas, including tie 6" length from the tubesheet crevice, exhibited a tight, dull, black corrosion oxide typical of service exposed Inconel 600 tubing, with no extraneous deposits.

B. Radiography - All tube support Intersection zones were radiographed using the double wall technique. The first support zone exhibited %0.010" maximum

• ' ell reduction while the second support zone had approximately 0.020"-0.025" wall loss. The 3rd, 4th, 5th, 6th, and 7th showed no detectable wall loss. Standards shot with each exposure revealed that 1 mil of wall reduction could be detected.

C. Eddy Current Examination - All segments containing tube support plate Intersections were eddy current tested using 400, 200, and 100 kHz multi-frequency techniques. The results were very similar to those obtained from radiography. The first TSP Intersection revealed a 20% indication, the second two indications of 40 and 60%, and the remaining intersections had no evidence

, of wall loss. A simulated tube support plate section was fitted over the tube at the second TSP intersection location and the signal obtained was similar to that observed in the in plant inspection. When the support plate simulant was placed over the first TSP intersection, however, there was no discernable tube indication because of the small amount of wall penetration, %20%. ,

l D. Profilometry - Detailed profilometry of the OD at the affected first and second intersections generally supported the other findings; the maximum OD  ;

reduction agreed with the X-ray and E/C estimates of wall loss.

l C ONCLUS IONS The results of the Initial non-destructive examination indicated local OD wall loss in the center of the first and second TSP intersections. All other areas examined were normal and free of any evidence of distress. The eddy current, I

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1. Tube Removal Access for remot ing peripheral tubes from the primary side is limited by the curvature of the channel head. In order to remove the selected tube, it was necessary to part the tube, within the tubesheet, at an elevation approximately 6" below the secondary side. This operation was performed from the primary side.

The secondary side was then entered and the tube was again parted below the first anti-vibration bar support at the top of the tube bundle. The bent end was straightened, an inside diameter gripper was inserted in the tube, and the tube was hydraulically raised vertically through the tube support plates. Only 1000 pounds force was required to break the tube loose (a low load indicating freedom from restrictions in the tubesheet crevice and tube support plate intersections).

As the tube was withdrawn manually hend over hand above the top (seventh) tube support plate, it was cut into random lengths approximately 30" long to aid in the removal and subsequent packaging and shipment. Care was taken to avoid cutting the tube near the tube support plate intersections. Also, small paint dabs were placed on each section to indicate its orientation with regard to the wrapper and shell.

After visually examining the tube sections at the plant, they were cut into somewhat shorter segments, packaged, and trucked to the Forest Hills Site for the non-destructive examination.

The ends of each cut segment were numbered sequentially, starting at the top (U-bend) end. Figure 1 describes the Idsntification of the seven relevant

_ sections, each about 12" long across each of the tube support plate intersections.

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2. Non-destructive Examination of Tube R34c79 A. Visual Examination and Photography - All tube sections containing support plate intersections were photographed at 4 rotations (0 , 90 ,180 , 270 ) .

As shown in the attached photographs, only the first and second intersections I

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radiographic and profilometric results were all consistent, Indicating about a 0.010" local wall reduction at the first and a 0.025" local wall reduction at the second TSP intersection. The laboratory eddy current examinations generally reproduced and confirmed the in plant examination results.

The cause of the observed local wall reduction could not be determined from the non-destructive examination. That required destructive metallography and micro-analytical examinations which were subsequently performed and reported separately In Westinghouse Research Report 80-5D9-PRARI-R1, " Examination of Prairle Island 2 Inconel Alloy 600 Steam Generator Tubes," R. G. Aspden, dated March 10, 1980.

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