ML18114A640

Steam Generator Tube Insp & Preventative Plugging Program

ML18114A640
Person / Time
Site:	Surry
Issue date:	04/30/1979
From:	VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
Shared Package
ML18114A639	List: ML18114A638 ML18114A640
References
NUDOCS 7906050367
Download: ML18114A640 (16)

Text

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• Steam Generator Tube Inspection and Preventive Plugging Program*

Surry Power Sta~Unit No. 1 April, 1979~~~--

1. Inspection Program The steam generator tube inspection program is intended to encompass those regions where significant degrees of tube deformation or wastage may have occurred.

Regions where significant deformation may have occurred are.

determined by the finite element analysis.which, whencombineci with tube strain tests, yields tube hoop strains versus tub.e location and extent of plate deformation. Additional inspections are defined for certain areas, particularly the wedge and.-*pa t.ch plate regions.. The inspection programs in the wedge and patch plate regions are based on previous leaker histories and gauging results from the Surry and Turkey Point sites.

Inspections for O.D. wastage were performed in the cen~ral tube sheet regions of all steam generators. This was to identi:l::y any tubes having significant wastage, particularly in proximity to tube dents.

• The boundaries of all inspections are shown in Figures 1, 2, 3, and 4.

The specific bases for the inspection boundaries are as follows:

1) The hot leg inspection boundary encompasses the 17.5% strain boundary as determined by finite element analysis. Since full closure was observed in Surry Unit 1 during the April 1977 inspection, Surry Unit l is regarded as being beyond full closure by approximately 18 EFPM 's. The tube hoop strain contours calculated for 18 EFPM's were utilized to determine the 17.5% boundary for this inspection. The tube hoop strain contours for 18 EFPM's are shown in Figure 5.

In previous inspections, when much less plant specific inspection data was available, the 15% strain boundary was used as the basis for the inspection program. We now have the benefit of extensive plant specific information which indicates the conservatism of the 15% boundary and the ade-quacy of the 17. 5% boundary. Specifically, while the 15%

strain boundary now covers almost the entire tube sheet, significant tube restriction activity remait].s confined to areas immediately adjacent to previous activity. The validity of this approach is confirmed by inspect:i.on results.

The 17.5% boundary is supplemented by additional inspections where significant activity could be expected based on past

2 e e experience. The overall hotleg program, based on the 17.5% strain boundary and on past experience is sho,m in Figure 1 (solid line).

2) The cold leg inspection boundary was based on the 17.5%

strain boundary and on past experience. The cold leg inspection boundary is shown in Figure 1 (dotted line).

3) When a restricted tube was found close to the inspection

.boundary, the inspection was expanded.in that area.

4) The central tubesheet regions of all steam generators were inspected to monitor for O.D. wastage. During the previous inspection in December 1978, two tubes in the central tubesheet*area of steam generator C were**

found to be leaking. As a result, additional inspec-tions of the cent1:al tubesheet area were performed at that time as explained in our letter of December 29, 1978.

While no reaking tubes were found in the central tubesheet area of any steam generator during this outage, the central tubesheet inspections were repeated during the current inspection as a precautionary measure. The boundaries of the O.D. wastage inspections are shown in Figures 2, 3 and 4.

Based on these criteria and on inspection results, the inspection boundaries are considered adequate and conserva-tive.

2. Visual Inspection Results Prior to the shutdown, a very small primary to secondary leak w:as identified in steam generator C. The leakage was estimated*to be in the range .004 to .006 gpm.

During the inspection outage, all steam generators were inspected for evidence of leakage. No evidence of leakage was found in steam generators A or B. As expected, two leaking tubes were found in the hot leg of C steam generator. The locations of the leaking tubes were Row 20 - Column 8 and Row 5 - Column 75. In both cases the leaks were slow drips under 200 psi differential pressure. This confirms the small magnitude of the leaks as estimated prior to shutdown.

3. Evaluation of Inspection Results The r2sults *of the inspection prograTIJ are presented in Figures 6, 7, an(,l 8. Tnese results support the adequacy of the inspection program and the plugging criteria.

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A. All tubes that restrict the .610" or the .650" probe are adjacent to areas of previous activity.

B. There were no tubes in steam generators A, B, or C that restricted the .540" probe.

C. All activity appears to be moving in a stable manner adjacent to previous activity.

D. Activity in the wedge areas was minimal for this inspection and appears consistent with previous experience at Surry. Based on the previous behavior of these areas, application of the plugging criteria should stabilize these regions.

E. On the cold leg side, all tubes in all steam generators met the gauging criteria with a

.610" probe and all tubes were satisfactorily U-bend inspected. Results indicate that cold leg activity continues to grow at a very slow

. rate as compared to hot leg activity.

4. Plugging Criteria The plugging rationale and criteria as defined below are con-sistent with those applied in previous inspections.

The plugging criteria applied to support seven month.s of operation are as follows. Note that while the complete plugging criteria are listed, some items do not apply to this inspection due to the small amount of activity detected.

A. All tubes which did not pass the 0.540 inch probe were plugged.

S. Additionally, two tubes beyond (i.e., higher row numbers) any tube in columns 15-79 which did not pass the 0.540 inch probe were plugged; for such tubes in columns 1-14 and 80-94, five tubes beyond were plugged on the hotleg side and four tubes beyond were plugged on the coldleg side.

C, All tubes which did not pass the 0. 610 inch probe were plugged.

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D. The tubes in any column for *which plugging under criteria (A), (B), or (C) above is implemented were also plugged in the lower row number tubes back to the tubeline if not already plugged.

E. As a conservative measure, tubes completely sur~

rounding any known leaky tubes including the di-agonally next tube will be plugged if not al-ready covered by the foregoing criteria.

F. In any given column which is surrounded by columns.

containing tubes with significant tube restriction or prior plugging, (thereby creating a "plugging valley" in the pattern) engineering judgement will be used to fill the bottom of the valley. In the peripheral tubelane areas near the three and nine o'clock wedges, tubes surrounding previously plugged tubes or tubes exhibiting high deformation activity will be plugged based on engineering judgement.

G. Additional preventive plugging will be implemented at the hot leg wedge locations. This plugging will include all tubes that:

1. Restrict the 0.540 inch probe

2. Restrict the 0.610 inch probe

3. Restrict the 0.650 inch probe at the periphery

4. Surround leakers and tubes that restrict the 0.540 inch probe including the diagonally next tube.

H. Application of the criteria specified in G, above, will be made on the basis of engineering judgement for cold leg wedge locations.

I. In those areas where additional inspections were performed to identify areas of significant wastage, all tubes with significant wastage and all tubes where wastage measurement could not be considered accurate due to masking effects, were plugged.

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6. Actual Plugging Pattern Figures 9, 10, and 11 indicate the plugging patterns for Surry 1 steam generators based on the plugging criteria described above.

Plugging totals for this inspection are as follows:

Plugged this Outage Total Plugged to Date Steam Generator A 5 874 Steam Generator B 1 644 Steam Generator C 22 986 At total of 2504 or 24.6% of the steam generator tubes are now plugged.

7. Handhole Inspections Handhole inspection using photographs were performed in all s.team generators. This inspection was to verify that the support plates had undergone no further degradation since the last inspection and that no new phenomena had developed. Inspection revealed that the condition of the visible support plates had not changed since the previous inspection and that no new phenomena were observed. The photographs will be availa-ble for inspection at the site.

8. Annulus Measurement Wrapper to shell annulus measurements were performed in steam generator C as part of a continuing program to monitor plate growth.

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Figure 1. Surry Unit 1 Gauging Program Hot leg - solid line Coli leg~ dotted line

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Figure 3, o. D. Wastage Inspection Surry Unit 1 Steam Generator B

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Figure 4. O.D. Wastage Inspection Surry Unit 1.

Steam Generator C

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Figure 6 Gauging Results X= ,,540 11 Probe Surry Unit No, 1 6. = , 610" Probe Steam Generator A 0 = .-650" Probe

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Gauging Results X= .540" Probe Figure 7 _I:, = , 610" Probe Surry Unit No. 1 Steam Generator B D = .650" Probe

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Figure 8 Gauging Results ><= , 540" Probe Surry Unit No. 1 b= . 610" Probe Steam Generator C Q= , 650" Probe

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Figure 9 Preyentive Plugging Program Surry Unit No. 1 Steam Generator A

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Figute 10 Preventive Plugging Program Surry Unit No. 1 Steam Generator B

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~-,vlANVJAY Figure 11 Preventive Plugg'ing Program Surry Unit No. 1 Steam Generator C