ML20134F358

Submits Addl Info Pertaining to Unit 2 SG Insp.Summary of Zion 2 U-bend History Encl

ML20134F358
Person / Time
Site:	Zion File:ZionSolutions icon.png
Issue date:	01/30/1997
From:	Hosmer J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9702070396
Download: ML20134F358 (9)

Text

., Commonweahh Illien Company I400 Opus Place Downers Grove, II. G)515-570 I January 30,1997 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk

Subject:

Additional Information Pertaining to Zion Unit 2 Steam Generator Inspection Zion Nuclear Power Station Unit 2 NRC Docket Number: 50-304

Reference:

Commonwealth Edison Company / Nuclear Regulatory Commission Meeting dated November 15,1996 At the November l$th meeting, the Commonwealth Edison Company (Comed) and t .e Nuclear Regulatory Commission (NRC) discussed the Zion Unit 2 steam generators inspection results. During that meeting the preliminary results of the structural assessment of Tube R01C72, Steam Generator 3 were discussed. Subsequent to that meeting, the finalized calculation was completed which confirmed the preliminary results that the burst pressure would be in excess of the difTerential pressure load associated with a margin of three against burst during normal operating conditions. As you requested this finalized i evaluation which has been reviewed and approved by Comed is provided in Attachment A. Also, provided in Attachment B is the summary of the Zion 2 U-bend history along with Comed's conclusion that the history reflects expected primary water stress corrosion cracking (PWSCC) with imFored Plus -

Point Probe sensitivity.

If you have any questions concerning this correspondence, please contact Denise Saccomando, Senior PWR Licensing Administrator at (630) 663-7283.

Sincerely, ahw John B. Hosmer Engineering Vice President i

Attachments l

cc: C. Shiraki, Zion Project Manager-NRR A. Vegel, Senior Resident inspector-Zion A. B. Beach, Regional Administrator-Rill Office of Nuclear Safety-IDNS I

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Attachment A

" Evaluation of Steam Generator 3, R01C72 U-Bend Indication" l

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NSD-RFK-96-040, Rev. I

From

Steam Generator Design & Analysis WIN: 224 - 5086 Date: January 27,1997

Subject:

Evaluation of Zion 2, SG 3, RIC72 U-Bend Indication 4 To: J. Pierce ec: T. Pitterle J. Houtman j G. Whiteman W. Cullen D. Malinowski J. Bingaman R Sdth Note: Revision 1 corrects two typographical errors contained in the original release. In Section 2 "or rectangular" was corrected to "of rectangular,"

and " Alloy 600 steam" was changed to " Alloy 600 and 690 steam."

The attached evaluation was performed in response to a request from Mike Sears and Keith Moser, both of Commonwealth Edison, to estimate the structural integri-ty of the subject tube. The conclusion of the evaluation is that the burst pressure would be expected to be in excess of the differential pressure load associated with a i margin to 3 against burst during normal operation conditions and 1.43 during postulated accident conditions, as indicated by the guidelines in draft Regulatory  ;

Guide 1.121. Please transmit the evaluation information to John Blomgren of Commonwealth Edison at Downer's Grove, and to Keith Moser at the Zion station.

If you have any questions regarding this letter, please address them to me at the above WIN number.

Sincerely,

&_ o&

Robert F. Keating, Advisory ngineer SG Design & Analysis

[

Zion 2, SG 3, R01C72 Indication Evaluation of a U-Bend Indication in

, Tube R01C72, SG 3, at Zion Unit 2 1.0 Introduction During the most recent inspection of the steam generator (SG) tubes at the Zion 2 nuclear power plant, axially oriented indications were reponed for which demonstration of tube integrity  !

i relative to the guidelines of draft Regulatory Guide (RG) 1.121 was deemed appropriate. One of the tubes, SG 3, RIC13, was in situ pressure tested to 5000 psi at ambient temperature, Reference 0. The normal operating (NOp) differential pressure, AP, during the last operating cycle was 1530 psi at temperature. Thus, the test pressure was 3.3 times the NOp AP.

Accounting for the reduction in the Dow stress of the tube material with temperatum, 8.8% per Reference 0, the test pressure was at an equivalent margin of 3.0 relative to normal operation.

The indication in the second tube developed a leak and testing was terminated at a pressure cormsponding to main steam line break (SLB) conditions. Since a pressure of 5000 psi could not be achieved by the test equipment, a structural analysis of the tube based on the eddy

.~urrent inspection reponed profile of the indication was requested by Commonwealth Edison.

2.0 Evaluation The basis for the analysis of the burst pressure was the burst correlation information presented in Reference 0 for throughwall axial cracks in straight tubing. Since the indication is not everywhere throughwall, the correlation result is adjusted to account for the strength of the ligament material. In essence, the indication or crack is analyzed as being of rectangular profile with a linear interpolation being made between the nondegraded and throughwall burst pressures i using the ratio of the indication depth to the thickness of the tube. For depths greater than l about 75 %, the interpolation is nonlinear to account for the fact that thin ligaments have a j smaller critical crack tip opening displacement (CTOD) than thick ligaments. The analysis is programmed in a Excel

• spreadsheet and actually calculates the burst pressure for every possible sub-crack of the main crack. The lowest burst pressure calculated is the value assumed for the tube _being analyzed. The cenified mill test repon propenies for the RIC72 tube, Reference 0, were used for the analysis.

The analysis summary sheet is attached. The indication profile as a function of length was adjusted to account for the look-ahead and look-behind characteristics,'i.e., end effects (EE), of the eddy current test (ECT) analysis signals. This is most apparent in the figure on the attachment where the depth given by the dashed line appears to increase at the right end of the indication. Using the actual material propenies, the estimated burst pressure for the indication D:\P!ANTsiCOM96\UBEND-AX.WP5 01/31/97 1

Zion 2, SG 3, R01C72 Indication 4  :

, is 4145 psi at normal operating conditions if the indication existed in the straight length of the tubing. References 0 and 0, present the results of burst tests conducted on fabricated straight-leg and U-bend indications in Alloy 600 and 690 steam generator tubes with nominal diameters

! of 7/8" and 3/4" and wall thicknesses of 0.050" and 0.043" respectively. The test msults

] demonstrate that a 39% increase in the burst resistance of a 1/2" long throughwall indication

located on the extrados of a 7/8" diameter tube which has been bent into the U-bend shape for a row 1 tube. Hence, the expected burst pressure for the indication in service would be about

5720 psi. This is a factor of 3.74 times the NOp AP or about 125% of the margin of 3

specified in RG 1.121 for normal operating conditions. This would be expected to be quite i sufficient to accommodate any potential ECT uncertainties. Moreover, an analysis of the

! profile with end effects led to a burst pressure prediction of almost 4800 psi or about 3.13 times j the NOp AP.

! It is noted that the guideline for margin during postulated accident conditions leads to a critical l applied pressure of 3657 psi. Since this is less than 4590 psi, 3AP, the normal operation j guideline govems. In addition, prior tests have demonstrated that the burst pressure of tubes

{ with axial cracks is not significantly affected by bending loads such as could be developed during earthquake conditions or by flow during other conditions.

3.0 Conclusions The burst pressure of the indication at normal opemting conditions is estimated to be greater than 5700 psi, or 3.74 times the normal operating pressure differential. This is about 1100 psi greater than, or 125 % of, the draft RG guideline regarding a margin of three relative to burst during normal opemtion. In summary, the guidelines of RG 1.121 were met at the end of the current cycle of operation with sufficient margin to accomodate significant ECT error.

I The average of three tests on extrados throughwall indications with the range of factors being 1.37 to 1.42.

DnPLANT5\COM96\UBEND-AX.WP5 01/31/97 2 l

Zion 2, SG 3, R01C72 Indication 4.0 References

1. Personal communication with M. Sears (Commonwealth Edison) on November 7,1996.

2. .WCAP-12522, "Inconel Alloy 600 Tubing - Material Burst and Strength Propenies,"

Westinghouse Electric Corporation (January,1990). 1

3. SG-95-03-010 (EPRI Licensable), " Burst Pressure Correlation for Steam Generator Tubes with Throughwall Axial Cracks," R. Keating, et al., Westinghouse Electric Corporation (February,1995).

4. Personal communication with K. Moser (Commonwealth Edison) on November 12,1996.

5. MT-SGMCE-144, " Burst Tests of Small Diameter U-Bends," A. Klein to C. Hirst,  ;

Westinghouse Electric Corporation (June 16, 1982).

6. STD-7.2.4-7180, "PWS 4.802 Final Repon," B. Gowda to E. McDonough, Westinghouse Electric Colporation (December 21,1987).  :

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Attichmtnt to NSD-RFK-96-040

- Zion Unit 2 - U-Bend Crack, SG 3, R01C72 - 1996 01/27/97 i I l OD t Rm Sf.LTL Sf. Nom Sf RT20P Sf. cert-RT Sf. cert-OT I O.875 0 050 0.4125 63.12 68.78 91.1 % 78.50 71.54 Pbar2Pb P0 P pn P.sec dP.nop dP. sib 3 dP.nop 1.4 dP. stb 15.301 9.147 2.250 0.720 1.530 2.560 4.590 3.657 l 1 I l

MRPC, Final Adjusted, Final I Axial Crack Extrados Crack Extrados Weak Link Function Using )

Location Depths Lengths Depths Lengths BKH2 Model l 9.41 0% 0.000 0% X. min 0.000 9.44 39 % 0.036 0% X. max 0.594 l 9.47 75 % 0.071 0% Length 0.594 9.50 88 % 0.107 88 % 0.000 Depth 93.6 %

9.53 96 % 0.143 96 % 0.036 Pb/Sf 0.058 9.56 97% 0.178 97 % 0.071 Pb. Nom 3.985 9.59 98 % 0.214 98 % 0.107 Pb.LTL 3.657 9.62 97% 0.250 97 % 0.143 Pb. Cert 4.145 9.65 98% 0.285 98 % 0.178 Ph.Thru 4.013 9.68 97 % 0.321 97 % 0.214 U-Bend location: Extrados 9.71 97 % 0.357 97 % 0.250 U-Bend strength factor 1.38 I 9.74 98% 0.392 98 % 0.285 l Pb. nom 5.500 )

9.77 99 % 0.428 99% 0.321 1 Pb.LTL 5.047 i 9.80 98% 0.464 98 % 0.357 l Pb. cert 5.721 9.83 98% 0.499 98 % 0.392 Pb. cert / dP.nop 3.74 1 9.86 99 % 0.535 99 % 0.428 iEstimated burst pressure j 9.89 99 % 0.571 99 % 0.464 ifor U-bend axial i 9.91 97 % 0.594 97 % 0.487 indication.

l 9.94 92 % 0.630 92 % 0.523 Extrados Length Adj 9.97 87 % 0.666 87 % 0.559 OD 0.8750 10.00 85% 0.701 0% 0.594 t 0.0500 10.03 90 % 0.737 0% Rm 0.4125 10.06 92 % 0.773 0% R. min 2.1875 ,

10.09 0% 0.808 0% Ex. Factor 118 9% j D. avg 87.5 % D. avg 93.6 % Heat 1733 j L 0.808 L 0.594 _. Sy 55 j Pb.600 3.299 Pb.600 4.145 Su 102 I Ratio Psib 1.3 Ratio Psib 1.6 _

Sf 78.5 l l Zion Unit 2 - U-Bend Crack; SG 3i R01C72 - 1996 l 100%

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4 RFK 1I31/97.915 AM

(-ME2o2F XLS} R01C72

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Attachment B Zion 2 U-Bend Information l

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r Zion 2 E-Bend Indications Row I U-Bend Indications 3/84 2 - 9/85. I Bobbin Coil Inspections 6/87 3 - 11/88 2 Bobbin CoilInspections 1/89 6 -4/90 28 U-Bend MRPC Inspections 12/92 36 - 2/95 35 U-Bend MRPC Inspections 9/96 64 + Point RPC Inspections Prior to To Fall 1996

- MRPC:

100% Row 1Each SG 25 Tubes Row 2 Each SG Fall 1996 Inspection (Z2R14)

- Plus Point 100% Row I & 2 Each SG

- 64 Tubes Plugged Due to U-Bend Indications 3 Indications Identifiable In Spring 1995 Data Review

- All Remaining Row 1 Tubes Preventatively Plugged All Zion Unit 1 Row 1 Tubes Were Preventatively Plugged in 1982

Conclusion:

Expected PWSCC Degradation With Improved Plus Point Sensitivity

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