ML092120202

LTR-SGMP-09-64 Rev. 2 Np, Surry, Unit 1, Support for Emergency Technical Specification Amendment to Address Permeability Variation Signals at the Tube Ends.

ML092120202
Person / Time
Site:	Surry
Issue date:	05/06/2009
From:	Westinghouse
To:	Office of Nuclear Reactor Regulation
Cotton, Karen - NRC/NRR/ADRO/DORL/LPL2-1
Shared Package
ML092160941	List: ML092120202
References
09-295A, TAC ME1911 LTR-SGMP-09-64, Rev 2 NP
Download: ML092120202 (7)

Text

Serial No. 09-295A Docket No. 50-280 Attachment 2 Westinghouse Electric Company LLC Letter (Non-Proprietary)

LTR-SGMP-09-64 Rev. 2 NP Attachment, "Surry Unit 1: Support for Emergency Technical Specification Amendment to Address Permeability Variation Signals at the Tube Ends," dated May 6, 2009 Surry Power Station Unit 1 Virginia Electric and Power Company (Dominion)

Westinghouse Non-Proprietary Class 3 LTR-SGMP-09-64 Rev. 2 NP-Attachment Westinghouse Electric Company Surry Unit 1:

Support for Emergency Technical Specification Amendment to Address Permeability Variation Signals at the Tube Ends May 6,2009 Westinghollse Electric Company LLC P.O. Box 158 Madison, PA 15663

© 2009 Westinghouse Electric Company LLC All Rights Reserved

LTR-SGMP-09-64 Rev. 2 NP-Attachment References

1. LTR-CDME-08-11, "Interim Alternate Repair Criterion (ARC) for Cracks in the Lower Region of the Tubesheet Expansion Zone", Westinghouse Electric Company, LLC, January 31,2008.

2. LTR-CDME-08-43, Revision 3, "Response to NRC Request for Additional Information Relating to LTR-CDME-08-11, Revision 3 P-Attachment", Westinghouse Electric Company, LLC, June 3, 2008.

3. LTR-SGMP-09-63," Assessment ofTube-end Indications at Surry Unit 1", Westinghouse Electric Company, LLC, May 4, 2009.

4. WCAP-17071 (proprietary), "H*: Alternate Repair Criteria for the Tubesheet Expansion Region in Steam Generators with Hydraulically Expanded Tubes (Model F)", April 2009.

A. Introduction During the spring 2009 inspection at Surry Unit 1, under the inspection program required to implement the Interim Alternate Repair Criteria (Reference 1 and Reference 2) for the tubesheet expansion region, multiple permeability variation signals were reported at the tube-ends in SG-B. Permeability variations are not degradation of the tube material but, if they cannot be resolved by eddy current techniques, they may mask signals of real degradation. Therefore, if unresolved, these indications must be treated as if they are indications of actual degradation. The permeability variations were reported at approximately 0.2 inches above the tube ends, consistent with the location of axial and circumferential tube end indications reported at other plants that have applied the IARC (Reference 1 and 2). Because the permeability variations may mask signals that would require plugging many of the tubes with these signals, it is necessary to perform an engineering evaluation of this condition.

Reference 3 provided an independent justification for leaving the tubes with tube-end permeability variations in service. The information in Reference 3 was transmitted to Dominion and forwarded in part to the USNRC staff. In a telephone conference on May 4,2009, the NRC staff requested additional information including the following:

1. An estimate of the mean value of H* and the value of H* at 95% probability at 50% confidence. The justification of H* is a current work in progress whose completion was scheduled for mid-June 2009. Because of the request from Dominion, it was agreed to provide an early estimate of the mean and probabilistic values of H*. The values of H* must be considered a preliminary estimate because the normal rigor of the internal review process could not been completed in the time available.

2. An evaluation of the maximum potential tube slippage under a set of bounding assumptions that are specified in this letter.

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LTR-SGMP-09-64 Rev. 2 NP-Attachment The following provides the requested information:

A. Preliminary Values of H*

H* is the length of undegraded tubing required to retain the tube in the tubesheet under limiting loading conditions as required by NE197-06, Revision 2. The technical justification of H* for the Model 51F SGs at Surry is a current work in progress, scheduled to be completed in mid-June 2009. The final report for H* for the Model F steam generator is complete (Reference 4). The estimates of the values of H* for the Surry Model 51F SGs utilize the same methods presented in Reference 4.

Based on the same assumption used in Reference 4, but considering the geometry specific to the Model 51F SGs, the mean value of H* was calculated. The structural difference between the Model51F SGs and the Model F SGs discussed in Reference 4 are principally the tube diameter ([ ] a,c,_ inch for the Model 51F SGs vs. [ ] a,c,_ inch for the Model F SGs) and tube pitch ([ ] a,c,_ inches for the Model 51F SGs vs. [ ] a,c,_ inch for the Model F SGs). Further, the operating conditions specific to the Surry Units were considered instead of the bounding Model F plant conditions.

The predicted mean value of H* for Surry Units 1 and 2 is [ ] a,c,_ inches from the top of the tubesheet, including a [ la,c,- inch allowance for the location of the bottom of the expansion transition and an allowance for thermal distribution in the tubesheet at normal operating conditions.

In reference 4, the whole bundle 95% probability, 50% confidence value of H* was principally determined by a square root sum of the squares (SRSS) approach based on the principal variables that affect the value of H* when it is assumed that residual contact pressure is zero. The Model51F SGs include a complement of [ ] a,c._ tubes. From standard binomial distribution calculations, the required deviation from mean is [ 1 a,c,_ standard deviations (sigma) to achieve 95% probability at 50% confidence for a population of [ 1a,c,_ without any failures.

Based on the SRSS approach at [ ] a,c,_ sigma, the 95/50 value of H* for the Surry SGs is estimated to be 12.5 inches. This value includes the adjustment of [ ] a,c,_ inch for the uncertainty in location of the bottom of the expansion transition and the correction for the normal operating condition tubesheet thermal distribution. Normal operating conditions are limiting for the value of H*. The value of H*

does not include the adjustment for referencing the crevice pressure distribution to the predicted value of H*. An estimate of this adjustment is obtained from Reference 4. For the Model F SG, a predicted value of H* of [ ] a,c,_ inches would require an additional crevice pressure adjustment of approximately [ ] a,c,_ inches, However, the Surry Unit 1 inspection results have confirmed that nearly the full length of the tube, minus the tube end portion in the 0.20 inch above the primary face of the tubesheet, exists and is free of defects. Therefore, no crevice pressure adjustment is necessary for the Surry Unit 1 preliminary value of H*.

B. Assessment of Slippage Based on a review of the tubesheet maps from Surry (Figures 2 and 3) which identifies all of the locations of the permeability variation (PVN) signals for SG B of Surry Unit I, the bounding hypothetical vertical displacement of a single tube end is calculated to be 8.7 inches at column number 71. The 4

LTR-SGMP-09-64 Rev. 2 NP-Attachment thickness of the Surry 1 Model 51 F tubesheet is [ ] a,c,e inches. This calculation conservatively assumes the following as initial conditions:

1. Each permeability variation signal is masking a completely severed tube,

2. No friction forces exist between the tube and the tubesheet.

3. The tubesheet does not bend or deform during any of the plant conditions (bending in the tubesheet will act to restrain vertical motion of the tubes),

The estimate for maximum potential vertical travel of a tube is based on using nominal tube and tubesheet dimensions (Le., a tube pitch of [ ] a,c,e inches and a nominal tube outside diameter of

[ ] a,c,e inch),

The tubes are installed concentrically in the tube bundle of a Model51F steam generator; that is, the center of the U-bends for all rows of tubes is located at the same elevation in the bundle. Therefore, the distance of potential motion is calculated by multiplying the number of consecutive tubes in a column with permeability variation indications on either the hot leg and cold leg of the tube bundle times the difference between the tube pitch and outside diameter of a tube. For columns with stayrods, two tube diameters were added to the vertical motion distance. A graph of the maximum travel of a tube end by tube bundle column number in SG B is provided in Figure 1. Figure 1 is based on a study of Figure 2 to determine the maximum number of contiguous tubes with tube end permeability variations in the same column.

All tubes in Surry Unit 1 SG B would be expected to remain well within the thickness of the tubesheet during all plant conditions as each set of "stacked" tubes would be immediately retained by an adjacent outboard tube without PVN signals.

There are no peripheral tubes with PVN signals in SG B. The outermost tubes with PVN signals are:

Row 22 Column 7 Row 45 Column 49 Row 45 Column 46 The circumferential extent of the PVN signals for two of the three tubes in question are less than the 94 degree acceptance criteria in the IARC and are acceptable for continued service without the proposed emergency change. The circumferential extent of the PVN signals on R45C49 and R45C 46 are 59 degrees and 38 degrees, respectively. The third tube has a PVN signal with a circumferential extent of 136 degrees. For each of the three outermost tubes, there are no indications on the hot leg side of the tube.

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LTR-SGMP-09-64 Rev. 2 NP-Attachment Figure 1 Surry Unit 1 SG B PV Indications Potential Slip Evaluation 10 9

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