ML20062A464

Nonproprietary, Reevaluation of U-Bend Tube Fatique for Kewaunee Plant Steam Generators

ML20062A464
Person / Time
Site:	Kewaunee
Issue date:	09/30/1990
From:	Wooten M WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML111661006	List: ML111661005 ML111661007 ML20062A464
References
SG-90-08-014, SG-90-8-14, WCAP-12712, NUDOCS 9010220096
Download: ML20062A464 (11)

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WESTINGHOUSE PROPRIETARY CLASS 3 WCAP-12712

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i REEVALUATION OF U-BEND i j

TUBE FATIGUE FOR THE- l l

j KEWAUNEE PLANT STEAM GENERATORS ,

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ISSUE DATE - SEPTEMBER 1990 .

PREPARED FOR WISCONSIN PUBLIC SERVICE CORPORATION i

APPROVED: N.%.. LdNC M. J. WOOTTEN, MANAGER-D  !

i STEAM GENERATOR TECHNOLOGY AND' ENGINEERING

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WESTINGHOUSE ELECTRIC CORPORATION -

NUCLEAR SERVICES DIVISION P. O. BOX 355 PITTSBURGH, PENNSYLVANIA 15230

'l Copyright by Westinghouse Electric 1990, - All Rights Reserved

FOREWORD This nonproprietary report bears a Westinghouse copyright' notice. The-NRC'is=

permitted to make the number.of copies of this'_ report necessary for its. {

internal use and such additional copies which are necessary:.in order to have one copy available for public viewing in the appropriate docket. files in the public document room in Washington, D.C. and in local'pupblic document rooms .;

l as may be required by NRC regulations if the number of copies submitted is_-_,  !

insufficient for this purpose. The NIU: is not-authorized to make copies'for the personal use of members of the public.who make use of the NRC public- '

docunient rooms. Copies of this report or portions thereof made by.the NRC must include the copyright notice.

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1 l Introduction The initial assessment for Kewaunee steam generator small radius tube fatigue was performed in late 1987 and early 1988 (Reference 1). The Kewaunee assessment was reviewed in light of more recent test results in early 1989 (Reference 2). In neither of the assessments were any tubes identified as requiring modification or corrective action.

The NRC has requested that Westinghouse reevaluate the Anti >

Vibration Bar, (AVB) positions and associated flow peaking factors for a number of early steam generators evaluations. This reevaluation is intended to take advantage of improvements in the methods for defining AVB positions and the larger flow peaking I

data base which has been built up since 1988. Kewaunee is included in this set since the initial evaluation was performed in late 1987 and early 1988.

AVB Position Mapping The AVB positions found in the Kewaunee steam generators in the first analysis (Reference 1) are relatively favorable. All interior tubes in rows 11 and higher were found to be supported.

Only one interior tube in row 10 was possibly unsupported. There were eighteen interior row 9 tubes which=may have been unsupported.

In Reference 2, the case of the unsupported row 8 tubes were considered and the assessment was made that the length of the AVBs installed in columns 12 through 84 is not great enough for the bars to be connected to the retainer ring if the AVB is

[ inserted beyond the bottom of row 7. Therefore, only AVB-configurations in which AVBs penetrate one row beyond the. subject tube need be considered when searching to find the maximum flow peaking factor for a row 8 tube. .The-configuration with this

! restriction which has the highest flow peaking factor is configuration 4c which has a flow peaking factor of ( la,c, l This corresponds to a peaking ratio of ( J a, c. From Figure 1 which is repeated from Reference 2 it can be noted that all tubes in row 8 have a maximum allowable peaking ratio of not less than

[ J a,c . Hence any row-8 tube between columns 12 and 84 is l acceptable whether or not it is supported.

i l It should be noted that Figure 1 presents the maximum allowable l peaking ratio by tube position for the operating conditions listed i below:

Steam Flow (per S/G) 3.53 X 106 lbm/hr Steam Pressure 739 psia Circulation Ratio ( ja,c

From inspection of the ECT data and AVB position maps given in l Reference 1 it was determined that the only region in either of the Kewaunee steam generators where tubes are potentially unsupported in rows 9 or 10 is from column 34 to column 64 in steam generator B. Therefore the reevaluation of the Kewaunee steam generator AVB maps was performed over the region of column 32 to column 71 in steam generator B._ All the ECT data from rows 8 through 12 was used in the evaluation of AVB positions in the region.

Figure 2 shows the map of AVB positions in steam generator A and is repeated from Reference 1 for completeness. Figure 3 is the i revised AVB map for steam generator B. The changes in the AVB map for steam generator B in going from Reference 1 to the present work are small but significant. The row 10 tube which was possibly unsupported (R10C4 9) has been shown to be unsupported but to have a configuration of adjacent bars which provides no flow peaking. One of the row 9 tubes (R9C35) which was originally shown to be unsupported and which could have had a high peaking '

with a small change in the AVB position has been shown to be supported. A row 8 tubes which was originally shown as unsupported with high flow peaking (R8C68) has been shown to be supported. From these maps the flow peaking factors for all unsupported tubes were determined. As noted above, for row 8 unsupported tubes, the adjacent tubes extending-below row 8 are assumed to extend into row 7 to the position which produces the largest flow peaking factor.

Allowable and Actual Flow Peaking Ratios The flow peaking factors, peaking ratios and maximum allowable peaking ratios for all unsupported tubes with flow peaking factors greater than one are given in Table 1. It should be notea chat the peaking ratio is the flow peaking factor divided by the flow peaking factor for North Anna R9C51. The AVB insertion patterns and associated flow peaking factors and peaking ratios are shown in Figure 4. The maximum allowable peaking ratios are taken from Figure 1 and represent the peaking ratio which causes the Stress ratio to be unity after operation over the design basis period.

Inspection of Table 1 shows that there are no tubes in either Kewaunee steam generator where the peaking ratio is greater than j [ J a,c of the maximum allowable peaking ratio.

1 Conclusions All of the tubes in the Kewaunee steam generators are acceptable for operation over the full design basis period of the plant l

' without any corrective action at the flow and pressure conditions given above. A change in operating conditions could lower the i

maximum allowable peaking ratio, however this ratio'could be decreased by as much as [ ja,e for the most limitng tube before l the actual peaking ratio would equal the maximum allowable peaking ratio.

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l Table 1 i Velocity Peaking Factors and Peaking Ratios for Kewaunee U-bend Flow

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Maximum Steam Row Column Type of AVB Peaking Peaking Allowable -l Generator Insertion No No Factor Ratio Peaking Ratio

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References

1. Susceptibility to High Cycle Fatigue of Steam Generator l i

Tubes - Kewaunee Nuclear Power Plant, STD-7.2.2.1-8217,. June.

27, 1988 j

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2. Kewaunee Steam Generators - Review of Tube Fatigue  !

Evaluation in Light of More Recent Test Results, WPS-89-116, 4 February 14, 1989 i

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