ML20237G428
| ML20237G428 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 08/17/1987 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| CON-NRC-87-081, CON-NRC-87-81 VPNPD-87-355, NUDOCS 8708240083 | |
| Download: ML20237G428 (5) | |
Text
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Wisconsin Electnc POWER COMPANY '
231 W. MICHIGAN,P.O. BOX 2046, MILWAUKEE,Wl 53201 (414)277 2345 l
VPNPD J55 i
NRC 081 l
August 17, 1987 U.S. NUCLEAR REGULATORY COMMISSION Document Control Desk Hashington, D.C.
20555 Gentlemen:
DOCKET 50-301 SLEEVING REPAIR OF STEAM GENERATORS POINT BEACH NUCLEAR PLANT, UNIT 2 The purpose of this letter is to inform the U.S. Nuclear Regulatory Commission of our plans to repair a limited number of Point Beach Nuclear Plant Unit 2 steam generator tubes by sleeving commencing with the scheduled Fall 1987 refueling outage.
The Fall 1987 Unit 2 outage is scheduled to begin October 2, 1987, and last through November 13, 1987.
In order to maintain the maximum number of tubes in service and thus prolong the life of the Unit 2 steam generators, Wisconsin Electric, Licensee for the Point Beach Nuclear Plant, is planning to selectively install' mechanical sleeves in tubes in the Unit 2 steam generators in accordance with Technical Specification 15.4.2.A.6.
Selection of tubes to be sleeved will be based on eddy current testing (ECT) piior to sleeving.
We expect that sleevimy can be accomplished without extending this scheduled refueling and maintenance outage.
As part of the ongoing maintenance and inspection programs at Point Beach Nuclear Plant, ECT has been performed on the Unit 2 steam-generators during past outages.
Results from the most recent inspections, conducted during the Fall 1986 outage, indicate a significant number of Unit 2 steam generator tubes with tube wall degradation less than the plugging limit as defined in Technical Specification 15.4.2.A.5(a).
The majority of the degradation is in the B steam generator cold leg where l
tube thinning was detected in prior years.
This thinning was L
believed to be arrested by a change in water chemistry (phosphate to all volatile treatment) in 1975; however, recent ECT has indicated some progression.
Whether this progression is real or due to differences in ECT techniques cannot be definitely h
8708240083 870817 PDR ADOCK 05000301 i
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Document Control Desk August 17, 1987 Page^2 l
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l determined.
The number of tubes in the A steam generator which-have shown similar degradation is minimal.. It is presently expected that 200 sleeves can be installed in the B steam gener-ator during this. year's outage, with similar limited sleeving
. planned for the refueliny and maintenance outages in 1988 and 1989.
Depending upon the results of the pre-s3eeving ECT or sleeve installation rate, there is the possibility that as many as 400 sleeves may be installed.
Based on previous ECT results, sleeving of the A steam generator is not expected to be necessary during this year's outage, but may be required in subsequent outages.
The sleeving program includes both repair and preventive sleeving.
Repair sleeving will be performed'on those tubes having degradation in excess of the plugging limit and which are technically capable of being sleeved.
Preventive sleeving will be performed on tubes having ECT indications which may exceed the plugging limit in future years and which are technically capable 1
of being sleeved.
As you know, Amendment Nos. 71 and 76 to Facility Operating License Nos. DPR-24 and DPR-27 respectively, were issued on April 4,
1983.
These amendments revised the Technical Specifications and permitted repair of degraded steam generator tubes by sleeving.
Point Beach Nuclear Plant sleeving repair was auth-orized by the Nuclear Regulatory Commission based on the follo-wing conditions relative to sleeving and ECT:
a.
Steam generator tubes that have been previously subject to explosive plugging shall not be sleeved; b.
Brazed joints shall not be employed; c.
Should eddy current testing indicate 40 percent or more degradation from the nominal tube wall thickness of a sleeve, the sleeved steam generator tube shall be plugged; and d.
Leak limits previously imposed on the repaired steam generators shall continue to apply.
In 1983, sleeving was performed on both Unit 2 steam generators.
The 1983 project was a preventive program to address the onset of tubesheet crevice defects.
Approximately 1500 tubes in the central region of the hot leg side in each Unit 2 steam generator were sleeved utilizing sleeves made of thermally treated Inconel 600.
The sleeves were installed using semi-remote tooling in conjuction with personnel entry into the steam generator channel head.
Westinghouse Electric Corporation performed this sleeving project in accordance with the sleeve design, process descrip-
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Document Control Desk August 17, 1987
_Page 3 tion, and analysis as reported in WCAP-9960, " Point Beach Steam Generator Sleeving Report," Revision 1, February 1982 (Propri-etary).
The limited scope sleeving planned for the Fall 1987 outage will also be performed by Westinghouse Electric Corporation consistent with WCAP-9960.
All of the conditions prescribed in the April 4, 1983 letter amending our license to allow repair of steam gener-ator tubes by sleeving will continue to apply.
However, improve-ments made in the process and materials since 1983 will be incor-porated.
The sleeving program planned for Unit 2 differs from the 1983 program in three areas:
- 1) the sleeves will be installed in the cold leg tube ends, whereas in 1983 sleeves were installed in the hot leg tube ends,
- 2) the sleeve material will be thermally treated Inconel 690 rather than thermally treated Inconel 600,
- 3) the sleeve installatisu process will utilize zero entry methods and remote tooling to the extent practicable, and
- 4) channel head decontamination will not be done.
These changes and the post-sleeving ECT are discussed below.
1)
Cold Leg Sleeve Installation The structural evaluation of the sleeve and tube assembly as described in WCAP-9960 for the hot leg conditions of pressure and thermal stresses bounds the conditions present in the cold leg side of the steam generator.
Therefore, the struc-tural analyses previously performed for hot leg conditions are applicable to cold leg sleeve installation.
The addition of a sleeve to the cold leg end of a tube which has been previously sleeved at the hot leg end will result in a flow rate reduction which is less than the incremental reduction in flow rate due to the hot leg sleeve.
Analyses indicate that the flow rate reduction for tubes sleeved in both tube ends is less than the flow rate reduction for two tubes sleeved in the hot leg end only.
For this reason, the current Fleeve-to-plug ratio for hot leg sleeves represents a bounding case.
Sleeve-to-plug ratios are currently being evaluated for tubes sleeved in both ends and will be used to determine equivalent plugging levels.
While there are presently no plans to install cold leg sleeves in unsleeved tubes, the analyses for hot leg sleeves would represent a bounding case.
Should cold leg sleeves be installed in unsleeved tubes, an appropriate sleeve-to-plug ratio would be determined.
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Document Control Desk August 17, 1987 Page 4 2.
Sleeve Material - Thermally Treated Inconel 690 Thermally treated Inconel 690 has demonstrated enhanced performance in primary and secondary side chemistry envi-ronments as compared to the previously used Inconel 600 materials.
Inconel 690 has been used in large scale sleeving programs at other PWRs since 1983 and is currently the tube material being used by Westinghouse in the fabrication of replacement steam generators.
Thermally treated Inconel 690 as a sleeve material is covered by the ASME Code Case N-20.
The design stress intensity values for Inconel 600 and 690 are identical.
Therefore, the primary stress intensity and maximum range of stress inten-sity allowables are equivalent.
In addition, analyses show that in the areas of the maximum primary stress intensity, maximum range of stress intensity and fatigue evaluation, Code allowable stress limits and usage factors are not exceeded with Inconel 690.
3.
Installation Methods Westinghouse has made significant advances since 1983 in the development of remote systems for use in sleeving appli-cations.
A remote system will be utilized to the extent practicable for each step of the sleeving process.
As a result of these remote methods, personnel exposure per installed sleeve is expected to be significantly less than during the 1983 sleeving projec-4.
Radioactive Waste Decontamination of the steam generator channel head will not be performed due to the relatively small scope of the sleeving program and due to the use of remote installation methods.
Therefore, no significant increase in radioactive l
waste generation is expected.
5.
Post-Sleeving Eddy Current Testing Following installation, all newly sleeved tubes will undergo full length ECT.
This testing has the dual purpose of veri-fying proper sleeve installation and establishing baseline data.
Use of a smaller diameter probe in the unsleeved por-tion of a tube will result in a sensitivity reduction.
This reduction in sensitivity will be quantified by comparing post-sleeving ECT data with the ECT data obtained with a
I Document Control Desk August 17,.1987 i
Page 5 larger diameter probe prior to sleeving Industry experi-ence indicates that ECT with this sensitivity reduction is l
adequate.for identifying and quantifying tube degradation.
WCAP-9960 will be revised to address-these differences.
Please contact us if you have any questions in regards to our I
steam generator tube sleeving plans.
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Very truly yours, E'
. hb t,/
/
C.
W.
Payt Vice President Nuclear Power Copies to NRC Regional Administrator, Office of Inspection and Enforcement, Region III; NRC Resident Inspector; R.
S. Cullen, PSCW
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