ML20207F277

Revised Application for Amends to Licenses DPR-42 & DPR-60, Incorporating Combustion Engineering SG Welded Tube Sleeve TR Rev

ML20207F277
Person / Time
Site:	Prairie Island
Issue date:	03/01/1999
From:	Sorensen J NORTHERN STATES POWER CO.
To:
Shared Package
ML20207F275	List: ML20207F271 ML20207F277 ML20207F290
References
NUDOCS 9903110211
Download: ML20207F277 (7)

Text

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UNITED STATES NUCLEAR REGULATORY COMMISSION 4

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l NORTHERN STATES POWER COMPANY 1

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PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NO. 50-282 1

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50-306 I

i REQUEST FOR AMENDMENT TO r

OPERATING LICENSES DPR-42 & DPR-60 LICENSE AMENDMENT REQUEST DATED FEBRUARY 5,1999 Northern States Power Company, a Minnesota corporation, requests authorization for changes to Appendix A of the Prairie Island Operating License as shown on the attachments labeled Exhibits A, B, and C. Exhibit A describes the proposed changes, l

reasons for the changes, safety evaluation and a significant hazards evaluation.

Exhibits B and C are copies of the Prairie Island Technical Specifications incorporating 1

the proposed changes.

This letter contains no restricted or other defense information.

l NORTHERN STATES P ER COMPANY By

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1. 61 P. 'Sorensen~

Bite General Manager Prairie Island Nuclear Generating Plant On this f day of blULA

/ff 9before me a notary public in and for said County, personally'a'pphased Joel P. Sorensen, Site General Manager, Prairie Island Nuclear Generatihg Plant, and being first duly sworn acknowledged that he is

'detidiad to execQte this document on behalf of Northern States Power Company, that

' he knows t?ie' contents thereof, and that to the best of his knowledge, information, and belief the statements made in i are t and that it is ot interposed for delay.

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l MARCIA K. LaCOIE

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Exhibit A Page 1 i

Exhibit A l

Prairie Island Nuclear Generating Plant

-l License Amendment Request February 5,1999 i

Evaluation of Proposed Changes to the Technical Specifications Appendix A of Operating License DPR 42 and DPR l a

1 c Pursuant to 10 CFR Part 50, Sections 50.59 and 50.90, the holders of Operating

- Licenses DPR-42 and DPR-60 hereby propose the following changes to Appendix A,

- Technical Specifications:

1 Irttroduction This amendment request proposes a change to Technical Specification (TS) 4.12,

" Steam ' Generator Tube Surveillance", to incorporate changes to the ABB Combustion

. Engineering (CE) sleeve design assumptions and installation techniques. ABB CE l

developed these changes to the sleeve design.

- Th'e current Prairie Island Technical Specifications (TS) allow steam generator tubes j

with eddy current indications requiring repair to be sleeved in accordance with

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Combustion Engineering. Report CEN-629-P Revision 2 and Addendum 1. The purpose i

of this license amendment is to obtain approval for repair of steam gen'erator tubes

. using Revision 3 to the Combustion Engineering report CEN-629-P, " Repair of -

. Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves."

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. Revision 3 to CEN-629-P incorporates Addendum '1 Revision 1 and includes the i

following major changes.

e' The operating conditions in Section 3 reflect bounding operating conditions in the affected plants, particularly lower secondary side operating pressures The information in Addendum i has been incorporated into Revision 3 e' ' The analyses in Section 8 hav(. been revised using the new conditions defined in

~ Section 3 e 4 Analysis in Section 8 has used the ASME Code allowable tensile strength of 80.0 ksi at 600. F resulting in a lower repair limit.-

c el Reference to the welded sleeve plug has been eliminated. The welded plug has -

been replaced by a torque rolled mechanical sleeve plug e - An attemative high pressure air system has been developed for cleaning the tube

- after brushing.

_The draft Regulatory Guide 1.121 per cent allowable degradation has decreased to e

45.4% with the decrease in assumption of tensile strength n,

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Exhibit A Page 2 The ABB CE TIG welded sleeves can be used to repair degraded SG tubing at tube support plate intersections or free span locations, within and above the tubesheet

,l region, or a combination of both within the same tube. ABB CE TIG welded sleeving has been determined to be an effective repair method and has successfully been licensed at plants with both 3/4" and 7/8" tubing and in both Westinghouse and Combustion Engineering plants.

The steam generators at Prairie Island are Westinghouse Model 51 steam generators with 7/8 inch low temperature mill-annealed Alloy 600 tubing and a partial depth hard roll expansion tubesheet region. The sleeving materialis thermally treated Alloy 690 tubing. This material has been used for sleeving by Combustion Engineering at Prairie Island since 1987.

A non-heat treated sleeve installed at Prairie Island in 1987 was removed in 1997 and metallurgically examined. This sleeve with 3358 EFPD of service showed no field service degradation in the sleeve, weld, or parent tubing in the above the tubesheet weld region.

A complete description of the sleeve designs and qualification testing is provided in Combustion Engineering Report CEN-629-P, Revision 03, " Repair of Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves", September 1998.

Proposed Chances Technical Specification 4.12, " Steam Generator Tube Surveillance", describes the inservice inspection program used to demonstrate steam generator operability. In order to incorporate Revision 3 to CEN 629-P, two items in Technical Specification 4.12 must be revised. A brief description of the proposed revisions is provided below. The specific wording changes to the Technical Specifications are shown in Exhibits B and C.

1. Proposed Changes to Technical Specification 4.12.D.1.(f)

The plugging limit for the Combustion Engineering sleeves is changed. "The repair limit for the pressure boundary region of any sleeve is 25% of the nominal sleeve wall thickness."

2. Proposed Changes to Technical Specification 4.12.0.3 The reference to the sleeving topical report is changed.

Tube repair, after April 1,1999 using Combustion Engineering welded sleeves shall be in accordance with the methods described in the following:

CEN-629-P, Revision 03-P," Repair of Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves"

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Exhibit A Page 3 i

' Justification l

The current Prairie Island Technical Specification 4.12.D.3 specifies the sleeving topical report revision number. The proposed Technical Specification change is requested to l

update the topical report revision number and to change the sleeve repair limit.in j

accordance with the topical report requirements.. The changes introduced in Revision 3 to the ABB CE sleeving topical report do not chang; the final installed configuration of l

tube sleeves.~ The net effect of these changes yields more conservative sleeve -

plugging criteria than that which is already approved and incorporates some j

improvements in the installation process that have been gained by experience.

t Safety Evaluation Introduction '

Repair of tubes by sleeving addresses tube degradation which requires plugging and which can occur in tubes within the tubesheet region, above the top of the tubesheet, at j

tube support plates, or in straight leg free span regions accessible to the sleeve j

installation equipment. Sleeves'can be used to span the degraded region in order to.

maintain structural.and leakage integrity of the steam generator tube during normal operating and postulated accident conditions. Currently, the Combustion Engineering welded sleeve is authorized for use at Prairie Island in accordance with Revision 2 and

Addendum 1 to CEN 629-P. Modifications to the repair limit due to changes in the f

. assumption for tensile strength, minor changes in the installation process, and j

consolidation of the topical report warrant review by the NRC at this time.

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. The prcposed amendment will modify Technical Specification 4.12, Steam Generator

. Tube Surveillance to accommodate the revised repair limit. A description of the sleeve

_ designs and installation requirements is provided in Combustion Engineering Report -

CEN-629-P, Revision 03-P, " Repair of Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves", September 1998.

Evaluation This amendment incorporates changes in the '

tural Analysis and installation

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Process. The Sleeve Design, Installation Et ation, inservice Examination,

. Corrosion Testing, Mechanical. Testing, and

.kage' Assessment are unchanged from

.the previous license amendment.

j installation Process l

The basic installation process for each type of sleeve involves cleaning of the inside diameter of the tube in the joint region, installation of the sleeve, hydraulic l

expansion of the sleeve in the weld joint region to provide sleeve to parent tube -

" contact, welding of the joint, ultrasonic examination of the weld, optional visual l examination of the weld, optional post weld heat treatment of the weld, i

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e Exhibit A Page 4 completion of the lower joint (welded or rolled), and eddy current examination of the sleeve.

Revision 3 to CEN 629-P discusses a new high pressure air method of cleaning the tube after brushing has been completed. Several programs tested for the effectiveness of the airjet cleaning method. The first program used air oxidized tubes with a visual examination of the inside diameter surface. The second and I

third programs involved cleaning contaminated tubing removed from operating steam generators. These samples were then sleeved, welded, and fully inspected with UT, VT, and ET producing acceptable welds.

1 Vacuum is applied to the end of the tube to collect debris dislodgeo b the airjet j

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to minimize the spread of radioactive contamination.

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Structural Analysis The Combustion Engineering welded and welded-hard rolled sleeves were designed to conform to the stress limits and margins of safety of the ASME i

Boiler and Pressure Vessel Code. The methodology used is in accordance with the Section ill of the 1989 Edition of the ASME Boiler and Pressure Vessel Code. Safety factors of 3 for normal operating conditions and 1.5 for accident conditions were applied. In performing the analytical evaluation on the sleeves, the operating and design conditions for all of the Westinghouse operating plants with 7/8 inch inconel tubes were considererl. Stress evaluations were done for j

the above the tubesheet sleeve weld (which is also the weld for the tube support sleeve) at the nominal weld height and at the minimum weld height and for the lower sleeve weld. Stress intensity values are less than the ASME Code allowable values and fatigue usage factors are less than 1. Evaluations of the i

tube support plate sleeve upper and lower welds show that the stresses and loads calculated for the FDTS upper weld are bounding. Details of this analysis are in CEN-629-P.

Using guidance in draft Regulatory Guide 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes" and the ASME Code, the % allowable degradation for Prairie Island is 45.4% sleeve wall thickness. Making allowances for non-destructive examination (NDE) uncertainty and degradation growth, a plugging criterion of 25% through wall degradation is proposed for degradation that can be appropriately sized. Other types of degradation located in the pressure boundary would be plugged on detection.

Conclusions

t Exhibit A Page 5 lh conclusion, Northern States Power believes there is reasonable assurance that the health and safety of the public will not be adversely affected by the proposed Technical Specification changes.

Determination of Sionificant Hazards Considerations The proposed amendment incorporates revision 3 to the ABB/ Combustion Engineering Topical Report CEN-629-P. Three types of changes are incorporated in CEN-629-P, Revision 3:

Editorial Changes (the inclusion of Addendum 1 to the Topical Report and the removal of reference to welded sleeve plug)

Changes in sleeve installation practices (the use of high pressure air for cleaning tubes)

Changes to the sleeve repair limit (the lower secondary side operating pressure of section 3 and the use of ASME Code allowable tensile strength result in changes to the analyses of Section 8 which, in turn, result in a lower repair limit and reduced allowable degradation)

The proposed changes to the Operating License have been evaluated to determine whether they constitute a significant hazards consideration as required by 10 CFR Part 50, Sec on 50.91 using the standards provided in Section 50.92. This analysis is provided below:

1.

The proposed amendment will not involve a sianificant increase in the probability or consecuences of an accident oreviously evaluated.

Editorial changes have no effect on probability or consequences of accidents previously evaluated. Changes in installation practices incorporate improvements gained by (,xperience in installing sleeves. Further, the changes in the installation practices wi!! change neither the final configuration of installed sleeves nor the post-installation NDE from that which is already approved. Accident induced steam generator tube leakage is not effected by these changes. Post installation non-destructive examination will be conducted using VT, UT, and ET as previously licensed. The changes in repair limits have lead to repair limits that are more conservative than those which have been previously approved. Thus, none of these changes willincrease the probability or consequences of previously evaluated accidents.

2.

The proposed amendment will not create the possibility of a new or different kind of accident from any accident previousiv analyzed.

Editorial changes cannot create the possibility of a new or different kind of accident.

Changes in installation practices incorporate improvements gained by experience in installing sleeves. Further, changes in installation practices do not change the final configuration ofinstalled sleeves from that which is already approved. The

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Page 6 chhnges'in repair limits have lead to repair limits that are more conservative than -

those which have been previously approved. Thus, none of these changes will create the possibility of a new or different kind of accident from any accident previously analyzed.

3. 'The proposed amendment will'not involve a sianificant reduction in the marain of safety.

Editorial changes have no effect on the margin of safety. Changes in installation practices incorporate improvements gained by experience in installing sleeves.

Further, changes in installation practices do not change the final configuration of-installed sleeves from that which is already approved. The changes in repair limits have1ead to repair limits that are more conservative than those which have been -

. previously approved. None of these changes will affect the tube plugging assumptions used in the PINGP accident analyses. Thus, none of these changes will reduce the margin of safety.

Based on the evaluation described above, and pursuant to 10 CFR Part 50, Section

' 50.91, Northern States Power Company has determined that operation of the Prairie Island Nuclear Generating Plant in accordance with the proposed license amendment request does not involve any significant hazards considerations as defined by NRC regulations in 10 CFR Part 50, Section 50.92.

Environmental Assessment Northern States Power has evaluated the proposed changes and determined that:

1. 3 The changes do not involve a significant hazards consideration, 2.

The changes do not involve a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or 3.

The changes do not involve a significant increase in individual or cumulative occupational radiation exposure.

Therefore, the proposed Technical Specification changes would not result in a significant radiological environmental impact.

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