ML20136B516

Application for Amend to License DPR-36,requesting Approval of Alternative Sleeving Repair Process for SG Tubes at Plant

ML20136B516
Person / Time
Site:	Maine Yankee
Issue date:	03/05/1997
From:	Sellman M Maine Yankee
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20136B523	List: ML20136B516 ML20136B526
References
MBS-97-07, MBS-97-7, MN-97-42, NUDOCS 9703110010
Download: ML20136B516 (12)

Text

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MaineYankee REllABLE ELECTRICITY SINCE 1972 329 BATH ROAD + BRUNSWICK. MAINE 04011 * (207) 798 4100

. March 5. 1997 MN-97-42' MBS-97-07 Proposed Change No. 205 United States Nuclear Regulatory Commission Attention: Document Control Desk 4 Washington. DC 20555

Reference:

(a) License No. DPR-36 (Docket No. 50-309)

(b) MYAPC Letter to USNRC dated December 6. 1994 (MN-94-118)

(c) USNRC Letter to MYAPC dated April 14. 1995 (d) MYAPC Letter to USNRC dated April 14. 1995 (MN-95-37)

, (e) USNRC Letter to MYAPC dated May 22. 1995 (f) Framatome Technologies (J.H. Taylor) Letter to USNRC (K.R.

Wichman) dated March 26, 1996 (g) Union Electric Letter ULNRC-3358 to USNRC dated April 12, 1996 l (Docket No. 50-483) i (h) Baltimore Gas and Electric Co. Letter to USNRC dated July 26.  ;

1996 (Docket Nos. 50-317 and 50-318)  !

(1) Houston Lighting & Power Letter ST-HL-AE-5352 to USNRC dated August 29, 1996 (Dockets Nos. 50-498 and 50-499)

(j) Framatome Technologies Letter JHT/96-45 to USNRC dated July 18, 1996 (Docket No. 50-483)

! (k) Union Electric Letter ULNRC-3451 to USNRC dated September 24 ,

, 1996 (Docket No. 50-483) i

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Subject:

Proposed Technical Specification Change No. 205 Maine Yankee Steam Generator Tube Repair Sleeving l Gentlemen:

, Maine Yankee hereby submits pursuant to 10CFR50.90, this application to amend t

sections of the Maine Yankee Technical Specifications. This proposed change requests approval of an alternative sleeving repair process for steam generator tubes at the Maine Yankee plant.

By Reference (b). Maine Yankee submitted a proposed Technical Specification change to permit sleeving repair using a Combustion Engineering sleeve design and weld process. The NRC approved this request by Reference (c). By Reference (d).

Maine Yankee submitted a proposed Technical Specification change to permit an equivalent sleeving repair using a Westinghouse sleeve design and laser weld process. The NRC approved this request by Reference (e).

The alternate sleeving repair process descri ud in this proposed Technical Specification change is a process developed by Framatome that results in an electrodeposited nickel sleeve which can repair tubes in locations above existing sleeves. During 1995. Maine Yankee installed tube repair sleeves in essentially Q all in-service steam generator hot leg tubes. This request is necessary to (

provide another repair option for degraded steam generator tubes. '

9703110010 970305 PDR ADOCK 05000309 P

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. MaineYankee tjnited. States Nuclear Regulatory Commission MN-97-42 Attention: Do ument Control Desk Page Two Electrosleeving* is a steam generator tube repair technique developed by Framatome Technologies Inc. In this method an ultrafine grained nickel is electrochemically deposited on the inner surface of a tube to form a structural repair of the degraded tube. The electrodeposition of nickel provides a continuous metallurgical bond that eliminates all leak paths and annular crevices. The electroformed sleeve provides a structural. leak-tight seal, without deforming or changing the microstructure of the parent tube. Thus.

Electrosleeving* does not require a post-installation stress relief.

The design and qualification of the Electrosleeve* complies with ASME Code Case N-569. The detailed anal Framatome Electrosleeve'yses and testing for installation inperformed to verify recirculation thegenerators

' steam adequacy of the (RSG) is provided in Framatome proprietary Topical Report BAW-10219P Revision 1, "Electrosleeving* Qualification for PWR Recirculating Steam Generator Tube Repair", which was transmitted to the NRC by Reference (f). That letter referenced the original proprietary affidavit provided by Framatome. It is Maine Yankee's understanding that Topical Report BAW-10219P is currently under review by the NRC staff for use at Callaway (Reference g). Calvert Cliffs Unit Nos. 1 and 2 (Reference h), and South Texas Project Nos. 1 and 2 (Reference 1). Two requests for additional information were issued related to the Callaway application. The responses to these requests were submitted to the NRC in References (j) and (k). Maine Yankee requests that NRC com)lete the review and a) proval of the topical report as part of this proposed Tec1nical Specification clange.

Maine Yankee has evaluated the proposed c.hange and has determined that it does not: involve a significant increase in the probability or consequences of an accident previously evaluated; create the possibility of a new or different kind of accident from any accident previously evaluated; or involve a significant reduction in a margin of safety. Therefore. the proposed change does not involve a significant hazards consideration as defined in 10 CFR 50.92. The evaluation is included in Attachment A.

Revised Technical Specification Pages 4.10-3. 4.10-5 and 4.10-6 are included as Attachment B. Revised Technical Specification Page 4.10-7 is included as Attachment C and only ap] lies if Maine Yankee Proposed Change No.169 is approved by the NRC before this 3roposed Change.

This proposed change has been reviewed and approved by the Plant Operating Review Committee. The Nuclear Safety Audit and Review Committee has also reviewed this submittal. A representative of the State of Maine is being informed of this request by a copy of this letter..

As part of the current refueling outage, Maine Yankee will be performing steam generator inspections These inspections will commence approximately April 1.

The Electrosleeving" process may be an essential repair option depending upon the results of the inspections.

'. MaineYankee United, States Nuclear Regulatory Commission MN-97-42 Attention: Document Control Desk Page Three In order to provide timely support for planning, steam generator tube repair and plant startup, we request timely NRC review and approval by May 1. Maine Yankee is prepared to provide additional information or meet with the Staff on short notice to facilitate this schedule.

We request that the amendment become effective immediately upon issuance. Please contact us should you have any questions regarding this matter.

Ver truly 'ours, f bt .

Michael B. Sellman President Attachments MBS/mwf c: Mr. Hubert J. Miller Mr. J. T. Yerokun Mr. P. J. Dostie Mr. Clough Toppan Mr. Uldis Vanags Mr. D. H. Dorman STATE OF MAINE Then personally appeared before me Michael B. Sellman, who being duly sworn did state that he is President of Maine Yankee Atomic Power Company, that he is duly authorized to execute and file the foregoing request in the name and on behalf of Maine Yankee Atomic Power Company, and that the statements therein are true to the best of his knowledge and belief.

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l ATTACHMENT A l

SUMMARY

DESCRIPTION OF THE PROPOSED CHANGES AND SIGNIFICANT HAZARDS EVALUATION

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\ ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION l l l l Descriotion of Prooosed Chanae l i The proposed change to Technical Specification 4.10 St.eam Generator Tube Surveillance provided in Attachment B would allow the use of Framatome Technologies Incorporated (FTI) Electrosleeving" process for steam generator tube repair at the Maine Yankee plant. The proposed change will provide Maine Yankee with an alternate method for sleeve repair of steam generator tubes which can be installed above an existing sleeve. l' Also, a note which no longer applies was removed from Table 4.10-2.

l Background 1 Maine Yankee has three vertical U-tube Series 67 recirculating st generators designed and manufactured by Combustion Engineering. Ea generator has 5703 tubes which are mill annealed Alloy 600. 0.750-inch outside diameter with a 0.048-inch average wall. The current Maine Yankee Technical Specifications require that steam generator tubes with imperfections that exceed the repair limit be repaired by plugging or be sleeved by a Combustion Engineering or a Westinghouse process. The FTI Electrosleeve" would provide an alternate method of sleeve repair which can be installed at any elevation in a tube, even if the target area is 1 above an existing sleeve.

l Electrosleeving" is a steam generator repair process where an ultra- l fine grained nickel is electrochemically deposited on the inner surface I of a tube to form a structural repair of the degraded tube. The electrodeposition of nickel provides a continuous metallurgical bond that eliminates all leak paths and annular crevices. The electroformed sleeve provides a structural, leaktight seal, with minimal residual stress, without deforming or changing the microstructure of the parent tube. Electrosleeving" does not require a post-installation stress l relief. Additionally, since the Electrosleeve" is in direct contact l r with the parent tube, flow restriction and loss of heat transfer surface  !

area is less than the previous sleeve designs. l l Structural Assessment 1

Electroformed sleeves have been designed using the 1989 Edition of the

( ASME Code and Code Case N-569. Stress analysis of the sleeved tube assemblies has been completed in accordance with the requirements of Subsection NB-3200. Although electrodeposited material is not currently identified in the Code, the material properties were determined in accordance with Appendix III of Section III. and used in the design of the electroformed sleeves.

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+ ATTACHMENT A

, SIGNIFICANT HAZARDS EVALUATION l The'results of the primary membrane stress intensity range evaluation of j the sleeve with the tube removed indicate that the ASME Code allowable j limits are not exceeded. That is, stress intensities are bounded by the minimum limits for the Electrosleeve" material. In addition, sleeve i- specimens with minimum bvJ length were fatigue tested in accordance l with ASME III. Article 11-1500 with no bond or sleeve failure, j 'Therefore the design of the sleeve pressure boundary meets the design

objectives of the original tubing.

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, The Electrosleeve" structural analysis utilizes a generic set of design 8

and transient loading inputs which are intended to bound all Combustion

Engineering Model 67 steam generators. The temperature and pressure

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variances used in the assumed operating conditions and generic i transients conservatively bound the Maine Yankee conditions. The i loading cycles that were applied to the Electrosleeve* analysis and

{ testing were those for a forty year plant i .fe cycle, rather than the i remaining life of the Maine Yankee plant. The results of the fatigue tests based upon these design cycles confirm the structural integrity of

! the installed sleeve.

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! The sleeve / tube wall, which is part of the reactor coolant pressure

{ boundary, will be monitored for initiation and progression of wall i degradation as required by Regulatory Guide 1.83. Regulatory Guide

! 1.121 and the ASME Code are used to develop the plugging limit of the i Electrosleeve* should sleeve wall degradation occur. Potentially degraded Electros1rwes* have been shown by test and analysis to retain burst strength in excess of three times.the normal operating pressure differential at end of cycle conditions. No credit for the presence of the parent tube behind the sleeve is assumed when performing the minimum wall / burst evaluation, although the tube would be in intimate contact with the sleeve.

An ultrasonic examination of the installed Electrosleeve" will be performed prior to placing the sleeve in service to verify correct sleeve position, proper sleeve to tube bonding, minimum acceptable sleeve thickness and to provide a baseline inspection of the new pressure boundary. l l

Leakage Assessment Leakage testing has shown that the Electrosleeve* is essentially leak tight during all plant conditions. In addition, burst testing of Electrosleeve" assemblies exposed to conditions considered to be more severe than expected dur ng all operating plant conditions has shown that Electrosleeving* does not introduce additional primary to Page A-2

\ ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION secondary leakcge during a postulated abnormal conditions. Flawed ]

Electrosleeves* were subjected to thermal and fatigue cycling and then l burst tested at pressures ranging from 6.6 to 11.8 ksi, which far '

exceeds the expected maximum pressure differential resulting from a loss  !

of secondary pressure. '

Corrosion Assessment 1

Electrodeposited nickel materials have performed well in-service with  ;

regard to corrosion. In comparison with Alloy 600. nickel is typically j less resistant to general attack in highly oxidizing acidic solutions than Alloy 600, but nickel is more resistant to IGA and SCC. This is consistent with experience in steam generator environments, where IGA  !

and SCC are the predominant modes of tube failure. Corrosion tests of l both nickel plating and the Electrosleeve" material in extreme j simulations of primary and secondary environments show that nickel i plating is not susceptible to SCC or IGA. Thus nickel plating is effective in protecting Alloy 600 tubing from PWSCC. There is negligible corrosion of the Electrosleeve" material in primary or  !

secondary environments, and sleeve exposure to the secondary environment i is minimal due to the nature of tight cracks in Alloy-600 tubing.

1 EPRI Report TR-105960 assesses sleeving experience, and identifies a J cause of corrosion as SCC of the parent tube due to high residual stress j from the sleeve installation process. The threshold residual stress levels are listed as 40ksi for PWSCC and 25 ksi for secondary side SCC.

The stress level in a locked tube resulting from the installation of an J Electrosleeve* has been measured as 3.2 ksi which is insignificant for  !

SCC. The EPRI report also identifies wastage of the sleeve / tube in a {

trapped crevice region as a cause of sleeving failure. The l Electrosleeve" effectively eliminates the crevices associated with j conventional sleeves. j It is concluded that general corrosion, crevice corrosion, pitting. SCC.

and IGA of the nickel Electrosleeve" material is not a concern in PWR environments.  !

Mechanical Integrity Assessment l 1

Mechanical testing of the Electrosleeves" indicates that the axial load  !

bearing capability exceeds the most limiting end cap pressure loading i established by Regulatory Guide 1.121. The Electrosleeve* structural l integrity requirements include safety factors inherent to the j requirements of the ASME Code. Installation of Electrosleeves"  !

restores the integrity of the primary pressure boundary. The structural Page A-3

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\ ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION analysis and mechanical performance of the Electrosleeves* are based on I installation in the hot leg of the steam generators, which is more limiting than the cold leg.

Sleeving of Previously Plugged Indications In the event that previously plugged tubes are unplugged and repaired using an Electrosleeve*, the sleeve installation requirements are no

different than those for active tubes. A new baseline inspection of the i

entire tube length must be performed prior to placing the sleeved tube back into service. The extent of the originally identified degradation indication should not affect Electrosleeve* installation.

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Summary ASME Code Case N-569 specifically identifies electrochemical deposition of material for steam generotor tube repair, and the FTI Electrosleeve" design has been qualified in accordance with these requirements. Based

upon Regulatory Guide 1.121 guidelines for tube degradation limits, appropriate sleeved tube repair criteria h M been established.

Qualified nondestructive examination techniques will be used to perform necessary Electrosleeve* and tube inspections for defect detection, and to verify proper installation of the Electrosleeve* In addition, Maine Yankee is committed to use only qualified processes for periodic inservice inspection, and will continue to evaluate improved inspection techniques as they are developed and qualified for use.

Sionificant Hazards Evaluation The proposed change to the Technical Specifications has been evaluated against the standards of 10 CFR 50.92 and has been determined'to not involve a significant hazards consideration. The proposed change does not:

1. Involve a significant increase in the probability or consequences of an accident previously evaluated.

The Electrosleeve* has been designed and qualified using the applicable ASME Boiler and Pressure Vessel Code and Code Case N-569, and it meets the objectives of the original steam generator tubing. The applied stresses and fatigue usage for the sleeve are bounded by the limits established in the ASME Code. Sleeve material property values were determined in accordance with ASME Code requirements, and these values were used for the structural and plugging limit analyses. Mechanical testing has shown that Page A-4

. ', ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION the structural strength of the nickel Electrosleeve" under normal, upset, and faulted conditions provides margin to the acceptance limits. These acceptance limits bound the most limiting burst margin (three times normal operating pressure differential) recommended by Regulatory Guide 1.121. Burst te. sting of Electrosleeved* tubes has demonstrated that no unacceptable levels of primary-to-secondary leakage are expected during any plant condition.

The Electrosleeve* Technical Specification depth-based plugging limit for the sleeve is determined using the guidance of Regulatory Guide 1.121 and the pressure stress equation of Section III of the ASME Code, as it was for the original tube. A bounding set of design and transient loading input conditions was used for the minimum wall thickness determination in the generic evaluation. Evaluation of the minimum wall thickness for normal, upset, and postulated accident conditions per the ASME Code indicates that the minimum wall thickness is acceptable.

A bounding wall degradation growth rate per cycle and a nondestructive examination uncertainty has been assumed for determining the Electrosleeve* plugging limit. The extent of l sleeve wall degradation which would require plugging sleeved tubes  !

is 20% through-wall, developed using the guidance of Regulatory Guide 1.121 as defined in Framatome Topical Report BAW-10219P, Revision 1.

Evaluation of the proposed Electrosleeved* tubes indicates no detrimental effects on the sleeve or sleeve / tube assembly from reactor system flow, primary or secondary coolant chemistries, thermal conditions or transients, or pressure conditions which may be experienced at Maine Yankee. Corrosion testing of Electrosleeve*/ tube assemblies indicates no evidence of Electrosleeve* or tube corrosion considered detrimental under anticipated service conditions.

The implementation of the proposed Electrosleeve" has no significant effect on either the configuration of the plant, or the manner in which it is operated. The hypothetical consequences of failure of an Electrosleeve" tube are bounded by the current steam generator rupture analysis described in Section 14.12 of the Maine Yankee Final Safety Analysis Report. Due to the slight reduction in diameter caused by the sleeve wall thickness, primary coolant release rates would be slightly less than assumed for the steam generator tube rupture analysis, and would therefore result Page A-5

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.. ', ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION in lower total primary fluid mass release to the secondary system. l The proposed change, therefore, does not significantly increase '

the probability or consequences of any-previously evaluated I accident. l l

2. Create the possibility of a new or different kind of accident from l any accident previously evaluated.

Electrosleeving* will not adversely affect any plant component.

Stress and fatigue analysis of the repair has shown that the ASME Code and Regulatory Guide 1.121 criteria are not exceeded.

Implementation of Electrosleeving* maintains overall tube bundle structural and leakage integrity at a level consistent with that of the original tubing during all plant conditions. Sleeving of I tubes does not-provide a mechanism resulting in an accident l outside the area affected by the sleeves. Any accident as a 1 result of potential tube or sleeve degradation in the repaired I portion of the tube is bounded by the existing tube rupture accident analysis.

Implementation of sleeving will reduce the potential for primary-to-secondary leak. age during a postulated steam line break while not significantly impacting available primary coolant flow area in the event of a LOCA. By effectively isolating degraded areas of .

the tube through repair, the potential for steam line break 4 leakage is reduced. These degraded areas are returned to a condition consistent with the design basis. While the ,

. installation of a sleeve reduces primary coolant flow, the reduction is far less than that caused by plugging and a much .

greater pr4 mary coolant flow area is maintained by sleeving versus l plugging.

Therefore, inclusion of the proposed change in the Technical Specifications would not create the possibility of a new or different kind of accident from any previously evaluated.

3. Involve a significant reduction in a margin of safety.

The Electrosleeve" repair of degraded steam generator tubes has been shown by analysis to restore the integrity of the tube bundle consistent with its original design basis condition. The

' tube / sleeve operational and faulted condition stresses are bounded

-by the ASME Code requirements and the repaired tubes are leak tight. The safety factors used in the design of sleeves for the Page A-6

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SIGNIFICANT HAZARDS EVALUATION repair of degraded tubes are consistent with the safety factors of the ASME Code used in: steam generator design. The effect of sleeving on the design transients and accident analyses has been reviewed based upon the installation of plugs and sleeves up to a conservative total of 1000 equivalent plugged tubes per steam generator.

The Electrosleeve" is qualified and examined in accordance with ASME Code Case N-569. The portions of the installed sleeve assembly which are part of the reactor coolant pressure boundary can be monitored for the initiation and progression of sleeve / tube.

wall degradation, thus satisfying the requirements of Regulatory Guide 1.83. The portion of the tube bridged by the sleeve is effectively removed from the pressure boundary, and the sleeve then forms the new pressure boundary. The areas of the_ tube assembly which require inspection are defined in Framatome Topical Report BAW-10219P, Revision 1. Since the installed sleeve constitutes a portion of the pressure boundary, a baseline inspection of these areas in accordance with Code Case N-569 is required prior to operation with sleeves installed. 1 l

Therefore, adoption of the proposed change would not involve'a significant reduction in safety margin for the plant. l l

Maine Yankee has concluded that the proposed change to the Technical -

Specifications does not involve a significant hazards consideration as  !

defined by 10 CFR 50.92. l Information Concernina an Environmental Assessment An Environmental Assessment is not required for the Technical Specification changes proposed by this Proposed Change because the requested changes to the Maine Yankee Technical Specifications meet the criteria for " actions eligible for categorical exclusion" as specified in 10CFR51.22(c)(9). The requested changes will have no impact on the environment. The changes do not involve a Significant Hazards Consideration as discussed in the preceding section. The requested changes do not involve a significant change in the types or significant increase in the amounts of any effluent that may be released off-site. Also, the requested changes do not involve a significant increase an individual or cumulative occupational radiation exposure.

Conclusion Therefore, based upon the reasoning presented above, Maine Yankee has Page A-7

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. ATTACHMENT A SIGNIFICANT HAZARDS EVALUATION determined that the requested change does not involve a significant hazards consideration.

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