ML20116E357

Application for Amends to Licenses DPR-53 & DPR-69,to Repair Defective SG Tubes by Electrosleeving

ML20116E357
Person / Time
Site:	Calvert Cliffs
Issue date:	07/26/1996
From:	Cruse C BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20116E360	List: ML20116E357 ML20116E377
References
NUDOCS 9608050222
Download: ML20116E357 (13)

Text

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CnAntEs 11. Cut'sE Baltimore Gas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant

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Nuclear Energy 1650 Calvert Cliffs Parkway Lusby, Maryland 20657 410 495-4455 July 26,1996 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 License Amendment Request: Electrosleeving Option for Steam Generator Tube Repair

REFERENCE:

Letter from Mr. J. It Taylor (Framatome Technologies Inc.) to Mr. K. R. Wichman (NRC), dated March 26, 1996, Topical Report BAW-10219P, Revision 1, "Electrosleeving Qualification for PWR Recirculating Steam Generator Tube Repair" 4

Pursuant to 10 CFR 50.90, the Baltimore Gas and Electric Company (BGE) hereby requests an Amendment to Operating License Nos. DPR-53 & DPR-69 to allow the repair of defective steam generator tubes by electrosleeving.

Currently, the Calvert Cliffs Technical Specifications allow defective tubes to be plugged and removed from service, or to be epaired by laser-welded sleeving technique developed by Westinghouse Electric Corporation. The proposed amendment will revise the appropriate Technical Specifications and their Bases to permit the electrosleeving repair technique developed by Framatome Technologies Inc. to be used at Calvert Cliffs. Electrosleeving is a steam generator tube repair method where an ultra-fine 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 macro-crevices. The electroformed sleeve provides a structural, leak-tight seal, without deforming or changing the microstructure of the parent tube. Thus, unlike the conventional welded sleeves, electrosleeving does not require a post-installation stress relief.

The summary description and safety analysis for the proposed electrosleeving repair technique is provided in Attachment (1). Baltimore Gas and Electric Company has evaluated the proposed revision to the Calvert Cliffs Technical Specifications and has determined that it does not involve a significant Pw m M A 9608050222 960726 1/

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hazards consideration as defined in 10 CFR 50.92 (refer to Attachment 2 for a complete discussion).

Attachments (3) and (4) provide the Technical Specifications marked-up pages for Units I and 2, respectively. The detailed report on the specific qualifications of the Framatome electrosleeving technique for Calvert Cliffs application is contained in the proprietary Topical Report BAW-10219P, Revision 1 "Electrosleeving Qualification for PWR Recirculating Steam Generator Tube Repair," dated March 1996 (transmitted to the NRC by the referenced letter). It is BGE's understanding that Topical Report BAW-10219P is currently under review by the NRC staff. Baltimore Gas and Electric Company requests that the NRC complete the review and approval of the topical Report as part of this application. 1 l

in addition, BGE has determined that operation with the proposed amendment would not result m any 1 significant change in the types, or significant increases in the amounts, of any effluents that may be )

released offsite, nor would it result in any significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR Sl.22(b), no environmental impact statement or environmental assessment is needed in connection with the approval of the proposed amendment.

These proposed changes to the Technical Specifications and our determination of no significant hazards have been reviewed by our Plant Operations and Safety Review Committee and Offsite Safety Review Committee, and they have concluded that implementation of these changes will not result in an undue risk to the health and safety of the public.

Baltimore Gas and Electric Company wishes to have electrosleeving as an option to repair defective steam generator tubes during the 1997 Unit 2 refueling outage, scheduled to begin on March 28,1997.

Therefore, BGE requests that the NRC review and approve the proposed amendment on or before March 15,1997.

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. i Document Control Desk i July 26,1996 l Page 3 l

. l Should you have questions regarding this matter, we would be pleased to discuss them with you.

Very truly yours, I

1 STATE OF MARYLAND -

TO WIT: 1 COUNTY OF CALVERT  :

I hereby certify that on the bbe day of ( [ ,19 b. befo me, the subscriber, a -

Notary Public of the State of Maryland in and f!1 r Pil Lbf Ab [Pt4 , personally appeared Charles. H. Cruse, being duly sworn, ard states that he is Vice President $ the Baltimore Gas and Electric Company, a corporation of the State of Maryland; that he provides the foregoing response for the purposes therein set forth; that the statements made are true and correct to the best of his knowledge, information, and belief; and that he was authorized to provide the response on behalf of said Corporation.

WITNESS my Hand and Notaria! Seal: M 10 N Notary Public l

My Commission Expires: M2 I Datd RED /GT/dtm Attachments: (1) Summary Description and Safety Analysis (2) Determination of No Significant Hazards (3) Unit 1 Marked-Up Technical Specification Pages (4) Unit 2 Marked-Up Technical Specification Pages cc: D. A. Brune, Esquire Resident Inspector, NRC J. E. Silberg, Esquire R.1. McLean, DNR Director, Project Directorate I-1, NRC J. H. Walter, PSC T. T. Martin, NRC J. E. Galford, Framatome A. W. Dromerick, NRC I

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ATTACHMENT (1) i 3

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SUMMARY

DESCRIPTION AND SAFETY ANALYSIS 4

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Baltimore Gas & Electric Company

Docket Nos. 50-317 and 50-318 July 26,1996 l

AUACHMENT m

SUMMARY

DESCRIPTION AND SAFETY ANALYSIS A. BACKGROUND Pressurized water reactor (PWR) steam generators (SGs) have experienced tube degradation related to corrosion phenomena, such as wastage, pitting, intergranular attack, stress corrosion cracking and crevice corrosion, along with other phenomena such as denting and vibration wear.

Tubes that experience excessive degradation reduce the integrity of the primary-to-secondary pressure boundary. Eddy current examination is used to measure the extent of tube degradation.

When the reduction in tube wall thickness reaches a calculated value commonly known as the plugging criteria, the tube is considered defective and a corrective action is taken.

Currently, the Calvert Cliffs Technical Specifications allow defective tubes to be plugged and removed from service, or to be repaired by laser-welded sleeving technique developed by Westinghouse Electric Corporation. The most widely used repair technique at many PWRs, including Calvert Cliffs, is removal of the degraded tube from service by istalling plugs at both ends of the tube. The installation of SG tube plugs removes the heat transfer surface of the plugged tube from service, and leads to a reduction in the primary coolant flow available for core cooling. The laser-welded sleeving option was recently approved by the NRC for Calvert Cliffs application (NRC Safety Evaluation Report, dated March 22,1996), but has not yet been used to repair defective SG tubes at Calvert Cliffs. The Westinghouse laser-welded sleeve is designed to span the degraded section of the tube and maintain the structural integrity of the SG tube under normal and accident conditions, and limits or prevents primary-to-secondary leakage through the sleeved section of the tube should the degradation deteriorate into a through-wall crack.

The proposed amendment will revise the appropriate Technical Specifications and their Dases to permit an electrosleeving repair technique developed by Framatome Technologies Inc. (FTI) to be used at Calvert Cliffs. Electrosleeving is a SG tube repair method where an ultra-fine 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 macro-crevices. The electroformed sleeve provides a structural, leak-tight seal, with minimal residual stress, without deforming or changing the microstructure of the parent tube. Thus, unlike the conventional welded sleeves, electrosleeving does not require a post-installation stress relief. Additionally, since the electrosleeve is in direct contact with the parent tube, flow restriction and loss of heat transfer area is negligible compared to the previous sleeve designs.

B. DESCRIPTION OF AMENDMENT REOUEST The proposed amendment would revise the Technical Specifications Surveillance Requirements for the Calvert Cliffs Nuclear Power Plant SG tubing (Technical Specifications Section 4.4.5 and associated Bases). This revision would allow the use of FTl electrosleeves to repair defective SG tubes. The marked-up Technical Specification pages in Attachments 3 and 4 (for Units 1 and 2, respectively) provide the details of the proposed changes.

[ NOTE: In previous Safety Evaluation Reports on sleeving repair, the Commission has required reduction of SG leakage limit from 500 gpd per SG, to 150 gpd per SG. Since Baltimore Gas and Electric Company has already implemented a change to Technical Specification 3.4.6.2 1

ATTACIIMENT (1)

SUMMARY

DESCRIPTION AND SAFETY ANALYSIS adopting a 100 gpd per SG leakage limit (NRC Safety Evaluation Report, dated July 13, 1992),

the implementation of electrosleeving repair at Calvert Cliffs will not affect this Specification.)

C. SAFETY ANALYSIS The principal accident associated with this proposed change is the SG tube rupture (SGTR) accident. The consequences associated with an SGTR event are discussed in Calvert Cliffs Updated Final Safety Analysis Report Section 14.15, " Steam Generator Tube Rupture Event."

The SGTR event is a penetration of the barrier between the Reactor Coolant System and the Main Steam System. The integrity of this barrier is significant from the standpoint of radiological safety in that a leaking SG tube allows the transfer of reactor coolant into the Main Steam System. In the event of SGTR, radioactivity contained in the reactor coolant mixes with water in the shell side of the affected SG. This radioactivity is transported by steam to the turbine and then to the condenser, or directly to the condenser via the turbine bypass valves, or directly to the atmosphere via the atmospheric dump valves, main steam safety valves, or the auxiliary feedwater pump turbine exhaust. Noncondensible radioactive gases in the condenser are removed by the condenser air removal system, and discharged to the plant vent. Tne l electrosleeving process will allow the repair of degraded SG tubes such that the function and l integrity of the tube is maintained; therefore, the SGTR accident is not affected.

The hypothetical consequences of failure of the electrosleeved tube would be bounded by the current SGTR analysis described above. 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 SGTR analysis (depending on the break location), and therefore, would result in lower total primary fluid mass release to the secondary system. Two or more electrosleeves on one tube would reduce the primary fluid flow through the electrosleeved tube assembly due to the series of diameter reductions the fluid would have to pass on its way to the break area. The overall effect would be reduced SGTR release rates. Since the impact of electrosleeving on heat transfer and flow restriction is insignificant compared to plugging, the effects of electrosleeve installation on SG performance is minimal. The Topical Report, described below, provides the electrosleeve-to-plug ratio for one and two electrosleeves installed in one tube. The proposed Technical Specification change to allow the use of electrosleeving process does not adversely impact any other previously evaluated design basis accident.

Evaluation of the proposed electrosleeved tubes indicates no detrimental effects on the electrosleeve or electrosleeved-tube assembly from reactor system flow, primary or secondary coolant chemistries, thermal conditions or transients, or pressure conditions as may be experienced at Calvert Cliffs. The detailed report on the specific qualifications of the FTI electrosleeving technique for Calvert Cliffs application is contained in the proprietary Topical Report BAW-10219P, Revision 1 "Electrosleeving Qualification for PWR Recirculating Steam Generator Tube Repair," dated March 1996. The summary of the results from the Topical Report are included in this Attachment. The Topical Report was transmitted to the NRC by a letter dated March 26,1996, from J. H. Taylor (FTI) to K. R. Wichman (NRC). It is BGE's understanding that Topical Report BAW-10219P is currently under review by the NRC staff.

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ATTACHMENT m

SUMMARY

DESCRIPTION AND SAFETY ANALYSIS ,

I Generic Structural Assessment J

Electrochemical depositioning material is not currently identified by American Society of )

Mechanical Engineers (ASME) Code for SG tube repair. Nevertheless, applicable portions of I the Code were used as guidance in the design of electroformed sleeves. Fatigue and stress analyses of the sleeved tube assemblies have been completed in accordance with the requirements of Section III, Subsection NB-3200 and applicable code cases, of the 1989 Edition ,

of the ASME Code. The results of the primary stress intensity evaluation, primary plus j secondary stress intensity range evaluation and fatigue evaluation indicate that the ASME Code l

allowable limits are not exceeded. That is, stress intensities are bounded by the minimum limits j for the electrosleeve material, derived using the ASME Code as guidance, and cumulative '

fatigue usage is less than 1.0. Therefore, the design of the electrosleeve pressure boundary meets the design objectives of the original tubing.

Per Regulatory Guide 1.83, the electrosleeve/ tube wall, which is part of the reactor coolant pressure boundary, is monitored for initiation and progression of wall degradation. Regulatory Guide 1.121, " Bases for PNgging Degraded PWR Steam Generator Tubes," and the ASME Code are used to develop the plugging limit of the electrosleeve should electrosleeve wall degradation occur. The plugging limit is determined to be 20% of nominal electrosleeve wall thickness. A bounding tube wall degradation growth rate per cycle and a non-destructive examination uncertainty has been assumed for determining the plugging limit. Potentially degraded electrosleeves are 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 electrosleeve is assumed when performing the minimum wall / burst 1 evaluation. The electrosleeve structural analysis utilizes a generic set of design and transient ,

I loading inputs which are intended to bound all Combustion Engineering Model 67 SGs. The temperature and pressure variances used in the assumed operating conditions and generic transients are bounding.

Several specimens were tested per ASTM procedure to verify the ductility and adhesion of the electrochemically deposited nickel material. The results show no areas of de-bonding and cracking. An ultrasonic inspection of the electrosleeve is performed prior to placing the sleeve in service to verify correct electrosleeve position, proper electrosleeve to tube bonding, minimum acceptable electrosleeve thickness, and to provide a baseline inspection of the new pressure boundary. The loading cycles that were applied to the electrosleeve analysis and testing were those for a 40-year plant life cycle. Therefore, the fatigue analysis is bounding for an operating plant. The results of the fatigue analysis indicate acceptable usage factors for the entire range of permitted electrosleeve thickness.

Leakage Assessment Burst testing of electrosleeves under conditions considered to be more severe than expected during all operating plant conditions has shown trat electrosleeving does not introduce additional primary-to-secondary leakage during a postulated steam line break event. Electrosleeves were subjected to thermal and fatigue cycling and then burst tested at pressure differentials greater than the normal operating differential pressure, which far exceeds the expected maximum feed 3

ATfACHMENT (1)

SUMMARY

DESCRIPTION AND SAFETY ANALYSIS line break or steam line break pressure differential. The tests have shown that the electrosleeve is essentially leak-tight during all plant conditions.

Corrosion Assessment Nickel has performed well historically with regard to corrosion. Accelerated corrosion tests also show that fine grained nickel exhibits resistance to stress corrosion cracking equal to or greater than rolled tube transitions. Therefore. any electrosleeve degradation can be detected by ,

scheduled nondestructive examination. I l

Corrosion testing of electrosleeves has been performed in simulated primary and secondary side SG environments. Upset conditions, sludge environments, and shutdown conditions have also been tested. Under all expected SG conditions, general corrosion was negligible. The electrosleeving material is not susceptible to stress corrosion cracking or intergranular attack in either the primary or secondary water environment.

MechanicalIntegrity Assessment Mechanical testing of electrosleeves indicates that the axial load bearing capability exceeds the most limiting pressure end cap loading established by Regulatory Guide 1.121. The electrosleeve structural integrity requirements include safety factors inherent to the requirernents of the ASME Code. Installation of electrosleeves restores the integrity of the primary pressure boundary and the tube is leak-tight. The structural analysis and mechanical performance of the electrosleeves are based on installation in the hot leg of the SGs, which is more limiting than the cold leg.

Electrosleeving of Previously Plugged Indications The electrosleeve installation requirements applicable to active tubes, which have been identified as containing degradation indications exceeding the repair limit, are no different for the ,

electrosleeving of previously plugged tubes. A new " baseline" inspection of the entire tube length must be performed prior to electrosleeve installation in a previously plugged tube. The extent of the originally identified degradation indication should not affect electrosleeve )

installation. l 4

Conclusion Although the ASME Boiler and Pressure Vessel Code does not currently identify electrochemical deposition of material for SG tube repair specifically, the FTl electrosleeve design meets or exceeds all applicable ASME Code requirements. Based on the Regulatory Guide 1.121 guidelines for tube degradation limits, appropriate electrosleeved tube repair criteria have been established. Qualified nondestructive examination techniques will be used to perform 4

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A'IIACHMENT (1)

SUMMARY

DESCRIPTION AND SAFETY ANALYSIS l

necessary electrosleeve and tube inspections for defect detection, and to verify proper installation of the electrosleeve. In addition, we are committing 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.

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ATTACHMENT (2)  ;

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DETERMINATION OF NO SIGNIFICANT HAZARDS 1

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Baltimore Gas & Electric Company Docket Nos. 50-317 and 50-318 July 26,1996

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. l A'ITACIIMENT (2)

DETERMINATION OF NO SIGNIFICANT IIAZARDS SIGNIFICANT IIAZARDS EVALUATION This evaluation of the hazards consideration involved with the proposed steam generator tube electrosleeving is focused on the standards set forth in 10 CFR 50.92(c):

The Commission may make afinal determination, pursuant to the procedures in 50.91, that a proposed amendment to an operating licensefor afacility licensed under 50.21(b) or 50.22 orfor a testingfacility involves no sigmficant ha:ards consideration, if the operation of the facility in accordance with the proposedamendment wouldnot:

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

2. Create the possibility of a new or diferent kind of accident from any accident previously evaluated; or

3. Involve a sigmficant reduction in a margin ofsafety.

Baltimore Gas and Electric Company (BGE) believes that the operation of the Calvert Cliffs Nuclear Power Plant, in accordance with the proposed steam generator tube electrosleeving amendment, will not create the possibility of any new accident, increase the probability or consequences of any previously evaluated accident, nor significantly reduce any margin of safety. Thus. BGE has concluded that this proposed license amendment involves no significant hazards consideration as defined in 10 CFR 50.92(c).

In support of this determination, a discussion of each of the significant safety hazards consideration factors with respect to the proposed license amendment is provided.

l. The nromsed amendment would not involve a significant increase in the probability or can.seauences ofan accidentpreviousiv evaluated.

The implementation of the proposed steam generator tube electrosleeving has been reviewed for impact on the current CCNPP licensing basis.

Since the electrosleeve is designed using the applicable American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code as guidance, it meets the objectives of the original steam generator tubing. The applied stresses and fatigue usage for the electrosleeve are bounded by the limits established in the ASME Code. American Society of Mechanical Engineers Code minimum material property values are used for the structural and plugging limit analysis. Mechanical testing has shown that the structural strength of nickel electrosleeves under normal, upset and faulted conditions provides margin to the acceptance limits. These acceptance limits bound the most limiting (three times normal operating pressure differential) burst margin recommended by Regulatory Guide 1.121. Burst testing of electrosleeved tubes has demonstrated that no unacceptable levels of primary-to-secondary leakage are expected during any plant condition.

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DETERMINATION OF NO SIGNIFICANT IIAZARDS As in the original tube, the electrosleeve Technical Specification depth-based plugging limit is detennined using the guidance of Regulatory Guide 1.121 and the pressure stress equation of Section Ill of the ASME Code. A bounding tube wall degradation growth rate per cycle and a nondestructive examination uncertainty has been assumed for determining the electrosleeve plugging limit.

Evaluation of the proposed electrosleeved tubes indicates no detrimental effects on the )

electrosleeve or electrosleeve-tube assembly from reactor system flow, primary or secondary

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coolant chemistries, thermal conditions or transients, or pressure conditions as may be '

l experienced at Calvert Cliffs. Corrosion testing of electrosleeve-tube assemblies indicates no l evidence of electrosleeve or tube corrosion considered detrimental under anticipated service l conditions. '

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The implementation of the proposed electrosleeve has no significant effect on either the l configuration of the plant, or the manner in which it is operated. The hypothetical consequences of failure of the electrosleeved tube is bounded by the current steam generator tube rupture analysis described in Section 14.15 of the Calvert Cliffs Updated Final Safety Analysis Report.

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release rates would be slightly less than assumed for the steam generator tube rupture analysis (depending on the break location), and therefore, would result in lower total primary fluid mass release to the secondary system I l

Therefore, BGE has concluded that the proposed change does not involve a significant increase i in the probability or consequences of an accident previously evaluated.

2. Would not create the nossibility of a new or different kind of accidentfrom any other accident previousiv evaluated.

As discussed above, the electrosleeve is designed using the applicable ASME Code as guidance;  ;

therefore, it meets the objectives of the original steam generator tubing. As a result, the l functions of the steam generators will not be significantly affected by the installation of the l proposed electrosleeve. Adhesion and ductility tests performed per ASTM standards verified that the electrosleeve will not fail by de-bonding or cracking. In addition, the proposed electrosleeve does not interact with any other plant systems. Any accident as a result of potential tube or electrosleeve degradation in the repaired portion of the tube is bounded by the existing tube rupture accident analysis. The continued integrity of the installed electrosleeve is periodically verified by the Technical Specification requirements.

The implementation of the proposed electrosleeves has no significant effect on either the I configuration of the plant, or the manner in which it is operated. Therefore, BGE concludes that this proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.

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DETEIO11 NATION OF NO SIGNIFICANT IIAZARDS l

3. Would not involve a sienincant reduction in a margin ofsaferv.

1 The repair of degraded steam generator tubes via the use of the proposed electrosleeve restores l

the structural integrity of the faulted tube under normal operating and postulated accident I conditions. The design safety factors utilized for the electrosleeve are consistent with the safety factors in the ASME Boiler and Pressure Vessel Code used in the original steam generator design. The repair limit for the proposed electrosleeve is consistent with that established for the steam generator tubes. The portions of the installed electrosleeve assembly which represent the reactor coolant pressure boundary can be monitored for the initiation and progression of ,

electrosleeve/ tube wall degradation, thus satisfying the requirements of Regulatory Guide 1.83.

Use of the previously identified design criteria and design verification testing assures that the margin to safety with respect to the implementation of the proposed electrosleeve is not significantly different from the original steam generator tubes.

Therefore, BGE concludes that the proposed change does not involve a significant reduction in a margin of safety.

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