L-2014-096, Inservice Inspection Plan - Fifth Inspection Interval Unit 3 Relief Request No. 1

Inservice Inspection Plan - Fifth Inspection Interval Unit 3 Relief Request No. 1

ML14098A036
Person / Time
Site:	Turkey Point
Issue date:	04/04/2014
From:	Kiley M Florida Power & Light Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-2014-096
Download: ML14098A036 (10)

Text

0FPL.

10 CFR 50.55a L-2014-096 April 4, 2014 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Re: Turkey Point Unit 3 Docket No. 50-250 Inservice Inspection Plan - Fifth Inspection Interval Unit 3 Relief Request No. 1 Pursuant to 10 CFR 50.55a(a)(3)(ii), Florida Power & Light Company (FPL) requests Nuclear Regulatory Commission (NRC) approval to use an alternative to the ASME Boiler and Pressure Vessel Code, Section Xl, 2007 Edition, including Addenda through 2008. FPL determined pursuant to 10 CFR 50.55a(a)(3)(ii) that compliance with specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Turkey Point Unit 3 is currently in its refueling outage for Cycle 27. During a visual inspection of the pressurizer heater sleeve penetrations, an indication of leakage in the annulus between the outer surface of the heater sleeve and the lower head bore at heater penetration 11 was found.

Because of difficulties in assessing the flaw and removing it, FPL is hereby requesting the NRC to review and approve the attached alternative to support placing the pressurizer back in service (Mode 4). Entry into Mode 4 from the current Unit 3 refueling outage is currently scheduled for April 14, 2014.

Please contact Robert Tomonto, Licensing Manager, at 305-246-7327 if you have any questions or require any additional information about this submission.

Very truly yours, Michael Kiley Site Vice President Turkey Point Nuclear Plant

Attachment:

Turkey Point Unit 3 Relief Request No. 1 for the 5 th Inspection Interval cc: Regional Administrator, USNRC Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant 40(,

Florida Power & Light Company 9760 SW 344th St., Florida City, FL 33035

Florida Power & Light Company L-2014-096 Attachment Page 1 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 Proposed Alternative in Accordance with 10CFR 50.55a(a)(3)(ii)

Hardship or Unusual Difficulty without Compensating Increase in Level of Quality or Safety REPAIR OF PRESSURIZER STAINLESS STEEL HEATER SLEEVE WITHOUT FLAW REMOVAL

1. ASME Code Component Affected Turkey Point Unit 3 Components: Pressurizer and pressurizer heater sleeve (nozzle)

Code Class: ASME Section III 1965 Edition, including Addenda through Summer 1965, Class A Examination Category: B-P Code Item Number: B15.10

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Description:==

Pressurizer heater sleeve internally welded to the pressurizer lower head cladding Size: 1.125" Nominal outside diameter, 0.095" wall thickness Material: Stainless steel SA-213 TP316 sleeve, austenitic stainless steel cladding, SA-216 Grade WCC lower head

2. Applicable Code Edition and Addenda

ASME B&PV Code Section Xl, "Rules for Inservice Inspection of Nuclear Power Plant Components" 2007 Edition, including Addenda through 2008.

Florida Power & Light Company L-2014-096 Attachment Page 2 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0

3. Applicable Code Requirement

Pursuant to 10 CFR 50.55a (a)(3)(ii) Florida Power and Light (FPL) requests an alternative to the requirements of ASME B&PV Code, Section Xl, IWB-3142.3 "Acceptance by Corrective Measures or Repair/Replacement Activity. A component containing relevant conditions is acceptable for continued service if the relevant conditions are corrected by a repair/replacement activity or corrective measures to the extent necessary to meet the acceptance standards of Table IWB-341 0-1 ."

4. Reason for Request

FPL conducted visual examinations of the pressurizer heater sleeve penetrations during the current Turkey Point Unit 3 Refueling Outage. These examinations revealed evidence of leakage in the annulus between the outer surface of the heater sleeve and the lower head bore at heater penetration #11. There was no leakage observed at the other heater penetrations. Manual nondestructive examination (NDE) was conducted from the sleeve bore using the eddy current method after the heater was removed from the heater sleeve. The examination did not reveal any flaw in the sleeve. Therefore, the most likely location of the flaw is located in the stainless steel weld between the heater sleeve and the stainless steel cladding buildup.

The heater sleeve is roll expanded into the lower head bore and welded with a partial penetration weld to the stainless steel cladding buildup on the inside of the pressurizer lower head. The partial penetration weld joint does not extend into the lower head carbon steel base material.

The cladding is final stress relieved prior to welding the heater sleeve thereto. The cladding is approximately 3/8" thick and one layer of cladding of approximately 3/16" thick remains beneath the partial penetration weld. The heater is fillet welded to the bottom of the sleeve and extends upward through the two heater lateral support plates in the pressurizer.

To remove the heater sleeve-to-pressurizer weld requires accessing the internal surface of the pressurizer and removal of the weld and any remaining sleeve base metal. Such an activity results in high radiation exposure to the personnel involved which is considered a hardship. Grinding and/or machining within the components also exposes personnel to safety hazards as well as possible foreign material remaining in the pressurizer that could later affect fuel performance.

Florida Power & Light Company L-2014-096 Attachment Page 3 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 FPL proposes to leave the upper portion of the existing heater sleeve and its weld to the pressurizer lower head cladding in service.

5. Proposed Alternative and Basis for Use PROPOSED ALTERNATIVE:

The original weld will not be corrected and the heater sleeve base material will be removed to approximately the mid wall of the pressurizer lower head. The heater sleeve will be repaired by relocating the pressure boundary weld from the inside surface of the pressurizer to the outside surface. The repair is in accordance with the Class 1 requirements of the ASME Boiler and Pressure Vessel Code Section II1.

The "half-nozzle" method will be used for the repair to penetration #11. The heater is removed and the heater sleeve is severed below the pressurizer lower head. The remaining lower portion of the heater sleeve is removed by boring to approximately mid-wall of the lower head. The removed portion of the stainless steel sleeve will be replaced with a section (half-nozzle) of low carbon stainless steel which will then be welded to the outside surface of the pressurizer lower head using low carbon stainless steel weld filler. A new heater will be welded to the bottom of the replacement lower sleeve using low carbon stainless steel weld filler. The upper portion of the sleeve, including the partial penetration weld, will remain in place. (See Figure 1)

Heater sleeve welds on pressurizers with Alloy 600 material have been repaired by the industry using a similar "half-nozzle" technique. The half-nozzle method has been used at Calvert Cliffs Unit 1 and St. Lucie Unit 2.

The portion of the original heater weld to the pressurizer was examined with a borescope. An area of discoloration - Y2" along the reinforcing fillet weld face was noted. However, no indication of cracking was identified in the discolored region or any other part of the weld that was viewed.

The original heater sleeve remnant and weld will not receive any additional NDE. The new lower heater sleeve-to-lower head and heater/plug-to-lower heater sleeve pressure boundary welds, on the exterior surface of the pressurizer, will be examined in accordance with the applicable requirements of the ASME Boiler and Pressure Vessel Code Sections III and XI.

Florida Power & Light Company L-2014-096 Attachment Page 4 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 BASIS FOR USE:

Since the heater sleeve material and sleeve-to-clad weld are generally not susceptible to a stress corrosion mechanism in the pressurizer environment it is presumed that the weld flaw(s) was the result of an original fabrication flaw that propagated from service.

Such service propagation could be a combination of thermal fatigue and/or SCC.

There has been no leakage at any other pressurizer heater sleeve location at Turkey Point unit 3 or unit 4. A review of industry operating experience (OE) from the 48 US PWRs with similar stainless steel heater sleeves welded to the interior clad surface, representing greater than 3800 heater sleeves and 23-42 years of service, has not identified a leak at this location. OE was identified at one US plant but the leak was at a location in the heater sleeve material outside of the pressurizer shell attributed to an anomaly in the tube adjacent to the weld. The greater than 3800 stainless steel pressurizer heater sleeves with 23-42 years of operating history represents greater than 100,000 sleeve years of service with occurrence of only this single leak in the weld.

This provides evidence of the excellent service history as well as the evidence of the lack of a generic condition.

The effects of propagation of any flaw(s) that remain in the original heater sleeve weld, by fatigue crack growth and stress corrosion cracking mechanisms are considered.

Postulated worst case flaws are assessed for flaw growth. The assessment concludes the structural integrity will not be adversely affected by postulated flaw(s) remaining in service for at least one fuel cycle.

Further characterization of the weld by NDE was not practical as discussed below. Due to its location in the inside of the lower pressurizer head, the original heater sleeve-to-pressurizer clad partial penetration weld is extremely difficult to access from the pressurizer manway, through the heater support plates and heaters, to perform NDE.

Also, if it was accessible, to fully characterize the flaw(s) causing leakage would require a volumetric examination method, such as an ultrasonic (UT) examination method.

However, the weld configuration around the sleeve outer diameter precludes UT coupling and control of the sound beam needed to perform flaw characterization and sizing, with reasonable confidence, of the measured flaw dimensions. If UT examination of the original partial penetration weld were attempted from the outside surface of the pressurizer lower head, the cladding interface would provide an acoustic mismatch that would severely limit this examination. This UT examination would also encounter scanning interferences due to adjacent heaters as well as the required long examination distances (i.e., metal paths) for interrogation of radial-axial oriented flaws at the opposite (inside) surface. These conditions would make accurate detection, characterization, and sizing of flaw(s) problematic.

Florida Power & Light Company L-2014-096 Attachment Page 5 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 Currently, there is no qualified UT technique for examination of the original partial penetration weld or adjacent carbon steel pressurizer lower head material from either the inside or outside surface. Radiography of this area is also impractical because of the inability to position either a source or film inside the pressurizer. Additionally, other NDE methods, such as liquid penetrant, magnetic particle, and eddy current would not provide useful volumetric information needed for flaw characterization.

It is reasonable to assume that the existing flaw(s) is contained within the weld only, since eddy current examination did not reveal any indication in the heater sleeve, and has not progressed significantly into the cladding beneath the weld.

The cladding is subjected to post weld heat treatment (stress relief). As a result, the residual tensile stress state during normal operation is significantly less than the tensile stress state in the weld, which has not been stress relieved. During operation the cladding stress may even be compressive because the stainless steel coefficient of thermal expansion is greater than that of the carbon steel lower head. Therefore, the force driving a crack through the weld will be greatly diminished as the crack enters the cladding. For stress corrosion cracking (SCC), the reduced stress will lead to lower growth rates, and for cyclic loading (fatigue) the stresses will be alternating about a significantly lower mean stress, leading to reduced crack growth per cycle. Therefore is it reasonable to assume that the flaw that resulted in the leak through the 3/16" partial penetration weld after 42 years of service would take greater than one 18-month cycle to grow an additional 3/16" through the remaining layer of clad to reach the clad/carbon steel interface.

The current inspection performed at Turkey Point Unit 3 is a VT-2 exam every refueling outage, meeting the NEI-03-08 recommended inspection guidance and frequency provided by the PWR Owners Group. This examination is performed with the insulation in place. The Turkey Point Unit 3 pressurizer lower head is insulated with glass or mineral fiber insulation. At the time of the initial inspection the insulation configuration provided gaps around the leaking penetration and several other heater sleeve locations to permit examination of the base metal. A complete bare metal visual was performed at all 78 penetrations to determine the extent of condition.

The bottom of the pressurizer is visually inspected for leakage every outage, therefore the leak occurred since the last inspection. Since it took many years for the leakage to occur, there is no reason to believe that significant growth into the cladding would occur in only a few additional fuel cycles, especially due to its lower residual stress state and since the sleeve-to-cladding weld is no longer pressure retaining.

Florida Power & Light Company L-2014-096 Attachment Page 6 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 Therefore, it is reasonable to assume that:

a) The existing flaw is completely contained within the pressurizer stainless steel cladding.

b) Crack growth from the cladding into the inside surface of the pressurizer lower head carbon steel base material will not occur over the next fuel cycle.

c) There are no flaw(s) driven by fatigue into the lower head carbon steel base material.

d) In the unlikely event that a, b, and c, are untrue, quantitative analysis of a similar configuration has demonstrated that a flaw starting at the cladding to base metal interface can grow for a significant length of time and remain stable with appropriate factors of safety.

Experience with fatigue flaw growth analysis in Combustion Engineering (CE) designed PWR pressurizers was performed by the PWROG in WCAP-1 5973-P-A Rev 0, as well as a plant specific analysis in NRC Accession ML11132A183. The initial postulated flaw was significantly larger in the CE design since the pressure boundary J-groove weld prep is cut into the low alloy carbon steel lower head of the pressurizer, resulting in a significantly larger initial flaw than the Turkey Point Unit 3 original weld prep which remains in the stress relieved clad (Figure 1). These fatigue crack growth analyses yielded acceptable results for a significant length of time, providing ample assurance that a flaw growth into the ferritic steel head would be stable for at least one cycle.

The qualitative fracture mechanics assessment concludes that it is acceptable to allow postulated flaw(s) to remain in service and demonstrates the acceptability of the condition for at least one fuel cycle. Therefore the proposed alternative is being requested for acceptance in accordance with IWB-3142.3 for the next 18-month fuel cycle.

Corrosion of the exposed carbon steel in the half nozzle repair is also considered. The "half-nozzle" repair has a small radial gap between the heater sleeve remnant and the replacement lower heater sleeve and the bore in the pressurizer lower head and a small axial gap between the bottom of the heater sleeve remnant and the top of the replacement lower heater sleeve. As a result, primary coolant (borated water) will fill this crevice. Carbon steels used for reactor coolant systems components are clad with stainless steel to minimize corrosion resulting from exposure to borated primary coolant.

Since the crevice regions are not clad, the carbon steel is exposed to borated water.

Florida Power & Light Company L-2014-096 Attachment Page 7 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 The carbon steel pressurizer lower head will not be significantly degraded by general corrosion as a result of the modification. Although some minor corrosion may occur in the crevice region on the carbon steel head the degradation will not proceed to the point that the structural integrity of the pressurizer will be adversely affected during its remaining service life, including the period of extended operation. Further, available laboratory data and field experience also indicate that continued propagation of cracks into carbon steel by a stress corrosion mechanism is unlikely.

For the carbon steel exposed to the primary coolant, galvanic corrosion, hydrogen embrittlement, SCC, and crevice corrosion are not expected to be a concern. Based on industry data and AREVA's experience, the corrosion rate of exposed carbon steel in the bore of the lower head is conservatively estimated to average 0.0018" per year with 10% shutdown time during the operating cycle and 0.0026" per year with 20% shutdown time during the operating cycle.

SCC of the stainless steel components (replacement heater sleeve and weld metals) is not likely because two of the three necessary synergistic elements of SCC (susceptible material and aggressive environment) are minimal or not present. Some residual stresses will likely be present adjacent to the weld in the replacement stainless steel items. However, this stress will likely not cause crack initiation or propagation because the other two necessary elements of SCC are minimal or not present.

Results of the stress analyses show that the structural integrity of the pressurizer will not be adversely affected for the remainder of its service life due to material loss in the lower head base material.

In conclusion, the ASME B & PV Code Section XI requirement, IWB-3142.3, is to correct a component containing a flaw(s). The proposed alternative is to relocate the pressure boundary weld to the outside surface of the pressurizer and not correct the item(s) containing the flaw(s) but show by qualitative assessment that the material and the presence of the postulated worst case flaw(s) will not be detrimental to the pressure retaining function of the pressurizer for one fuel cycle.

6. Duration of Proposed Alternative Relief is requested for 18-month fuel cycle. During the next fuel cycle additional analyses will be performed to justify the revised configuration with the postulated flaw(s) remaining in place for the current inspection interval for Turkey Point Unit 3 which expires on February 21, 2024.

Florida Power & Light Company L-2014-096 Attachment Page 8 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0

7. Commitment FPL will perform a bare metal visual examination of the Unit 3 pressurizer heater sleeve area during the next Cycle 28 refueling outage.

8. Precedents There are no known precedents for pressurizer stainless steel heater sleeve leakage requiring repair. The modified configuration is similar to various half-nozzle repairs performed by the industry for Alloy 600 items that have experienced leakage that have typically been caused by primary water SCC. However, there is a precedent for evaluating flaw growth in carbon steel and low alloy steel base material due to fatigue that is exposed to reactor coolant in the pressurizer environment. An evaluation has been submitted to the NRC as follows:

"ATTACHMENT (6) UNIT 1 PRESSURIZER HEATER SLEEVE AS-LEFT J-GROOVE WELD FLAW EVALUATION FOR IDTB REPAIR - NON-PROPRIETARY," Calvert Cliffs Nuclear Power Plant, LLC May 11, 2011, NRC Accession ML11132A183.

Florida Power & Light Company L-2014-096 Attachment Page 9 of 9 TURKEY POINT UNIT 3 FIFTH INSPECTION INTERVAL RELIEF REQUEST No. 1 Revision 0 0.11 Inches - Approximate Axial Gap Between Upper Sleeve Remnant &

Lower Replacement Heater Sleeve SS Replacement Lower Sleeve (0.03% Max C)

Figure 1 Penetration #11 Final Configuration