Text

Response to NRC Request for Additional Information to Byron Station Relief Request I3R-08
	ML062300200
Person / Time
Site:	Byron
Issue date:	08/18/2006
From:	Hoots D; Exelon Nuclear
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	BYRON 2006-0097, I3R-08
	Download: ML062300200 (32)
	v • d • e

Exd n August 18, 2006 LTR:

BYRON 2006-0097 File:

1.10.0101 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. 50-454 and 50-455

Subject:

Response to NRC Request for Additional Information to Byron Station Relief Request 13R-08

References:

(1)

Letter from Dave M. Hoots (Exelon Generation Company, LLC) to U. S.

NRC, 3~10-Year Inservice Inspection Interval, Relief Request I3R-08, Preventive Weld Overlays on Pressurizer Spray, Relief, Safety and Surge Nozzles and Associated Alternative Repair Techniques, dated April 28, 2006 (2)

Letter from Robert F. Kuntz. (U. S. NRC) to C. M. Crane (Exelon Generation Company, LLC), Byron Station, Units 1 and 2, Request for Additional Information RE: Relief Request I3R-08 Alternative To Weld Overlay requirements (TAC Nos. MD1761 and MD1762), dated August 8, 2006 During the review of the Reference 1 submittal, the NRC determined that additional information was required in order to complete their evaluation of the Byron Station, Units 1 and 2, 3~

10-Year Inservice Inspection Interval, Relief Request l3R-08, Preventive Weld Overlays on Pressurizer Spray, Relief, Safety and Surge Nozzles and Associated Alternative Repair Technique. The NRC requested a response to the questions contained in the Reference 2 transmittal. Attachment 1 to this letter provides the Exelon Generation Company, LLC response to these NRC questions.

Should you have any questions concerning this letter, please contact W. Grundmann, Regulatory Assurance Manager, at (815) 406-2800.

Respectfully,

~~~ots Site Vice President Byron Station Nuclear Generating Station

Attachments:

1) Response to Request for Additional Information to lnservice Inspection Interval, Relief Request 13R-08

2) White Paper Relaxation of the 100 Square Inch Size Limitation Code Case N-638 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request 13R-08 NRC Question 1:

In yoursubmittal dated April 28, 2006, you state that structural weld overlays are proposed for the welds listed on Table 1, page 6. Only one reference in the submittal is made stating that a full structural overlay will be the design (page 8 of 20). Since this is the only place that the design of the overlay has been referenced, please clarify whether full-structural overlays are to be performed and that no design/optimized overlays willbe implemented.

Exelon Generation Company, LLC (EGC) response to Question 1:

Byron Station will install full structural weld overlays of all pressurizer nozzle to safe-end welds. The design documents, CN-Cl-06-9, Byron Units 1 & 2 and Braidwood Units 1 & 2 Pressurizer Spray and Safety/Relief Nozzle Weld Overlay Repair Design, and CN-PAFM-06-25, Byron/Braidwood Pressurizer Surge Nozzle Weld Overlay Design, establish the required full structural weld thickness and length for overlays for the dissimilar metal safe end welds at the Pressurizer surge, spray, safety and relief nozzles based on plant specific geometry, loadings and ASME Section XI Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping, requirements.

The above referenced documents are currently prepared and are under review by EGC and an independent third party reviewer. These documents will be completed and approved for use during the Byron Station Unit 1 Fall 2006 refueling outage (B1 R14).

NRC Question 2:

Please indicate what types of nondestructive examinations (NDE) will be performedprior to the weld overlay installation. Ifpre-welding NDE is not to be performed expandyour justification for notperforming the NDEprior to welding for your full structural overlays.

EGC response to Question 2:

Byron Station will complete a bare metal visual examination of the Pressurizer Surge, Safety, Relief and Spray Nozzle immediately after the mirror insulation is removed from the nozzle and Dissimilar-Metal weld area. This is to ensure that no through wall cracks exist prior to applying the overlay. Prior to applying the overlay, the entire overlay area will be cleaned, including a distance at least 1.5 times the nozzle end thickness beyond the overlay on the nozzle side and 1.5 beyond the overlay area on the pipe side.

At the completion of the cleaning, a liquid penetrant test (PT) will be performed of the overlay area with an acceptance criteria that no indication greater than 1/16 is permitted. If any indication is found greater than 1/16, the indication will removed and the PT completed again. If any indication(s) do require repair, the repair will be completed and the area will again have a PT completed for final acceptance.

Page 1 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request l3R-08 Because of the configuration of the pressurizer nozzle to safe-end welds and the close proximity of the nozzle to safe-end to pipe, a qualified ultrasonic examination of the area, including the existing welds, cannot be performed.

NRC Question 3:

Please discuss your repair strategy as a result of pre-welding NDE. The cover letter indicates that full structural overlays willbe performed as a preemptive application, or as a repairapplication if a flaw is found. If a flaw is detected in the weld by NDE prior to weld overlay, confirm that the weld overlay thickness calculation is basedon the worst-case flaw.

EGC response to Question 3:

The design assumption in the previously referenced documents, CN-CI-06-9 and CN-PAFM-06-25, is the presence of a pre-existing flaw that extends the full circumference of the pipe and over the entire original wall thickness. This assumption is consistent with Code Case N-504-2, Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping, section (f). This design assumption provides for the most restrictive flaw condition that could be considered for the weld overlay thickness.

The above referenced documents are currently prepared and are under review by EGC and an independent third party reviewer. These documents will be completed and approved for use during the Byron Station Unit 1 Fall 2006 refueling outage (Bi Ri 4).

NRC Question 4:

For an overlay that extends over an adjacent weld (ifit occurs), please discuss in detail your strategy for expansion of examinations if an unacceptable flawis found by post-welding NDE of the weld overlay that was not scheduled for an inservice examination that outage.

EGC response to Question 4:

Although adjacent welds (i.e., pipe to safe-end welds) will be overlayed, none of these welds are scheduled for Inservice Inspection in the upcoming Fall 2006 Byron Station Unit 1 refueling outage. Any expansion of the examination scope due to unacceptable flaws in the adjacent welds will be based on an evaluation of the unacceptable flaw characteristics. This evaluation will include whether other elements in the segment or segments are subject to the same root cause conditions. No additional examinations will be performed if there are no additional elements identified as being susceptible to the same root cause conditions. If the evaluation does identify a common degradation mechanism, then further examinations would be performed on those elements.

Page 2 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request 13R-08 NRC Question 5 Please identify when the flaw evaluations and shrinkage stress effects analyses required under Code Case N-504-2(g), Items 2, and 3, willbe performed as they relate to your outage schedule.

EGC response to Question 5:

Flaw evaluations in accordance with Code Case N-504-2(g) Item 2 are covered under Calculations CN-PAFM-06-67, Byron and Braidwood Units 1 and 2 Pressurizer Surge Nozzle Structural Weld Overlay Fatigue Crack Growth Evaluation, CN-MRCDA-06-8, Byron and Braidwood Units 1 and 2 Pressurizer Spray Nozzle Fatigue Crack Growth Analysis for Weld Overlay Repairs, and CN-MRCDA-06-1 6, Byron and Braidwood Units 1 and 2 Pressurizer Safety and Relief Nozzle Fatigue Crack Growth Analysis for Weld Overlay Repairs.

Shrinkage stress effects analyses in accordance with Code Case N-504-2(g) Item 3 are covered under Calculations, CN-PAFM-06-1 00, Byron Unit 1 PSARV Piping Stress Evaluation Due to Shrinkage Weld Over-Lay (SWOL), CN-PAFM-06-101, Byron Unit 1 (CAE) Surge Line Analysis for the Shrinkage Effect at Nozzle Weld Over-Lay Location, CN-PAFM-06-102, Byron Unit 1 (CAE) Spray Line Analysis for the Shrinkage Effect at Nozzle Weld Over-Lay Location, and CN-PAFM-06-109, Byron Unit 1 Support Evaluation for Surge, Spray and PSARV Line Due to Shrinkage Weld Over-Lay (SWOL).

The above referenced documents are currently prepared and are under review by EGC and an independent third party reviewer. These documents will be completed and approved for use during the Byron Station Unit 1 Fall 2006 refueling outage (Bi R14).

NRC Question 6:

On page 11 of your submittal, you indicate that The maximum area of an individual weld based on the finished surface over the ferritic material will exceed 100 sq. in. and will be on the order of 300 sq. in. As you note, a portion of your basis for acceptability is the staffs approval of the Susquehanna Steam Electric Station overlay. To support your basis for meeting an acceptable level of quality and safety, identify the similarities and differences in the overlay designs and stresses with Susquehanna that apply to Byron Station Units 1 and 2.

EGC response to Question 6:

The NRC acceptance of the Susquehanna relief request was not based on specific design and stresses but on the industry work demonstrating the acceptability of larger areas of ambient temperature temper bead welding. Because the basis was not specific to Susquehanna, Byron Station referred to that approval. Since the initial submittal of the Byron Station Relief Request I3R-08, the American Society of Mechanical Engineers (ASME) has approved Code Case N-638-3, Similar and Dissimilar Metal Welding Using Page 3 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request I3R-08 Ambient Temperature Machine GTAW Temper Bead Technique, which increased the 100 square inch limitation to 500 square inches.

The technical basis accompanying that Case revision provides an expanded basis for the change in area limitation. A copy of the technical basis, White Paper Relaxation of the 100 Square Inch Size Limitation Code Case N-638 is included as Attachment 2 to this letter to provide additional basis for justification of the Byron Station relief request.

Additionally, in a June 28, 2006 letter to Calvert Cliffs, the NRC approved a relief request for weld overlays based on operational experience and the technical basis included in this same white paper.

Furthermore, it is noted that since the nozzle-to-safe-end welds and the weld overlays are fabricated from austenitic materials with inherent toughness, no cracking in the overlays is expected to occur due to the shrinkage associated with the weld overlay.

With respect to the low alloy steel material in the nozzle, many temper bead weld overlays have been applied in the nuclear industry to these nozzle-to-safe end locations.

In no instance has there been any reported cracking due to the weld overlay application.

The stiffness and high toughness inherent in the low alloy steel nozzle is expected to protect against any cracking and limit any distortion that might occur in the nozzle.

Byron Station will be measuring and evaluating the axial shrinkage to validate that the calculations (i.e., CN-PAFM-06-100, CN-PAFM-06-101, CN-PAFM-06-1 02 and CN-PAFM-06-109) are in accordance with ASME Code Case N-504-2(g) Item 3. Also, any cracking that might occur will be detected by the final non-destructive examination (NDE) of the weld overlay. Laboratory testing and field experience have documented and qualified the temper bead weld overlay repair for nozzle-to-safe-end welds and these efforts and experience have demonstrated that this technique provides a quality, sound repair that maintains structural integrity, thus demonstrating an acceptable level of quality and safety.

In addition to the technical justification above, the ferritic area of the nozzle to be overlayed is less than 100 square inches on all nozzles except the surge line nozzle.

The surge line nozzle is marginally over the 100 square inches.

The following table lists the estimated square inch areas of overlay. This table identifies both the total surface area of weld overlay coverage and the surface area of weld overlay coverage over the ferritic nozzle.

Nozzle ID Estimated Total Surface Area of Weld Overlay (square inches)

Estimated Surface Area of Weld Overlay on Ferritic Nozzle (square inches)

Spray PN-02 158 30 Relief PN-03 219 SafetyPN-04 221

~~~P~05 217 Safety PN-06 217 PN-07 485 108 Page 4 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request I3R-08 NRC Question 7:

On page 12 of your submittal, you identified the start time for the 48-hour hold time from ambient temperature for post welding NDE to completion of the third layer welding.

On July 17, 2006, the staffsubmitted a no vote to N-638-X, which dealt with shortening the 48-hour hold time. The 48 hour5.555556e-4 days 0.0133 hours 7.936508e-5 weeks 1.8264e-5 months hold time, from the time when a weld has reached ambient temperature after the completion of welding, is reasonable because it provides defense in depth for repairs on P-3 materials that do not receive preheat orpostweld heat treatment as part of the weld repairprocess. It is the staffs position that the white paper and its referenced EPRI Report (GC-111050) do not provide a technical justification to reduce the current48-hour hold time requirements. Please provide justification in terms of deterministic evidence and/or actual test data that demonstrates that the time boundary you request is sufficient to identify any hydrogen cracking, or withdraw your request for relief from this requirement.

EGC response to Question 7:

Byron Station recognizes that the NRC does not agree on the justification for starting the 48-hour hold after the third layer is applied, therefore, Byron Station will follow the current requirement in Code Case N-638-1 and start the 48-hour hold time after the last layer is applied and the weld has reached ambient temperature.

NRC Question 8:

On page 2 of your submittal, you identify Regulatory Guide 1.147, Rev. 14 as an applicable requirement. On page 12 of yoursubmittal, you identify Code Case N-638-2 as the basis for not performing the full UT of the 1.5T band for structural weld overlays.

This Code Case is not approved or conditionally approved for use in Regulatory Guide 1.147, Rev. 14. Since the Code Case you reference has not been approved for use by the staff, please submit an acceptable technical justification for relief from the UT coverage requirements.

EGC response to Question 8:

For clarification, it needs to be identified that Code Case N-638-i is only being used for welding on and directly adjacent to the P-No. 3 ferritic nozzle materials, since only these locations require ambient temperature Gas Tungsten Arc Welding (GTAW) temper bead welding in lieu of the Code required post-weld heat treatment. Therefore, the N-638-i ultrasonic examination of a band around the area to be welded of at least 1.5 times the component thickness or 5, whichever is less, is only required on the nozzle side of the weld overlay and does not apply to both sides of the weld overlay as indicated in the NRC request for additional information.

Page 5 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request 13R-08 The following information is offered to further demonstrate the acceptability of not performing the ultrasonic examinations of the ferritic nozzle material band around the area to be welded of at least 1.5 times the componentthickness or 5, which ever is less.

When the ambient temperature GTAW temper bead Code Case provisions were initially developed in 1997, little experience was available for ambient temperature GTAW temper bead welding. Although developmental testing indicated the acceptability of the process, conservative provisions were added to the Code Case because little actual field experience was available for welding without the temper bead pre-heat and post-bake temperature requirements. One such conservative provision was the requirement to examine a band around the area to be welded of at least 1.5 times the component thickness or 5, which ever is less, using surface and ultrasonic methods. The intent of such examinations was to ensure that no adverse effects impacted the ferritic steel base material as a result of the ambient temperature temper bead welding process.

The adverse effect considered by ASME was the potential for delayed hydrogen cracking. Delayed hydrogen cracking is only a potential concern when welding on ferritic materials or using ferritic filler materials and is not a concern for welding on austenitic materials such as stainless steel safe-ends and stainless steel piping or using austenitic Alloy 52M filler materials. For austenitic weld overlays covered by the Byron Station relief request, the concern is limited to the heat-affected zone in the P-No. 3 nozzle material at the weld overlay to nozzle interface.

For comparison, it is helpful to look at the requirements in ASME Section XI, Subsubarticle IWA-4630, Temper Bead Welding of Dissimilar Materials, compared to those in Code Case N-638-1. IWA-4630, in ASME Section XI, 2001 Edition through the 2003 Addenda, applicable to the Byron Station 3~Interval, addresses repairs where a defect is excavated and the resulting cavity is welded using the dissimilar metal temper bead welding process. When using IWA-4630, a volumetric examination of the IWA-4610(a) preheated band is not required by IWA-4634, Examination, for dissimilar metal temper bead welding. IWA-4634 mandates a surface examination of this pre-heated band and of the weld itself. This surface examination of the pre-heated band was imposed because a surface examination is best suited to identify unlikely but detrimental surface breaking cracking caused by elevated pre-heat and potential hydrogen cracking at the component surface in the heat-affected zone and base metal immediately adjacent to the welded cavity. IWA-4634 also mandates a volumetric examination of the deposited weld metal itself, but imposes no volumetric examination requirement for the pre-heated band. Volumetric examination of the band was not considered necessary.

Based on the experience gained since the initial development of ambient temperature GTAW temper bead provisions, and the experience with temper bead welding performed in accordance with IWA-4600 procedures, and based on a comparison of the examination differences in Case N-638-1 and IWA-4630, ASME began processing a revision to Case N-638-1 in 2004 to eliminate the examination of the adjacent base metal band and required the welded excavation be examined in accordance with the Construction Code. This revision became Code Case N-638-2, as referenced in the basis for the Code Case N-638-1 modification in the Byron Station Relief Request I3R-08.

Page 6 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request I3R-08 Furthermore, Code Case N-638-i and the temper bead welding techniques in IWA-4600 are written to address repair welds where a defect is excavated and the resulting cavity is filled using a temper bead technique. For IWA-4630 dissimilar metal temper bead welding in the 2001 Edition, through 2003 Addenda, surface examination of an extended band around the weld is specified as described above. For Code Case N-638-1, the surface and volumetric examination of a band of equivalent size around the weld was imposed as a conservative measure as described above. However, an excavated cavity configuration differs significantly from the weld overlay configuration addressed in Code Case N-504-2 and Appendix Q, Weld Overlay Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Weldments. For an excavated cavity, the fusion line between the weld and the cavity is more critically oriented for hydrogen cracking than the fusion line between a weld overlay and the underlying base metal and/or original welds. For weld overlays, potential hydrogen cracking associated with the Pressurizer weld overlays would be limited to the heat-affected zone in the P-3 nozzle material at the weld overlay to nozzle interface. Potential hydrogen cracking in the heat-affected zone at the toe of the weld overlay is best identified by a surface examination. Potential hydrogen cracking in the heat-affected zone in the weld overlay to nozzle interface under the weld overlay is best identified by a UT examination of the weld overlay. These potential causes of cracking are addressed by the Byron Station proposed modification to N-638-1, which examines the adjacent band and the weld with a surface examination, as required by N-638-i, and examines the weld overlay by UT examination in accordance with Case N-504-3, Appendix Q and demonstrated PDI UT procedures for examination of weld overlays, but eliminates the UT examination of the adjacent band.

Therefore, based on the above information, the Byron Station proposed modification to N-638-i adequately examines the appropriate areas and volumes to address the potential types and locations of cracking, thereby assuring an acceptable level of quality and safety. The N-638-1 ultrasonic examination of the band outside of the weld overlay offers no additional benefit in terms of quality or safety.

In addition to the above justification, there are obstructions that limit performance of the N-638-i ultrasonic examinations. Although this is not the basis for the Byron Station modification to N-638-1 to not perform the ultrasonic examination, it is provided for further information. In the following discussion, the ultrasonic (volumetric) examination requirement for the band is the entire base metal below the band surface. The ultrasonic inspection is to be conducted in accordance with Appendix I of the ASME Code Section Xl.

With respect to the weld overlay process on Pressurizer nozzle dissimilar metal welds, the Code Case N-638-i defined band and examination volume would encompass the nozzle base metal volume in the regions of the outside diameter (OD) nozzle tapered surface and, for some nozzles, a part of the nozzle larger cylindrical diameter. Such surfaces are not conducive for gaining full coverage of the examination volume due to non-coupling of the ultrasonic test probes over the surface. Obstructions causing this non-coupling include the edge of the weld overlay, the transition between the OD nozzle taper and the nozzle larger cylindrical diameter, and the nozzle outer blend area that transitions to the nozzle to shell weld.

Page 7 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request I3R-08 Appendix I of the ASME Code Section XI, 2001 Edition through the 2003 Addenda requires that the ultrasonic examination be conducted in accordance with ASME Code Section V, Article 4 and all supplements of Appendix I except Supplement 9 Scan Angles. These requirements include straight beam scanning for laminar and planar reflectors and angle beam scanning for planar reflectors. The straight beam scanning will most likely not detect any delayed hydrogen cracking due to mis-orientation of the cracking with respect to the beam and to the anticipated near surface location of such cracking. Essentially the straight beam is a repeat of the nozzle material examination required by the Construction Code. The angle beam examinations will be largely impacted by the outer diameter surface configuration. To maximize angle beam examination coverage would entail a series of special transducers to be applied even though the most effective angle beam transducers would be those configured to detect near surface breaking planar reflectors. However, the most effective NDE method for detection of near surface breaking planar reflectors is not with a volumetric method but with a surface examination method, as discussed above. Therefore, performing a limited UT examination of the adjacent nozzle ferritic material band provides no additional benefit in terms of quality and safety.

In conclusion, based on the above information, the Byron Station proposed modification to Case N-638-i adequately examines the appropriate areas and volumes to address the potential types and locations of cracking, thereby assuring an acceptable level of quality and safety. The Case N-638-i ultrasonic examination of the band outside of the weld overlay offers no additional benefit in terms of quality or safety. Because the Case N-638-i ultrasonic examination of the band outside of the weld overlay offers no additional benefit in terms of quality or safety, performing a limited ultrasonic examination only serves to increase radiological dose for UT examiners.

NRC Question 9:

On page 10 of yoursubmittal, you state that the Byron Station Third Interval ISI Program is based on the ASME 2001 Edition, through 2003 Addendum, which is the basis for relief from the IWA-5000 requirements. Please identify anypertinent Code paragraphs from your ISI Code of record or staffacceptable Code Cases to support your request for relief.

EGC response to Question 9:

The Byron Station request does not petition to use Code Case N-504-2 in its entirety.

Code Case N-504-2 was utilized as a basis for designing the structural weld overlays.

In addition, the Byron Station request does not ask for relief from the requirements of IWA-5000, System Pressure Tests,. The modification to N-504-2 addressed in the Byron Station request is to use the provision of IWA-4540, Pressure Testing of Class 1, 2 and 3 Items, of Section Xl 2001 Edition through 2003 Addenda, which does not require a hydrostatic test and that a system leakage test may be used instead.

This system leakage test is performed in accordance with the requirements of IWA-5000. The proposed Byron Station modification to Case N-504-2 simply notes that the Page 8 of 9 Response to Request for Additional Information to Inservice Inspection Interval, Relief Request I3R-08 provisions in Section XI will be used. Basis for this is further illustrated in that Non-mandatory Appendix Q, required by the NRC to be used along with Case N-504-2, does not take exception to the pressure test requirements of IWA-4540, thereby allowing the use of either a hydrostatic test or a system leakage test.

Page 9 of 9 White Paper Relaxation of the 100 Square Inch Size Limitation Code Case N-638