RS-11-045, Inservice Inspection Relief Request I3R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations

Inservice Inspection Relief Request I3R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations

ML110830837
Person / Time
Site:	Byron
Issue date:	03/24/2011
From:	Hansen J Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-11-045
Download: ML110830837 (9)

Text

Exelon Generation www.exeloncorp.com 4300 Winfield Road Nuclear Warrenville, IL 60555 10 CFR 50.55a RS-11-045 March 24, 2011 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 Byron Station Unit 1 Facility Operating License No. NPF-37 NRC Docket No. STN 50-454

Subject:

Byron Station Unit 1 Inservice Inspection Relief Request 13R-19: Alternative Requirements for the Repair of Reactor Vessel Head Penetrations

References:

(1) Westinghouse WCAP-15987, Revision 2-A, "Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations, II December 2003 (2) Letter from H. N. Berkow (U. S. NRC) to H. A. Sepp (Westinghouse Electric Company), "Acceptance for Referencing - Topical Report WCAP-15987-P, Revision 2, 'Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetration,' (TAC NO. MB8997)," dated July 3,2003 (3) Letter from R. Gibbs (U. S. NRC) to C. M. Crane (Exelon), "Byron Station, Unit No.2 - Relief Request 13R-14 for the Evaluation of Proposed Alternatives for Inservice Inspection Examination Requirements (TAC No.

MD5230)," dated May 23,2007 (4) Letter from R. Kuntz (U. S. NRC) to C. M. Crane (Exelon), "Westinghouse Electric Company, Request for Withholding Information from Public Disclosure for Byron Station, Unit No.2 (TAC No. MD5230)", dated May 16, 2007, ADAMS Accession No. ML071290249 In accordance with 10 CFR 50.55a, "Codes and standards," paragraph (a)(3)(i), Exelon Generation Company, LLC (EGC), is requesting relief from the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," on the basis that the proposed alternatives would provide an acceptable level of quality and safety.

Specifically, a relief request is being proposed to perform an alternative repair technique using the embedding methodology of Reference 1 on the reactor Vessel Head Penetration (VHP) housings and J-groove welds of Byron Station Unit 1. The embedded flaw methodology to be used has been approved generically by the NRC in the Reference 2 Safety Evaluation. The details of this request are contained in Byron Station Relief Request 13R-19 attached to this letter.

March 24, 2011 U. S. Nuclear Regulatory Commission Page 2 During the current Byron Station Unit 1 Spring 2011 Refueling Outage, EGC performed volumetric examinations of the VHPs in accordance with 10 CFR 50.55a(g)(6)(ii)(D), which specifies the use of Code Case N-729-1, with conditions. Examination results for the nozzles at VHPs 64 and 76 did not meet the applicable acceptance criteria and therefore these nozzles require repair. There are recordable flaw indications that were found on the outside of VHPs 64 and 76 below the J-groove welds that are from 28% to 31% of the nominal thickness. Bare metal visual examinations of the VHPs 64 and 76 did not show evidence of leakage.

Examinations are ongoing during the current Refueling Outage for the remaining VHPs.

The repair process has conservatively assumed the indications are the result of Primary Water Stress Corrosion Cracking (PWSCC) and embedding the flaw within PWSCC resistant materials (Le., Alloy 52 weld metal) will assure structural integrity of the VHP nozzles.

Supporting the embedded flaw methodology application to the VHPs for Byron Station Unit 1 is the analysis provided in Westinghouse WCAP-16401-P, Revision 0, "Technical Basis for Repair Options for Reactor Vessel Head Penetration Nozzles and Attachment Welds: Byron and Braidwood Units 1 and 2." This WCAP provides the technical basis for the use of an embedded repair involving the VHP housing and/or the VHP housing attachment weld (Le., the J-groove weld) by evaluating the bounding loading conditions, fatigue crack growth predications, and fracture mechanics results. WCAP-16401-P, Revision 0, was previously provided in support of Reference 3, (Refer to Reference 4).

EGC requests that this repair alternative be verbally approved by March 29, 2011, to support the VHP repair and restoration/restart activities at Byron Station Unit 1. While EGC recognizes the burden associated with an accelerated review and approval of 13R-19, the need for a repair of VHPs at Byron Station Unit 1 as a result of these examinations was unexpected.

Byron Station Unit 1 has previously been ranked as a low susceptibility plant with an Effective Degradation Year rating of 3.195 (as of February 2011) with a very low probability of PWSCC initiation and consequently, there was no expected need to prepare and submit, for NRC review, a contingency Relief Request for an alternative repair methodology in advance of the Byron Station Unit 1 refueling outage.

There are no regulatory commitments contained in this submittal. If you have any questions about this letter, please contact Mr. Richard W. Mcintosh at (630) 657-2816. - Byron Station Relief Request 13R-19, "Alternative Requirements for the Repair of Reactor Vessel Head Penetrations"

151 Program Plan Unit 1, Third Interval 10 CFR 50.55a RELIEF REQUEST 13R-19 Revision 0 (Page 1 of 7)

Request for Relief Alternative Requirements for the Repair of Reactor Vessel Head Penetrations In Accordance with 10 CFR 50.55a(a)(3)(I) 1.0 ASME CODE COMPONENT'S) AFFECTED Component Numbers 1 RC01 R Reactor Vessel

Description:

Alternative Requirements for the Repair of Reactor Vessel Head Penetrations (VHPs) and J-groove Welds Code Class: Class 1 Examination Category: ASME Code Case N-729-1 Code Item: B4.20 Identification: Byron Unit 1 VHP Numbers 1 through 78 Drawing Numbers: 185282E Revision 1, 185283E Revision 1, and 185286E Revision 2 2.0 APPLICABLE CODE EDITION AND ADDENDA Inservice Inspection and Repair/Replacement Programs: American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, 2001 Edition, through 2003 Addenda.

Code of Construction (Reactor Vessel): ASME Section III, 1971 Edition through Summer 1973 Addenda.

Examinations of the VHPs are performed in accordance with 10 CFR 50.55a(g}(6}(ii}(D},

which specifies the use of Code Case N-729-1, with conditions.

3.0 APPLICABLE CODE REQUIREMENT IWA-4000 of ASME Section XI contains requirements for the removal of defects from and welded repairs performed on ASME components. The specific Code requirements for which use of the proposed alternative is being requested are as follows:

ASME Section XI, IWA-4421 states, that Defects shall be removed or mitigated in accordance with the following requirements:

(a) Defect removal by mechanical processing shall be in accordance with IWA-4462.

(b) Defect removal by thermal methods shall be in accordance with IWA-4461.

(c) Defect removal or mitigation by welding or brazing shall be in accordance with IWA-4411.

(d) Defect removal or mitigation by modification shall be in accordance with IWA-4340.

Note that use of the "Mitigation of Defects by Modification" provisions of IWA-4340 is prohibited per 10 CFR 50.55a(b}(2}(xxv}.

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For the removal or mitigation of defects by welding, ASME Section XI, IWA-4411 states, in part, the following.

Welding, brazing, and installation shall be performed in accordance with the Owner's Requirements and ... in accordance with the Construction Code of the item ...

The applicable requirements of the Construction Code required by IWA-4411 for the removal or mitigation of defects by welding from which relief is requested are as follows.

Base Material Defect Repairs:

For defects in base material, ASME Section III, NB-4131 requires that the defects are removed, repaired, and examined in accordance with the requirements of NB-2500.

These requirements include the removal of defects via grinding or machining per NB-2538. Defect removal must be verified by a magnetic particle or Liquid Penetrant (PT) examination in accordance with NB-2545 or NB-2546, and if necessary to satisfy the design thickness requirement of NB-3000, repair welding in accordance with NB-2539.

ASME Section III, NB-2539.1 addresses removal of defects and requires defects to be removed or reduced to an acceptable size by suitable mechanical or thermal methods.

ASME Section III, NB-2539.4 provides the rules for examination of the base material repair welds and specifies they shall be examined by the magnetic particle or PT methods in accordance with NB-2545 or NB-2546. Additionally, if the depth of the repair cavity exceeds the lesser of 3/8-inch or 10% of the section thickness, the repair weld shall be examined by the radiographic method in accordance with NB-5110 using the acceptance standards of NB-5320.

Weld Metal Defect Repairs ASME Section III, NB-4451 states; that unacceptable defects in weld metal shall be eliminated and, when necessary, repaired in accordance with NB-4452 and NB-4453.

ASME Section III, NB-4452 addresses elimination of weld metal surface defects and specifies defects are to be removed by grinding or machining.

ASME Section III, NB-4453.1 addresses removal of defects in welds and requires the defect removal to be verified with magnetic particle or PT examinations in accordance with NB-5340 or NB-5350. In the case of partial penetration welds where the entire thickness of the weld is removed, only a visual examination is required to determine suitability for re-welding.

As an alternative, the proposed repair will be conducted in accordance with the appropriate edition of ASME Section III and the alternative requirements, based on WCAP-15987, Revision 2-A, "Technical Basis for the Embedded Flaw Process for

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Repair of Reactor Vessel Head Penetrations," December 2003, (Refer to Reference 1),

proposed below.

4.0 REASON FOR THE REQUEST During the ongoing Byron Station Unit 1 refueling outage, Exelon Generation Company, LLC (EGC) was conducting examinations of the reactor Vessel Head Penetrations (VHPs) in accordance with Code Case N-729-1, as amended by 10 CFR 50.55a. Flaw indications have been found on the Outside Diameter (00) of Control Rod Drive Mechanism (CRDM) VHP 64 and 76 below the J-groove attachment weld on the underside of the reactor vessel head.

Ultrasonic testing (UT) identified three recordable flaws and PT identified a fourth flaw from which depth is less than detectable by UT. VHP 64 has one axially oriented recordable flaw 0.52 inches in length with a through-wall depth of 0.1 n inches, and the PT identified an axial flaw of 0.15 inches in length. VHP 76 has two recordable flaws, one recordable flaw that is 0.52 inches (axially oriented) with a through-wall depth of 0.194 inches, and a recordable flaw that is 0.84 inches (circumferentially oriented) in length and a through-wall depth of 0.187 inches.

These flaw indications located in the VHP tube material are below the J-Groove weld.

Relief is requested from the requirements of ASME Section XI, IWA-4411 to perform permanent repair of defects identified in VHPs 64 and 76 and future defects that may be identified in Byron Unit 1 VHPs in accordance with the rules of the ASME Section III Construction Code as described in this relief request.

Specifically, relief is requested from:

• The requirements in ASME Section III, NB-4131, NB-2538, and NB-2539.1 to eliminate base material defects prior to repair welding.

• The requirements in ASME Section III, NB-4451, NB-4452, and NB-4453.1 to eliminate weld metal defects prior to repair welding.

• The requirements of NB-2539.4 to perform radiographic examination when repair cavities exceed the lesser of 3/8-inch or 10% of the section thickness.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE EGC proposes to use the less intrusive embedded flaw process (Reference 1) for the repair of VHP as approved by the NRC (Reference 2).

Consistent with WCAP-15987-P, Revision 2-P-A methodology, the following repair requirements are proposed for 00 and J-groove weld repairs.

1. An unacceptable axial or circumferential flaw in a tube below a J-groove attachment weld will be sealed off with an Alloy 52 or 52M weldment. Excavation or partial excavation of such flaws will not be required. The embedded flaw repair technique

lSI Program Plan Unit 1, Third Interval 10 CFR 50.558 RELIEF REQUEST 13R-19 Revision 0 (Page 4 of 7) may be applied to 00 axial or circumferential cracks below the J-groove weld because they are located away from the pressure boundary, and the proposed repair of sealing the crack with Alloy 690 weld material would isolate the crack from the environment as stated in Section 3.6.1 of the NRC staff Safety Evaluation for WCAP-15987-P, Revision 2-P-A.

2. Unacceptable radial flaws in the J-groove attachment weld will be sealed off with a 360 degree overlay of Alloy 52 or 52M covering the entire weld. No excavation will be required. The overlay will extend onto and encompass the outside diameter of the penetration tube. The seal weld will extend beyond the Alloy 600 weld material by at least one half inch as stated in the NRC Safety Evaluation for WCAP-15987-P, Revision 2-P-A.

3. If EGC determines an excavation is desired (e.g., boat sample), then

• The excavation will be filled with Primary Water Stress Corrosion Cracking (PWSCC) resistant weld material (Le., Alloy 52 or 52M material).

• It is expected that a portion of the indication will remain after boat sample excavation; however, a PT examination will be performed on the excavation to assess the pre-repair condition.

• Depending on the extent of the excavation, the repair procedure requires the Alloy 52 or 52M weld material to extend a minimum of 0.50 inches outboard of the Alloy 82-stainless steel clad interface.

4. Unacceptable axial tube flaws extending into the J-groove attachment weld will be sealed with Alloy 52 or 52M as in Item 1 above. In addition, the entire J-groove attachment weld will be overlaid with Alloy 52 or 52M to embed the axial crack in the seal weld on the penetration. The overlay will extend onto and encompass the outside diameter of the penetration tube. The seal weld will extend beyond the Alloy 600 weld material by at least one half inch as stated in the NRC Safety Evaluation for WCAP-15987-P, Revision 2-P-A.

5. For weld overlays performed on the J-groove attachment weld, the interface boundary between the J-groove weld and stainless steel cladding will be located to positively identify the weld clad interface to ensure that all of the Alloy 82 material of the J-groove weld is overlaid during the repair.

6. Prior to application of the Alloy 52 or 52M repair weld layers on the clad surface, a minimum of three passes (one layer) of Alloy ER309L shall be installed at the periphery of the weld overlay (at the repair-to-clad interface).

7. For all of the above flaw configurations, the finished repair will be examined in accordance with Reference 2, Section 5, Item 3, Table "Repair NDE" column to ensure acceptability. Specifically, the entire surface of the overlay will be examined by PT, using the applicable acceptance standards of ASME Section III. Additionally, the penetration tube will be examined from the Inside Diameter (10) surface using UT to confirm that the repair process did not introduce any new flaws or adversely

151 Program Plan Unit 1, Third Interval 10 CFR 50.558 RELIEF REQUEST 13R-19 Revision 0 (Page 5 of 7) change the size or characteristics of the previously identified flaw(s). The volumetric examination will be performed in accordance with ASME Code Case N-729-1 with conditions as specified in 10 CFR 50.55a(g)(6)(ii)(O) to satisfy the "lSI NOE of the repair" required in the Table of Reference 2. Since 10 CFR 50.55a(g)(6)(ii)(O) notes that once a licensee implements Code Case N-729-1 , as conditioned in the regulation, the First Revised NRC Order EA-03-009 no longer applies to that licensee and shall be deemed to be withdrawn, examining the repair in accordance with N-729-1 is an "Inspection consistent with the NRC Order EA-03-009 dated February 11 , 2003 and any subsequent changes* and meets the intent of Note 2 of the Reference 2 Table.

8. The embedded flaw repair weld will be three layers thick for applications to the J-groove attachment welds, and at least two layers thick for application to base metal locations.

9. For all embedded flaw repairs, examinations of the overlay and original penetration during subsequent outages will be performed in accordance with the requirements of Code Case N-729-1 with conditions as specified in 10 CFR 50.55a(g)(6)(ii)(O).

As discussed in WCAP-15987-P, Revision 2-P-A, the embedded flaw repair technique is considered a permanent repair. As long as a PWSCC flaw remains isolated from the Primary Water (PW) environment, it cannot propagate. Since an Alloy 52 or 52M weldment is considered highly resistant to PWSCC, a new PWSCC flaw cannot initiate and grow through the Alloy 52 or 52M overlay to reconnect the PW environment with the embedded flaw. Structural integrity of the affected J-groove weld and nozzle will be maintained by the remaining unflawed portion of the weld overlay. Alloy 690 and Alloy 52 are highly resistant to stress corrosion cracking, as demonstrated by multiple laboratory tests, as well as over ten years of service experience in replacement steam generators.

The residual stresses produced by the embedded flaw technique have been measured and found to be relatively low, indicating that no new flaws will initiate and grow in the area adjacent to the repair weld. Therefore, fatigue driven crack growth is not a mechanism for further crack growth after the embedded flaw repair process is implemented.

The small residual stresses produced by the embedded flaw weld will act constantly, and, therefore, will have no impact on the fatigue effects in this region. Since the stress would be additive to the maximum and minimum stress, the stress range will not change, and the already negligible usage factor for the region will not change.

WCAP-16401-P, Revision 0 (Reference 3) provides the plant-specific analysis performed for Byron Station using the same methodology as WCAP-15987-P, Revision 2-P-A. This analysis provides the means to evaluate a broad range of postulated repair scenarios to the reactor vessel head penetrations and J-groove welds relative to ASME Code requirements for allowable size and service life.

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Additionally, the post-repair examinations, consisting of UT and PT testing will be performed in accordance with ASME Code Case N-729-1 with conditions as required by 10 CFR 50.55a(g)(6)(ii)(D) prior to return to service.

Future examinations of reactor vessel head penetrations and J-groove welds repaired utilizing the embedded flaw repair process, along with submission of any necessary reports, will be in accordance with 10 CFR 50.55a(g)(6)(ii)(D), which requires implementation of Code Case N-729-1 with certain conditions.

The above proposed alternative, as supported by the referenced generic and plant specific technical bases, is considered as an alternative to Code requirements that provides an acceptable level of quality and safety.

EGC will utilize the flaw repair and evaluation acceptance criteria specified in Reference 1 as approved by the NRC in the Reference 2.

In accordance with Section 5, "Conditions and Limitations," of the Reference 2 Safety Evaluation, EGC has concluded that the NRC flaw evaluation guidelines (Reference 5) have been followed and the appropriate Non-Destructive Examinations (NDE) listed in the Reference 2, Section 5 Table will be implemented for the repairs to VHP at Byron Station.

For the reasons stated above, the embedded flaw repair process is considered to be an alternative to Code requirements that provides an acceptable level of quality and safety, as required by 10 CFR 50.55a(a)(3)(i).

6.0 DURATION OF THE PROPOSED ALTERNATIVE The duration of the proposed alternative is for the remainder of the Byron Station Unit 1 Third Inservice Inspection Interval currently scheduled to end in July 15, 2016.

7.0 PRECEDENTS In Reference 2, the NRC generically approved the embedded flaw repair process described in Reference 1. Requests to use the embedded flaw technique to repair cracks on the 00 of VHPs as well as to repair flaws in the J-groove attachment welds of VHPs have been previously approved by the NRC on a plant specific basis. The NRC approved a similar repair for Byron Station Unit 2 in Reference 9.

This alternative incorporates lessons that are learned regarding the significant radiation dose incurred for weld overlay repair surface examinations at Beaver Valley, Unit 2, during the fall 2009 outage repair activities, which were discussed in the previously approved 10 CFR 50.55a request for Beaver Valley, Unit 2, (Refer to Reference 8). As such, this alternative requests provisions that permit original construction code acceptance criteria for the post weld overlay surface examination, and a barrier layer of ER309L filler material, prior to the application of three Alloy 52M repair weld layers on the clad surface, at the periphery of the weld overlay (at the repair-to-clad interface).

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8.0 REFERENCES

1. Westinghouse WCAP-15987-P, Revision 2-P-A, "Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations," December 2003

2. Letter from H. N. Berkow (U. S. NRC) to H. A. Sepp (Westinghouse Electric Company), "Acceptance for Referencing - Topical Report WCAP-15987-P, Revision 2, 'Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations,' {TAC NO. MB8997)," dated July 3,2003

3. Westinghouse WCAP-16401-P, Revision 0, "Technical Basis for Repair Options for Reactor Vessel Head Penetration Nozzles and Attachment Welds: Byron and Braidwood Units 1 and 2"

4. Letter LTR-NRC-03-61 from J. S. Galembush (Westinghouse Electric Company) to Terence Chan (U. S. NRC) and Bryan Benney (U.S. NRC), -Inspection of Embedded Flaw Repair of a J-groove Weld," dated October 1,2003

5. Letter from R. J. Barrett (U. S. NRC) letter to A. Marion (Nuclear Energy Institute),

"Flaw Evaluation Guidelines, n dated April 11, 2003.

6. Byron Station, Unit No.2 - Relief Request 13R-14 for the Evaluation of Proposed Alternatives for Inservice Inspection Examination Requirements (TAC NO. MD5230)

7. American Society of Mechanical Engineers Boiler and Pressure Vessel Case N-729-1, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration WeldsSection XI, Division 1"

8. Letter from N. L. Salgado (U. S. NRC) to P. A. Harden (FirstEnergy), "Beaver Valley Power Station, Unit No.2 - Relief Request Regarding an Alternative Weld Repair Method for Reactor Vessel head Penetrations J-Groove Welds (TAC No. ME4176),*

Request 2-TYP-3-RV-03, February 25, 2011 (ADAMS Accession No. ML110470557).

9. Letter from R. Gibbs (U. S. NRC) to C. M. Crane (Exelon), "Byron Station, Unit No.2

- Relief Request 13R-14 for the Evaluation of Proposed Alternatives for Inservice Inspection Examination Requirements (TAC No. MD5230)," dated May 23,2007.