(l Xcel Energy@

OCT 2 0 2014

U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60

L-PI-14-1 02 10 CFR 50.55a

Supplement to 10 CFR 50.55a Request 2-RR-4-10 Associated with the Fourth Ten-Year Interval for the lnservice Inspection Program (TAC No. MF4794)

By letter dated September 3, 2014 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 14247A639), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), submitted for NRC approval 10 CFR 50.55a Requests associated with the fourth ten-year interval for the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, lnservice Inspection (lSI) Program. By email dated October 2, 2014 (ML 14276A011), the NRC Staff requested additional information (RAI) on the September 3, 2014 (ML 14247A639), 10 CFR 50.55a Request 2-RR-4-1 0. The enclosure to this letter provides supplemental information in response to the NRC Staff RAison 10 CFR 50.55a Request 2-RR-4-10.

If there are any questions or if additional information is needed, please contact Mr. Dale Vincent, P.E., at 651-267-1736.

Summary of Commitments

This letter contains no new commitments and no revisions to existing commitments.

P~ ,PiP;? ;d.,;, .da-rf.Jo,-,

Kevin Davison Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota

Enclosures (1)

1717 Wakonade Drive East • Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page2

cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC

Enclosure

By letter dated September 3, 2014 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML 14247A639), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), submitted for NRC approval 10 CFR 50.55a Requests associated with the fourth ten-year interval for the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, lnservice Inspection (lSI) Program. By email dated October 2, 2014 (ML 14276A011), the NRC Staff requested additional information (RAI) on the September 3, 2014 (ML 14247A639), 10 CFR 50.55a Request 2-RR-4-1 0.

NRC RAI:

The NRC staff has reviewed your application for relief requests numbered 2-RR-4-10 and concluded that supplemental information is required to enable the staff to make an independent assessment regarding acceptability of the proposed relief request. Specifically, the NRC staff requests that NSPM supplement the application by providing a timeline of events that covers when the problem was discovered, when the NRC was first told, and includes specific details of any flaw evaluation, if done.

NSPM Response:

The presence of an indication of a flaw in the 22 RSG was documented as an action request (AR) in the NSPM corrective action program (CAP). An apparent cause evaluation (ACE) was performed to support resolution of the AR. A timeline of events leading to submittal of this 10 CFR 50.55a request, which is based on the ACE, is provided in the following table. Some of the dates may be approximate because they are based on personnel recollection of events during preparation of the ACE.

2012

November 2012

12/4/2012

1/24/2013

RSG 22 Weld S/C003 is completed and all ASME Section Ill fabrication examinations, including radiographs, are reviewed and accepted by AREVA and NSPM. The weld joint meets the fabrication code and the vessel ASME "NPT" mark is applied.

Informational lSI examinations are performed by AREVA and witnessed by PINGP nondestructive examiner (NDE) Level Ill and PINGP Authorized Nuclear Inspector (ANI) in Chalon, France. Draft report includes a disposition of the subsurface indication in RSG 22 Weld S/C003 that uses ASME Section XI Table IWC-351 0-1 for evaluating flaws in material less than 50 ksi yield strength; the report also includes an interpolation error.

AREVA informs NSPM RSG Project personnel of the flaw during a phone call. RSG Project personnel informed AREVA that AREVA is responsible for the disposition in accordance with ASME Section XI.

NSPM RSG Project receives the AREVA lSI report. Report is routed for PINGP NDE Level Ill and ANI review.

Page 1 of 4

Enclosure- 10 CFR 50.55a 2-RR-4-1 0 RAis

2/4/2013

2/10/2013

3/5/2013

3/29/2013

3/29/2013

4/17/2013

5/22/2013

6/17/2013

7/2/2013

7/21/2013

9/9/2013

NSPM RSG Project Management identifies interpolation error in the AREVA lSI report and notifies AREVA by formal letter. NSPM RSG Project personnel continue review and approval process of the AREVA lSI report; comments in the formal letter to AREVA are tracked for resolution.

NSPM RSG Project Management initiates an AR in the corrective action program titled, "Preliminary lSI Exam -Indication on RSG 22 Weld S/C003", to document the lSI indication. AREVA documents containing the interpolation error and inappropriate use of Table IWC-351 0-2 are attached to the AR and submitted for PINGP lSI engineer review. A letter identifying the interpolation error is attached to the AR. An action in the AR is assigned to the PINGP lSI engineer to perform a condition evaluation (CE).

PINGP lSI engineer completes CE stating that the "informational only" exam is not credited under pre-service or in-service inspection, and that if the indication is identified during pre-service (PSI) or in-service (lSI) examination, it will be dispositioned as required. NSPM personnel documented that no further action was required.

PINGP Program Engineering Manger reviews completed CE and dispositions the AR to COMPLETE status.

All NSPM comments are incorporated into the AREVA lSI report. PINGP NDE Level Ill and ANI complete their reviews and sign the report. Report for RSG 22 Weld S/C003 remains preliminary because the final exam and disposition cannot be performed until after the field hydrostatic test.

RSGs delivered to PINGP. Delivery report signed by NSPM RSG Project Management with annotation regarding RSG 22 lSI UT indication and the pending resolution following the hydrostatic test and official lSI exam.

NSPM RSG Project Management identifies a concern with use of Table IWC-351 0-1 due to material properties that exceed the 50 ksi material strength limitation.

NSPM RSG Project Design Engineering initiates an AR titled, "UT Indication on RSG Tube-sheet to Lower Shell Weld S/C003". AR is intended to resolve the lSI indication and does not focus on the use of Table IWC-351 0-1. Corrective Action (CA) assignments within the AR are assigned for review by Regulatory Affairs and RSG Project Engineering.

NSPM RSG Project personnel notify AREVA of questions regarding the various evaluations and risks, and asks for AREVA to consider the possibility of on-site repair. AREVA does not reply to the request to consider onsite repair.

Regulatory Affairs completes the CA assignment and concludes that no NRC report is needed and recommends Engineering determine whether the subject flaw conforms to the Code and if not, a relief request will be required after the final exam (post hydro). Engineering has not completed their CA review assignment.

AREVA Report 51-9209148-DRAFT, "PINGP Unit 2 RSG Fracture Mechanics Evaluation of UT Flaw Indication", is received and routed for review by NSPM RSG Project Design Engineering and PINGP NDE Level Ill. Report includes

Page 2 of 4

Enclosu~e- 10 CFR 50.55a 2-RR-4-1 0 RAis

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justification for using Table IWC-351 0-1.

NSPM completes review of AREVA Report 51-9209148-DRAFT. PINGP NDE Level Ill has no comments, however RSG Project personnel note several

9/27/2013 comments, including additional questions regarding the path through the code that permits the use of Table IWC-351 0-1. NSPM comments are forwarded to AREVA via formal letter.

RSG Project Design Engineering consults with industry experts (Reedy and Associates), NSPM subject matter experts (Monticello and Fleet) and AREVA and also researches NRC past precedent.

Final AREVA report concludes indication meets Code acceptance criteria by invoking IWA-1320 and applying Table IWB 3510-1 for disposition of the flaw (RSG was designed, fabricated and tested as an ASME Section Ill Class 1

11/27/2013 vessel).

The report hinges on code paragraph IWA-1320(c) which states, "where all components within the system boundary or isolable portions of the system boundary are classified to a higher class than required by the group classification criteria, the rules of IWA-1320(a) may be applied to the higher classification, provided the rules of the applicable Subsection are applied in their entirety."

Post hydrostatic lSI examination is completed (official lSI exam). PINGP NDE

12/14/2013 Levell II requests confirmation from RSG Project Management and Engineering (with copy to his supervisor) that Table IWC-3510-1 is to be used for the disposition and notes that the indication is acceptable per Table IWC-351 0-1.

lSI UT Report 2013U040 is issued to document the indication and acceptance

12/14/2013 per Table IWC-351 0-1. Report is prepared by PINGP NDE personnel, reviewed by PINGP NDE Level Ill, and approved by PINGP lSI Program Engineering Supervisor.

12/16/13 lSI UT Report 2013U404 is provided to NRC Region Ill Inspectors performing inspection of RSG installation activities, per 12/9/13 request.

'

RSG 22 hydrostatic testing is completed which completes the ASME

12/19/2013 Fabrication code requirements, an ASME N-1 Certification is issued and the vessel code "N" Stamp is applied. The vessel meets all ASME Section Ill Code requirements.

RSG Project Management completes the AR reviews of the completed Engineering and Regulatory Affairs CA assignments and initiates another CA

12/20/2013 assignment for the PINGP lSI engineer to insure linkage between AREVA report and PSI exam report for demonstrating acceptability. The AREVA evaluation is attached to the AR.

2/19/2014 PINGP lSI engineer reviews PSI UT Report 2013U040 and AREVA report and questions if path through the code is acceptable.

3/7/2014 PINGP lSI engineer initiates a new AR to document inappropriate use of IWA-1320 and Table IWC-351 0-1 for flaw acceptance.

6/5/2014 PINGP lSI engineer and Regulatory Affairs discuss disposition of the RSG 22 flaw indication with NRC in a conference call. NSPM provides the basis for

Page 3 of 4

Enclosure- 10 CFR 50.55a 2-RR-4-1 0 RAis

6/17/2014

8/21/2014

9/3/2014

concluding the intent of ASME XI has been met and that a 1 OCFR50.55a Request is not required. NRC generally concurs with a recommendation to solicit further industry expert opinion.

PINGP lSI engineer solicits additional industry expert opinion and concludes that use of IWA-1320 and Table IWC-351 0-1 is inappropriate and that the Code does not provide a path for reconciliation of the lSI indication in Class 2 material greater than 50 ksi; therefore a 10 CFR 50.55a request is required.

PINGP lSI engineer and Regulatory Affairs have conference call with NRC to discuss pending 10 CFR 50.55a Requests. Included in the discussion is 2-RR-4-1 0, "Alternative Acceptance Criteria for 22 Replacement Steam Generator Indication of Flaw".

NSPM submits 10 CFR 50.55a Request 2-RR-4-1 0.

AREVA provided a fracture mechanic evaluation of the preservice UT indication of a flaw in the lower shell to tubesheet weld as a proprietary document. To accept the AREVA evaluation, NSPM performed Engineering Change (EC) Evaluation 24335 (EC EVAL 24335), "Evaluation of Flaw in Tubesheet-to-shell weld of 22 Replacement Steam Generator", which summarized the basis for accepting the flaw. EC EVAL 24335, without its Attachment 10.1, is attached to this enclosure as Attachment 1.

Page 4 of 4

Attachment 1

Engineering Change (EC) Evaluation 24335 (EC EVAL 24335) "Evaluation of Flaw in Tubesheet-to-shell weld of 22 Replacement Steam Generator"

3 pages follow

EC Evaluation

NUMBER: EC EVAL 24335 REVISION: 0 MINOR REV.: - SHEET NO: 1 OF 3

TITLE: EVALUAITON OF FLAW IN TUBESHEET-TO-SHELL WELD OF 22 REPLACEMENT STEAM GENERATOR

DATE: 7/18/14

COMP. BY: DWNT01

1. Purpose & Summary Result

1.1. In 2R28 an indication was identified during a preservice examination of the tubesheet-to-shell weld of the 22

Replacement Steam Generator (RSG). The indication could not be dispositioned under ASME Section XI IWC

for Class 2 components due to the material strength of the RSG exceeding the allowable yield strength for

application of Table IWC-351 0-1. AREVA provided an evaluation that shows the indication is acceptable under

ASME Section XI IWB for Class 1 components. The purpose of this evaluation is to bring the AREVA

evaluation "PINGP Unit 2 RSG Fracture Mechanics Evaluation of UT Flaw Indication" Document No. 51-

9209148-000 into a site process to support and provide verification and validation for a NRC relief request. The

relief request will propose using the acceptance standards of ASME Section XI IWB for class 1 vessels as an

alternative to IWC for class 2 vessels on the basis it provides an acceptable level of quality and safety.

1.2. This evaluation summarizes the methodology, analysis and results of the attached AREVA evaluation (see

attached AREVA evaluation for a more detailed analysis). The AREVA evaluation shows that the flaw in the

tubesheet-to-shell weld of the 22 replacement steam generator (RSG) meets the acceptance standards of 1WB-

3112(a) for Class 1 components.

2. Methodology

2.1. The Class 1 rules in Section XI provide a clear path for evaluating flaws in high strength materials. Table IWB-

351 0-1 may be used for high strength materials if, in part, it can be demonstrated that the material is as tough

as similar material with yield strengths below 50 ksi. Fracture mechanics data from several sources was

collected to demonstrate that the fracture toughness requirements are met for the 22 RSG.

2.2. Once toughness is demonstrated, the dimensions of the flaw are compared to the allowable flaws sizes in Table

IWB-3510-1 to show the flaw is acceptable. ·

3. Acceptance Criteria

3.1. There are no acceptance criteria. The purpose of this evaluation is to bring the AREVA evaluation into a site

process so it can be used to supporfa NRC relief request.

4. Inputs

5.

6.

7.

4.1. AREVA evaluation "PINGP Unit 2 RSG Fracture Mechanics Evaluation of UT Flaw Indication". AREVA

document No. 51 - 9209148- 000 dated 11/12/2013.

References

5.1. None.

Assumptions

6.1.1.None.

Analysis

7.1. Establish an Analytical Expression for the Fracture Toughness Curve in Figure G-2210-1 of ASME Section Ill. ·

EC Evaluation

NUMBER: EC EVAL 24335 REVISION: 0 MINOR REV.: - SHEET NO: 2 OF 3

TITLE: EVALUAITON OF FLAW IN TUBESHEET-TO-SHELL WELD OF 22 REPLACEMENT STEAM

GENERATOR

7.1.1. From the AREVA evaluation the analytical expression of the curve is:

KIR = 26.78 + 1.223 exp [ 0.0145 (T- RTNDT + 160)]

Where:

KIR = reference stress intensity factor, ksi"in

T =crack tip temperature, oF

RTNDT = reference nil-ductility temperature, oF

DATE: 7/18/14

COMP. BY: DWNT01

7.2. Demonstrate that the Fracture Toughness of the SA-508 Grade 3 Class 2 Used in the 22 RSG is Above

the Reference Stress Intensity Factor (KIR).

7.2.1.1. From the AREVA evaluation, a total of six heats of SA-508 Grade 3 Class 2 material were tested in

the product forms (base metal, SAW weld metal, and heat affected zone material) associated with the

UT flaw indication in the PINGP 22 RSG. Since the dynamic fracture toughness data obtained from

these tests have all been shown to be above the reference stress intensity curve in Figure G-2210-1 of

the ASME Code Section Ill, the material may be considered to be fully compliant with the flaw

evaluation requirements for Class 1 inspections based on satisfaction of the fracture toughness

provision ofTable IWB-3510-1.

7.3 Compare the Flaw Dimensions to the Acceptance Standards of Table IWB-351 0-1.

7.3.1 From the AREVA evaluation:

Material thickness, t = 3.00 in.

Distance to surface, S = 0.82 in.

Flaw depth, 2a = 0.30 in.

Flaw length, I = 0.45 in.

Aspect ratio, all = 0.33 (rounded to 0.35)

Depth-to-thickness ratio, aft= 0.05 (or 5.0%)

Y = (S/t)/(a/t) = S/a = 5.4 > 0.4 (classified as a subsurface flaw)

Set Y = 1.0 (maximum permitted by Note 4 ofTable IWB-3510-1)

( EC Evaluation

NUMBER: EC EVAL 24335 REVISION: 0 MINOR REV.: -

TITLE: EVALUAITON OF FLAW IN TUBESHEET-TO-SHELL WELD OF 22 REPLACEMENT STEAM GENERATOR

SHEET NO: 3 OF 3

DATE: 7/18/14

COMP. BY: DWNT01

Allowable Flaw Depth-to-Thickness Ratio (aft) Obtained by Interpolation from Table IWB-351 0-1

Allowable a/t (%)

Aspect Thickness, t (in.) Ratio, a/1 (%) 2.5 in. 3.00 in. 4.0 in.

0.35 9.0% 7.7% 5.1%

Conclusion: The flaw is acceptable since the actual depth-to-thickness ratio (aft) of 5:0% is less than the

allowable value of 7.7%.

8. Conclusions

8.1. The AREVA evaluation shows the flaw in the tubesheet-to-shell weld of the 22 RSG to be acceptable under the

acceptance standards of IWB-3112(a) for Class 1 components.

9. Plant Impact I Future Needs

9.1. Incorporation of the AREVA evaluation into a site process supports and provides verification and validation for a

NRC relief request to use the acceptance standards of ASME Section XIIWB for class 1 vessels as an

alternative to IWC for class 2.

10. Attachments

1 0.1. AREVA evaluation

"PINGP Unit 2 RSG Fracture Mechanics Evaluation of UT Flaw Indication". AREVA document No. 51 -

9209148-000 dated 11/12/2013. (18 pages).

~ ;-f)' I Prepared by: /6ac.0vtl, ,

Technical Review by: --~--.~~4--~---+-L _______ Date: ff ""6 .. ; <..(