ML120600603

Request for Additional Information Regarding Request for Relief I3R-08 (TAC Nos. ME6024, and ME6025)

ML120600603
Person / Time
Site:	Braidwood
Issue date:	03/09/2012
From:	Mozafari B Plant Licensing Branch III
To:	Pacilio M Exelon Nuclear
Mozafari B
References
TAC ME6024, TAC ME6025
Download: ML120600603 (5)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 9, 2012 Mr. Michael J. Pacilio President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BRAIDWOOD STATION, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION REGARDING REQUEST FOR RELIEF 13R-08 (TAC NOS. ME6024, AND ME6025)

Dear Mr. Pacilio:

By letter to the U.S. Nuclear Regulatory Commission (NRC) dated April 11 ,2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML111020263), as supplemented by letters dated June 6, 2011, and November 2, 2011 (ADAMS Accession Nos.

ML111580106 and ML113070349, respectively), Exelon Generation Company, LLC (the licensee) submitted request for relief, 13R-08, from certain examination requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) at Braidwood Station, Units 1 and 2. Specifically, the licensee proposed using rdot mean square (RMS) error criteria for sizing flaws that are greater than the requirements of ASME Code Case N-695, "Qualification Requirements for Dissimilar Metal Piping Welds," (N-695) and N-696, "Qualification Requirements for Appendix VIII Piping Examinations Conducted From the Inside Surface" (N-696).

The NRC staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. During a discussion with your staff on February 23, it was agreed that you would provide a response by March 12,2012, as described in our email (ADAMS accession No. ML12058A005.)

M. J. Pacilio -2 The NRC staff considers that timely responses to requests for additional information help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-2020.

Brenda Mozafari, Project Manager Plant licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-456 and STN 50-457

Enclosure:

Request for Additional Information cc w/encl: Distribution via Listserv

REQUEST FOR ADDITIONAL INFORMATION REQUEST FOR RELIEF 13R-08 BRAIDWOOD STATION, UNITS 1 AND 2 DOCKET NOS. STN 50-456 AND STN 50-457 The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the Relief Request (RR) 13R-08. After examining the sizing uncertainties associated with the higher root mean square (RMS) errors and reviewing the available data, the NRC staff finds insufficient technical basis for the proposed alternative in RR 13R-08. Adding the difference between the procedure root mean square (RMS) error and 0.125 inches to any measured flaw depth fails to consider the effects of surface conditions and the maximum individual sizing errors associated with increasing RMS errors. The NRC staff requests the licensee either reconsider the adjustment that will be made to the measured flaw size as outlined below or commit to submit a flaw evaluation, for any flaws identified during the examination along with the information outlined below, for NRC staff review and approval.

The NRC staff is currently reviewing the implications of the large flaw depth sizing uncertainty associated with inner diameter (10) examinations of full penetration welds. Until the NRC staff has finished the review, larger values will need to be added to the measured flaw size, or the NRC staff will need to review any flaw evaluations, on a case-by-case basis, on flaws found in piping welds sized from the 10 as a condition to granting relief. Note, that the later approach may impact the unit restart from the outage if the staff has not had adequate time to review and approve the flaw evaluation, including the measured flaw adjustment used in the evaluation.

One possible alternative the NRC staff finds has sufficient technical justification is to add twice the RMS error to the depth of a flaw prior to performing a flaw evaluation. This addition of twice the RMS error would cover evaluations of flaws found during 10 inspections of welds with poor 10 geometries (greater than 1/32 probe lift off). Licensees desiring to adjust the measured flaw depth differently from the above will need to provide justification for any such adjustment, such as documentation of a very smooth surface and the absence of ridges that would cause transducer lift off, compatible material type/grain structure, demonstrated effectiveness on these surfaces, etc. The staff will need to ensure that any value used will result in a reasonable assurance of structural integrity and leak tightness of any weld evaluated, or that any mitigation will result in a reasonable assurance of structural integrity and leak tightness considering the possible uncertainty in the measured flaw size.

The RMS error values given in RR 13R-08 for the Supplement 10 and combined Supplement 2 and 10 procedure qualifications are 0.189 and 0.245 inches, respectively. The procedure qualification RMS error values show that the Supplement 2 'flaws were more challenging to depth-size than the Supplement 10 flaws. The combined Supplement 2 and 10 RMS error is a combination of the larger but undefined RMS error of the Supplement 2 qualification and the lower 0.189 inch RMS error for the Supplement 10 qualification. The NRC staff believes that RMS error should be established separately for Supplement 2 and Supplement 10, I.e., the Enclosure

- 2 combined Supplement 2 and 10 RMS error value should not be used. Please address how the RMS error values will be used in regard to supplement 10 welds and supplement 2 welds.

Also, the NRC staff believes it is appropriate to determine the RMS error based on the procedure qualification and the personnel qualifications. The RMS error should be an average of the RMS error of the qualified person who analyzes the data and the procedure qualification.

Alternatives to this may be proposed and will need to be justified to and accepted by the NRC staff. The staff will need to ensure that any value used will result in a reasonable assurance of structural integrity and leak tightness of any weld evaluated, or that any mitigation will result in a reasonable assurance of structural integrity and leak tightness considering the possible uncertainty in the measured flaw size. Please provide a justification for using an RMS error value derived differently than described above.

If twice the RMS error is not to be added to the depth of the measured flaw, the NRC staff requests that the licensee commit in their request for additional information response that flaw evaluations of any flaws found in the inspections covered by RR 13R-08 will be submitted to the NRC for review and approval prior to reactor startup. When submitting the evaluation, in addition to the typical information provided in a flaw evaluation, the following additional information will need to be included:

• The measured flaw size(s).

• The RMS error that was added to the measured flaw size and how the RMS error was established. The RMS depth-sizing error for the personnel conducting the examination.

The licensee may propose a smaller addition (less than twice the RMS error) to the flaw depth. A smaller addition to the flaw depth will need to be technically justified, which should include, as a minimum, a demonstration that the welds are easier to inspect than the Performance Demonstration Initiative Supplement 10 ID specimens (e.g., no probe lift-off, less than 1/32-inch surface waviness) in the area near the flaw and the area used for depth-sizing. Smooth ID surfaces and other factors will be taken into account by NRC staff when reviewing the flaw evaluation.

• If the procedure uses eddy current, the determination by eddy current if the flaw is or is not surface breaking.

• The ID profile of the weld, pipe, nozzle, and safe end (as applicable) in the region at and surrounding the transducer locations used to depth size the flaw.

• The suspected flaw degradation mechanism and the process used to determine the degradation mechanism.

ML120600603 *via email OFFICE LPL3-2/PE LPL3-2/PM LPL3-2/LA DE/EPNB/BC LPL3-2/BC LPL3-2/PM NAME PHernandez BMozafari KGoldstein TLupold* JZimmerman BMozafari DATE 03/01/12 03/06/12 03/07/12 02/24/12 03/09/12 03/09/12