TMI-11-030, Response to Request for Additional Information - Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds

Response to Request for Additional Information - Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds

ML110680332
Person / Time
Site:	Three Mile Island
Issue date:	03/09/2011
From:	David Helker Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME4795, TMI-11-030
Download: ML110680332 (5)

Text

10 CFR 50.55a TMI-11-030 March 9, 2011 U.S.Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Three Mile Island Nuclear Station, Unit 1 Renewed Facility Operating License No.DPR-50 NRC Docket No.50-289

Subject:

Response to Request for Additional Information

-Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds

References:

1)Letter from P.B.Cowan (Exelon Generation Company, LLC)to U.S.Nuclear Regulatory Commission,"Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds," dated September 30, 2010 2)Letter from P.Bamford (U.S.Nuclear Regulatory Commission) to M.J.Pacilio,"Three Mile Island Nuclear Station, Unit 1 Request for Additional Information Regarding Relief Request RR-10-02, Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds (TAC NO.ME4795)," dated February 28,2011 In the Reference 1 letter, Exelon Generation Company, LLC(Exelon)requested relief to perform a weld overlay of pressurizer spray nozzle to safe-end and safe-end to elbow dissimilar metal welds at Three Mile Island Nuclear Station (TMI), Unit 1.In the Reference 2 letter, the U.S.Nuclear Regulatory Commission requested additional information.

Attached is our response to questions 2, 3 and 4.As discussed in Reference 2, the response to question 1 will be provided by April 28, 2011.There are no regulatory commitments contained in this submittal.

If you have any questions conceming this letter, please contact Tom Loomis at (610)765-5510.Respectfully, David P.Helker Manager-Licensing Exelon Generation Company, LLC Response to Request for Additional Information Relief Request RR-10-02 Concerning the Weld Overlay of Dissimilar Metal Welds March 9, 2011 Page 2

Attachment:

Response to Request for Additional Information

-Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle toEnd and Safe-End to Elbow Dissimilar Metal Welds cc: Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, TMI USNRC Project Manager,[TMI]USNRC ATTACHMENT Response to Request for Additional Information

-Submittal of Relief Request RR-10-02 Concerning the Weld Overlay of the Pressurizer Spray Nozzle to Safe-End and Safe-End to Elbow Dissimilar Metal Welds Response to Request for Additional Information Relief Request RR*10*02 Concerning the Weld Overlay of Dissimilar Metal Welds March 9, 2011 Page 1 of 2 Question: 2.In section 5 of RR*10-02 (page 4, fourth paragraph) the licensee states that weld preheat and heat input are monitored through the use of calibrated contact pyrometers or thermocouples.

Please clarify exactly which instrument, contact pyrometer or thermocouples, will be used.If thermocouples will be used, please identify what steps will be taken to ensure that the temperature reading will be accurate and discuss whether the use of the thermocouples will satisfy subarticles IWA*4610(a) and IWA-4624.1 (d)of the American Society of Mechanical Engineers Boiler and Pressure VesselCode,Section XI, 2004 edition.Response: Weld preheat and heat input will be monitored through the use of a calibrated contact pyrometer.

Thermocouples will not be used during the installation of the weld overlay.Question: 3.On page 5 of RR-10-02, the licensee states that it intends to install one or more weld barrier layer(s)to prevent hot cracking in stainless steel materials similar to that installed during the 2007 weld overlays.The staff notes that some licensees have reported cracking in the weld overlay during and after the installation on Alloy 82/182 welds and stainless steel pipes.Please discuss any measures that will be taken to minimize potential cracking in addition to the barrier layer(s).Response: Exelon Generation Company, LLC (Exelon)and the implementation vendor are aware of the hot cracking that was observed when welding Alloy 52M over a buffer layer that had been applied on cast stainless steel during weld overlay installations at other plants in 2009 and 2010.In order to minimize the potential for cracking during installation of the pressurizer spray nozzle weld overlay at TMI, Unit 1, appropriate criteria and parameters have been established for control of the welding process.As an example, the welding heat input"power ratio" range has been determined to minimize weld metal contamination from the existing plant materials.Theoverlay design includes no welding on cast stainless steel material, as only wrought materials are involved.Additionally, the wrought base material chemistries (from the Certified Material Test Report data)and weld geometry will be reviewed to determine the level of risk for hot cracking when welding Alloy 52M over stainless steel base material.This review will result in the specific mitigation efforts that will be employed during the installation of the weld overlay.Weld parameters and techniques specially developed for welding over stainless steel and Alloy 82/182 welds will be implemented to prevent cracking.Question: 4.Section 6 of RR-10-02 states that the duration of the proposed alternative associated with the weld overlay is the remaining service life ofthecomponents, including future plant life extension.

It does not identify any difference in the duration of the proposed alternative between the design of the overlay, and the aspects of the request that relate to subsequent inservice examinations.

Examination techniques may be improved in the future beyond what is Response to Request for Additional Information Relief Request RR-10-02 Concerning the Weld Overlay of Dissimilar Metal Welds March 9, 2011 Page 2 of 2 specified in the relief request Also, emergent issues could impact what future examination requirements may be appropriate.

Therefore, the staff requests that the application be changed or clarified such that the examination aspects of the proposed alternative apply only to the fourth 10-year inservice inspection interval.Alternatively, please justify why the proposed duration for future inservice examinations is acceptable.

Response: The design and installation of the structural weld overlay are applicable to the remaining service life of the plant As discussed in Section 5 of the relief request: "Subsequent inservice examinations will be scheduled and performed in accordance with the requirements of Nonmandatory Appendix Q or alternate schedules accepted by the NRC (for example adoption of ASME Code Case N-770 as proposed by 75FR24324)." In summary, TMI, Unit 1 will perform the fourth ten-year lSI interval examinations as described above.Subsequent lSI interval examinations will be performed in accordance with NRC requirements applicable to the interval.