ML13338A284
| ML13338A284 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/22/2013 |
| From: | Mark D. Sartain Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 13-566, TAC MF2520 | |
| Download: ML13338A284 (8) | |
Text
009" Dominion Nuclear Connecticut, Inc. m 5000 Dominion Boulevard, Glen Allen, VA 23060 DominEoN Web Address: wwv.dom.com November 22, 2013 U.S. Nuclear Regulatory Commission Serial No.13-566 Attention: Document Control Desk NLOS/WDC RO Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR ALTERNATIVE REQUEST RR-04-16 FOR THE USE OF ENCODED PHASED ARRAY ULTRASONIC EXAMINATION TECHNIQUES (PAUT) IN LIEU OF RADIOGRAPHY (TAC NO. MF2520)
In a letter dated August 1, 2013, Dominion Nuclear Connecticut, Inc. (DNC) requested relief from the requirements of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code Section III for Millstone Power Station Unit 2 (MPS2). Specifically, DNC requested approval to use encoded Phased Array Ultrasonic Examination Techniques (PAUT) as an alternative to radiographic examination to satisfy nondestructive examination requirements for ASME Class 2 carbon steel circumferential pipe weld joint applications. In a letter dated October 1, 2013, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) to DNC related to the alternative request. DNC agreed to respond to RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6 by November 25, 2013 and RAI Questions 1, 3.b and 4 by February 28, 2014.
The attachment to this letter contains DNC's response to RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6.
If you have any questions regarding this submittal, please contact Wanda Craft at (804) 273-4687.
Sincerely, Mark D. Sartain Vice President - Nuclear Engineering and Development
Attachment:
Response to Request for Additional Information for Alternative Request RR-04-16 Proposed Alternative to ASME Section III.
Commitments made in this letter: None Aw~2l
Serial No.13-566 Docket No. 50-336 Page 2 of 2 cc: U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd Suite 100 King of Prussia, PA 19406-2713 James S. Kim Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2A 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No.13-566 Docket No. 50-336 ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR ALTERNATIVE REQUEST RR-04-16 PROPOSED ALTERNATIVE TO ASME SECTION III MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.
Serial No.13-566 Docket No. 50-336 Attachment, Page 1 of 5 In a letter dated August 1, 2013, Dominion Nuclear Connecticut, Inc. (DNC) requested relief from the requirements of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code Section III for Millstone Power Station Unit 2 (MPS2).
Specifically, DNC requested approval to use encoded Phased Array Ultrasonic Examination Techniques (PAUT) as an alternative to radiographic examination to satisfy nondestructive examination requirements for ASME Class 2 carbon steel circumferential pipe weld joint applications. In a letter dated October 1, 2013, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) to DNC related to the alternative request. This attachment provides DNC's response to RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6. DNC will respond to RAI Questions 1, 3.b and 4 by February 28, 2014.
Question 2 The hardship associated with the use of radiographic testing was described as an increased radiological dose to the people performing the inspections. What is the expected reduction in radiological dose that would result from the use of ultrasonic testing in lieu of radiographictesting for the welds covered in RR-04-16?
DNC Response The hardship addressed in the alternative request was based on the safety risk associated with performing radiographic examinations, which includes the planned exposure and the potential for accidental exposure associated with transporting, positioning and exposing the radiation source required for the examination. Planned exposure varies based on a number of factors such as source strength, set up time, local area dose rates, number of boundary guards required, and the potential for reexamination if repairs are required.
Currently, a total of 55 radiography exams are included in the scope of the MPS2 refueling outage 22 (2R22). This scope assumes examination of the 23 welds associated with the feedwater piping replacement project with PAUT being used in lieu of RT for 19 of those welds. Radiographic examination was performed on 24 welds during the last MPS2 refueling outage (2R21), which resulted in a total exposure of 251 mrem. It is estimated that performing PAUT in lieu of RT on 19 of the 23 welds associated with the feedwater piping replacement project would result in a planned exposure savings of approximately 50-100 mrem.
Reducing the potential of accidental exposure is an equally important consideration.
Accidental exposures can occur as a result of human error, equipment malfunction or inadequate boundary control. The potential for an accidental exposure is a function of the total number of radiographic examinations being performed during the outage.
Serial No.13-566 Docket No. 50-336 Attachment, Page 2 of 5 Therefore, removing 19 welds from the radiography scope provides a reduction in the potential for an accidental exposure.
Question 3 The technical basis for the reliable detection and characterization of fabrication flaws has thus far assumed that the inspections will be conducted from both sides of the weld.
The few experimental evaluations that have explored the reliability of single-sided ultrasonic testing (UT) suggest that detecting fabrication flaws, especially lack of fusion defects, using single sided UT misses flaws found by inspections conducted from both sides (see EPRI Report 1021181 page A-5 and the paper "An Empirical Study on Ultrasonic Testing in Lieu of Radiography for Nuclear Power Plants"in the Proceedings of the 9 th internationalconference on NDE in relation to structural integrity for nuclear and pressurized components). As the technical basis for the detection and characterization of flaws from one side of the weld has not been established, the following information on the single-sidedexaminations is required:
- a. Which welds described in RR-04-16, based on the current designs, would require single-sided inspections and which welds would be inspected from both sides of the welds?
- c. As the replacement piping has not been installed, and it is possible to design the system to allow access to both sides of the weld. What would be the hardship or unusual difficulty and the expected increase in personnel radiation dose caused by designing the replacement Feedwater system to not require single-sided ultrasonicexaminations for fabrication defects?
- d. It is possible for some components to be fabricatedoutside of containment in a shop setting. What would be the hardship or unusual difficulty and expected increase in radiationdose to personnelfrom performing radiographyon the welds that require single-sided ultrasonic examinations in a low-radiationenvironment?
- e. What would be the hardship or unusual difficulty and expected increase in radiationdose to personnel that would be caused by performing radiographyonly on the welds that would require single-sidedultrasonicexaminations?
DNC Response
- a. The following table lists the welds where UT is currently planned to be used to satisfy the volumetric examination requirements. The column listed as access identifies the welds where the configuration allows the scanning to be performed from either both sides of the weld (dual) or only a single side.
I I Serial No.13-566 Docket No. 50-336 Attachment, Page 3 of 5 SG 1- A Train ID/Weld No. Configuration Size Access 1A/AC-G-1 3-A 900 long radius (LR) elbow 18" SCH 60 (0.750" Dual to 900 LR elbow nominal wall) 9Q0 LR elbow to 18" SCH 60 (0.750" 1B/AC-G-1 2-A pipe at containment (CTMT) Dual penetration nominal wall) 18" SCH 60 (0.750" 1C/N/A CTMT pipe to flue nominal wall) Single 1DIN/A Flue to pipe inside CTMVIT 18" SCH 60 (0.750" Single nominal wall) 1E/AC-G-11-A Pipe to 900 LR elbow 18" SCH 60(0.750" Dual nominal wall) 1F/AC-G-10QA 900 LR elbow to 900 LR 18" SCH 60 (0.750" Dual elbow nominal wall) 1G/AC-G-09-A 900 LR elbow to pipe 18" SCH 60 (0.750" Dual nominal wall) 1H/AC-G-08-A Pipe to pipe 18" SCH 60 (0.750" Dual nominal wall) 1LIAC-G-1 6 6" auxiliary feedwater 6" (0.280" nominal Single 1L/AC-G-16____ (AFW) nozzle to pipe wall) Single 1M/AC-G-17 6" AFW pipe to LR elbow 6" (0.280" nominal Dual
_____ _____ _____ ____wall) _ _ _ _ _
S,G B Train ID/Weld No. Configuration Size Access 2AIBC-G-14 Check valve to 18" SCH 60 (0.750" Single 90° LR elbow nominal wall) Single 900 LR900 elbow elbw L to to 18" SCH 60 (0.750" 2B/BC-G-13 pipe at CTMT 18" SCH Dual penetration nominal wall) 18" SCH 60 (0.750" Dual 2C/NA Pipe to Pipe nominal wall) Dual 2D/NA CTMVIT pipe to flue 18" SCH 60 (0.750" Single 2D/NA__TMTpipetoflue nominal wall) Single 2E/N/A Flue to pipe inside 18" SCH 60 (0.750" Single CTMT nominal wall) Single 2F/BC-G-12 Pipe to 900 LR Elbow 18" SCH 60 (0.750" Dual nominal wall)
Serial No.13-566 Docket No. 50-336 Attachment, Page 4 of 5 SG B Train ID/Weld No. Configuration Size Access 2G/BC-G-1 1 90* LR elbow to vertical 18" SCH 60 (0.750" Dual pipe nominal wall) 2K/BC-G-16 6" AFW nozzle to pipe 0.280" nominal wall Single 2L/BC-G-17 6" AFW pipe to valve 0.280" nominal wall Single
- c. The components of the weld joints are identified in the table. The associated welds have been designed to accommodate dual-sided examination to the extent practical. Single-side examinations will be performed where piping connects to an existing nozzle or valve as these components are not scheduled for replacement under the project. Replacement of these components to support dual-sided examination would result in additional dose and added cost.
Additionally, the containment penetration flue head configuration does not permit UT examination from both sides of the weld.
- d. Currently seven of the above listed welds are planned to be welded in the shop prior to installation. Four of the seven shop welds are identified as having single-side access for UT examination. Although the dose associated with RT examination of these welds has not been quantified, qualitative experience shows that the majority of the dose for a given RT exam is incurred by the RT crew during the RT examination exposure process. Consequently, some dose is incurred for any RT examination, whether in the shop or in the field whereas, shop UT examination incurs no dose and presents no risk of accidental exposure.
- e. The table provided in response to Question 3.a identifies 8 welds with limited examination access. As discussed in response to Question 2, the planned dose savings is relatively small (50-100 mrem). However, the eight welds represent one third of the total population of welds to be replaced. Reducing the population of welds subject to RT examination provides a corresponding reduction in the potential of an accidental exposure.
Question 5 The relief request defines the required examination zone as 100 percent of the weld volume and the weld-to-base metal interface on each side. Does this examination zone include Y2 inch or Y2 of the wall thickness or some other buffer area? Please provide a drawing of the examination area to be covered by the ultrasonic examinations. If a Y2 inch or Y2 t buffer area around the weld is not to be used, please describe how the inspection procedure will conservatively include, in light of possible inner diameter and
Serial No.13-566 Docket No. 50-336 Attachment, Page 5 of 5 outer diameter repairs, the entire volume of the weld and fusion zone in the examination.
DNC Response A sketch of the typical examination volume described in the request is included below.
The intent of the examination is to detect flaws associated with the welding process, which will be located within the weld and the fusion zones of the weld to base metal interface. The examination volume includes 100% of the weld volume and the weld to base metal interface on each side of the weld. This volume will be used to calculate coverage of the required examination volume. If the weld requires repair that extends the weld volume beyond the designed joint boundaries, the volume of the repairs will be included in the required examination volume. The progress of the weld process will be tracked to determine if any repairs are made and compensated for in the scan plan. No additional buffer will be included in the volume examined.
Weld / Examination Volume Question 6 Radiographic testing provides an archival-qualityrecord of the examination that can be stored and interpreted after several decades. Encoded electronic data requires backup and proprietarydata formats may become obsolete in the future. How will the ultrasonic results be stored and protected from data loss and future changes in hardware and software that could renderthe data unreadable?
DNC Response The electronic data files for the UT examinations will be stored as part of the archival-quality record. In addition to the electronic data, hard copy prints of the data will also be included as part of the record that allows viewing without the use of hardware or software.