ML14063A206
| ML14063A206 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/27/2014 |
| From: | Mark D. Sartain Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 13-566A, TAC MF2520 | |
| Download: ML14063A206 (15) | |
Text
Dominion Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, VA 23060 AlDominion-Web Address: www, doix.com February 27, 2014 U.S. Nuclear Regulatory Commission Serial No. 13-566A Attention: Document Control Desk NLOSA/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 as an alternative to radiographic examination for ASME Class 2 carbon steel circumferential pipe weld joints to satisfy nondestructive examination requirements. 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. In a letter dated November 22, 2013, DNC responded to RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6.
The attachment to this letter contains DNC's response to the remaining RAI Questions 1, 3.b and 4.
If you have any questions regarding this submittal, please contact Wanda Craft at (804) 273-4687.
Sincerely, Mark D. Sartain Vice President - Nuclear Engineering
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 Ao4T
Serial No. 13-566A 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 Mohan C. Thadani Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 B 1 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station
Serial No. 13-566A 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. 13-566A Docket No. 50-336 Attachment, Page 1 of 12
Background
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 for ASME Class 2 carbon steel circumferential pipe weld joints to satisfy nondestructive examination requirements. 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. In a letter dated November 22, 2013, DNC responded to RAI Questions 2, 3.a, 3.c, 3.d, 3.e, 5, and 6. This attachment provides DNC's response to RAI Questions 1, 3.b and 4.
Question 1 Please provide examples of successful detections and characterizationsof fabrication flaws, including lack of fusion defects, lack of penetration defects, cracks, slag, and porosity in representative welds using a representative ultrasonic procedure. Include flaw maps showing the true state for examples of each type of flaw including those found by penetrant testing, the ultrasonic results including detection and characterizationof flaws, and the radiographicresults for these specimens.
DNC Response The following nine figures provide examples of the ultrasonic testing (UT) data representing successful detections and characterizations of typical fabrication flaws from the Dominion procedure qualification data. These figures provide examples of lack of fusion defects, lack of penetration defects, cracks, slag inclusions, and porosity, which were implanted into the welded mockups. These mockups represent the weld configurations and welding processes to be used for the replacement welds. The flaw map for each of these examples is included in the applicable figures. No surface examinations were performed for the implanted flaws. Radiography was performed for each mockup weld. The radiography was performed using typical ASME Section V, Article 2 techniques with an Iridium 192 radiation source. The planar flaws identified in Figures 1, 3, 5, and 6 were not detected with the radiographic examination performed.
The UT procedure qualification has demonstrated 100% flaw detection capability.
100% of the near and far side circumferential flaws were detected when evaluated as single side access. 100% of the axial flaws were detected using the circumferential beam direction data. The detected flaws were accurately categorized as either planar or volumetric type flaws. The flaws categorized as volumetric flaws were accurately length-sized within 0.25" of the implanted size.
Serial No. 13-566A Docket No. 50-336 Attachment, Page 2 of 12 Figure 1 Weld I - Flaw 9, Lack of Fusion FLAW 9 Upstream (Near Side) Detection Using Second Leg Down Stream (Far Side) Detection Using First Leg
Serial No. 13-566A Docket No. 50-336 Attachment, Page 3 of 12 Figure 2 Weld 2 - Flaw 10, Porosity Upstream Detection Using First Leg Down Stream Detection Using First Leg
Serial No. 13-566A Docket No. 50-336 Attachment, Page 4 of 12 Figure 3 Weld 2 - Flaw 16, Crack
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FLAW 16 F0.090 IU: ... ... . .7 IT Upstream Detection Using First Leg DDi Down Stream Detection Using First Leg I
Serial No. 13-566A Docket No. 50-336 Attachment, Page 5 of 12 Figure 4 Weld 2 - Flaw 18, Slag Inclusion FLAW 18 Upstream Detection Using First Leg Down Stream Detection Using First Leg
Serial No. 13-566A Docket No. 50-336 Attachment, Page 6 of 12 Figure 5 Weld 3 - Flaw 1, Lack of Fusion O.40" Upstream (Near Side) Detection Using First and Second Legs
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77=:;
Down Stream (Far Side) Detection Using First Leg I
Serial No. 13-566A Docket No. 50-336 Attachment, Page 7 of 12 Figure 6 Weld 3 - Flaw 4, Crack FLAW 4 Upstream Detection Using First Leg Down Stream Detection Using First Leg
Serial No. 13-566A Docket No. 50-336 Attachment, Page 8 of 12 Figure 8 Weld 8 - Flaw 12, Crack FLAW 12 F 0.180" i2}
Upstream (Far Side) Detection Using First and Second Legs Down Stream (Near Side) Detection Using First and Second Legs
Serial No. 13-566A Docket No. 50-336 Attachment, Page 9 of 12 Figure 9 Weld 8- Flaw 19, Incomplete Penetration RAW 19 Upstream Detection Using First Leg Down Stream Detection Using First Leg
Serial No. 13-566A Docket No. 50-336 Attachment, Page 10 of 12 Question 3 The technical basis for the reliable detection and characterizationof 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 structuralintegrity 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:
- b. If single-sided ultrasonic inspections are to be used in lieu of radiographic testing for welds covered in RR-04-16, please provide a technical basisjustifying the use of single-sided examinations for fabricationdefects in the subject welds.
DNC Response Mockups containing eight welds representative of the welds to be examined in the field were fabricated to evaluate the capabilities of the ultrasonic examination techniques to be used. These mockups are summarized in the following table. To maintain security of the mockups to support blind personnel demonstrations and future procedure enhancement demonstrations, only general statements of the mockup designs are provided.
Summary of the UT in Lieu of RT Mockups Weld Diameter/l W Nominal Thickness Configuration Weld Process 1 ~~18" / 0.75" Pipe to Elbow SMW-Rmingel GTAW - Root and Hot Pass SMAW - Remaining Weld
/ 0.75" 218" Elbow to Pipe GTAW - Root and Hot Pass 2 1 SMAW - Remaining Weld 3 18" / 0.75" Elbow to Elbow GTAW - Complete Weld GTAW - Root and Hot Pass 4 6"/0.280" Pipe to Pipe SMAW - Remaining Weld 5 6" / 0.280" Elbow to Pipe GTAW - Complete Weld GTAW - Root and Hot Pass 6 6" / 0.280" Elbow to Pipe SMAW - Remaining Weld 7 18" / 0.75" Elbow to Pipe GTAW - Complete Weld GTAW - Root and Hot Pass 8 18" / 0.75" Elbow to Pipe SMAW - Remaining Weld
Serial No. 13-566A Docket No. 50-336 Attachment, Page 11 of 12 Each of the eight welds was examined with RT, applying ASME Section V, Article 2 techniques typically used for field RT examinations. An interpretation of the radiographic film resulted in 30% of the implanted flaws not being detectable with the RT method. The flaws not detected with RT were all lack of fusion and crack planar flaws. The implanted volumetric flaws, i.e., inclusions and porosity, were all detected.
No surface examinations were performed for these welds.
Each of the eight welds was examined ultrasonically with three independent scans that included upstream axial beam direction, downstream axial beam direction, and circumferential beam directions (clockwise and counter clockwise). The data analysis was performed to evaluate each axial beam scan independently to represent limited single side access conditions. Addressing each scan direction independently provided 116 circumferential flawed grading unit opportunities to be used for the procedure qualification and provided an independent evaluation of each of the circumferential flaws from both sides of the weld. This approach resulted in 35% of the circumferential flawed grading units being evaluated as far side of the weld flaws and the remaining 65% being evaluated as near side of the weld flaws. The implanted flaws consisted of 27% being volumetric (inclusions and porosity) and 73% of the flaws being planar (lack of fusion, incomplete penetration, and cracks) that are representative of the welding processes being used.
When compared to volumetric or far side planar fabrication flaws, near side planar flaws are more difficult to detect with standard ultrasonic examination techniques due to the orientation of the flaws with the ultrasonic beam. The use of multiple examination angles and full V-path encoded phased array techniques demonstrate enhanced flaw detection capabilities for both near and far side weld access conditions. The procedure qualification has demonstrated 100% flaw detection capability. 100% of the near and far side circumferential flaws were detected when evaluated as single side access.
100% of the axial flaws were detected using the circumferential beam direction data.
The detected flaws were accurately categorized as either planar or volumetric type flaws. The flaws categorized as volumetric flaws were accurately length-sized within 0.25" of the implanted size.
In summary, the Dominion procedure qualification has demonstrated that the ultrasonic examination techniques are more reliable for the detection of critical planar fabrication flaws than the standard RT examination techniques used for weld examinations. In addition, the procedure qualification has demonstrated effective and reliable examination capabilities for both near and far sided examination access. The demonstrated procedure is effective for proper categorization of detected flaws and accurate length-sizing of volumetric flaws. The demonstrated procedure meets all of the requirements of the demonstration process outline within RR-04-16.
Serial No. 13-566A Docket No. 50-336 Attachment, Page 12 of 12 Question 4 The current technical basis for performing ultrasonic inspections in lieu of radiography assumes that the weld crowns will be removed and machined or ground flush. Will the weld crowns of the welds covered in RR-04-16 be machined or ground flush priorto the proposed ultrasonic inspections? If the weld crowns are not to be ground flush, please provide a technical basis, including a detailed description of the ultrasonic inspection procedure, showing that inspections with the weld crown present are able to reliably detect and characterizefabrication flaws.
DNC Response The weld crowns will be ground flush prior to the ultrasonic examination.