RS-11-087, Supplemental Information Supporting Relief Request 13R-08: Alternative Requirements to ASME Code Requirements for Class 1 Pressure Retaining Welds
| ML111580106 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 06/06/2011 |
| From: | Hansen J Exelon Nuclear, Exelon Generation Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RS-11-087, TAC ME6024, TAC ME6025 | |
| Download: ML111580106 (21) | |
Text
RS-1 1-087 10 CFR 50.55a June 6, 2011 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN-456 and STN-50-457
Subject:
Supplemental Information Supporting Relief Request 13R-08: Alternative Requirements to ASME Code Requirements For Class 1 Pressure Retaining Welds
References:
- 1. Letter from J. L. Hansen (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Third 10-Year Inservice Inspection Interval Relief Request 13R-08, Alternative Requirements to ASME Section XI Appendix VIII (Supplements 2 and 10), Examinations of Class 1 Pressure Retaining Welds Conducted from the Inside Surface In Accordance with 10 CFR 50.55a(a)(3)(i),"
dated April 11, 2011
- 2. Letter from N. J. DiFrancesco (U. S. Nuclear Regulatory Commission) to M. J. Pacilio (Exelon Generation Company, LLC), "Braidwood Station, Units 1 and 2 - Unacceptable With Opportunity to Supplement Re: Relief Request 13R-08, Alternative Requirements To ASME Code Requirements For Class 1 Pressure Retaining Welds (TAC Nos. ME6024 and ME6025)," dated May 25, 2011 In Reference 1, Exelon Generation Company, LLC, (EGC) submitted relief request 13R-08, Revision 0, to the U. S. Nuclear Regulatory Commission (NRC) for review and approval. This alternative requested relief from certain examination qualification requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Xl. EGC proposed the use of root mean square (RMS) error values.
In Reference 2, the NRC provided the results of the acceptance review of the relief request. The NRC concluded that supplemental information is needed to enable the NRC to make an independent assessment regarding the acceptability of the proposed relief request. The NRC requested that EGC supplement the relief request by June 6, 2011, to address the information requested. In response to this request, EGC is providing the attached information.
There are no regulatory commitments contained in this submittal. Should you have any questions concerning this letter, please contact Ms. Lisa A. Schofield at (630) 657-2815.
June 6, 2011 U. S. Nuclear Regulatory Commission Page 2 JeffkejL(Hansen Manager - Licensing Exelon Generation Company, LLC
Attachment:
Response to Request for Supplemental Information cc: NRC Regional Administrator, Region III NRC Senior Resident Inspector - Braidwood Station NRR Project Manager - Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety
ATTACHMENT Response to Request for Supplemental Information NRC Request 1 The request was submitted in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(a)(3)(i). At a public meeting dated November 30-December 1, 2010, the NRC gave a presentation titled, "NRC Request for Dissimilar Metal Weld Performance Demonstration Data on ID [inside diameter] Depth Sizing Error," (ADAMS Accession No. ML103400206). The presentation stated that an RR should be based on impracticality (10 CFR 50.55a(g)(5)(iii)).
(a) Please change the 10 CFR reference accordingly to 10 CFR 50.55a(g)(5)(iii).
(b) Provide the necessary information to support a request for impracticality.
(c) Since the Mechanical Stress Improvement Process is performed from the outside Diameter (OD), include a discussion on accessibility of the subject welds for depth sizing cracks from the OD surface using state-of-the-art, Appendix VIII, qualified ultrasonic (UT) test techniques.
Response to Question 1(a)
EGC agrees that 10 CFR 50.55a(g)(5)(iii) is appropriate for this request. In accordance with 10 CFR 50.55a(g)(5)(iii), EGC requests relief from the RMS error requirements for depth sizing contained in Code Cases N-695 and N-696 on the basis that the current requirements are impractical based on the discussion provided in the response to Question 1(b).
Response to Question 1(b)
To date, although examination vendors have qualified for detection and length sizing of flaws in accordance with the ASME Code requirements for examinations from the inner diameter surface, these same vendors have not met the established RMS error of 0.125-inch for flaw indication depth sizing. The EGC ISI vendor has demonstrated the ability to depth size flaw indications in dissimilar metal welds with a RMS error of 0.189-inch instead of the 0.125-inch RMS error required by Appendix VIII Supplement 10 (Code Case N-695) and an RMS error of 0.245-inch instead of the 0.125-inch RMS error required by the combined Appendix VIII Supplement 2 and 10 qualification (Code Case N-696).
Numerous attempts by these inspection vendors to meet the Supplement 10 (Code Case N-695) and combined Supplement 2 and 10 (Code Case N-696) required RMS error value for flaw depth sizing when examining from the inside diameter have been unsuccessful. Process enhancements including new delivery systems, new transducers, and software modifications have been implemented but did not achieve the desired improvements in performance. This result indicates that the ASME Code acceptance standard for flaw depth sizing is impractical for use with the ID ultrasonic examination technology employed in the qualification efforts. At this time, additional attempts to improve the depth sizing RMS error value are not warranted since the technology has not evolved significantly since the most recent efforts.
In addition, it is indicated in the response to Question 1(c) that UT examinations from the OD surface are constrained by the short safe end length.
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ATTACHMENT Response to Request for Supplemental Information Braidwood Unit 1 and Unit 2 welds were fabricated prior to implementation of Appendix VIII qualification requirements. Current vendors are incapable of meeting the stringent 0.125 inch RMS error flaw depth sizing tolerance requirement when examining from the inside diameter surface. Compliance with the Performance Demonstration Initiative (PDI) qualification program without alternative implementation would necessitate significant modification to the reactor coolant system welds. Alterations such as this may result in reduced structural integrity of the reactor coolant pressure boundary. Even with such modifications, the vendor depth sizing accuracy issue would not likely be addressed.
Response to Question 1(c)
In 2008, EGC requested that the MSIP' vendor provide an assessment of the capability to perform Appendix VIII, qualified UT test techniques from the OD surface in order to perform the required pre- and post-stress mitigation volumetric examinations (for flaw detection and flaw depth sizing). This assessment was conducted using phased array UT techniques that have been performance demonstrated using the PDI process.
Application of such OD techniques is impacted by the short length of safe end and the nozzle OD taper transition, and the need for additional surface conditioning. An example of this assessment is shown in Figures 1-1 and 1-2 for the Braidwood Unit 2 'A' inlet and outlet nozzle to safe end welds, respectively. The estimated lack of coverage for these welds for flaw detection, and the relatively short scanning distances that restrict the number of test angles for both flaw detection and flaw depth sizing resulted in the decision to apply ID surface techniques.
This configuration is typical for the remainder of the Braidwood Unit 2 nozzle to safe end welds, and the Braidwood Unit 1 nozzle to safe end welds.
Thus, accessibility to the OD surface is available for flaw depth sizing however its use is limited by geometry and surface condition constraints. The effectiveness of the techniques will be reduced.
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ATTACHMENT Response to Request for Supplemental Information Axial Scanning for Circumferential Flaws Circumferential Scanning for Axial Flaws Figure 1-1: Braidwood Unit 2 Inlet Nozzle to Safe End Weld with Phased Array UT Techniques Shown (Weld profile developed from OD contour gages and UT thickness measurements from the OD surface)
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ATTACHMENT Response to Request for Supplemental Information Axial Scanning for Circumferential Flaws Circumferential Scanning for Axial Flaws Figure 1-2: Braidwood Unit 2 Outlet Nozzle to Safe End Weld with Phased Array UT Techniques Shown (Weld profile developed from OD contour gages and UT thickness measurements from the OD surface)
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ATTACHMENT Response to Request for Supplemental Information NRC Request 2 The request states that "EGC contacted the Electric Power Research Institute (EPRI) NDE Center on February 7, 2011, and confirmed that no vendor has successfully demonstrated compliance with the Code." At a public meeting dated December 2 and 3, 2008, the NRC gave a presentation titled, "NRC Perspectives on Inside Diameter Pipe Examinations Depth Sizing Root Mean Square Error," (ADAMS Accession Nos. ML090760523 (memo) and ML090760695 (presentation)) with conclusions and recommendations for demonstrating RMS error depth sizing by licensees and vendors. At a public meeting dated May 27 and 28, 2009, the EPRI-Performance Demonstration Initiative (PDI) identified the differences between the test sets used for successful qualifications from the OD and unsuccessful qualifications from the inside diameter (ID) surfaces (ADAMS Accession Nos. ML091760056 (memo), and ML091590560 (presentation)). Currently, the PDI program does not have or considered assembling from other programs test sets with conditions similar to test sets used for depth sizing qualification from the OD.
(a) Provide a discussion on the last time the UT vendor participated in an Appendix VIII, Supplement 2 or 10, ID performance demonstration and any future scheduled Appendix VIII, Supplement 2 and 10, or other (non-Appendix VIII) future programs involving ID performance demonstrations.
(b) Provide a discussion on the time and effort necessary to secure mockups for site-specific vendor ID RMS error demonstrations.
(c) Provide a discussion on the availability of mockups for future outages at Braidwood Station, Units 1 and 2.
Response to Question 2(a)
The EGC UT vendor's base Appendix VIII Supplement 2 and 10 performance demonstration for ID applied techniques was performed under the PDI program in November 2002. In 2003, an attempt was made with modifications in the transducers, delivery equipment, and analysis process to improve upon the previous performance. The 2003 effort, with the integration of surface profiling into the data analysis process, significantly improved the vendor's flaw depth sizing results. Additional procedure extensions demonstrated in 2003 and 2004 to add the UT examination of safety injection nozzle to safe end welds and core flood nozzle to safe end welds were completed.
The EGC UT vendor has no future scheduled Appendix VIII, Supplement 2 and 10 or other (non-Appendix VIII) future programs involving ID performance demonstrations. The UT vendor is engaged with a limited round robin test program in Japan where blind cracked samples are inspected, and the subject samples are destructively examined to determine the actual crack depth.
Response to Question 2(b)
The PDI sample set developed for the industry took approximately two and a half years to design and fabricate. The sample set was fabricated using vintage material from canceled reactors that contain geometric and material conditions that are representative of the Page 5
ATTACHMENT Response to Request for Supplemental Information configurations found in the U. S. fleet. Based on discussions with EPRI - PDI personnel, it is estimated that it would take approximately one and a half years to fabricate site specific mock-ups.
Based on the current ultrasonic examination technology, there would be no benefit to design and build site-specific mock-ups for Braidwood station and attempt further vendor ID RMS error demonstrations.
Response to Question 2(c)
There are no plans to design and build new mock-ups and there are no known mock-ups in the industry that are more representative than the current available sample sets that are fabricated using vintage material from canceled reactors containing geometric and material conditions representative of the U.S. fleet configurations.
The current PDI sample set provides a conservative representation of the Braidwood configurations. The fabrication of additional samples with slightly different geometric conditions would not improve the overall procedure performance to an acceptable level.
NRC Request 3 Licensees have located representative mockups (smooth ID surfaces similar to their welds) containing cracks within the industry. The UT vendors have used these mockups to demonstrate ID depth sizing RMS error capabilities. Also, vendors have independently participated in blind and non-blind round robin demonstrations on mockups containing representative cracks.
(a) Provide a discussion of EGC's effort to provide representative mockups containing cracks (or simulated cracks with crack like responses) with ID surfaces similar to the surfaces used for successful OD depth sizing qualifications.
(b) Provide a discussion of your vendor's participation in ID depth sizing demonstration that may have been independent of the PDI program. If available, include a description of the specimens (ID surface waviness, configurations, and materials) and cracks, type of tests (blind or non-blind), differences between the procedures and personnel used for the demonstrations and those being proposed for examining the subject welds, summary of results and RMS values, and the organization sponsoring or proctoring the demonstrations.
Response to Question 3(a)
There are no plans to design and build new mock-ups, and there are no known mock-ups in the industry that are more representative of the Braidwood configuration than the PDI sample set currently available for vendor ID RMS error demonstrations.
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ATTACHMENT Response to Request for Supplemental Information Response to Question 3(b)
EGC's inspection vendor has participated in three non-ASME Code required performance demonstrations associated with depth sizing of planar flaws in dissimilar metal welds. The demonstrated techniques were conducted from the ID surface. Each of these demonstrations used ultrasonic test procedures and equipment nearly identical to those to be applied for the Braidwood Unit 1 and Unit 2 reactor pressure vessel (RPV) nozzle to safe end weld examinations. Summary information on these demonstrations is provided below.
The first demonstration was conducted in 2002/2003 as part of an open procedure qualification for a Swedish nuclear power plant and was performed under the auspices of the Swedish Qualification Centre (SQC). The test sample, supplied by the power plant owner, consisted of six partial ring segments that when put together formed a 360° test piece. The inner diameter was 597mm (23.5") and the weld thickness was 84mm (3.3"). The materials of construction included a stainless steel clad SA508 Class 1A ferritic steel forging buttered with Inconel' and welded to a SA312 Type 316 stainless steel forging. The weld material was Inconel'. The ID surface was smooth. Of the twenty-five defects within the segments, ten were ID surface-connected branched cracks confined to the weld and buttering. Details of these ID surface flaws are provided in Table 3-1. This defect matrix included both circumferential and axial cracks. Table 3-1 also provides the UT measured through-wall dimension for each of the defects and the RMS error value. It is noted that if the RMS error adjustment of 0.064" (1.63mm), consistent with the EGC Relief Request, is added to each of the UT measurements, the adjusted RMS error value is 0.133" (3.39mm).
The second demonstration was conducted in 2007 as part of a weld inlay equivalency site specific demonstration and was performed under the auspices of EPRI. This block was a full-scale, 360° mock-up and is approximately 41-inches long, 27.5" ID and 2.9" thick. It contains a dissimilar metal weld (Inconel' buttering and Inconel' weld metal) between a SA-508 ferritic steel forging (nozzle) and a 316 stainless steel forging (safe end). An Alloy 52 weld inlay was added to three of the four quadrants across the dissimilar metal weld. The inlay thickness for each of the three quadrants was 0.2-inch, 0.07-inch, and 1.0-inch for the 2nd, 3rd and 4th quadrants, respectively. Four alternative planar flaws were added to each of the three inlaid quadrants. These four flaws are essentially identical to flaws in the PDI 601 Series Practice Mock-up. The ID surface included a 10° - 15° taper on the safe end. Details of the flaws are provided in Table 3-2; this defect matrix included both circumferential and axial cracks.
Table 3-2 also provides the UT measured through-wall dimension for each of the sixteen defects and the RMS error value. If the RMS error adjustment of 0.064" (1.63mm) was added to each of the UT measurements the adjusted RMS error value is 0.082" (2.08mm).
The third demonstration was conducted in 2010 as the initial test in a series of round robin examinations on RPV nozzle to safe end welds. This round robin was proctored by a Japanese entity. Examinations were conducted blind on six individual test coupons. Each test coupon consisted of a dissimilar metal Alloy 82/182 buttering/weld between a ferritic steel forging and a stainless steel safe end, and contained a single axial stress corrosion crack. Each test coupon was approximately 736mm (29") in diameter and was approximately 73mm (2.9") thick. The ID surface was smooth. Each test coupon was destructively analyzed to determine the actual crack depth. Information on the flaws is noted in Table 3-3; this defect matrix included only axial cracks. Table 3-3 also provides the UT measured through-wall dimension for each of the six Page 7
ATTACHMENT Response to Request for Supplemental Information defects and the RMS error value. If the RMS error adjustment of 0.064" (1.63mm) was added to each of the UT measurements the adjusted RMS error value is 0.125" (3.17mm).
Each of these test samples included variables common to dissimilar metal welds - multiple materials with different acoustic properties, and dendritic and coarse-grained microstructures.
These two variables lead to inaccuracies in locating the ultrasonic response from a planar flaw extremity within the weld and buttering. Demonstrations 1 and 3 did not involve additional ultrasonic examinations to determine the ID surface profile which is used to compensate for beam propagation in the weld. Also different in each of these test samples is the type of planar flaw, the flaw morphology, and the actual dendritic structure of the weld and buttering. These differences between the demonstrations are factors in the variation in RMS error values. When the three data sets from Tables 3-1, 3-2 and 3-3 are combined the RMS error is 0.094" (2.4mm).
Note that these data sets do not include the RMS error adjustment of 0.064" (1.63mm).
Table 3-1: Defect Matrix for Open Procedure Qualification - ID Surface Connected Planar Flaws Only Flaw Description Orientation Ligament Truth Truth UT-Measured (mm) Length Through- Through-Wall Dimension Wall Dimension (mm/in) Dimension (mm/in)
(mm/in)
Flaw 1.1 - Branch Circ / 9° skew / 0 17.83 / 0.70 6.11 / 0.24 8.58 / 0.34 Crack (in weld) 10° tilt Flaw 1.2 - Branch Circ / 0° skew / 0 22.08 / 0.87 9.1 / 0.36 11.30 / 0.44 Crack (in buttering) 9° tilt Flaw 1.3 - Branch Circ / 1° skew / 0 30.17 / 1.19 12.19 / 0.48 9.60 / 0.38 Crack (in buttering) 0° tilt Flaw 1.4 - Branch Circ / 0° skew / 0 70.05 / 2.76 26.03 / 1.02 27.79 / 1.09 Crack (in buttering) 2° tilt Flaw 1.5 - Branch Circ / 10° skew / 0 70.5 / 2.78 33.7 / 1.33 36.0 / 1.42 Crack (in weld) 10° tilt Flaw 2.1 - Branch Ax / 10° skew / 0 17.4 / 0.68 6.4 / 0.25 7.0 / 0.28 Crack (in 8° tilt buttering/weld)
Flaw 2.2 - Branch Ax / 8° skew / 0 12.38 / 0.49 6.28 / 0.25 5.49 / 0.22 Crack (in buttering) 0° tilt Flaw 2.3 - Branch Ax / 11° skew / 0 17.1 / 0.67 8.35 / 0.33 9.7 / 0.38 Crack (in weld) 10° tilt Flaw 2.4 - Branch Ax / 8° skew / 0 21.05 / 0.83 8.88 / 0.35 11.99 / 0.47 Crack (in 0° tilt buttering/weld)
Flaw 2.5 - Branch Ax / 0° skew / 0 43.7 / 1.72 17.95 / 0.71 20.7 / 0.82 Crack (in 9.5° tilt buttering/weld)
RMS Error 2.13 / 0.084 RMS Error with Vendor 3.39 / 0.133 Tolerance Adjustment Page 8
ATTACHMENT Response to Request for Supplemental Information Table 3-2: Defect Matrix for Open Weld Inlay Equivalency Test Demonstration - ID Surface Connected Planar Flaws Only Flaw Description Orientation Ligament Truth Truth UT-Measured (mm) Length Through- Through-Wall Dimension Wall Dimension (mm/in) Dimension (mm/in)
(mm/in)
Flaw 1-Q2 (Thermal Circ / 8° skew / 0 45.72 / 1.80 8.61 / 0.339 9.4 / 0.37 Fatigue Crack) 0° tilt Flaw 1-Q3 (Thermal Circ / 8° skew / 0 45.72 / 1.80 8.61 / 0.339 10.67 / 0.42 Fatigue Crack) 0° tilt Flaw 1-Q4 (Thermal Circ / 8° skew / 0 45.72 / 1.80 8.61 / 0.339 9.14 / 0.36 Fatigue Crack) 0° tilt Flaw 2-Q2 (Thermal Circ / 0° skew / 0 66.80 / 2.63 8.89 / 0.35 8.64 / 0.34 Fatigue Crack) 0° tilt Flaw 2-Q3 (Thermal Circ / 0° skew / 0 66.80 / 2.63 8.89 / 0.35 8.38 / 0.33 Fatigue Crack) 0° tilt Flaw 2-Q4 (Thermal Circ / 0° skew / 0 66.80 / 2.63 8.89 / 0.35 9.4 / 0.37 Fatigue Crack) 0° tilt Flaw 3-Q2 (Alternative Axial / 11° skew 0 12.7 / 0.50 9.5 / 0.374 10.16 / 0.40 Planar Flaw) / 0° tilt Flaw 3-Q3 (Alternative Axial / 11° skew 0 12.7 / 0.50 9.5 / 0.374 9.4 / 0.37 Planar Flaw) / 0° tilt Flaw 3-Q4 (Alternative Axial / 11° skew 0 12.7 / 0.50 9.5 / 0.374 6.86 / 0.27 Planar Flaw) / 0° tilt Flaw 12-Q2 (Thermal Circ / 5° skew / 0 77.47 / 3.50 20.7 / 0.815 20.57 / 0.81 Fatigue Crack) 0° tilt Flaw 12-Q3 (Thermal Circ / 5° skew / 0 77.47 / 3.50 20.7 / 0.815 20.57 / 0.81 Fatigue Crack) 0° tilt Flaw 12-Q4 (Thermal Circ / 5° skew / 0 77.47 / 3.50 20.7 / 0.815 19.56 / 0.77 Fatigue Crack) 0° tilt Flaw 1 (Thermal Circ / 8° skew / 0 45.72 / 1.80 8.61 / 0.339 9.4 / 0.37 Fatigue Crack) 0° tilt Flaw 2 (Thermal Circ / 0° skew / 0 66.80 / 2.63 8.89 / 0.35 9.91 / 0.39 Fatigue Crack) 0° tilt Flaw 3 (Alternative Axial / 11° skew 0 15.24 / 0.60 9.5 / 0.374 11.18 / 0.44 Planar Flaw) / 0° tilt Flaw 12 (Thermal Circ / 5° skew / 0 77.47 / 3.50 20.7 / 0.815 20.07 / 0.79 Fatigue Crack) 0° tilt RMS Error 1.09 / 0.043 RMS Error with Vendor 2.08 / 0.082 Tolerance Adjustment Page 9
ATTACHMENT Response to Request for Supplemental Information Table 3-3: Defect Matrix for Blind Round Robin Program - Axial Flaws Only Flaw Description Orientation Ligament Truth Truth UT-Measured (mm) Length Through- Through-Wall Dimension Wall Dimension (mm/in) Dimension (mm/in)
(mm/in)
M1 (SCC) Axial 0 Not provided 30.0 / 1.18 29.85 / 1.18 M2 (SCC) Axial 0 Not provided 9.3 / 0.37 4.68 / 0.18 M3 (SCC) Axial 0 Not provided 16.7 / 0.66 14.19 / 0.56 M4 (SCC) Axial 0 Not provided 15.4 / 0.61 9.41 / 0.37 M5 (SCC) Axial 0 Not provided 4.0 / 0.16 2.33 / 0.09 M6 (SCC) Axial 0 Not provided 22.9 / 0.90 15.92 / 0.63 RMS Error 4.38 / 0.17 RMS Error with Vendor 3.17 / 0.125 Tolerance Adjustment NRC Request 4 Starting in 2004 (ADAMS Accession No. ML050690198), EPRI has requested licensees to make surface profilometry measurements of DMWs and adjacent similar metal welds to identify scanning gaps greater than 1/32-inches between the component surface and probe.
(a) Provide a discussion (surface waviness, probe lift-off, probe foot-print, etc) on any previously performed profilometry of the subject welds, including approximate coverage affected by gaps exceeding 1/32-inches and restrictions from counter bores and pipe curvatures (such as elbow curvature away from weld).
(b) Include a discussion on changes to the subject welds that minimizing examination effects from gaps greater than 1/32-inches and surface restrictions.
(c) If the same vendor is performing the next examination of the subject welds, include a discussion on the improvements made to their UT technique for minimizing examination effects from gaps greater than 1/32-inches and surface restrictions.
(d) Provide a cross section sketch of the weld areas showing the base metal, weld, butter, and cladding and identify the materials (stainless steel, carbon steel, Inconel').
Response to Question 4(a)
Profilometry using UT methods was performed on the ID surfaces of the Braidwood Units 1 and 2 nozzle to safe end and safe end to pipe/elbow welds in the last 10-Year reactor vessel ISI inspections (Braidwood Unit 1 - 2007, Braidwood Unit 2 - 2008). In both units the surface conditions of the nozzle to safe end welds were relatively smooth with no lack of coverage noted in four scan directions (in, out, CW and CCW). Gaps between the transducer and the surface of greater than 1/32-inch are flagged by the profilometry software and reported as lack of coverage.
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ATTACHMENT Response to Request for Supplemental Information In both units, the safe end to pipe/elbow welds have counter-bores that result in gaps between the transducer and surface greater than 1/32-inch. Localized manual grinding and weld shrinkage may also have created localized roughness/waviness regions within the counter-bore regions.
The 1/32-inch value is considered as an essential parameter for OD examinations, but offers a conservative reference for the ID inspection since ID surface performance demonstrations are conducted on test samples that have surface conditions that exceed this value.
Figures 4-1 and 4-2 provide representative profilometry profiles for Braidwood Unit 2 outlet nozzle and inlet nozzle pipe welds, respectively. Braidwood Unit 1 profiles are similar.
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ATTACHMENT Response to Request for Supplemental Information Figure 4-1: Typical Profile - Braidwood Unit 2 Outlet Nozzle (22°) Weld Profile at 0° Azimuth (Braidwood Unit 1 profiles are similar)
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ATTACHMENT Response to Request for Supplemental Information Figure 4-2: Typical Profile - Braidwood Unit 2 Inlet Nozzle (293°) Weld Profile at 232.5° Azimuth (Braidwood Unit 1 profiles are similar)
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ATTACHMENT Response to Request for Supplemental Information Response to Question 4(b)
EGC and its inspection vendor are not planning on doing any modifications to the subject welds.
The examination volume coverage in the last 10-Year RVISI inspections (Braidwood Unit 1 -
2007, Braidwood Unit 2 - 2008) was acceptable.
Response to Question 4(c)
The EGC inspection vendor will not be changing its UT technique from that applied in the last 10-Year RVISI inspections (Braidwood Unit 1 - 2007, Braidwood Unit 2 - 2008). As in the last 10-Year RVISI inspections, the EGC inspection vendor will supplement the UT techniques with eddy current examinations that will cover the ID surface and counter-bore geometry regions and are used to assist in the characterization of surface-breaking flaws. Supplemental visual examinations using other delivery devices such as a remotely-operated submersible will be used as necessary to help resolve ultrasonic and eddy current test indications.
In the last 10-Year RVISI inspections, no flaw indications were recorded with the combination of the UT and eddy current examinations.
Response to Question 4(d)
Figures 4-3 and 4-4 provide representative sketches of the inlet nozzle to safe end weld, and the outlet nozzle to safe end weld configurations for Braidwood Unit 1. Figures 4-5 and 4-6 provide representative sketches of the inlet nozzle to safe end weld, and the outlet nozzle to safe end weld configurations for Braidwood Unit 2. These sketches were developed from design drawings and were used for the 2007 10-Year RVISI (Braidwood Unit 1) and 2008 10-Year RVISI (Braidwood Unit 2) inspections.
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ATTACHMENT Response to Request for Supplemental Information Figure 4-3: Braidwood Unit 1 Inlet Nozzle to Safe End Welds Page 15
ATTACHMENT Response to Request for Supplemental Information Figure 4-4: Braidwood Unit 1 Outlet Nozzle to Safe End Welds Page 16
ATTACHMENT Response to Request for Supplemental Information Figure 4-5: Braidwood Unit 2 Inlet Nozzle to Safe End Welds Page 17
ATTACHMENT Response to Request for Supplemental Information Figure 4-6: Braidwood Unit 2 Outlet Nozzle to Safe End Welds Page 18
ATTACHMENT Response to Request for Supplemental Information NRC Request 5 The request states that, "Applying the difference between the RMS error and the achieved RMS error to the actual flaw being sized will ensure a conservative bounding flaw depth value."
The growth of primary water stress corrosion cracking (PWSCC) in DMW can be relatively fast and can increase with greater crack depths. Experience shows that UT normally under sizes the depth of deep cracks. The proposed add-on is approximately 1/9 of the worse case error for DMW and 1/6 of the worse case error for austenitic-to-austenitic welds. The conditions influencing PWSCC growth and depth sizing accuracy reduces any conservatism that may exist in the proposed alternative. The origin of the proposed alternative was considered a short term solution until vendors were qualified.
(a) Please consider limiting the RR duration to the next refueling outage for Braidwood Station, Units 1 and 2, or refueling outages through 2014.
Response to Question 5(b)
For Braidwood Station, Units 1 and 2, EGC requests relief from the RMS error requirements contained in Code Cases N-695 and N-696 for Class 1 examinations conducted from the inside diameter surface up to and including the A1R17 and A2R17 refueling outages (currently scheduled in fall 2013 and spring 2014, respectively).
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