ML20137W727
| ML20137W727 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 04/14/1997 |
| From: | Kraft E COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| ESK-97-085, ESK-97-85, NUDOCS 9704180199 | |
| Download: ML20137W727 (7) | |
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Commonwealth Illison Q>mpany Quad Cities Generating Station 4
22710 2(X4h Asenue North s
Cordova, IL 61212-9740 T,et.w;4u224 i
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- ESK-97-065 t
April 14,1997 t
United States Nuclear Regulatory Commission Washington, DC 20555
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Attention:
Document Control Desk
Subject:
Quad Cities Nuclear Power Station Unit 1 Response to Request For Additional Information (RAI) Regarding Alternative to 10CFR 50.55a(g)(6)(ii)(A) Augmented Reactor Pressure Vessel (RPV) Examination NRC Docket No.50-254 k
References:
(a)
R M. Pulsifer (USNRC) letter to Comed, subject RAI, dated February 13,1997 (b)
E. S. Krail, Jr. (Comed) letter to USNRC, Results of Augmented Examination of the RPV Shell Welds and Relief Request Pursuant to 10CFR50.55a(g)(6)(ii)(A), dated November 22,1996 The purpose of this letter is to provide Comed's response to a Request for Additional Information [ Reference (a)]. Our response is provided in Attachment A.
In summary, Quad Cities Unit I augmented RPV examination was conducted using demonstrated techniques as required by Appendix VIII of ASME Section XI,
" Performance Demonstration for Ultrasonic Examination Systems," and therefore, was performed with current industry state-of-the-art techniques. The weld examinations performed provide reasonable assurance that inservice flaws unacceptable for continued -
operation have not developed when 100 percent of total weld coverage is considered.
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Therefore, an acceptable level of quality and safety has been achieved with ultrasonic jt examinations performed on accessible portions of the circumferential and longitudinal i
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9704180199 970414 PDR ADOCK 05000254-PDR 800Su P
Ihh A Unicom Company
April 14,1997 Ifyou have any questions concerning this letter, contact Mr. Charles Peterson, Regulatoiy Affairs Manager, at (309) 654-2241, extension 3609.
i Respectfully,
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E. S. Kraa, Site Vice President Quad Cities Station -
Attachment:
(A) Response to RAI cc:
A. B. Beach, Regional Administrator, Region III R. M. Pulsifer, Project Manager, NRR C. G. Miller, Senior Resident Inspector, Quad Cities M. T. Anderson, INEL Research Center W. D. Leech, MidAmerican Energy Company j
D. C. Tubbs, MidAmerican Energy Company j
F. A. Spangenburg, Regulatory Affairs Manager, Dresden INPO Records Center i
Office of Nuclear Facility Safety, IDNS DCD License (both electronic and hard copies) i 1
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Attachment A Response to Request for Additional Information ESK Letter 97-085 (Page 1 of 5)
Discussi.pa 2.1 Provide the date of the augmentedRPVexamination. In addition, provide a history of the examinationsperformed on the RPVto date. The licensee stated that the augmented examination wasperformed utili:ing the GERIS.systemfrom within the reactorpressure vessel. Describe how the examinations were performed on the vesselfor the previous intervals. Did the vessel receive a 100 percent baseline, i
Respons to 21 The augmented RPV examination was performed during the period ofFebruary 18,1996
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through March 4,1996.
.l The history of RPV examinations for Category B-A, item Bl.11 and Bl.12 welds is as
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follows:
Subsequent to RPV fabrication,100% baseline radiographic examinations were performed as required. During 1972, limited ultrasonic (UT) baseline examinations were conducted.
These baseline UT examinations consisted of approximately 18 feet of vertical seam weld on course No. 4, approximately 6 feet of vertical seam welds on course No. 3, and i
approximately 8 feet ofcourse No.3 to course No.4 circumferential seam weld. The remainder of the welds were inaccessible.
Previous inservice UT examinations were performed from the OD surface for the accessible portions of the vertical welds on course No.4. For example, between 1974 and j
1994, portions of the following welds, VSC4-99, VSC4-219, VSC4-261, and VSC4-339 had twenty-two cumulative UT examinations performed with no recordable indications.
These four welds are located adjacent to the main steam nozzles in an area above the bio-shield wall where access is provided by removing the upper portions of vessel insulation.
All four wdds were examined in 1994 in accordance with ASME Section XI 1989 i
Edition.
2.2 Considering that the augmented vessel examination is a one time requirement, and consideringpast examinations have been performedfrom the outside surface, discuss increasing examination coverage 'sfrom the outside surface.
l Attachmsnt A Response to Request for Additional Information ESK Letter 97-085 (Page 2 of 5)
Response to 2.2 A review of past examination results indicates that three welds RPV-CW-LHC1, RPV-VSC3-197 and RPV-VSC4-219 have had limited examinations performed from the OD surface in areas limited to the GERIS 2000. These preservice baseline examinations were performed prior to radiological conditions. Additionally welds RPV-VSCl-55, RPV-VSCl-77, RPV-VSCl-197, RPV-VSCl-317, RPV-VSC3-77, and RPV-VSC3-317 may have limited access via the nozzle access windows. Access to the examination areas is limited by the size and location of the bio-shield nozzle access windows and the
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configuration of the removable insulation surrounding the nozzles. Comed and GE personnel performed a walkdown to evaluate acces.sibility and to determine if manual examinations could be performed on the OD to supplement the ID coverage. This walkdown, which required 146mR to perform, determined that it is virtually impossible to remove and replace insulation inside the bioshield wall and the welds were not accessible i
or minimal single sided coverage would be attained. Comed has determined that greater than 10 man Rem would be required to perform the manual examinations. Performing j
additional manual examinations would incur unnecessary radiological exposure which is not commensurate with an increase in quality and safety.
Weld RPV-VSC4-219 is located above the level of the bio-shield and was manually examined in 1994 during the current ISI Third Interval in accordance with ASME Section XI 1989 Edition. Coverage of weld RPV-VSC4-219 was increased to > 90% by i
supplemental scanning from the outside surface and Code reliefis not required.
2.3 The licensee noted that 53 indications were detected by the augmented examination. The licensee stated that all of theseflaws were determined to be i
fabrication relatedJ1aws. Provide the basisfor this determination.
1 Response to 2.3 The method used for determining the probable nature of a flaw is by reviewing the ultrasonic characteristics of the indication and comparing them with the characteristics of the expected flaw types.
In general flaw indications in reactor pressure vessels can be attributable to one of several general categories:
- 1. Inherent flaws in the base material such as laminations and plate segregates.
- 2. Fabrication flaws in the weld filler material such as inclusions and porosity.
- 3. Fabrication flaws aligned with the weld tusion line such as lack of fusion and inclusions.
4 Fabrication flaws in the clad / base material interface such as lack of bond and inclusions.
- 5. Service induced flaws.
Attachment A Response to Request for Additional Information 4
ESK Letter 97-085 (Page 3 of 5) 2 The characteristics of the flaw indications to be reviewed include:
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- 2. Location of the flaw within the weld cross section relative to the clad / base material interface, ID and OD surfaces.
- 3. Comparison of the flaw signal characteristics with known flaw types.
The flaw indications recorded in 1996 were determined by this review process as being attributed to fabrication flaws aligned with the weld fusion line or flaws within the weld filler material. The recorded flaws are not similar to simulated service induced flaws, i.e.
j cracks, observed in practice and test samples.
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It should be noted that the Code does not differentiate between inherent, fabrication or service induced flaws. The Code provides for only two flaw categories for ultrasonic.
testing; laminar and planar. All flaws whether inherent, fabrication or service induced are evaluated using the same acceptance standards.
2.4 Based on the review of the limitations listed by the licensee, it appears that one of the mainfactors resulting in the noncompliance with Code-required coverage is associated with the manipulator lower limit. For reactorpressure vessel longitudinal welds RPV-VSC1-SS andRPV-VSC1-317, coverage 's ofless than 90 percent were obtained andfor circumferential weldIU'V-CW-LHC1, 0 percent coverage was obtained. Providefurther discussion on these limited examinations.
It appears that modification of the manipulator mayprovide additional reachfor increasedcoverage.
Response to 2.4 Comed has evaluated the feasibility of modifying the inspection tooling. This lower head to shell course I weld (RPV-CW-LHCl) remains essentially inaccessible to the Geris 2000 Invessel system due to obstructions related to the internal vessel components. For example the increased coverages for the welds in question would be:
RPV-VSCl-55 insignificant additional coverage, current coverage 85.7%.
RPV-VSCl-317 estimate 10% additional covert.ge, would increase current coverage to 95.7%.
RPV-CW-LHCl estimate 13.3% additional coverage, would increase current coverage to 13.3%.
Note: The estimated increase in coverage is based on drawing review and equipment capability and may be significantly less than estimated.
Att chm:nt A Response to Request for Additional Information ESK Letter 97-085 (Page 4 of 5)
Modification of the GERIS 2000 invessel tooling would not significantly increase the examination coverage for the welds in question.
2.5 1he licensee noted that the procedurefor performing the augmented examination was an alternate method. In addition, it is stated that the procedure was not in strict compliance with ASME Section XI 1989 Edition, Paragraph IWA-2232; ASME Section VArticle 4; or NRC Regulatory Guide 1.150. It isgenerally agreed that quahpcation by demonstration wouldprovide a basis to conclude that thefaw detection capabilities of a procedure will be at least equal to that ofpast examinations. However, performance demonstration does notpreclude the y
requirement to satish the Code ofrecordfor a plant or other commitments that the licensee may have made. As such, describe the differences between the requirements associated with the Code ofrecordand commitmentsfor the licensee 'splant, and the procedure implemented to satisfy the subject examinations. Venfy that scanning ofwelds wasperformedfrom both sides of the i
weld on the same surface wherefeasible. These shoulilhave includedscanning for rejectors orientedparallel and transverse to the weld.
Response to 2.5 1
The procedures used for the examination of Quad Cities Unit 1 RPV were submitted and accepted by the Authorized Nuclear Inservice Inspector as an alternate examination i
method permitted by IWA-2240 of ASME Section XI 1989 Edition. The procedures were demonstrated to representatives of the Performance Demonstration Initiative (PDI) and the performance demonstration was accepted as evidence that the demonstrated 1
method was " equivalent or superior to the specified method". The use of.PDI qualified i
procedurea results in a more sensitive examination for the detection of flaws than the Code i
described techniques. Therefore, the Code of record requirements have been satisfied.
NRC Regulatory Guide 1.150 Paragraphs 3.2 and 7e indicate that the use of alternative volumetric NDE techniques, as permitted by the ASME Code are acceptable alternatives to the requirements ofIWA-2000. In addition, a detailed comparison of the Regulatory 4
l Guide and the alternate method and procedures utilized has been performed. Comed has
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concluded that the examination of Quad Cities Unit I meets the intent ofRegulatory Guide 1.150.
Scanning with the GERIS 2000 is performed using a fixture containing 14 search units.
These search units are; two 0 longitudinal, four 70 refracted longitudinal, four 45 shear wave, and four 60 shear wave. The angle beam search units are positioned to direct the beams parallel to and transverse to the weld in two opposing directions.
Attachm:nt A Response to Request for AdditionalInformation ESK Letter 97-085
.(Page 5 of 5) i The accessible welds were scanned from both sides of the weld on the same (ID) surface where feasible. Additionally, the examination procedure has been successfully demonstrated for effective single sided examination. Scanning was performed for reflectors oriented parallel and transverse to the weld.
In conclusion, Quad Cities Unit I augmented RPV examination was conducted using demonstrated techniques as required by Appendix VIII of ASME Section XI,
" Performance Demonstration for Ultrasonic Examination Systems", and therefore, was performed with current industry state-of-the-art techniques. The weld examinations performed provide reasonable assurance that inservice flaws unacceptable for continued operation have not developed when 100 percent of total weld coverage is considered.
3 Therefore, an acceptable level of quality and safety has been achieved based with ultrasonic examinations performed on accessible portions of the circumferential and longitudinal RPV shell welds.
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