ML20217E303
| ML20217E303 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 03/20/1998 |
| From: | Stanley H COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-97-06, GL-97-6, NUDOCS 9803300446 | |
| Download: ML20217E303 (15) | |
Text
w-Coromonweahh Edison Company
$4GD Opus Place Downers Grove, IL 60515 570I March 20,1998 '
U.S. Nuclear Regulatory Commission Washington, DC 20555 Attention:
Document Control Desl:
Subject:
Braidwood Station Units 1 and 2 Byron Station Units 1 and 2 NRC Dockets Numbers: 50-456 and 50-457 NRC Dockets Numbers: 50-454 and 50-455 Commonwealth Edison Company (Comed) Response to NRC Generic Letter 97-06, " Degradation Of Steam Generator Internals" dated December 30,1997
Reference:
NRC Generic Letter 97-06, " Degradation of Steam Generator Internals" dated December 30,1997 The Referenced letter transmitted the Nuclear Regulatory Commission (NRC) Generic Letter 97-06," Degradation of Steam Generator Internals." This letter requested a 90 day response which addresses any program in place to detect degradation of Steam Generator Internals and a description of the inspection plan, including the scope, frequency, methods and equipment. Attached is the Commonwealth Edison Company's (Comed) response.
I amrm that the content of this transmittalis true and correct to the best of my knowledge, information and belief. If you have any questions concerning this correspondence, please contact this omce.
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March 20,1998 Attachment cc:
Byron Project Manager - NRR Braidwood Project Manager - NRR Senior Resident inspector - Braidwood Senior Resident Inspector - Byron Regional Administrator-Rill Office of Nuclear Safety-IDNS
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- Attachment Introduction This repon provides the information requested in the U.S. NRC Generic Letter 97-06,
- " Degradation Of Steam Generator Internals," dated December 30,1997 for Comed's Byron and Braidwood Nuclear Stations.
Byron Units I and 2
- Originally, Byron Unit I contained four Westinghouse Model D-4 recirculating pre-heat steam generators (SGs). Each SG contained 4,578 mill annealed Inconel-600 U-bend i tubes. The support plates for the Model D-4 are made of carbon steel with drilled holesc Byron Unit I has replaced the Model D-4 generators with Babcock & Wilcox International (BWI) steam generators (SGs) during the Fall of 1997. Each BWI SG contains 6,633 thermally treated Inconel-690 U-bend tubes. The support plates for the BWI SGs are made of 410S stainless steel lattice grids. For the purpose of this response, historical inspection references to the Byron Unit 1 SGs will be associated with the Model D-4 SGs and future inspection programs will be applicable to the BWI SGs.
. Byron Unit 2 contains four Westinghouse Model D-5 recirculating pre-heat SGs. Each SG contains 4,570 thermally treated Inconel-600 U-bend tubes. The support plates for the Model D-5 SGs are made of Type 405 stainless steel with a quatrefoil hole design.
Braidwood Units 1 and 2 Braidwood Unit 1 contains four Westinghouse Model D-4 recirculating pre-heat SGs.
Each SG contains 4,578 mill annealed Inconel-600 U-bend tubes. The support plates for the Model D-4 are made of carbon steel with drilled holes. Braidwood Unit 1 is scheduled to replace the Model D-4 SGs with BWI SGs in the Fall of 1998. The support plates for the BWI SGs are made of 410S stainless steel lattice grids. For the purpose of this response, historical inspection references to the Braidwood Unit 1 SGs will be associated
'with the Model D-4 SGs and future inspection programs will be applicable to the BWI
. SGs.
Braidwood Unit 2 contains four Westinghouse Model D-5 recirculating pre-heat SGs.
' Each SG contains 4,570 thermally treated Inconel-600 U-bend tubes. The support plates for the Model D-5 SGs are made of Type 405 stainless steel with a quatrefoil hole design.
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Reauired Information Item #(1):
Discussion of any program in place to detect degradation of steam generator internals and a description of the inspection plans, including the inspection scope, frequency, methods and equipment.
Comed's Byron and Braidwood nuclear stations have implemented secondary side inspection programs to detect degradation of SG internals. These inspection programs include: sludge lancing, foreign object search and retrieval (FOSAR),
inspections in conjunction with the 3.0 Volt Interim Plugging Criterion, video camera inspections prior to and after chemical cleaning, and pre-heater water box degradation inspections. The following are elements of these inspection programs.
Eddy current inspection of the tube support plates (TSPs), is detailed in Comed's response to item (1a).
Video camera inspection of the SG secondary side internals is detailed in Comed's response to Item (lb).
As documented in Comed's response to Item (Ic), no SG secondary side degradation has been identified as a result of the secondary side inspections. These inspection programs have confirmed that Byron and Braidwood nuclear stations SG secondary side internals are intact and comply with current licensing bases.
In accordance with Comed's Steam Generator Program, Byron and Braidwood will perform future secondary side inservice inspection of the internals. Details of the steam generator secondary side internals inservice inspection plans are provided following Comed's response to item (1c).
Reauired Information Item #(la)
Whether inspection records at the facility have been reviewed for indications of tube support plate signal anomalies from eddy-current testing of the steam generator tubes that may be indicative of support plate damage or ligament cracking. If the addressee has performed such a review, include a discussion of the findings.
Comed's Eddy Current insperticas of Tube Supp_ ort Plates:
Scope 100% of the tube-to-tube support plates intersections have been inspected with eddy current and the results have been reviewed for tube support plate anomalies.
Frequency At present,100% of the tube-to-tube support plate intersections are inspected e
each refueling outage with eddy current.
In the future, BWI SGs (Byron Unit 1, Braidwood Unit 1) will be inspected with eddy current in accordance with the EPRI PWR Steam Generator Examination Guidelines Revision 5, sampling plan requirements, at a minimum.
Method Carbon Steel Support Plates with Drilled Holes - Model D-4 (Byron 1, e
Braidwood 1).
In addition to the conventional bobbin coil method described below, eddy current testing techniques have been developed by EPRI to inspect drilled carbon steel support plates for ligament cracking (Reference 1).
Comed has used this eddy current technique for detection of cracked support plates during the April 1997 Braidwood Unit I refuel outage, Byron Unit 1 November 1995 mid-cycle outage and Byron Unit 1 April 1996 refuel outage.
For the most recent Braidwood SG inspection (April 1997), Comed used the Zetec Computer Data Screening (CDS) software for identification of cracked TSPs. The CDS software was qualified in accordance with Reference 1.
Stainless Steel Support Plates with a Quatrefoil Hole Design - Model D-5 (Byron Unit 2, Braidwood Unit 2).
The tube-to-tube support plate intersections are inspected with the conventional bobbin coil probe for identifying distorted TSP signals, anomalies and to verify proper location of the TSPs. Comed's SG data analysis guidelines instruct the data analysts to examine each TSP for a i
distoned signal. If the TSP is identified to be distorted the proper three letter analysis code is reported. The distorted signal is characterized using diagnostic testing techniques (e.g., rotating coil technology [RCT]).
During the bobbin probe inspection analysis, indications ofloose parts are evaluated and specific instructions are given to the data analysts for reponing loose parts at the TSPs.
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, Equipment 1 Instrumentation - Zetec MlZ-18/30 equipment for data acquisitionc e
' Probes e
Bobbin - 0.610" OD standard magnetic bias differential bobbin coils with coil spacing and widths of.060 inches.
Rotating Pancake Coil - pancake coil designs of 0.080", 0.115" and a Plus -
Point coil.
Eddy Current Inspection Details Byron Unit I (D-4) Response:
e In conjunction with the 3.0 Volt Interim Plugging Criterion, Byron Station conducted an extensive secondary side inspection to demonstrate that the secon'dary side internals were not degraded and their support structure could limit the tube support plates displacement in the event of an accident.
These requirements are identified in the two 90 day reports for the mid-cycle outage (BlP02), #96-0074, dated March 19,1996, and refuei outage (B1R07), #96-5101, dated June 19,'1996.
4 Areas Inspected and Results of the Inspections:
Support Plates:
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During the B1P02 mid-cycle steam generator inspection (November 1995), the top support plate was inspected with an eddy current technique developed by EPRI (Reference 1) for identification of cracked TSPs. The inspection was performed on all four steam generators in the area of the three anti-rotation devices. Fifty tube-to-tube support intersections were inspected at each anti-rotation device.
In addition, the presence of each tube support plate was verified for all inservice SG tubes as part of the normal eddy current analysis. No degradation was identified.
The BIR07 (April 1997), SG inspection included eddy current inspection in the area of the three anti-rotation devices per EPRI's technique (Reference 1). Fifty tube-to-tube support plate intersections were inspected in the area of each anti-rotation device.
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7 In addition, the presence of each tube support plate was verified for all inservice SG tubes as part of the normal eddy current analysis. No degradation of the tube support plates was identified.
Byron Unit 2 (D-5) Response:
Areas Inspected and Results of the Inspections:
Suppon Plates:
The stainless steel TSPs with a quatrefoil hole design are vastly difTerent than the carbon steel drilled hole TSPs. As a consequence, the EPRI eddy current technique (Reference 1) cannot be used to detect cracked TSP support ligaments in a Model D-5 SG.
During each refueling outage,100% of the tube support plate intersections are inspected with the conventional bobbin coil probe for identifying distorted TSP signals, anomalies and to verify proper location of the TSPs. To date, no degradation or missed locations of the support plates has been observed.
Braidwood Unit I (D-4) Response:
In conjunction with the 3.0 Volt Interim Plugging Criterion, Braidwood Station conducted an extensive secondary side inspection to demonstrate that the secondary side internals were not degraded and their suppon structure could limit the tube support plates di placement in the event of an accident.
Areas Inspected and Results of the Inspections:
Support Plates:
During the AlR05 refuel outage (October 1995), the top support plate was inspected with an eddy current technique developed by EPRI (Referen e 1) for identification of cracked TSPs. The inspection was performet an all four steam generators in the area of the three anti-rotation devices at the top support plate. Fifly tube to tube support intersection were inspected at each anti-rotation device. In addition the presence of each tube support plate was verified for all inservice SG tubes as part of the normal eddy current analysis. No degradation was identified.
The AlR06 (April 1997), refuel outage included eddy current inspection using the EPRI program (reference 1) for identification of cracked TSPs. The eddy current inspection was performed on all four SGs for 100% of the tube support plate intersections.
The inspection was perforrned using the Zetec Computer Data Screening (CDS) sonware. The CDS sonware was used as the primary analysis with a manual analyst used as secondary. The two analyses were compared to determine if any discrepancies existed between the analyses. No degradation was identified for the 100% inspection performed on the TSPs.
- Patch Plates:
During the Braidwood October 1995 and April 1997 SG inspections, the patch plates on all four SGs were inspected witi addy current. No degradation was identified.
Braidwood Unit 2 (D-5) Response:
Areas inspected and Rg_sults of the inspecti_g_nr Support Plates:
e The stainless steel TSPs with a quatrefoil hole design are vastly different than the carbon steel drilled hole TSPs. As a consequence, the EPRI eddy current technique (Reference 1) cannot be used to detect cracked TSP support ligaments in a Model D-5 SG.
During each refueling outage,100% of the tube support plate intersections are inspected with the conventional bobbin coil probe for identifying distorted TSP signals, anomalies and to verify proper location of the TSPs. To date, no degradation or indication of miss location of the support plates has been observed.
Erosion / Corrosion in the Pre-Heater Water Box Region:
Prior to the A2R06 (September 1997), SG inspection, Westinghouse released technical bulletin NSD-TB-97-05 dated September 11,1997 (Reference 3). The technical bulletin applies to owners with pre-heat SG models D-4 and D-5. The notification addressed erosion / corrosion in the pre-heater water box region
The Westinghouse technical bulletin and sketch of an as-designed water box region of a model D4 steam generator was discussed during the analyst's training and testing of the Comed site specific performance demonstration (SSPD) program.
The bobbin coil probe was used along with a low frequency of(20 kHz) for screening and detection ofloose parts. No degradation or loose part indications were found in the water box region during the eddy current inspection.
Reauired Information Item #(Ib)
Whether visual or v.deo camera inspections on the secondary side of the steam generators have been performed at the facility to gain information on the condition of steam generator internals (e.g., support plates, tube bundle wrappers, or other components). If the addressee has performed such inspections, include a discussion of the findings.
Byron and Braidwood stations have visually inspected the steam generator secondary side during sludge lancing operations, FOSAR activities, before and after chemical cleaning (Byron Unit 1 only), and have performed pre-heater water box degradation inspections (Braidwood Unit 2 only) and inspections in conjunction with the 3.0 Volt Interim Plugging Criterion.
Scope Visual / video camera inspections are used during FOSAR activities, insertion of e
sludge lance equipment, and for cleanliness inspection of the top of tubesheet after sludge lancing. Additional detailed secondary side inspections have been performed and are discussed in the individual Byron and Braidwood plant responses below.
Frequency At present, sludge lancing and FOSAR activities are performed each refueling outage in all four SGs. The visual inspection associated with these activities is performed at this time.
The visual inspection associated with sludge lancing and FOSAR activities will include the steam generators selected for inspection as part of the sample plan.
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Method Methods fo'r visually inspecting the secondary side internals include video e
probes and cameras delivered with robotic equipment, hand held boroscopes, and visual observations of sludge lancing equipment insertion through the hand hole cover.
Equipment Visual / Video equipment includes Welch Allen @ probes and boroscopes 'n e
addition to specialty vendor equipment from Framatome Technologies Incorporated (FTI) and Brooks Associates Incorporated.
Visual / Video Inspection Details Byron Unit i Response:
e Following the secondary side chemical cleaning of the Byron Unit 1 SGs during BIR06 (September 1994), a video camera inspection of the secondary side internals was conducted.
Areas Inspected and Results of the Inspections:
The top of tube sheet was inspected with a video camera on all four SGs before and aRer sludge lancing. No degradation was observed.
The third support plate on the hot leg side was inspected with a video camera on all four SGs. No degradation was present.
The fiRh support plate on the hot leg side was inspected with a video
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camera on SGs B, C and D. No degradation was present.
The finh and sixth support plate on the cold leg side was inspected with a video camera on SGs A and B. In addition the fourth support plate on the cold leg side was inspected with a video camera on SG A. No degradation was observed.
1 The tenth and eleventh top support plate was inspected with a video camera on SGs A and B. No degradation was observed.
In conjunction with the 3.0 Volt Interim Plugging Criterion, Byron Station conducted an extensive secondary side inspection to demonstrate that the secondary side internals were not degraded and their support structure could limit the tube support plates displacement in the event of an accident.
This inspection was conducted during November 1995.
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Areas Inspected and Results of the inspections:
- Tie Rod Nuts:
A video camera inspection was performed on 7 of the 10 tie rod nuts in one of the four Byron Unit 1 SGs. The tie rod nuts were found to be tight against the top support plate with no evidence of degradation.
Vertical Blocks:
During B1R07,24 vertical bars below the flow distribution baffle in each SG were inspected with a video camera. This inspection included the welded attachments to the wrapper. Once again, no degradation was observed.
Inspection for Wrapper Drop:
Verification that the wrapper had not shifted was performed during
. BIR07 by assuring there were no obstructions when inserting the sludge lance equipment through the wrapper opening in each SG. No shift in the wrapper location was identified.
Byron Unit 2 Response:
A visual assessment of the secondary side cleanliness was performed in the areas of quatrefoils to determine the need for additional cleaning during the i
Byron Unit 2, September 1996 refueling outage.
1 Areas Inspected and Results of the inspections:
Support Plates:
A video camera inspection was performed at the fifth and eighth -
support plates in SG C. No degradation was identified.
Inspection for Wrapper Drop:
Verification that the wrapper had not shifted was performed by assuring there were no obstructions when inserting the sludge lance equipment through the wrapper opening in each SG, No shift in the wrapper location was identified.
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t Braidwood Unit 1 Response:
In conjunction with 3.0 Volt Interim Plugging Criterion Braidwood Station Unit I conducted an extensive secondary side inspection to demonstrate that the secondary side internals were not degraded and their support structure could limit tube support plate displacement in the event of an accident. This inspection was conducted during October 1995.
Areas inspected and Results of the Inspections:
Top Support Plate:
A thorough video camera inspection was performed by Brooks on one of the four Braidwood Unit 1 SGs. The emphasis for this inspection was placed on determining if degradation similar to those seen in foreign units was present. No degradation was found as a result of this visual inspection.
Tie Rod Nuts:
A video camera inspection was performed by Brooks on 8 of the 10 tie rod nuts in one of the four Braidwood Unit 1 SGs. The tie rod nuts were found to be tight against the top support plate with no degradation present.
Vertical Blocks and Wedges at Top TSP:
During this Braidwood Unit i SG outage approximately 5 wedges and 89 vertical bars were also inspected with a video camera. This inspection included the welded attachments to the wrapper. Once again no degradation was identified.
Vertical Blocks at Flow Distribution Baffle:
72 vertical bars below the flow distribution baffle in each SG were inspected with a video camera during the Braidwood Unit 1 SG outage.
This inspection included the welded attachments to the wrapper. No degradation was observed.
Inspection for Wrapper Drop (October 1995 and April 1997):
Verification that the wrappcr had not shifled was performed by assuring there were no obstruction, when inserting the sludge lance equipment through the wrapper opening in each SG. No shift in the wrapper location was noted.
.o Braidwood Unit 2 Response:
e A visual assessment of the secondary side cleanliness was performed in the areas of quatrefoils to determine the need for additional cleaning during the Braidwood Unit 2, April 1996 SG outage.
Areas inspected and Results of the Inspections:
Support Plates:
A video camera inspection was performed by Brooks at the top and fifth support plates in one SG. No degradation was found.
Pre-heater Water Box Region:
A video camera inspection of the water box region was conducted to look for foreign objects and degradation in one SG. No degradation was identified.
Inspection for Wrapper Drop:
Verification that the wrapper had not shifted was performed by assuring there were no obstructions when inserting the sludge lance equipment through the wrapper opening in each SG. No shift in the wrapper location was noted.
Reauired Information Item #(le)
Whether degradation of steam generator internals has been detected at the facility, and how the degradation was assessed and dispositioned.
For both the Byron and Braidwood Stations no SG secondary side internals degradation has been found.
Future Inservice Inspection Plan Westinghouse Model D-4 (Braidwood Unit 1) l Braidwood Unit 1 is scheduled to operate until the steam generator replacement outage scheduled for September 1998. Therefore, no future secondary side inspections will be performed.
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a Westinghouse Model D-5 (Byron Unit 2 and Braidwood Unit 2) e Tube Support Plate; 100% of the tube support plate intersections will be inspected each refueling outage with the conventional bobbin coil probe for identifying distorted tube support plate signals, anomalies and to verify proper location of the TSPs.
Any distortion at the tube support plate identified by the bobbin coil probe would be characterized and dispositioned using RCT.
Wrapgr Drop;
- 1. Each outage that the sludge lancing is to be performed, verify that the sludge lance equipment can be inserted without interference.
2.
Ifinterference with the sludge lance equipment is detected, the lower wrapper support blocks should be visually inspected.
IIADsition Cone Girth Wskt In accordance with ASME Section XI Inservice Inspection requirements for the steam generator girth welds, the current inspection frequency is at least once per ten year interval.
Pre-heater Water Box Erosion / Corrosion:
Eddy current inspections of peripheral and T-slot tubes within the pre-heater will be undertaken at each scheduled refueling outage to detect loose parts and any tubes with significant tube wall degradation. The water box inspections will be performed starting with the Byron Unit 2 (B2R07) April 1998 outage.
Additional Visugl/ Video inspection-During the course of a steam generator inspection, if additional secondary side entries and visual inspections are conducted, the secondary side internals and supports in the general vicinity will be included in the inspection.
BWI Model 7720 (Byron Unit I and Braidwood Unit 1)
Tube Lattiggjupport Grid:
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For each tube selected per the eddy current inspection plans,100% of the lattice bar tube support grid intersections will be inspected with the conventional bobbin coil probe to identify distorted tube support grid signals and anomalies and to verify proper location of the tube support grid. Any distortion at the tube support grid intersection identifed by the bobbin coil probe would be characterized and dispositioned using RCT.
Wrapper Drop:
- 1. Each outage that the sludge lancing is to be performed, verify that the sludge lance equipment can be inserted without interference.
2.
Ifinterference with the sludge lance equipment is detected, the lower wrapper support blocks should be visually inspected.
Transition Cone Girth Weld; In accordance with ASME Section XI Inservice Inspection requirements for the steam generator girth welds, the current inspection frequency is at least once per ten year interval.
Additional Visual / Video Inspection:
During the course of a steam generator inspection, if additional secondary side entries and visual inspections are conducted, the secondary side internals and supports in the general vicinity will be included in the inspection.
Reauired Information Item #2:
If the addressee currently has no program in place to detect degradation of steam generator internals, include a discussion and justification of the plans and schedule for establishing such a program, or why no program is needed.
Currently, Comed's secondary side steam generator inspection programs are in accordance with NEI 97-06 Steam Generator Program Guidelines (Reference 2).
A response to requested information Item # 2 is not applicable to Comed.
REFERENCES:
- 1. EPRI Report SG-96-05-003," Report on the Inspection of Applicability To The Detection of Potentially Degraded Tube Support Structures"
- 2. NEI 97-06," Steam Generator Program Guidelines," December 1997 1 K:he generic:gt:9706 resp de15
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