ML20137C807
| ML20137C807 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 03/20/1997 |
| From: | Hosmer J COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9703250134 | |
| Download: ML20137C807 (9) | |
Text
_ _.
Gimmonw cahh IMhon G>mpany I400 Opus Place Downers Grove, IL 6615-57o1 March 20,1997 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention:
Document Control Desk
Subject:
Byron Station Unit I and Braidwood Station Unit 1 Inservice Inspection Relief Requests 12R-20 and NR-33 NRC Docket Numbers: 50-454 and 50-456 The Commonwealth Edison Company (Comed) requests approval in accordance with 10CFR50.55a(a)(3), to use the American Welding Society (AWS) Standard in lieu of the requirements of 10CFR50.55a(g) for the repair activities of containment structures at Byron Unit I and Braidwood Unit 1.10CFR50.55a(g) invokes ASME XI(1992 Edition with 1992 Addenda) which requires that the, " damaged reinforcement steel shall be repaired by any method permitted in the original Construction Code or in ASME Section Ill, Division 2 wita or without the removal of the damaged steel." During steam generator replacement concrete removal activities, damage may result to existing rebar requiring the need for repair methods.
The original construction Code for Byron and Braidwood was the 1973 ASME Section III, j
Division 2. Subsection CC-4334.7 only allows welding of reinforcing steel with carbon equivalents equal to or less than 0.55% Byron and Braidwood reinforcing steel has a carbon equivalent of greater than 0.55% At the time of construction, compliance with this section of the ASME Code was not an issue because welding repairs were not performed on the rebar.
During the steam generator replacement project, compliance with the 1973 ASME Section III will result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety; therefore, the requirements of 10CFR50.55a(a)(3)(ii) are setisfied. AWS D1.4-92 is proposed as an alternative to perform weld repair of containment reinforcing steel which will provide a level of safety and quality equivalent to the current design and licensing basis.
Comed requests approval of this exemption by October 1,19f 7, to facilitate use during the steam generator replacement. Attachment A contains Relief Request 12R-20 for Byron Unit I and Attachment B contains Relief Request NR-33 for Braidwood Unit 1. If you have any questions concerning this correspondence please contact this otTice.
Sincerely, M
John B. Hosmer Engineering Vice President
[f Attachments cc:
G. Dick, Byron /Braidwood Project Manager-NRR C. Phillips, Senior Resident Inspector-Braidwood S. Burgess, Senior Resident Inspector-Byron Office of Nuclear Safety-IDNS k
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9703250134 970320 PDR ADOCK 05000454 0,5hIEfElE!E,5lE,4 A I!nicum Company
Attachment A BYRON UNIT I l
INSERVICE INSPECTION j
REl,IEF REOUEST 12R-20 K:nla\\bybwd\\sgrp\\rebar
BYRON UNIT 1 INSERVICE INSPECTION RELIEF REOUEST 12R-20 (Page1of3)
COMPONENT IDENTIFICATION 4
Code Class:
CC l
4
References:
IWL-4000 10 CFR 50.55a l
1992 Edition with 1992 Addenda
==
Description:==
Alternative Requirements for the Repair of Concrete Containment Reinforcing Steel.
)
CODE REOUIREMENT 10CFR50.55a(g) has invoked ASME Section XI (1992 Edition with 1992 Addenda) for the repair activities of containment structures. ASME Section XI, Subsection IWl 4220 requires that the
" damaged reinforcing steel shall be repaired by any method permitted in the original Ccnstruction j
Code or in ASME Section III, Division 2, with or without the removal of the damaged steel". The
~
original Construction Code for Byron was the 1973 ASME Section III, Division 2 (issued for trial use and comment). Subsection CC-4334.7 only allows welding of reinforcing steel with carbon 4
equivalents equal to or less than 0.55%.
BASIS FOR RELIEF 4
Pursuant to 10 CFR 50.55a(a)(3)(ii), reliefis raluested on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
To facilitate replacement of the steam generators at Byron Unit 1, a construction opening will be created in the containment building during the Steam Generator Replacement outage (SGRO).
Containment concrete removal activities involve the use of automated chipping machines to remove concrete. Once exposed, the reinforcing steel will be cut and removed. As part of the containment restoration efTort, stub ends of the reinforcing steel that remain in-place at the edges of the opening will be Cad-welded with replacement reinforcing steel to reconstruct pre-outage reinforcing steel patterns. For containment restoration, all reinforcing steel must have the required cross section which was specified in the original design specification. Although every attempt will be made to protect the reinforcing steel (stub end areas) during the concrete removal process, physical damage (nicks) in the reinforcing steel base metal may occur. As per the original construction specification, F-2722, nicks in excess of 1/8" will be evaluated by engineering. Unacceptable nicks must be removed or repaired prior to restoration of the containment wall structure. Welding is the only way to repair the base metal to restore its original cross sectional area.
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i i
RELIEF REOUEST 12R-20 (Page 2 of 3)
The structural design approach used for the Byron Unit 1 Containment Structure is that the capacity to resist design basis loads is provided by the unbonded post-tensioning system. The post-tensioning system provides the effect of an inward pressure which counteracts the effects created by a postulated accident. The reinforcing steel bar at the Byron Unit 1 is classified as temperature steel and is added to the containment for crack control and to minimize shrinkage and temperature l
effects and does not have the primary role of carrying applied loads.
l l
l Using material certifications, it has been detennined that the reinforcing steel in the area of the construction opening at Byron has a carbon equivalent in excess of 0.55% (approximately 0.65%).
l Therefore, reliefis requested from the 1973 ASME Section Ill, Division 2 code requirement CC-l 4334.7 which only allows for welding of reinforcing steel which has carbon equivalents equal to or l
l less than 0.55%.
The Steam Generator Replacement Project at the R. E. Ginna Nuclear Power Station used AWS i
D1.4-92 for base metal repair and structural welding of their reinforcing steel as part of their contamment restoration activities. Ginna has a non-ASME containment structure and, as such, was using AWS standards consistent with their original construction design basis. 'Ihe contairunent dome at Ginna is a conventional reinforced concrete structure with #18 reinforcing steel bars. In the Ginna case, the reinforcing steel plays a primary role of carrying applied loads.
i Compliance with the AWS standards provided Ginna with an acceptable level of safety as per their t
design and licensing basis.
Since the Byron containment reinforcing steel does not have the primary role of carrying applied loads, the Ginna application of AWS D1.4-92 for the welding of containment reinforcing steel represents a more safety significant use than what is required for Byron. Use of AWS DI.4-92 l
will provide a level of safety and quality equivalent to the current Byron design and licensing basis.
i Welding procedures and welding personnel to be used in the containment restoration actisities at Byron following Steam Generator Replacement will meet the requirements of AWS DI.4-92.
Procedural controls that comply with the requirements of Table 5.1, Table 5.2, and Paragraph 5.7 of AWS D1.4-92 for welding electrode selection, storage, pre-heat, and interpass temperatures ensure that the requirements of the AWS standard will be met for base metal weld repair of reinforcing steel with carbon equivalent content in excess of 0.55%.
By employing approved procedures and using welders qualified per the AWS DI A-92 code requirements, weld repair for damaged reinforcing steel will be performed to a level of quality and safety which has previously been accepted for use in containment structure applications.
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9 RELIEF REOUEST 12R-20
)
(Page 3 of 3)
If strict compliance with 10CFR50.55a(g) were required, base metal repair by welding would not be allowed by 1973 ASME Section III, Division 2 for the Byron Unit I reinforcing steel due to its 1
carbon equivalent content being in excess of 0.55%. As a result, if a stub end of the reinforcing steel (where Cad-weld splices will be attached during the restoration of the containment opening) were nicked in excess of 1/8" and evaluated as unacceptable, additional chipping of concrete to expose an undamaged section of reinforcing steel would be required. Additional concrete chipping unnecessarily increases the size of the construction opening and increads the possibility of additional damage to more reinforcing steel; thus, requiring further expansion of the opening size.
The expansion on any side of the containment opening would require extension of the elevated work platform being used for the containment opening restoration. This would require additional safety measures and structures to ensure worker safety. Additional concrete removal to avoid i
reinforcing steel weld repair would not provide any compensating increase in quality or safety since, in either case, the containment is being restored to its original design basis condition. Weld repair of containment reinforcing steel in accordance with AWS D1.4-92 would avoid unnecessary removal of additional containment concrete and potential undesirable work conditions.
Accordingly, use of AWS D1.4-92 is requested based on the hardship provisions of 10CFR50.55a(a)(3)(ii).
PE OPOSED ALTERNATE PROVISIONS He American Welding Society (AWS) Standard D1.4-92 is proposed as an alternative to perform weld repair of containment reinforcing steel. AWS D1.4-92 allows welding of reinforcing steels with any carbon equivalent value provided the welding procedures are approved to the requirements of the standard including the following: low hydrogen electrodes of the appropriate strength level are used, the electrode storage conditions are controlled to preserve their low hydrogen characteristics, and the appropriate minimum preheat and interpass temperatures are maintained.
APPLICABLE TIME PERIOD This relief will be required for the Byron Unit 1 Steam Generator Replacement Outage which is scheduled for the Fall Refueling Outage in 1997.
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Attachment B BRAIDWOOD UNIT 1 INSERVICE INSPECTION RELIEF REOUEST NR-33 K:nla\\bybwdisgrp\\rebar
I
.q BRAIDWOOD UNIT 1 INSERVICE INSPECTION 4
RELIEF REOUEST NR-33 (Page 1 of 3)
COMPONENT IDENTIFICATION Unit:
Braidwood Unit 1 1
Code Class:
References:
IWL-4000 10 CFR 50.55a 1992 Edition with 1992 Addenda
==
Description:==
Altemative Requirements for the Repair of Concrete Containment Reinforcing Steel.
1 CODE REOUIREMENT 10CFR50.55a(g) has invoked ASME Section XI (1992 Edition with 1992 Addenda) for the repair 1
activities of contamment structures. ASME Section XI, Subsection IWL-4220 requires that the
" damaged reinforcing steel shall be repaired by any method permitted in the original Construction i
Code or in ASME Section III, Division 2, with or without the removal of the damaged steel" The original Construction Code for Braidwood was the 1973 ASME Section III, Division 2 (issued for trial use and comment). Subsection CC-4334.7 only allows welding of reinforcing steel with carbon equivalents equal to or less than 0.55%
BASIS FOR RELIEF Pursuant to 10 CFR 50.55a(a)(3)(ii), reliefis requested on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
To facilitate replacement of the steam generators at Braidwood Unit 1, a construction opening will be created in the containment building during the Steam Generator Replacement outage (SGRO).
Containment concrete removal activities involve the use of automated chipping machines to remove concrete. Once exposed, the reinforcing steel will be cut and removed. As part of the containment restoration efTort, stub ends of the reinforcing steel that remain in-place at the edges of the opening will be Cad-welded with replacement reinforcing steel to reconstruct pre-outage reinforcing steel patterns. For containment restoration, all reinforcing steel must have the required cross section which was specified in the original design specification. Although every attempt will be made to protect the reinforcing steel (stub end areas) during the concrete removal process, physical damage (nicks) in the reinforcing steel base metal may occur. As per the original construction specification, L-2722, nicks in excess of 1/8" will be evaluated by engineering. Unacceptable nicks must be removed or repaired prior to restoration of the containment wall stmeture. Welding is the only way to repair the base metal to restore its original cross sectional area.
K:nla\\bybwd\\sgrp\\rebar
RELIEF REOUEST NR-33 (Page 2 of 3)
The structural design approach used for the Braidwood Unit 1 Containment Structure is that the capacity to resist design basis loads is provided by the unbonded post-tensioning system. The post-tensioning system provides the effect of an inward pressure which counteracts the effects created by a postulated accident. The reinforcing steel bar at the Braidwood Unit 1 is classified as temperature steel and is added to the containment for crack control and to minimize shrinkage and j
temperature effects and does not have the primary role of carrying applied loads.
j Using material certifications, it has been determined that the reinforcing steel in the area of the construction opening at Braidwood has a carbon equivalent in excess of 0.55% (approximately 1
0.65%). Therefore, reliefis requested from the 1973 ASME Section III, Division 2 code requirement CC-4334.7 which only allows for welding of reinforcing steel which has carbon equivalents equal to or less than 0.55%.
He Steam Generator Replacement Project at the R. E. Ginna Nuclear Power Station used AWS D1.4-92 for base metal repair and structural welding of their reinforcing steel as part of their i
containment restoration activities. Ginna has a non-ASME containment structure and, as such, was using AWS standards consistent with their original constmetion design basis. The containment dome at Ginna is a conventional reinforced concrete structure with #18 reinforcing steel bars. In the Ginna case, the reinforcing steel plays a primary role of carrying applied loads.
Compliance with the AWS standards provided Ginna with an acceptable level of safety as per their design and licensing basis.
Since the Braidwood containment reinforcing steel does not have the primary role of carrying applied loads, the Ginna application of AWS D1.4-92 for the welding of containment reinforcing steel represents a more safety significant use than what is required for Braidwood. Use of AWS D1.4-92 will provide a level of safety and quality equivalent to the current Braidwood design and licensing basis.
Welding procedures and welding personnel to be used in the containment restoration activities at Braidwood following Steam Generator Replacement will meet the requirements of AWS D1.4-92.
Procedural controls that comply with the requirements of Table 5.1, Table 5.2, and Paragraph 5.7 of AWS D1.4-92 for welding electrode selection, storage, pre-heat, and interpass temperatures ensure that the requirements of the AWS standard will be met for base metal weld repair of reinforcing steel with carbon equivalent content in excess of 0.55%.
By employing approved procedures and using welders qualified per the AWS Dl.4-92 code requirements, weld repair for damaged reinforcing steel will be performed to a level of quality and safety which has previously been accepted for use in containment structure applications.
K:nla\\bybwd\\sgrp\\rebar
RELIEF REOUEST NR-33 (Page 3 of 3)
If strie: compliance with 10CFR50.55a(g) were required, base metal repair by welding would not be allowed by 1973 ASME Section Ill, Division 2 for the Braidwood Unit I reinforcing steel due to its carbon equivalent content being in excess of 0.55%. As a result, if a stub end of the reinforcing steel (where Cad-weld splices will be attached during the restoration of the containment opening) were nicked in excess of 1/8" and evaluated as unacceptable, additional chipping of concrete to expose an undamaged section of reinforcing steel would be required. Additional concrete chipping unnecessarily increases the size of the construction opening and increases the possibility of additional damage to more reinforcing steel, thus requiring further expansion of the opening size. The expansion on any side of the containment opening would require extension of the elevated work platform being used for the containment opening restoration. This would require additional safety measures and structures to ensure worker safety. Weld repair of containment reinforcing steel in accordance with AWS D1.4-92 would avoid unnecessary removal of additional containment concrete and potential undesirable work conditions. Accordingly, use of AWS D1.4-92 is requested based on the hardship provisions of 10CFR50.55a(a)(3)(ii).
PROPOSED ALTERNATE PROVISIONS The Amcian Welding Society (AWS) Standard D1.4-92 is proposed as an alternative to perform weld repair of containment reinforcing steel. AWS D1.4-92 allows welding of reinforcing stec!s with any carbon equiva! cut value provided the welding procedures are approved to the requirements of the standard including the following: low hydrogen electrodes of the appropriate strength level are used, the electrode storage conditions are controlled to preserve their low hydrogen characteristics, and the appropriate minimum preheat and interpass temperatures are maintained.
APPLICABLE TIME PERIOD l
This relief will be required for the Braidwood Unit i Steam Generator Replacement Outage which is scheduled for the Spring Refueling Outage in 1998.
O i
1 i
I J
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