ML20217C168

Safety Evaluation Accepting Request for Relief from ASME Code,Section Iii,Div 2 for Repair of Damaged Concrete Reinforcement Steel

ML20217C168
Person / Time
Site:	Byron, Braidwood
Issue date:	09/22/1997
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20217C152	List: ML20217C147 ML20217C168
References
NUDOCS 9710010239
Download: ML20217C168 (6)

Text

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y k UNITED STATES

• P; NUCLEAR REGULATORY COMMISSION i

l WASHINGTON. D.C. asseMo01

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1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RE0 VEST FOR RELIEF FROM ASME CODE. SECTION III.

DIVISION 2. REPAIR RE0VIREMENTS TO REPAIR DAMAGED REINFORCEMENT STEEt COMMONWEALTH EDISON COMPANY BYRON STATION. UNIT 1. AND BRAIDWOOD STATION. UNIT 1 DQGET NOS. STN 50 454 AND STN 50-416

1.0 INTRODUCTION

As required by 10 CFR 50.55a(g) nuclear power facility aiping and components must meet the applicable requirements of Section XI of tie American Society of

. Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (hereafter referred to as the Code).Section XI of the ASME Code specifies Code-acceptable repair methods for flaws in piping, components and structures that are in-service.Section XI also requires that the repairs are performed in accordance with the requirements of the original construction code (ASME Code.

Section III. Division 1 or Division 2).

Alternatives to the ASME Code requirements may be used by nuclear licensees when authorized by the Director of the Office of Nuclear Reactor Regulation if the proposed alternatives to the requirements are such that they are shown to provide an acceptable level of quality and safety in lieu of the ASME Code requirements [10 CFR 50.55a(a)(3)(1)). or if compliance with the ASME Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety [10 CFR 50.55a(a)(3)(ii)).

A licensee may also submit requests for relief from certain ASME Code requirements when it has determined that conformance with certain ASME Code requirements is impractical for its facility [10 CFR 50.55a(g)(5)(111)].

Pursuant to 10 CFR 50.55a(g)(6)(1), the Commission will evaluate determinations of impracticality and may grant relief and may impose alternative requirements as it determines is authorized by law. Such relief may be granted giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.

2.0 BACKGROUND

By letter dated March 20, 1997. Commonwealth Edison Company (Comed. the licensee), submitted to the NRC a' request for relief from the requirements of ASME Code.Section III. Division 2. for the repair of damaged concrete reinforcement steel. The relief is required because during the scheduled lTA 188 u ?J8?J 6 P PDR

. 1 2-steam generator replacement project the licensee will create a construction opening in the containment buildings of the Byron. Unit 1. and Braidwood.

Unit 1. nuclear generating stations.

Containment concrete removal activities involve the use of automated chipping machines to remove concrete. Once exposed the reinforcing steel will be cut and removed. Stub ends of the reinforcing steel will be cad welded with i

replacement reinforcing steel to reconstruct the pre outage reinforcing steel  !

pattern. All steel is required to have a cross section that was specified in '

the original design specification. Although every attempt will be made to protect the reinforcing steel stub end area, physical damage in the reinforced steel may occur. Unacceptable damaged areas must be removed or repaired prior to restoration of the containment structure. Welding is the only wa

> repair the base metal to restore its original cross sectional area. yThe to original Construction Code for Byron.- Unit 1. and Braidwood. Unit 1. was the -)

' 1973 ASME Code.Section III. Division 2. Subsection CC-4334.7 only allows welding of reinforcing steel with carbon content equal to or less than 0.55 percent.- Byron. Unit 1. and Braidwood. Unit 1. reinforcing steel has a carbon i

' content equivalent or greater than 0.55 percent. At the time of construction.

compliance with this subsection of the ASME Code was not an issue because weld j repairs were not performed on the reinforcing steel. '

The licensee submitted Request for Relief Nos. 12R 20 for Byron. Unit 1. and 1

NR-33 for Braidwood. Unit 1 which request relief from the requirements of Subsection CC-4334 of the ASME Code. Section-III. Division 2. The relief is i

{ needed during the Steam Generator Replacement Outage (SGRO) which is scheduled

, for the fall Refueling Outage in 1997 for Byron. Unit 1. and for the fall 1998 Refueling Outage for Braidwood. Unit 1. The information provided by the

licensee in support of the request has been evaluated and the bases for disposition are documented below.

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[ 2.1 ASME Code Requirement: (as stated) j 10 CFR 50.55a(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 Construction Code or in ASME Section I!I. Division 2 with or without the removal of the damaged steel". The original Construction Code for Byron [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 percent.

2.2 Licensee's Code Relief Request: (as stated)

Pursuant to 10 CFR 50.55a(a)(3)(11). the licensee requested relief from the requirements of subsection CC-4334 of the ASME Code.Section III.

Division 2.

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. 3-2.3 Licensee's Basis for Requesting Relief: (as stated)

Pursuant to 10 CFR 50.55a(a)(3)(11), relief is 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 j quality and safety, i

To facilitate replacement of the steam generators at Byron. Unit 1

, [Braidwood. Unit 1), a construction opening will be created in the

! containment building during the Steam Generator Replacement Outage (SGR0). Containment concrete removal activities involve the use of

.! automated chipping machines to remove concrete. Once ex)osed, the l' reinforcing steel will be cut and removed. As part of t1e containment restoration effort, stub ends of the reinforcing steel that remain in-4 place at the edges of the opening will be Cad welded with replacement reinforcing steel to reconstruct pre outage reinforcing steel )atterns.

For containment restoration. all reinforcing steel must have tie 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-:.722 [L 2722 for Braidwood), 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.

l The structurai design approach used for the Byron. Unit 1 [Braidwood.

Unit 1)ContainmentStructureisthatthecapacitytoresistdesign 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 4

reinforcing steel bar at the Byron. Unit 1 [Braidwood. Unit 1] is

classified as temperature stee1

g. _ ._... ,g.u,g vi 7ik FETh w,,and_is rumoge added to the containmenLfot_._..

ena temperature ettects ana __.

i does not have the primary role of carrying applied loads.

Using material certifications it has been determined that the

. reinforcing steel in the area of the construction opening at Byron (Braidwood] has a carbon equivalent in excess of 0.55 percent 1 (approximately 0.65 percent). Therefore, relief is requested from the 1973 ASME Section Ill. 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 percent.

TheSteamGeneratorReplacementProjectattheR.E.GinnaNuclearPower Station used AWS D1.4-92 for base metal repair and structural welding of their reinforcing steel as part of their containment restoration activities. Ginna has a non-ASME containment structure and, as such, was using AWS standards consistent with their original construction d

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design basis. The containment dome at Ginna is a conventional reinforced concrete structure with #18 reinforcing steel bars. In the

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< 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 per their design and licensing basis.

Since the Byron (Braidwood] containment reinforcing steel does not have J

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 [Braidwood).

Use of AWS D1.692 will provide a level of safety and nuality equivalent

to the current Byron (Braidwood] design and licensing basis, Welding procedures and welding personnel to be used in the containment restoration activities at Byron [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 percent.

By employing approved procedures and using welders qualified per the AWS l D1.4 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.

. If strict compliance with 10 CFR 50.55a(g) were required, base metal i

repair by welding would not be allowed by the 1973 ASME Section III, i Division 2 for the Byron Unit 1 [Braidwood, Unit 1] reinforcing steel due to its carbon equivalent content being in excess of 0.55 percent.

As a result, if a stub end of the reinforcing steel (where Cad weld

. splices will be attached during the restoration of the containment i

opening) were nicked in excess of 1/8" and evaluated as unacceptable,

) _ _.__...___.gtttcng. 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. Additional concrete removal to avoid reinforcing steel weld repair would not provide any compensating increase in quality or safety since, in either case, the containment is being restered to its original design basis condition. Weld repair of contain:ent Feinforcing steel in accordance with AWS D1.4-92 would avoid unnecessary removal of additional containment concrete and potentially undesirable work conditions. Accordingly, use of AWS D1.4-92 is requested based on the hardship provisions of 10 CFR 50.55a(a)(3)(11).

5 2.4 Proposed Alternative Provisions: (as stated)

The American Welding Society (AWS) Standard D1.4-92 is proposed as an alternate 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 3rocedures are approved to the require'nents of the standard including tie 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.

3.0 EVALUATION The licensee has requested relief from ASME Code requirements stated in Subsection CC-4334 of the ASME Code.Section III. Division 2. Subsection CC-4334.7 only allows welding of reinforcing steel with carbon content equal to or less than 0.55 percent. Byron. Unit 1. and Braidwood. Unit 1.

reinforcing steel has a carbon content ecu1 valent of greater than 0.55

• percent. Weld repairs were not performec on the reinforcing steel during construction. The relief is needed to support welding that may be required during the SGR0 which is scheduled for the fall Refueling Outage in 1997 for Byron. Unit 1, and for the fall Refueling Outage in 1998 for Braidwood.

Unit 1.

The licensee has proposed to use the American Welding Society (AWS) Standard D1.4-92. Structural Welding Code. Reinforcing Steel as an alternate to perform weld repair of containment reinforcing steel. AWS D1.4 92 allows welding of reinforcing steels with any carbon equiv61ent value provided the welding procedures are qualified and approved to the requirements of the standard ,

including:-low hydrogen electrodes of the appropriate strength level are used, the electrode storage conditions are controlled to preserve their low hydrogen i characteristics, and the appropriate minimum preheat and interpass temperatures are maintained. In addition. AWS 01.4 92 requires that welders ,

. qualified per AWS D1.4-92 requirements are used to perform weld repair for damaged reinforcing steel. These provisions are sufficient to ensure material integrity. Further. if strict com '

Code is imposed upon the licensee,pliance base metal with repairthe byrequirementswelding would of notthe be ASME allowed by 1973 ASME Code.Section III. Division 2, for the Byron. Unit 1. and Braidwood. Unit 1. reinforcing steel due to its carbon equivalent content being'in excess of.0.55 percent. 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 reqJired. Additional concrete

- chipping unnecessarily increases the size of the construction opening and increases the >ossibility of additional damage to more reinforcing steel, thus requiring furtier expansion of the opening size.

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' l 6-Therefore, the staff finds that the licensee has provided an acceptable alternative to the requirements of the ASME Code,Section III, Division 2.

Subsection CC 4334.

4.0 CONCLUSION

The NRC staff concludes that the licensee has provided an acceptable alternative to the requirements of the ASME Code,Section XI, and ASME Code, Section 111. Division 2. Furthermore, the staff finds that performance of repair of damaged reinforcing steel in accordance with the requirements of the ASiE Code.Section III, Division 2, would result in hardship upon the licensee since it would require additional chipping of concrete. Additional concrete l chipping unnecessarily increases the size of the construction opening and increases the possibility of additional damage to more reinforcing steel.

l Additional concrete chi) ping is not in the best interest of alant safety.

given the adequacy of tie licensee's alternative program. Tie staff, therefore, concludes that authorization of the licensee's alternative program for the repair of containment rebar associated with steam generator replacement would provide aa acceptable level of quality and safety.Pursuant to 10 CFR 50.55a(a)(3)(ii), the alternative may be authorized.

Principal Contiibutor: G. Georgiev '

Date: September 22, 1997 i

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