ML052290483
| ML052290483 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/16/2005 |
| From: | Cowan P AmerGen Energy Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 5928-05-20226 | |
| Download: ML052290483 (12) | |
Text
10 CFR 50.55a 5928-05-20226 August 16,2005 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Three Mile Island, Unit 1 Facility Operating License No. DPR-50 NRC Docket No. 50-289
Subject:
Request for Relief to Utilize Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division I Pursuant to 10 CFR 50.55a(a)(3)(i), AmerGen Energy Company (AmerGen), LLC is requesting relief from American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Rules for lnservice Inspection of Nuclear Power Plant Components, on the basis that the proposed alternative provides an acceptable level of quality and safety.
Specifically, this proposed alternative concerns the use of Code Case N-638-1. This code case allows the use of automatic or machine Gas Tungsten Arc Welding (GTAW) temper bead technique without the use of preheat or postweld heat treatment on specified Class 1 components.
We request your review and approval of this request by October 15, 2005, in order to support modifications planned for the upcoming Three Mile Island, Unit 1 refueling outage.
If you have any questions, please contact Mr. Thomas R. Loomis (610-765-5510).
Respectfully, Pamela B. Cowan Director - Licensing & Regulatory Affairs AmerGen Energy Company, LLC
U.S. Nuclear Regulatory Commission August 16,2005 Page 2 Attachments: 1) Relief Request RR-00-22
- 2) Description of the Modification cc:
S. J. Collins, Regional Administrator, Region I, USNRC D. M. Kern, USNRC Senior Resident Inspector, TMI P. S. Tam, Senior Project Manager, USNRC File No. 05056
Request for Relief From ASME Section XI to Use of Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAVV Temper Bead Technique,Section XI, Division 1
TMI, Unit 1 Proposed Alternative to 10 CFR 50.55a Page 1 THREE MILE ISLAND, UNIT 1 RELIEF REQUEST RR-00-22 ASME Code Components Affected ASME Class 1 components
Applicable Code Edition and Addenda
Three Mile Island, Unit 1 Inservice Inspection Program complies with the ASME Code Section XI, 1995 Edition, 1996 Addenda. The third ten-year interval began on April 20, 2001, and is scheduled to conclude on April 19,201 1.
Applicable Code Requirement
As required by ASME Boiler and Pressure Vessel Code (Code),Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 1995 Edition, through the 1996 Addenda:
- 1. IWA-4600(b)(l), Alternative Welding Methods, states - The welding methods of IWA-4620, IWA-4630, or IWA-4640 may be used in lieu of the welding and nondestructive examination requirements of the Construction Code or Section Ill, provided the requirements of IWA-4610 are met.
As required by ASME Code Section XI, 1995 Edition, through 1996 Addenda:
- 1. IWA-4610(a), General Requirements For All Materials, states in part - The area to be welded plus a band around the area of at least 1-1/2 times the component thickness or 5 in., whichever is less, shall be preheated and maintained at a minimum temperature of.... 300F for the GTAW process during welding.
- 2. IWA-4633.2(d), Gas Tungsten-Arc Welding, which is a subsection to IWA-4630 (Dissimilar Materials) states in part - After at least 3/16 in. of weld metal has been deposited, the weld area shall be maintained at a minimum temperature of 3OO0F for a minimum of 2 hr in P-No. 1 materials.
Reason for Request
In accordance with 1 OCFR50.55a(a)(3)(i), Three Mile Island (TMI), Unit 1 is requesting relief from IWA-4610 and 4633.2 with regards to the use of preheat or postweld heat treatment on Class 1 components.
In lieu of these requirements, TMI, Unit 1 proposes to utilize Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1. Specifically, TMI, Unit 1 is proposing to perform a portion of the modification with a remotely operated weld tool, utilizing the
TMI, Unit 1 Proposed Alternative to 10 CFR 50.55a Page 2 machine Gas Tungsten Arc Welding (GTAW) process and the ambient temperature temper bead method with 50F minimum preheat temperature, as described in Code Case N-638-1. TMI, Unit 1 is requesting the use of the Code Case in its entirety, for the remainder of the interval for all Class 1 components, as specified in the Code Case.
Proposed Alternative and Basis for Use AmerGen Energy Company, LLC (AmerGen) will implement the requirements of ASME Code Case N-638-1 for applicable Class 1 components. N-638-1 will be utilized for, but not limited to, a pressurizer vent nozzle modification scheduled for the upcoming refueling outage in Fall 2005.
Currently, Regulatory Guide 1.147, Revision 13, Inservice inspection Code Case Acceptability, ASME,Section XI, Division l, dated January 2004, lists Code Case N-638 as an acceptable Section XI Code Case for use. TMI, Unit 1 proposes to use Revision 1 to Code Case N-638 as part of the replacement of Alloy 82/182/600 penetrations on the TMI, Unit 1 pressurizer during the upcoming Fall 2005 refueling outage. Code Case N-638-1 was included in proposed Revision 14 to Regulatory Guide 1.147 as discussed in Federal Register Notice FR 46597, dated August 3, 2004 (issued as Draft Regulatory Guide DG-1125, Inservice Inspection Code Case Acceptability, ASME Section XI, Division l, dated April 2004). Revision 14 has not yet been formally approved by the NRC.
Current plans are to utilize Code Case N-638-1 to perform modifications of the 1-inch vent nozzle located on the top of the pressurizer. As discussed in a conference call with the NRC on July 7, 2005, TMI, Unit 1 has embarked on an extensive mitigation strategy for Alloy 82/182/600 pressurizer welds. Of the 16 pressurizer penetrations containing Alloy 82/182/600 that were identified in our July 27, 2004 response to Bulletin 2004-01 (Reference 2), current plans have been established to mitigate the identified welds during the upcoming outages. These plans include mitigation of seven (7) locations in the upcoming fall of 2005 refueling outage (T1 R16) which include the I-inch vent nozzle located on the top of the pressurizer. This line is identified in Figure 2A of our response to Bulletin 2004-01 (Reference 2).
Current Code requirements require a 300F minimum preheat temperature when welding on the pressurizer head base material including maintenance thereof for two (2) hours after completion of the 3/16 inch of weld deposit. In order to perform this treatment on the 1-inch vent nozzle weld pad, an additional radiation dose of 700 mRem to 1 Rem is expected. TMI, Unit 1 will avoid this additional dose through the use of Code Case N-638-1, in its entirety. TMI, Unit 1 will also comply with the additional condition specified in the draft Revision 14 to Regulatory Guide 1.147 concerning UT examinations as stated below:
UT volumetric examinations shall be performed with personnel and procedures qualified for the repaired volume and qualified by demonstration using representative samples which contain construction type flaws. The acceptance criteria of NB-5330 in the 1998 Edition through 2000 Addenda of Section I l l apply to all flaws identified within the repaired volume.
TMI, Unit 1 Proposed Alternative to 10 CFR 50.55a Page 3 Framatome ANP, the modification vendor, will be developing the appropriate techniques to address this additional condition.
Performing the heat treatments is also expected to add 36 additional hours to the modification.
As discussed in the Reply section of Code Case N-638, this Code Case can be applied
...without the specific preheat or post weld heat treatment of the Construction Code, when it is impractical, for operational or radiological reasons, to drain the component...
Code Case N-638 would not be applicable to the modification of the 1 -inch line because the preheat and post weld heat treatment does not require the draining of the component (i.e., the pressurizer).
The applicability of this Code Case was revised in the Reply section of Code Case N-638-1 such that this revision of the Code Case can be applied to the I-inch vent nozzle modification. The Reply section was revised to state that this Code Case can be applied I...without the specific preheat or postweld heat treatment of the Construction Code, when it is impractical to drain the component or impractical for radiological reasons.
This administrative clarification provided in Code Case N-638-1 extends the impracticality to draining the component or impractical for radiological reasons. The previous version (Code Case N-638) was only applicable to the impracticality associated with the draining of the component, and the radiological consequences involved in draining the component.
Therefore, Code Case N-638-1 would be applicable to the 1 -inch vent nozzle modification because, as stated previously, performing the modification in accordance with the ASME Code requirements would result in an additional radiation dose of 700 mRem to 1 Rem, which is a provision described in Code Case N-638-1. TMI, Unit 1 will avoid this additional dose through the use of Code Case N-638-1, in its entirety, and the application of the additional condition specified in the draft Regulatory Guide 1.147, Revision 14.
The technical content of the code cases remain essentially the same.
Based on the previous NRC acceptance of Code Case N-638, and the administrative clarification provided in the Reply section of N-638-1, use of Code Case N-638-1 with the additional draft Regulatory Guide 1.147, Revision 14 condition will provide an acceptable level of quality and safety.
A Description of the Modification that will be used for the vent nozzle modification, including a discussion of the modification, the procedure qualification and weld quality, is contained in Attachment 2.
Duration of ProDosed Alternative TMI, Unit 1 is requesting the use of the Code Case in its entirety, for the remainder of the interval for all Class 1 components, as specified in the Code Case.
TMI, Unit 1 Proposed Alternative to 10 CFR 50.55a Page 4 References
- 1) NRC Bulletin 2004-01, Inspection of Alloy 82/182/600 Materials Used in the Fabrication of Pressurizer Penetrations and Steam Space Piping Connections at Pressurized-Water Reactors, dated May 28, 2004
- 2) Letter from K. Jury (Exelon Generation Company, LLC and AmerGen Energy Company, LLC) to U. S. Nuclear Regulatory Commission, dated July 217, 2004
ATTACHMENT 2 Description of the Modification Description of the Modification Page 1 The vent nozzle is a small bore Alloy 600 nozzle that penetrates the upper head of the pressurizer.
AmerGen plans to perform the half-nozzle modification on this penetration as described below (see Figure 1):
a) The attached vent piping will be removed from the nozzle.
b) A portion of the existing Alloy 600 nozzle outside the pressurizer head and the original NiCrFe weld pad surrounding the vent nozzle will be removed.
c) A weld buildup (i.e. -weld pad) will be deposited at the outer surface of the pressurizer head centered at the vent nozzle opening. The weld pad will be deposited using the Machine Gas Tungsten Arc Welding (GTAW) ambient temperature temper bead process and austenitic stainless steel filler metal.
d) The weld pad will then be prepared to accept a new austenitic stainless steel nozzle that is attached using a partial penetration J groove weld using austenitic stainless steel filler metal.
e) The austenitic stainless steel piping will be welded to the new nozzle using austenitic stainless steel filler metal.
The original NiCrFe (Alloy 82/182) nozzle to head weld and a portion of the original Alloy 600 nozzle within the pressurizer head wall thickness will remain in place at the junction of the nozzle to pressurizer head inside surface. The original weld will no longer function as the pressurizer pressure boundary nozzle to pressurizer head weld.
The use of the ambient temperature temper bead repair described in Code Case N-638-1 is proposed to be used only for the weld pad application in the modification process.
A)
Procedure Qualification Results of procedure qualification work undertaken to date on P-No. 1 Group No. 2 and P-No. 3 Group No. 3 base material indicate that the ambient temperature temper bead process produces sound and tough welds. Industry experience also indicates that the GTAW temper bead process has the capability of producing acceptable welds on P-No.3 Group No. 3 as well as P-No.1 Group No. 2 ferritic steel base materials.
To ensure the acceptability of the process for the current application, Framatome, ANP (FANP) has reviewed prior welding procedure qualification test data using machine GTAW ambient temperature temper bead welding on low alloy steel P-NO.3 Group No. 3 base materials in accordance with Code Cases N-638 and N-638-1. The qualifications were performed at room temperature under similar conditions as the current application.
The results of this procedure qualification work indicate that the process produces sound and tough welds.
The existing qualification work can be compared to the current process. Specifically, the existing Code Case N-638 and N-638-1 qualifications were performed on P-No. 3 Group No. 3 base materials, which have a higher hardenability and propensity for hydrogen embrittlement than the pressurizer head base material (P-No. 1 Group No. 2). These Description of the Modification Page 2 qualifications used similar low heat input controls as will be used in this application.
These qualifications did not include a post weld heat soak. The successful qualification of the ambient temperature temper bead welding process demonstrates that the proposed alternative provides an acceptable level of quality and safety.
FANP has completed a machine GTAW procedure qualification record (PQR) using P-No.1 Group No. 2 test assembly base material. This material is the same P-No. Group No. base material as the pressurizer head base material and A-No. 8, F-No. 6 austenitic stainless steel filler metal which is the same A-No. and F-No. as will be used on the pressurizer weld pad.
The base material used in the PQR test coupon was SA-516 Grade 70. The test plate was 3% in. thick and the groove was 1 in. deep. At least 6 in. of full thickness base material surrounded the cavity. The maximum interpass temperature was less than 150°F during welding.
B) Weld Quality The repair technique has been demonstrated as an acceptable method for performing pressurizer nozzle modifications. The ambient temperature temper bead technique has been approved by the ASME Committee per Code Cases N-638 and N-638-1. The ambient temperature temper bead technique has also been previously approved by the NRC as having an acceptable level of quality and safety (Three Mile Island, Unit I (NRC Safety Evaluation Report dated July 21, 2004), and Crystal River, Unit 3 (NRC Safety Evaluation Report dated January 6,2004)). Code Case N-638 has also been approved in Regulatory Guide 1.147 Revision 13 and Code Case N-638-1 has been included in the proposed Revision 14 of Regulatory Guide 1.147.
As documented in EPRl Report GC-111050, Ambient Temperature Preheat for Machine GTAW Temperbead Applications, dated November 1998, carefully controlled heat input and bead placement allow subsequent welding passes to relieve stress and temper the Heat Affected Zone (HAZ) of the base material. The use of the machine GTAW temper bead process will allow precise application of highly controlled weld beads. The very precise control over these factors afforded by the machine GTAW process provides effective tempering of the HAZ.
The machine GTAW temper bead process uses a welding process that is inherently free of hydrogen. The GTAW process relies on bare welding electrodes and bare wire filler metal with no flux to trap moisture. An inert gas blanket provides shielding for the weld and surrounding metal, which protects the region during welding from the atmosphere and the moisture it may contain and typically produces porosity free welds. In accordance with the weld procedure qualification, welding grade argon is used for the inert gas blanket. To further reduce the likelihood of any hydrogen evolution or absorption, specific controls to ensure the non-consumable welding electrodes, filler metal and weld region is free of all sources of hydrogen will be used. Argon flow rates are adjusted to assure adequate shielding of the weld without creating a venturi affect that might draw oxygen or water vapor from the ambient atmosphere into the weld.
Description of the Modification Page 3 Typically preheat and post weld heat treatment are used to mitigate the effects of the solution of atomic hydrogen in ferritic materials prone to hydrogen embrittlement cracking. The susceptibility of ferritic steels is directly related to their ability to transform to martensite with appropriate heat treatment. The P-No. 1 Group No. 2 material of the pressurizer head is able to produce martensite from heating and cooling cycles associated with welding; however, it is much less susceptible to martensite formation than P-No. 3 Group No. 3 base material.
In accordance with Code Case N-638-1, and as specified in the process control documents, the surface to be welded around the pressurizer vent nozzle penetration will be cleaned to ensure freedom from potential sources of hydrogen. Appropriate controls will also be implemented on the filler metal used as well as the shielding gas.
The first three layers will be deposited, to obtain at least a 118 in. minimum thickness, using austenitic stainless steel filler metal using machine GTAW and cold wire feed. The heat input will be controlled within *lo% of the heat input used during the welding procedure qualification.
Particular care will be taken in placement of weld layers beyond the first layer, near the weld toe, to ensure the HAZ is properly tempered.
The balance of welding, beyond the third layer, will be deposited with heat inputs within the maximum used during the procedure qualification.
A thermocouple(s), supplemented by a contact pyrometer(s), will be used to insure maximum interpass temperature of 350°F is met during welding.
Description of the Modification Page 4 FIGURE 1 Half-Nozzle Modification Weld Pad Original Nozzle Remnant Original Structural J Weld Remnant