ML20059L252
| ML20059L252 | |
| Person / Time | |
|---|---|
| Issue date: | 11/03/1993 |
| From: | Conrad H Office of Nuclear Reactor Regulation |
| To: | Strosnider J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 9311160396 | |
| Download: ML20059L252 (5) | |
Text
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MEMORANDUM FOR:
Jack R. Strosnider, Chief Materials and Chemical Engineering Branch Division of Engineering THRU:
Edmund J. Sullivan, Chief Inservice Inspection Section Materials and Chemical Engineering Branch FROM:
Herbert F. Conrad, Sr. Materials Engineer Materials and Chemical Engineering Branch l
Division of Engineering
SUBJECT:
SUMMARY
OF MEETING HELD ON SEPTEMBER 8, 1993 WITH WESTINGHOUSE ON THE STATUS OF THE STEAM GENERATOR DIRECT TUBE REPAIR PROGRAM t
On September 8, 1993, the NRC staff met with representatives of Westinghouse Electric Corporation to discuss the status of the steam generator direct tube repair (DTh) program. Also in attendance were representatives of Southern Nuclear Co. (Farley Nuclear Plant), Duquesne Light Co. (Beaver Valley Power t
Station) and Commonwealth Edison Co. (Byron and Braidwood Units).
Westinghouse has provided the NRC with two versions of the view graphs and r
hand-outs used during the meeting: WCAP-13866 (Proprietary) and WCAP-13867 (Non-Proprietary), " Presentation Materials, September 8, 1993, DTR Status Meeting", September 1993. The list of attendees is attached.
(Enclosure 1)
Westinghouse and the NRC discussed the overall program, strategies, recent process developments, qualification plan, and schedules involving successful licensing of the Direct Tube Repair (DTR) program. The intent of the meeting was to update the NRC of recent process advancements and to discuss the qualification test plan.
The following topics were discussed by Westinghouse:
1.
Status of weld process development 2.
Inspectability issues and test results 3.
DTR qualification test descriptions 4.
Qualification test plan methodology The purpose of the meeting was to discuss the QualificatSn Test Matrix which was briefly discussed in the first meeting of June 29, 1993. Westinghouse presented the qualification test matrix and outlined test samples used to develop the crack propagation characteristics and the leak and burst i l' characteristics of a DTR intersection.
In addition, Westinghouse discussed d,
advancements made in the DTR process development. Westinghouse stated that
'W they would update the NRC on developments in the process as they occur in dfM o (k/ ]/
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i order to expedite the review and approval of the DTR program. The meeting was-intended to present the particulars of the test matrix and stimulate feedback from the NRC.
The detailed content of the discussions is considered to be proprietary information by Westinghouse, however Westinghouse has supplied the i
following non-proprietary summary:
LASER WELDED DIRECT TUBE REPAIR PROCESS FOR STEAM GENERATORS The Direct Tube Repair (DTR) process is based on the restoration of degraded tubes in steam generators by the controlled melting of the tube wall from the inside surface using the focused energy of a laser beam. The process is autogenous, i.e., does not require a filler metal.
The objective is to either heal the crack completely by melting or restore up to 80 percent of the tube wall thickness.
Westinghouse believes that the process can be used to repair axial or circumferential cracks initiated from either the inside or outside surface of the tube. They expect post-weld stress relief to provide acceptable corrosion margins and that the integrity of the repair can be verified using conventional non-destructive examination (NDE) methods such as eddy current or ultrasonic testing.
The driving force for the development of the DTR process is that current mechanical methods for addressing steam generator tube degradation, such as plugging and sleeving, have inherent drawbacks.
Both those approaches reduce flow through the generator and, beyond a certain point, adversely affect plant performance. The DTR process would have an insignificant effect on the thermal-hydraulic performance of the steam generator.
It could be applied to address degradation in tubes that are currently plugged (after deplugging),
j above the existing sleeved sections of tubing, above dented tubes, and in the peripheral regions of the generator that are currently inaccessible for j
repair.
Development work on the DTR process was initiated by Westinghouse at their Corporate Science & Technology Center in 1990. A limited amount of testing on the autogenous weld repair approach yielded encouraging results. Testing performed in 1992 at the Waltz Hill Site included making welds in tubes with j
simulated axial and circumferential indications, with secondary side moisture,
'and with oxidized tubes. The effects of stress relief on mechanical properties has been investigated. The inspectability of the DTR welds using eddy current and ultrasonic techniques has been studied. Mechanical (burst and tensile) and accelerated corrosion tests have been also performed on weld samples.
According to Westinghouse, mechanical strength data showed a slight i
reduction for deep weld repairs, but still within ASME Code limits.
Ongoing work is focused on optimizing weld process parameters prior to developing a comprehensive data base on mechanical properties, corrosion life, residual crack propagation, etc., using welds made on degraded samples. Both PWSCC and OSDCC degradation mechanisms are being addressed.
1
-1 4
Westinghouse has prepared an ASME BPVC Code Case Inquiry seeking approval of 1
the DTR process for steam generator tube repair under Section XI rules. The supporting data for securing ASME approval will be the same as the NRC i
licensing data base, 1
The staff noted that the following issues need to be resolved:
1.
Section XI requires that cracks be removed prior to performing repair welding.
The licensee should address complif.. 1 with the ASME B&PV Code or the regulatory basis for its acceptance.
2.
What is the technical basis for the return to service of tubes with cracks under the repaired area of the tube?
3.
Will a qualiiiration program be used to validate the inspectability of the DTR repaired tube in order to demonstrate the soundness of the repaired region and meet the requirements of periodic inservice inspection.
If inspection of the repaired tube will not be conducted to demonstrate its soundness, explain why process control is considered adequate.
4.
Qualification of inspection methods to support examination of repaired areas of tubes in accordance with technical specification inservice inspection requirements and establishment of post DTR tube repair criteria.
4 5.
Will a test loop such as was done to qualify materials for use in BWR's be used for more realistic corrosion testing?
OrtiGMi. 3d?: '. :
Herbert F. Conrad, Sr. Materials Engineer Materials and Chemical Engineering Branch Division of Engineering DISTRIBUTION:
Central Files EMCB RF HConrad ESullivan DE RF R.,fssa Fublic Document Room
- SEE PREVIOUS CONCURRENCES or ncE
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- DE:EMCB NAME HConrad:tc ESullivan JStrosnider DATE 10/18/93 10/18/93 11/1/93 0FFICIAL RLCORD COPY FILENAME: G:\\CONRAD\\
SUMMARY
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ENCLOSURE 1
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List of Attendees Name Reoresemine H. F. Conrad NRC/EMCB R. A. Hermann NRC/NRR A. G. Panagos CECO G. Kammmiciner Duquesne Light J. Houtman Wesunghouse T. Spry CECO R. E. Mullins Southern Nuclear D. E. Mansfield Southern Nuclear T. A. Pitterle W#n.Amse W. R. Junker W#nghause R. J. Jacko W#nghause B. R. Nair Westinghouse M. D. Hecht Westmghouse G. W. Whiteman Wein*hnuse W. Cullen W#nghe=taa C. Hsu NRC/AEOD K. J. Karwoski NRC/EMCB R. Assa NRC/NRR E. Murphy NRC/EMCB J. B. Hickman NRC/DRPW J. Bmer CECO R. Gesier CECO 9
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l Westinghouse has prepared-an ASME B?VC Code Case Inquiry seeking approval of I
the DTR process for steam generator tube repair under Section XI rules. The supporting data for securing ASME approval will be the same as the NRC licensing data base.
The staff noted that the following issues need to be resolved:
~
l
' 1.
Section XI requires that cracks be removed prior to performing repair l
welding. The licensee should address compliance with the ASME B&PV Code.
~
or the regulatory basis for its acceptance.
2.
What is the technical basis for the return to service of tubes with.
cracks under the repaired area of the tube?
4 3.
Will a qualification program be used to validate the inspectability of i
the DTR repaired tube in order to demonstrate the soundness of the repaired region and meet the requirements of periodic inservice inspection.
If inspection of the repaired tube will not be conducted to demonstrate its soundness, explain why process control is considered adequate.
4.
Qualification of inspection methods to support examination of repaired areas of tubes in accordance with technical specification inservice 3
inspection requirements and establishment of post DTR tube repair f
criteria.
S.
Will a test loop such as was done to qualify materials for use in BWR's be used for more realistic corrosion testing?
[
Herbert F.
onrad, Sr. Materials Engineer Materials and Chemical Engineering Branch Division of Engineering DJSTRIBUTI0th Central Files EMCB RF HConrad ESullivan DE RF
- SEE PREVIOUS CONCURRENCE
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0FFICIAL RECORD COPY FILENAME: G:\\CONRAD\\
SUMMARY
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