ML17180B337
| ML17180B337 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 08/16/1995 |
| From: | Stang J NRC (Affiliation Not Assigned) |
| To: | Farrar D COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML17180B338 | List: |
| References | |
| NUDOCS 9508210185 | |
| Download: ML17180B337 (3) | |
Text
{{#Wiki_filter:*' UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 August 16, 1995 Mr. D. L. Farrar Manager, Nuclear Regulatory Services Commonwealth Edison Company Executive Towers West III, Suite 500 1400 OPUS Place Downers Grove, Illinois 60515
SUBJECT:
RESOLUTION OF CORE SHROUD CRACKING AT DRESDEN, UNIT 3, AND QUAD CITIES, UNIT 1 (TAC NOS. M91298 AND 91299)
Dear Mr. Farrar:
During refueling outages in the spring of 1994, Commonwealth Edison Company (ComEd) discovered cracking in the circumferential welds in the core shrouds at Dresden, Unit 3, and Quad Cities, Unit 1. ComEd provided documentation for the NRC staff review and approval concluding that the cracked core shrouds could maintain margins against failure as specified in Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code). The NRC staff reviewed the ComEd analysis and by letter dated July 21, 1994, issued a safety evaluation (SE) which concluded that the cracked shrouds will satisfy ASME Code margins against weld failure for 15 months of operation above cold shutdown. During the NRC staff review uncertainties were identified in the following parts of ComEd's analyses:
- 1.
the sizing of the crack in the HS weld;
- 2.
the recirculation line break load analysis; and
- 3.
core shroud movement under postulated accident loads assuming complete failure of the HS weld. The staff's independent evaluation used conservative assumptions to account for the uncertainties identified in ComEd's analyses; however, as discussed in Section 2.6 of the July 21, 1994, SE, ComEd was requested to provide the following confirmatory analyses to the NRC by December 15, 1994:
- 1.
a computerized 3-dimensional asymmetric depressurization analysis for the recirculation line break, including assumptions and entry level conditions,,.
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. 3. the WHAM calculations for the recfrcul_~tio*n 'JJne :~reak', Jnc.lt,Jding assumptions and entry level condition<s,, a~d,. -: -, ~"'... /*'*.:. ~.. ~'... 1,~ ~ff a detailed analysis of shroud moveme~t,~ assti~in~ i~360° through-wall crack, following postulated events, including all assumptions, entry. level conditions, calculational technique~~ arid ~driservatisms. In your evaluation of seismic considerations, the:~analysis should be based on the most limiting seismic input motion (;'}.e. ;**-Golden~Gate Park, time* history, and El Centro, ~nd Housner). By letter dated September 2; 1994, November 15, 1994, and December 14, 199{, ComEd provided additional information to address each of the above uncertainties. The NRC staff has reviewed the ~bove information, and based Qn the enclosed SE,.the NRC ~taff finds the conclusion reached in our July 21, 1994, SE, that the cracked. shrouds will satisfy ASME Code margins against weld failure for 15 months of operation above cold shutdown, remains valid.
- Satisfying the ASME Code margins against failure provides reasonable assurance that.the core shrouds at Dresden, Unit 3, and Q~ad Cities, Unit ),*will.re~ain intact even under postuljted licensing basis and beYond licensing bas~s accident conditions.. Therefore, Dresden, Unit 3, and Quad Cities, Unit 1, ~a~
continue to operate without undue risk to the public h~alt~ and safety.* The NRC staff is ~urrently reviewing plan~ for.a permanent repair of th~ entire cor~ shroud at -Oresden and Qu~d Cities. If you have any questions concern~ng~this SE~ please ionta~t me at . (301) 415~1345.
- Docket Nos.. 50-249 arid 50-254 Enclosu~e:
S~fety.Evaluation cc w/encl.: '*See ne~t page. Sincerely,.. - ~
- original ~igned by.
Jo~n F~ Stang, Project*~anager Project Director~te III-2 Division of Re~cto~ P~ojects - III/IV Office.. o~.'.Nu5l ttar "Re~5to'(* R~gul at ion ~ )
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D. L. Farrar Commonwealth Edison Company cc: Michael I. Miller, Esqu-ire Sidley and Austin One First National Plaza Chicago, Illinois 60603 Mr. Thomas P. Joyce Site Vice President Dresden Nuclear Power Station 6500 North Dresden Road Morris, Illinois 60450-9765 Mr. J. Heffley Station Manager Dresden Nuclear Power Station 6500 North Dresden Road Morris, Illinois 60450-9765 U.S. Nuclear Regulatory Commission Resident Inspectors Office Dresden Station 6500 North Dresden Road Morris, Illinois 60450-9766 Regional Administrator U.S. NRC, Region III 801 Warrenville Road Lisle, Illinois 60532-4351 Illinois Department of Nuclear Safety Office of Nuclear Facility Safety 1035 Outer Park Drive Springfield, Illinois 62704 Chairman Grundy County Board Administration Building 1320 Union Street Morris, Illinois 60450 Dresden Nuclear Power Station Unit Nos. 2 and 3 Quad Cities Nuclear Power Station Unit Nos. 1 and 2 Mr. Stephen E. Shelton Vice President Iowa-Illinois Gas and Electric Company P. 0. Box 4350 Davenport, Iowa 52808 Mr. L. William Pearce Station Manager Quad Cities Nuclear Power Station 22710 206th Avenue North Cordova, Illinois 61242 U.S. Nuclear Regulatory Commission Quad Cities Resident Inspectors Office 22712 206th Avenue North Cordova, Illinois 61242 Chairman Rock Island County Board of Supervisors 1504 3rd Avenue Rock Island County Office Bldg. Rock Island, Illinois 61201 Warren Bilanin, EPRI Task Manager 3412 Hillview Ave~ Palo Alto, California 94303 Robin Dyle, Technical Chairman BWRVIP Assessment Task Southern Nuclear Operating Company Post Office Box 236 40 Inverness Center Parkway Brimingham, Alabama 35201}}