ML17180A835
| ML17180A835 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities  |
| Issue date: | 07/21/1994 |
| From: | Stang J Office of Nuclear Reactor Regulation |
| To: | Farrar D COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML17180A838 | List: |
| References | |
| TAC-M89493, TAC-M89871, NUDOCS 9407250053 | |
| Download: ML17180A835 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 Docket Nos. 50-249 and 50-254 Mr. D. L. Farrar Manager, Nuclear Regulatory Services Commonwealth Edison Company Executive Jowers West III, Suite 500 1400 OPUS Place Downers Grove, Illinois 60515
Dear Mr. Farrar:
July 21, 1994.
SUBJECT:
RESOLUTION OF CORE SHROUD CRACKING AT DRESDEN, UNIT 3, AND QUAD CITIES, UNIT 1 (TAC NOS. M89871 AND M89493)
During current refueling outages, Commonwealth Edison Company (ComEd or the licensee) discovered cracking in the circumferential welds in the core shrouds at Dresden, Unit 3, and Quad Cities, Unit 1.
By letter dated June 13, 1994, ComEd concluded, based upon its analyses, 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) for 24 months for Dresden, Unit 3 and for 18 months for Quad Cities, Unit 1.
ComEd has provided additional information in response to requests by the NRC staff.
Section 4.0 of the enclosed Safety Evaluation (SE) provides a detailed listing of all correspondence ComEd has provided.
The staff evaluated ComEd's June 13, 1994, submittal and all supplemental documentation in accordance with 10 CFR 50.55a to determine if the degraded shrouds have adequate safety margins to meet the requirements of the ASME Code.
The staff also evaluated.the potential risks associated with cracked shroud operation that were not considered as part of the original licensing basis.
During 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 enclosed SE, ComEd is 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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- 2.
the WHAM calculations for the recirculation line break, including assumptions and entry level conditions, and
- 3.
a detailed analysis of shroud movement, assuming a 360° through-wall crack, following postulated events, including all assumptions, entry level conditions, calculational techniques, and conservatisms.
In your evaluation of seismic considerations, the analysis should be based on the most limiting seismic input motion (i.e., Golden Gate Park, time history, and El Centro, and Housner).
While, based on its assessment, ComEd has proposed operation for a full cycle, considering the uncertainties identified above, coupled with the staff disallowing any enhancement of the structural integrity of the shroud. by the presence of the inside diameter fillet weld at HS in its analysis, the staff's conservative evaluation has concluded that the cracked shrouds will satisfy ASME Code margins against weld failure for 15 months of operation above cold shutdown.
Satisfying the ASME Code margins against failure provides reasonable assuiance that the core shrouds at Dresden, Unit 3, and Quad Cities, Unit 1, will -remain intact, even under postulated licensing basis and beyond licensing basis accident conditions. Therefore, Dresden, Unit 3, and Quad Citie~. Unit 1, can be safely returned to operation without undue risk to the public health and safety.
ComEd has indicated that over the nexi 6 months, plans for a permanent repair of the entire core shroud will be developed.
These plans should be discussed with the staff at the earliest opportunity.
The reporting and/or recordkeeping requiremeQts contained in this letter affect fewer*than ten respondents; therefore, OMB clearance is not necessary under P. L 96-511.
If you have any questions concerning this SE, please contact Mr. John Stang at.
(301) 504-1345.
Enclosure:
Safety Evaluation cc w/enclosure:
See next page Sincerely,
~~~i~
John F. Stang, Pfoject Manager Project Directorate 111-2
- Division of Reactor Projects - Ill/IV Office of Nuclear Reactor Regulation
,..i
--i Mr. D. L. Farrar e
- 2) -
e July 21, 1994 LA:PO I I I -2
- 2.
- 3.
the WHAM calculations for the recirculation line break, including assumptions and entry level conditions, and a detailed analysis of shroud movement, assuming a 360° through-wall crack, following postulated events, including all assumptions, entry level conditions, calculational techniques, and conservatisms.
In your evaluation of seismic considerations 1 the analysis should be based on the most limiting seismic input motion (i.e., Golden Gate Park, time history, and El Centro, and Housner).
While, based on its assessment 1 ComEd has proposed operation for a full cycle, considering the uncertainties identified above, coupled with the staff disallowing any enhancement of the structural integrity of the shroud by the presence of the inside diameter fillet weld at HS in its analysis the staff's conservative evaluation has concluded that the cracked shrouds wiil satisfy ASME Code margins against weld failure for 15 months of operation above cold shutdown.
Satisfying the ASME Code margins against failure provides reasonable assurance that the core shrouds at Dresden, Unit 3, and Quad Cities, Unit l, will remain intact, even under postulated licen~ng basis and beyond licensing basis accident conditions. Therefore, Dresden, Unit 3, and Quad Cities? Unit 1, can be safely returned to operation without undue risk to the public nealth and safety.
ComEd has indicated that over the next 6 months, plans for a permanent repair of the entire core shroud will be developed.
These plans should be discussed with the staff at the earliest opportunity.
The reporting and/or recordkeeping requirements cont~ined in this letter affect fewer than ten respondents; therefore, OMB clearance is not necessary under P. L.96-511.
If you have any questions concerning.this SE, please contact Mr. John Stang at (301) 504-1345.
\\._
Enclosure:
Safety Evaluation cc w/enclosure:
See next page 0: POii I -2 Sin-cerely, Original signed by:
John F. Stang, ~roject Mariager Project Directorate 111 Division of Reactor Projects - Ill/IV Office of Nuclear Reactor Regulation 7 121/94 YES/NO YES/NO ISTRIBUTION:
NRC & Local PORs POI 11-2 r/f (2)
R. Zinmerman A. rh*adani J. Roe I
C. Moore (2)
J. Stang c.* Patel E. Butcher M. Rubin II t r I. -
I I
I I
I I
'I I OGC
-. o.~rinkman ACRS (10) 7 J. Zwol1nsk1 USS YES/NO
Mr. 0. L. Farrar Commonwealth Edison Company cc:
Michael I. Miller, Esquire Sidley and Austin One First National Plaza Chicago, Illinois 60690 Mr. G. Spedl
.Pl ant Manager Dresden Nuclear Power Station 6500 North Dresden Road Morri~,.Illinois 60450-9765 U. S. Nuclear Regulatory Commission Resident Inspectors Office Dresden Station 6500 North Dresden Road Morris, Illinois 60450-9766
- Chairman Board of Supervisors of Grundy County Grundy County Courthouse Morris, Illinois 60450 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 Mr. Stephen E. Shelton Vice President Iowa-Illinois Gas and Electric Company P. 0. Box 4350 Davenport, Iowa 52808 Mr. Guy Campbell Station Manager Quad Cities Nuclear Power Station 22710 206th Avenue North Cordova, Illinois 61242 Dresden Nuclear Power Station, Unit 3 Quad Cities, Unit 1 Quad Cities Resident Inspectors Office U. S. Nuclear Regulatory Commission 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