ML17180A801

Forwards RAI Re Core Shroud Cracking at Facilities

ML17180A801
Person / Time
Site:	Dresden, Quad Cities
Issue date:	06/23/1994
From:	Stang J Office of Nuclear Reactor Regulation
To:	Farrar D COMMONWEALTH EDISON CO.
References
NUDOCS 9406300047
Download: ML17180A801 (6)

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June 23, 1994

Docket Nos. 50-249 and 50-254 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:

REQUEST FOR ADDITIONAL INFORMATION CONCERNING CORE SHROUD CRACKING AT DRESDEN, UNIT 3, AND QUAD CITIES, UNIT 1 By letters dated June 6, 1994, June 13, 1994, and June 14i 1994, the Commonwealth Edison Company (CECo) provided additional information concerning the cracking of the core shroud and justification for the operation of Dresden, Unit 3, and Quad Cities, Unit l, with the degraded shrouds.

Based on the NRC staff review of the information, the staff finds that the additional information is required to allow the staff to justify restart of Dresden, Unit 3, and Quad Cities, Unit 1, with the degraded core shrouds.

Please provide a response in writing by Monday, June 27, 1994.

This schedule is based on the NRC staff review of the information and providing a safety evaluation prior to restart of Dresden, Unit 3, on j~ly 10, 1994.

The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance i~ not required under P.L.96-511.

If you have any questions concerning this action, please contact me at (301) 504-1345.

Sincerely,

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I Original signed by Chandu Patel for John F. Stang, Project Manager Project Directorate 111-2 Division of Reactor Projects - Ill/IV Office-of Nuclear Reactor Regulation

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Mr. D. L. Farrar Commonwealth Edison Company cc:

Michael I. Miller, Esquire Sidley and Austin One First National Plaza Chicago, Illinois 60690 Mr. G. Spedl Plant Manager Dresden ~uclear 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 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 Dresden Nuclear Power Station Unit No. 3

Mr. D. l. Farrar Commonwealth Edison Company cc:

Mr. Stephen E. Shelton Vice President Iowa-Illinois Gas and Electric Company P. 0. Box 4350 Davenport, Iowa 52808 Michael I. Miller, Esquire

• Sidley and Austin One First National Plaza Chicago, Illinois 60690 Station Manager Quad Cities Nuclear Power Station 22710 206th Avenue North Cordova, Illinois 61242 Quad Cities Resident Inspectors Office U. S. Nuclear Regulatory Commission 22712 206th Avenue North Cordova, Illinois 61242 Chairman Rock Island County Board 0f Supervisors 1504 3rd Avenue Rock Island County Office Bldg.

Rock Island, Illinois 61201 Illinois Department of Nuclear Safety Office of Nuclear Facility Safety 1035 Outer Park Drive Springfield, Illinois 62704 Regional Administrator*

U. S. NRC, Region.III 801 Warrenville Road Lisle, Illinois 60532-4351 Quad Cities Nuclear Power Station Unit No. 1

MATERIALS QUESTIONS REQUEST FOR ADDITIONAL INFORMATION CONCERNING CORE SHROUD CRACKING AT DRESDEN. UNIT 3. AND QUAD CITIES. UNIT 1 DOCKET NOS. 50-249 AND 50-254

1.

Provide for both Dresden, Unit 3, and Quad Cities, Unit 1, the number of effective full power years of operation.

2.

Provide information concerning the reactor coolant water chemistry for both units from the time of startup to the present and its effect on the core shroud cracking.

3.

Provide justification that the 45 degree Ultra Sonic (UT) transducer would reliably detect all cracks in the core shroud if the cracking is tight or geometry is unfavorable.

In addition, the justification should provide a detailed explanation of why bounding flow depth at the H5 weld is 1.241 inches.

4.

Provide justification to rule out cracking coming from the inside of -

shroud at the H5 weld from the toe of the fillet weld.

5.

Provide a map of the UT measurements on the H5 weld.

6.. ~

Provide a comparison of the Boiling Water Reactor Owners Group core shroud screening criteria to that used for the Dresden and Quad Cities core shroud inspection.

7.

Is the Dresden and Quad Cities H5 fabrication similar to that of Brunswick (i.e., double V grooved, backgouged)?

8.

Provide verification of the dimension of the fillet weld.

9.

Provide justification that the crack growth rate in your June 13, 1994, submittal is bounded based on the water chemistry during the early years of operation at Dresden and Quad Cities. _Could deeper cracks be expected based on water chemistry?

10.

Provide justification that crack propagation path predictions have correctly incorporated the effects of residual stresses. Could the crack propagate through an alternate path (i.e., up through the cylinder)?

11.

Provide stress distribution profile information across the H5 weld.

12.

What is the status of the use of hydrogen addition to the reactor coolant at Dresden and Quad Cities.

13.

Provide the detailed results of the Dresden and Quad Cities boat sample metallurgical analyses.

14.

Provide a detailed justification and clarification for the bases of crack depth sizing on the H5 weld geometry using only UT detection capability.

15.

What are the fracture toughness properties in the short transverse direction for the heavy stainless steel plate of the top guide support ring and the core plate support ring?

16.

Justify why limit load analysis is appropriate for the stress distributions associated with the H5 weld and fillet finite element analysis.

Is bending appropriately considered?

17.

What is the predicted/measured reduction in residual stresses with the cracking at the H5 weld?

18.

Provide an assessment of the operating margin against uncertainties in the approach used to size the H5 weld crack by UT.

Probabilistic Questions I.

Provide the probabilities and bases of the design bas~s events as well as the data sources for the postulated event frequency.

Also, provide

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the contribution to the core damage frequency and release frequency for these events.

2.

Are the shroud cracks in conjunction with the steamline break or recirculation pipe break events incorporated in the IPE study? If so, provide the information.

Mechanical Engineering Questions

1.

Provide complete structural/mechanical analysis of the core shroud, assuming worst-case degradation of the H5 weld up to and including a 360-degree thru wall crack at H5 for upset, emergency and faulted plant conditions (e.g., main steam line break (MSLB), recirculation line break (RCLB), SSE and most severe load combinations).

Evaluate the effect of three-dimensional shroud movement (e.g., uplift/tilting and subsequent dropping, tilting, lateral motion, etc.)* on the structural integrity and functionality of reactor internal components,. equipment and support structures.

Analysis package should fully describe all analytical assumptions with justifications, conservatisms, methodology (e.g., analytical models and boundary constraints, development and application of loads, stress and deflection calculations}, and conclusions.

Also provide information to verify that any computer codes used in the analysis have been properly benchmarked.

y Reactor Systems Questions

1.

What is the total flow value of the LPCI system under accident conditions (i.e., LOCA, large break and steamline break) with postulated worst-case single failure, and what are the limiting single failure assumptions applied and their impacts on injection flow?

2.

What is the minimum core water level needed to assure adequate cooling following a OBA LOCA?

3.

Provide the operating and design basis faulted condition loads for the H5 weld.

Identify the methodologies for determining the faulted condition loads and justify why the methodologies,are appropriate (e.g.,

WHAM, RETRAN, approximate 3-D blowdown flow analysis).

Provide all assumptions with justification conservatisms and initial and final conditions.

In addition, provide all benchmarking and experimental data to justify the use of a 11 codes.

4.

Provide unavailibility data. for the following ECCS scenarios:

1 core spray out; 1 LPCI out; both core sprays out; 1 LPCI injection valve unavailable; and common mode LPCI loop-select logic unavailable.

Reanalyses Question

1....

In the May 26, 1994, meeting between the NRC and CECo concerning the core shroud, CECo indicated it would reevaluate continued operation after 6 months if the unit restarted without repairing the H5 weld.

Please provide the details of the proposed reevaluation and all other actions to be taken by CECo.

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