ML20210B424

Discusses AEC 721213 Request for Addl Info Re Facility Torus Header Support Design.Items 1-3 Will Be Available in Mar 1973 When GE Analysis Completed.Listed Repairs Corrected Deficiencies in Sys as Reported in 720705 & 1206 Ltrs

ML20210B424
Person / Time
Site:	Monticello, 05000000
Issue date:	01/12/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20209J032	List: ML20209J028 ML20209J102 ML20209J362 ML20209J414 ML20209J428 ML20209J450 ML20209J504 ML20210A204 ML20210A316 ML20210A365 ML20210A410 ML20210A454 ML20210A522 ML20210A538 ML20210A585 ML20210A633 ML20210A720 ML20210B005 ML20210B037 ML20210B073 ML20210B140 ML20210B165 ML20210B193 ML20210B233 ML20210B262 ML20210B269 ML20210B312 ML20210B376 ML20210B424
References
FOIA-87-40 363, NUDOCS 8705050314
Download: ML20210B424 (2)

Text

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. HS9 NORTNERN 5TATES POWER COMPANY MIN N S A PO kt e. MIN N E S OTA 5 5 40,

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Mr. Donald J. Skovholt D 'M" Assistant Director for Operating Reactors Directorate of Licensing k -

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United States Atomic Energy Commission w # M 5 ' 2.b Washington, D. C. 20545 Dear Mr. Skovhoitt MONTICELLO NUCLEAR CENERATING PLANT Docket No. 50-263 License No. DPR-22 Information Relating to Torus Ring Header Supports Your letter of December 13, 1972, requested five pieces of information concerning the adequacy of the Monticello torus ring header support design. In the event the specified information could not be obtained within 30 days, a schedule for sub-mitting it to the Commission was to be provided.

Requested Items 1, 2, and 3 will be available in March, 1973 when analyses being conducted by the General Electric Company are scheduled to be completed. A reply will be prepared, including Itema 4 and 5. following completion of this investi-gation.

The General Electric investigation is based on testing conducted in October, 1972 at the Quad uities Plant. It is intended that conclusions will be reported on a generic b. asis. Results obtained to date indicate that there is no reason for concern over the design of the Monticello ring header. Indications of possible design deficiencies which may arise during the course of the investigation will be immediately made known to the Commission and the utilities involved. Further-more, is is our understanding that members of the AEC staf f have reviewed the status of this program and the content of the projected report.

Our own experience has indicated that the most likely source of problems experienced with torus ring header supports is improper fabrication and installation. As reported to the Directorate of Regulatory Operations, Region !!!, by letters of July 5,1972, and December 6,1972, the following repairs were necessary at Monti-cello to correct installation deficiencies in the systems

1. Umraded, fully threaded bolts were replaced with ASME Grade A325 bolts with no threads in the load bearing region. Bolts were fitted with locking nuts.

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F Mr. Donald J. Skovholt 2 January 12, 1973

2. All torch-cut bolt holes were filled and replaced with drilled holes.

3. Torus butt plates and padeyes were welded all around with 1/4-inch fillet.

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4. All hanger welds were subjected to magnetic particle inspection.

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5. Static load analysis was conducted and all hanger loads were balanced.

These repairs restored the torus ring header support system to original design conditions. In addition, the substitution of the higher strength bolt (original design bolt was ASME Grade A307) has resulted in a substantial upgrading of the ability of the system to withstand dynamic loading.

Yours very truly, W o.

L. O. Mayer, p.E.

Director of Nuclear Support Services t.oM/DMM/vm cc B. H. Crier l

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