ML20024G549
| ML20024G549 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 01/12/1973 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102120644 | |
| Download: ML20024G549 (3) | |
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NORTHERN STATES POWER C0MPANY M I N N EC A P O L. l e. M I N N E S O T A 9940t Q) v.
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Mr. Donald J. Skovholt
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Assistant Director for Operating Reactors
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Directorate of Licensing United States Atomic Energy Commission 7, g',
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Dear Mr. Skovholt:
MONTICELLO NUCLEAR GENERATING 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 tne 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 Items 4 and 5, following completion of this investi-gation.
The General Electric investigation is based on testing conducted in October, 1972 at the Quad Cities Plant.
It is intended that conclusions will be reported on a generic basis.
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, it is our understanding that members of the AEC staff 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 prob 1ces experienced 1
with torus ring header supports is improper fabrication and installation.
As reported to the Directorate of Regulatory operations, Region III, by letters of July 5, 1972, and December 6, 1972, the following repairs were necessary at Monti-cello to correct installatien deficiencies in the system:
1.
l'rgraded, fully threaded bolts were replaced with l
ASME Grade A325 bolts with no threads in the load l
bearing region.
Bolts were fitted with locking l
nuts.
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'4 9102120644 $$$6a I
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January 12, 1973 2.
All torch-cut bolt holes were filled and repinced with L
drilled holes.
I 3.
Torus butt plates and padeyes were welded all around with 1/4-inch f111et.
4.
All hanger velds were subjected to magnetic particle inspection.
5.
Static load analysis was conducted and all hanger loads were balmiced.
I These repairs restored the torus ring header support system to original design I
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 leading.
Yours very truly.
ha L. O. Mayer, p.E.
Director of Nuclear Support Services LJM/DMM/vm cc B. H. Grier i
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