ML19224C486
| ML19224C486 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/20/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 7907020451 | |
| Download: ML19224C486 (1) | |
Text
'o UNITED STATES J (,
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! % s.,1/ *n NUCLE AR REGULATORY COMMISSION
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REGION V REhi o, p'.s,.g g
1990 N. CAllFORN;'k DOULEVARD
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SUITE 202. WALNUT CREE K PLAZA e,,,,
WALNUT CREEK, CALIFORNIA 945%
June 20, 1979 Docket tio. 50-312 Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Attention:
Mr. John J. Mattimoe Assistant General Manager Gentlemen:
This Information flotice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities.
Flo specific action or response is requested at this time.
If further t;RC evaluations so indicate, an IE Circular or Bulletin will be issued to recncmend or request specific licensee actions.
If you have questions regarding 'ae matter, please contact the Director of the appropriate f;RC Regional Office.
Sincerely, l$e[i 8
R. H. Engelken Director
Enclosure:
IE Information tiotice fio. 79-17 cc w/ enclosure:
R. J. Rodriguez, 3 MUD L. G. Schwieger, SMUD 272 015 790702 0 V6]
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND EflFORCEMENT WASHINGTON, D.C.
20555 June 20, 1979 IE Information Notice No. 79-17 SOURCE HOLDER ASSEMBLY DAMAGE FROM MISFIT BETWEEN ASSEMBLY AND REACTOR UPPER GRID PLATE Description of Circumstances:
Recently, the NRC was informed of a problem at two Westinghouse PWR facilities resulting from an apparent misfit between secondary source holder assemblies and the reactor upper grid plate.
The misfit problern was first identified by Carolina Power & Light, licensee for H. B. Robinson Unit 2, who informed the NRC or. May 6,1979, of the circum-stances.
During the current refueling outage at H. B. Robinson 2, CP&L deter-mined that two secondary source holder assemblies had been damaged during the previous refueling in February 1978, by a misfit between the assembly and the reactor upper grid plate.
The misfit resulted from insufficient clearance (i.e. 1/2 to 3/4 inch) between the source holder assembly hub and the grid plate at the core locations containing thermocouple mixing vanes.
This lack of sufficient clearance caused minor deformation of the upper grid plate com-ponents at the core location and of the source holder assemblies.
The deforma-tion also resulted in some bending of the fuel rods in the assembly, however, in no case did this bending result in fuel cladding perforation.
On May 16, 1979, the licensee of D. C. Cook Unit 1 informed the NRC that the present refJeling outage would be extended 15 to 20 days to remove the reactor head, which had already been reinstalled following completion of refueling, to correct th.s misfit problem. They learned of the problem from Westinghouse.
Subsequently, the licensee's inspection revealed that the source holder assembly hubs were in contact with the vanes. The source holder was removed from one assembly readily with no apparent damage while in the cther the source holder was found stuck in the assembly. The problem was corrected prior to return to operations.
The secondary source assembly rods are normally inserted into rod cluster control assemblies and placed at symmetrical locations in the core.
Each such assembly contains a symmetrical grouping of four secondary source rods and be'. ween zero and twenty burnable poisan rods.
Locations in the assembly not filled with a source or burnable pois:c rod contain a thimble plug. The lack of sufficient clearance for these g'r;&hbsawidlir m ad. ; '
only at the core locations which c DUPLICATE DOCUMENT /_7 9n 1 ()
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