ML19224C483
| ML19224C483 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay, Diablo Canyon |
| Issue date: | 06/20/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7907020448 | |
| Download: ML19224C483 (1) | |
Text
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REGION V q'~ c'#[o TE N oi 1990 N. CALIFORNIA BOULEVARD SUITE 202, WALNUT CREEK PLAZA
- ,,,e" WALNUT CR EE K, CALIFC,RNIA 94596 June 20,1979 Docket tios. 50-133 50-275 50-323 Pacific Gas and Electric Company 77 Beale Street San Francisco, California 94106 Attentien:
Mr. Philip A. Crane, Jr.
Assistant General Counsel Gentlemen:
This Information ?!otice is provid;d as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability ta their fac.ilities.
flo specific action or response is requested at this time.
If further flRC evaluations so indicate, an IE Circular or BLiletin will be issued to recommend or request specific licensee actions.
If you have questions regarding the matter, please contact the Director of the appropriate flRC Regional Office.
Sincerely, 0 -. -
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R. H. Engelken Director.
Enclosure:
IE Information riotice tio. 79-17 cc w/ enclosures:
W. Barr, PG&E W. A. Raymond, PG&E R. Ramsay, PG&E (Diablo Canyon) 272 009 J. D. Worthington, PG&E E. Weeks, PG&E (Humboldt Bay) 7907020 L/9'I
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEP31T WASHINGTON, D.C.
20555 June 20, 1979
'F Information Notice No. 79-17 SOURCE HOLDER ASSEMBLY DAMAGE FROM MISFIT BETWEEN ASSEM M AND REACTOR UPPER GRID PLATE Description of Circumstances:
Recently, the NRC was informed of a problem at two Westingbouse PWR facilities resulting from an apparen misfit between secondary source holder assemblies and the reactor upper gris plate.
Tne misfit problem was first identified by Carolina Power & Light, licensee for H. B. Robinson Unit 2, who informed the NRC on 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 sourt.e 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 refueling outage would be extended 15 to 20 days to remove the reactor head, which had already been reinstalled following completion of refueling, to correct this 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 other 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 between zero and twenty burnable poiscn rods.
Locations in the assembly not filled with a source or burnable poison rod contain a thimble plug.
The lack of sufficient clearance for these sote:r M'
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