ML18348A632

Abnormal Occurrences (AO) Report No. 75-20 Covering Shutdown Rod No. 16. Appears to Be Similar to AO-75-18 and AO-75-19

ML18348A632
Person / Time
Site:	Palisades
Issue date:	09/15/1975
From:	Bixel D Consumers Power Co
To:	Purple R Office of Nuclear Reactor Regulation
References
AO-75-20
Download: ML18348A632 (3)

Text

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Mr Robert A. Purple Division of Reactor Licensing US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255, LICENSE DPR PALISADES PLANT, A0-75-20 Attached is Abnormal Occurrence (AO) Report No 75-20 covering dropped shutdown rod No 16. This occurrence appears to be similar to A0-75-18 and A0-75-19 and an investigation into the cause of these failures has begun .

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David A. Bixel Assistant Nuclear Licensing Administrator CC: JGKeppler, USNRC File

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• 1. Report No: A0-75-20.

ABNORMAL OCCURRENCE REPORT Palisades Plant

2. a. Report Date: September 15, 1975.

b. Occurrence Date: September 5, 1975.

3. Facility: Palisades Plant, Covert, Michigan.

4. Identification of Occurrence: Control Rod No 16 dropped into the core.

This incident was identified as an abnormal occurrence by Technical Specifications 3.10.6(c). The shutdown rods shall not be inserted below their exercise limit until all regulating rods are inserted.

5. Conditions Prior to Occurrence: The plant was operating at the steady state power level of 80% .*

6. Description of Occurrence: At 1210 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.60405e-4 months <br /> on September 5, 1975, Control Rod No 16 dropped into the core. Turbine runback reduced plant power to 70%. Plant power was further reduced to 60%. To comply with, administra-tive limits, an unsuccessful attempt was made to retrieve the control rod .

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8.

Designation of Apparent Cause of Occurrence:

incident was a shorted clutch coil.

The apparent cause of the Analysis of Occurrence: Control Rod No 16 was classified inoperable under Section 3.lo.4(b) of the plant Technical Specifications. Plant operation was continued with one inoperable rod (under an administrative limit of 60%.) until the evening lighting load had passed. The plant was then shut.

down to effect necessary repairs.

Core flux tilts were calculated and demonstrated to be within the limits of Technical Specifications, Section 3.10.3 Reactivity of the dropped rod was less than 0.2%. (Technical Specifications limit on potential ejected rod worth is about 1%.)

9. Corrective Action: The immediate corrective action was to replace the clutch.* While the dropping of a control rod is an anticipated event pro-vided for within the plant Technical Specifications (and generally does not represent a safety problem), we recognize that a generic problem may exist with the control rod drive mechanism (CRDM) clutches. As indicated in A0-75-18 and A0-75-19, we have begun an investigation of the clutch failures that have recently occurred and hope to determine the mode and/or cause of the failures.

Preliminary information indicates that a high clutch coil temperature may be associated with these failures. To alleviate this problem we have re-duced clutch coil voltage and expect to accomplish a reduction of about 25% in the power dissipation within the clutch coils.

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• 10. Failure Data:

a. CRDM No 16 manufacturer is Combustion E?gineering, Inc and the piece is J-2966-163-00L The dual clutch assembly manufacturer is Combustion Engineering, Inc and the piece number is CND-SE-3998-1.

b. This mode of failure on CRDM clutches has occurred in the past at the Palisades Plant. See A0-73-9 transmitted by letter dated August 20, 1973, A0-75-18 transmitted by letter dated August 28, 1975 and A0-75-19 transmitted by letter dated September 9, 1975 .

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