ML18348A629

Abnormal Occurrence (AO) Report No. 75-19 Covering Dropped Shutdown Rod No. 11. Similar to AO-75-18 and Investigation Into the Cause of the Failures Has Begun

ML18348A629
Person / Time
Site:	Palisades
Issue date:	09/09/1975
From:	Bixel D Consumers Power Co
To:	Purple R Office of Nuclear Reactor Regulation
References
AO-75-19
Download: ML18348A629 (3)

Text

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• consumers

• Power company General Offices: 212 West Michigan Avenue, .Jackson, Michigan 49201

• Area Code 517 788-0550 September 9, 1975 Mr Robert A. Purple Division of Reactor Licensing US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255, LICENSE DPR PALISADES PLANT, A0-75-19 Attached is Abnormal Occurrence (AO) Report No 75-19 covering dropped shutdpwn

.rod Noll. This occurrence appears to be similar to A0-75-18 and.an investiga-tion into the cause of these failures has begun.

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

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• ABNORMAL OCCURRENCE REPORT Palisades Plant

1. Report No: A0-75-19.

2. a. Report Date: Sept 9, 1975.

b. Occurrence Date: August 30, 1975.

3. Facility: Palisades Plant, Covert, MI.

4. Identification of Occurrence: Control Rod No 11 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 0811 hours0.00939 days <br />0.225 hours <br />0.00134 weeks <br />3.085855e-4 months <br /> on August 30, 1975, Control Rod No 11 dropped into the core. Turbine runback reduced plant power to 70%.

Plant power was further reduced to 60%. *

7. Designation of Apparent Cause of Occurrence: The apparent cause of the incident was a shorted clutch coil.

8. Analysis of Occurrence: Control Rod No 11 was classified inoperable under Section 3.10.4(b) of the plant Technical Specifications. Plant operation can continue with one inoperable rod.

Core flux tilts were calculated to be 7% to 8% which is within the limits of Technical Specification Section 3.10.3. Reactivity of the dropped rod was less than 0,2%. (Technical Specifications limit on potential ejected rod worth is 1%.)

9. Corrective Action: The imme~iate corrective action was to replace the clutch.

While the dropping of a control rod is an anticipated event provided 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. In an effort to resolve this problem, 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.

Clutch coil operating conditions are being checked as a part of this investi-gation.

10. Failure Data:

• a. CRDM No 11 manufacturer is Combustion Engineering, Inc and the piece is J-2966-163-001.

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• 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 and A0-75-18 transmitted by letter dated August 28, 1974 .

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