05000298/LER-2003-006, Regarding Manual Reactor Scram Initiated Due to Transmission Line Structure Fire
| ML033630594 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 12/19/2003 |
| From: | Jason Christensen Nebraska Public Power District (NPPD) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NLS2003127 LER 03-006-00 | |
| Download: ML033630594 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| 2982003006R00 - NRC Website | |
text
Nebraska Public Power District Always there when you need us NLS2003 127 December 19, 2003 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
Licensee Event Report No. 2003-006 Cooper Nuclear Station, NRC Docket 50-298, DPR46 The subject Licensee Event Report is forwarded as an enclosure to this letter.
Sincerely, Christensen Plant Manager
/rar Enclosure cc: Regional Administrator USNRC - Region IV Senior Project Manager USNRC - NRR Project Directorate IV-I Senior Resident Inspector USNRC NPG Distribution INPO Records Center Records COOPER NULEAR STATION P.O. Box 98 / Brownville, NE 68321-0098 Telephone: (402) 825-3811 / Fax: (402) 825-5211 www.nppd.com
I
Abstract
On October 28, 2003, at 0130 hours0.0015 days <br />0.0361 hours <br />2.149471e-4 weeks <br />4.9465e-5 months <br />, a fire occurred on a wooden transmission structure located between the main generator output and the 345KV switchyard. Due to the imminent loss of the main generator output line to the switchyard, a manual scram was performed at 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br />. All control rods inserted and Primary Containment Isolation System Group Isolations for Primary Containment, Reactor Water Cleanup and Secondary Containment initiated as expected due to vessel level shrink. The Emergency Core Cooling Systems did not initiate. During water level recovery an overfeed condition caused the operating Reactor Feedwater pump to trip and a second manual scram was inserted in anticipation of a low level scram signal. Normal shutdown procedures were entered at 0300 hours0.00347 days <br />0.0833 hours <br />4.960317e-4 weeks <br />1.1415e-4 months <br /> and a vessel cool-down was initiated. The transmission structure fire was reported out at 0647 hours0.00749 days <br />0.18 hours <br />0.00107 weeks <br />2.461835e-4 months <br />.
The fire occurred when dust accumulation on the insulators and structure became wetted and created a path for stray electrical currents from phase to phase, or phase to ground across the wooden cross arm.
The cause of this event is the failure to properly ground the insulator strings on the wooden structure.
The damaged wooden structure and associated line disconnect switch were removed on October 30, 2003. Grounding cables were installed on a similar structure on November 24, 2003.
JRCFORM 366 (7-2001)
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(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A)
The root cause of the event is the failure to properly ground the insulator strings on the wooden structure cross member.
SAFETY SIGNIFICANCE
There is no impact on Probabilistic Risk Assessment (PRA) assumptions due to this event. All equipment responded as expected and DG 2 unavailability is captured by the average test and maintenance terms utilized in the PRA model. The PRA model assumes a frequency of once per year for transients of this type. This event alone has a negligible impact on this assumed frequency of occurrence. The Conditional Core Damage Probability (CCDP) for this event with DG 2 unavailable was 7.19E-07/year. The risk incurred during the manual scram and subsequent reactor shutdown was less than 1 E-6 CCDP and is not risk significant.
This event is not considered a Safety System Functional Failure as defined in NEI 99-02, Revision 2, Regulatory Assessment Performance Indicator Guideline.
CORRECTIVE ACTIONS
Immediate Action A manual scram was inserted to de-energize the generator main transformer output line and the fire was extinguished by 0647 hours0.00749 days <br />0.18 hours <br />0.00107 weeks <br />2.461835e-4 months <br /> on October 28, 2003.
A visual inspection of a similar 345 kV structure identified that the insulator strings on that structure were not grounded. The inspection was performed on October 28, 2003.
Insulator strings on additional 345 kV transmission structures were verified by design to be grounded.
The damaged wooden structure and associated line disconnect switch on the main generator output line were evaluated and determined to not be required. The structure and line disconnect switch were removed. This action was completed on October 30, 2003.
Long Term Actions Grounding of the insulator strings on the identified 345 kV structure was completed on November 24, 2003.
PREVIOUS EVENTS LER 2003-004, 'Manual Reactor Scram due to Main Turbine High Vibration," reported a manual initiation of the Reactor Protection System.
a ATTACHMENT 3 LIST OF REGULATORY COMMITMENTS© Correspondence Number: NLS2003127 The following table identifies those actions committed to by Nebraska Public Power District (NPPD) in this document. Any other actions discussed in the submittal represent intended or planned actions by NPPD. They are described for information only and are not regulatory commitments. Please notify the Licensing & Regulatory Affairs Manager at Cooper Nuclear Station of any questions regarding this document or any associated regulatory commitments.
COMMITTED DATE
COMMITMENT
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