05000400/LER-2004-003, Unit 1 Automatic Reactor Trip Due to Rod Control Card Failure
| ML041900267 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 07/02/2004 |
| From: | Waldrep B Progress Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| HNP-04-081 LER 04-003-00 | |
| Download: ML041900267 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4002004003R00 - NRC Website | |
text
Progress Energy U.S. Nuclear Regulatory Commission ATrN: NRC Document Control Desk Washington, DC 20555 Serial: HNP-04-081 10CFR50.73 SHEARON HARRIS NUCLEAR POWER PLANT UNIT 1 DOCKET NO. 50-400/LICENSE NO. NPF-63 LICENSEE EVENT REPORT 2004-003-00 Ladies and Gentlemen:
The enclosed Licensee Event Report 2004-003-00 is submitted in accordance with 10 CFR 50.73. This initial report describes an automatic reactor trip - turbine trip. Event Notification EN 40730 previously reported this event in accordance with 10 CFR 50.72.
Please refer any questions regarding this submittal to Mr. John Caves, Supervisor -
Licensing/Regulatory Programs, at (919) 362-3137.
Sincerely,
(
t4ep B. C. Waldrep Plant General Manager Harris Nuclear Plant BCW/kmh Enclosure c:
Mr. R. A. Musser (HNP Senior NRC Resident)
Mr. C. P. Patel (NRC-NRR Project Manager)
Mr. W. D. Travers (NRC Regional Administrator, Region II)
Progress Energy Carolinas. Inc.
Harris Nuclear Plant P. 0. Box 165 New Hill, NC, NC 27562
I'!i
Abstract
On May 6, 2004 at 12:52 PM EDT, the reactor automatically trippod from 100% power due to a power range flux rate signal. The operations staff responded to the event in accordance with applicable plant procedures. The plant was stabilized at normal operating no-load reactor coolant system (RCS) temperature and pressure following the reactor trip.
The trip was caused by the failure of a regulation card in the Rod Control System [M]. This resulted in the loss of stationary gripper coil current to the Control Rod Drive Mechanisms (CRDMs) for one of the three Shutdown Banks of control rods. Loss of stationary gripper coil current resulted in the insertion of the four associated control rods into the reactor core which led to the high power range negative flux rate trip.
Corrective actions included replacing the failed card with a spare and performing visual inspection and testing of additional cards in the Rod Control System Power Cabinets. These actions were completed prior to plant startup.
NRC FORM 366 (7-2000)
(If more space Is required, use additional copies of (If more space Is required, use additional copies of NRC Forn 366A)
Ill.
SAFETY SIGNIFICANCE (Continued)
Potential Safetv Consequences The potential safety consequences under alternate conditions are bounded by plant design. The most credible single failure assumption is the loss of one Nuclear Instrumentation System (NIS) channel [IG]. This results in a reduced ability for the NIS and Automatic Rod Control System to detect the core power redistribution characteristic of the event. In cases where a power range high neutron negative flux rate trip intercedes, the trip occurs when two of the three remaining channels reach the trip setpoint. In cases where the plant stabilizes at a new equilibrium condition without a reactor trip, no further protective action is required. The assumption that one NIS channel is lost has no impact on the RPS response. Therefore, consideration of other single failures within the protection system revealed no impact on the potential safety consequences of this event as well.
Given that the plant was operating within the design conditions at the time of the failure in the rod control system, there are no alternate scenarios that would result in significant adverse safety consequences.
IV.
CORRECTIVE ACTIONS
The faulty stationary gripper card was replaced with a spare card, which restored proper stationary gripper coil currents in Power Cabinet SC.
Diagnostic tests were conducted along with visual inspections on the one hundred cards in the power cabinets as well as forty-five spare cards. Cards with diagnostic test problems or visual imperfections were repaired. No significant discrepancies were identified during the diagnostic activity. None of the additional cards tested exhibited component failures similar to the regulation card that caused the trip.
V.
PREVIOUS SIMILAR EVENTS
No previous HNP events are known where a card failure in the rod control system resulted in a bank of control rods inserting into the core and a subsequent reactor trip. HNP LER 2003-003-00 described an event where a failure of a transistor on a printed circuit board (PCB) resulted in a main feedwater pump trip and subsequent reactor trip. The corrective action for that event was to modify the feedwater control system such that failure of the same PCB would not cause a main feedwater pump trip and subsequent reactor trip. The corrective action for the event described in the LER would not prevent this event because no actions were specified for the rod control system. Plant modifications to improve reliability are being prioritized to provide the greatest impact on reducing the frequency of unplanned scrams.
VI.
COMMITMENTS
There are no commitments included in this report.