Seems like a lot of "unknown causes" in this event ... doesn't it? I'm just including the "Event Text" here because the rest is hard to format so it's readable. - Judy

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|Power Reactor |Event Number: 36602 |

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FACILITY: SEQUOYAH REGION: 2 |NOTIFICATION DATE: 01/18/2000

UNIT: [] [2] []

STATE: TN |NOTIFICATION TIME: 11:40[EST]|

RXTYPE: [1] W-4-LP,[2] W-4-LP

EVENT DATE: 01/18/2000

+------------------------------------------------+

EVENT TIME: 10:51[EST]

NRC NOTIFIED BY: DAVID PORTER

LAST UPDATE DATE: 01/18/2000

HQ OPS OFFICER: FANGIE JONES

+------------------------------------------------+

EVENT TEXT +------------------------------------------------+

INADVERTENT SAFETY INJECTION DUE TO ELECTRICAL FAULT AND REACTOR TRIP

Technicians were performing a modification to the vital inverter 2-IV when a safety injection signal was generated due to an electrical problem on vital instrument bus 2-IV. When the technicians were lifting a lead on the sync signal input to the inverter 2-IV in accordance with the modification, an inadvertent safety injection signal was generated. When the safety injection actuated, only Train 'A' safety injection occurred. The cause of the reactor trip is unknown at this time though it is expected with a safety injection. The operators followed the emergency procedures and started the Train 'B' safety injection and residual heat removal pumps; the train 'B' centrifugal charging pump started automatically (reason unknown and being investigated). The 2A-A motor-driven auxiliary feedwater pump tripped for unknown reasons. The #2 steam generator atmospheric relief valve controller appears to have failed, which required operators to take manual control and close the relief valve. An event investigation has been initiated, and all problems will be answered before the unit is restarted.

The plant is currently stable in Mode 3 with heat removal via the atmospheric reliefs and feedwater via the 2B-B motor-driven and turbine-driven auxiliary feedwater pumps. All rods fully inserted. The safety injection signal was from the 'Low Steam Generator Pressure' section, and the main steam isolation valves closed automatically. The plant has no steam generator tube leaks.

The licensee notified the NRC Resident Inspector.

-- Anonymous, January 19, 2000

Answers

It seems to me that the number of normal reactor trips is down compared to normal, since y2k. Anyone got any stat's?

-- Anonymous, January 19, 2000

Judith, Preliminary notifications to the NRC are made soon after an event occurs, and it's not unusual for the root causes to be determined that early, depending on the nature of the event. The causes must be determined prior to restart.

xBob, sorry, I don't have any stats on reactor trips handy, but these are rather sporadic, sometimes not many over a month or two, sometimes many in a week or few days, with typically varying causes. I believe that you might find some documents on the NRC site that summarize trip events for previous years.

Regards,

-- Anonymous, January 19, 2000

Thanks FactFinder, good succinct synopsis.

-- Anonymous, January 20, 2000