05000278/LER-2004-002
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
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| 2782004002R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 3 was in Mode 1 and operating at approximately 100% rated thermal power when the event occurred. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On 9/14/04, at approximately 0400 hours0.00463 days <br />0.111 hours <br />6.613757e-4 weeks <br />1.522e-4 months <br />, during the performance of a routine surveillance functional test of the 'D' channel of Emergency Core Cooling system (ECCS) compensated trip system, Instrument and Controls (I&C) Technicians experienced an unexpected test result and immediately halted the testing. It was promptly recognized that an electrical lead in the circuitry for the High Pressure Coolant Injection (HPCI) system was previously lifted and had not been properly restored during functional surveillance testing. The location of the lifted lead in the circuitry resulted in the inability to automatically trip the HPCI turbine on high water level (i.e.
Level 8). (EDS: LT) Troubleshooting of the ECCS compensated trip system determined that the failure to restore the electrical lead occurred during the testing of the 'C' channel of the ECCS compensated trip system on 8/3/04. The cause of this event was due to inadequate verification practices during the MC testing performed on 8/3/04 and an inadequate procedure step to independently verify the connection was properly restored. The electrical lead was re-connected on 9/14/04 by 1200 at which time the automatic trip of the HPCI turbine on high water level was restored to service.
Analysis of the Event
There were no actual safety consequences associated with this event.
The automatic trip of the HPCI turbine on high water level was inoperable from 8/3/04 at approximately 1227 hours0.0142 days <br />0.341 hours <br />0.00203 weeks <br />4.668735e-4 months <br /> to 9/14/04 at approximately 1200 hours0.0139 days <br />0.333 hours <br />0.00198 weeks <br />4.566e-4 months <br />. During this time period the failure to re-land the lifted lead in the ECCS compensated trip system would have prevented the HPCI system from tripping automatically when a high water level (Level 8) in the reactor pressure vessel (RPV) is signaled. The level 8 signal uses the 'C' and 'D' instrument signals from the ECCS Compensated Trip system. Both level signals are required to trip HPCI (2 out of 2 logic coincidence). The RPV High Level trip function is to prevent an RPV overfill condition that may lead to water hammer in the main steam lines and to prevent potential HPCI turbine damage due to moisture carryover from the RPV. During the surveillance test, leads are lifted to prevent the insertion of a HPCI trip (Level 8) signal during testing. The failure to re-land the lifted leads prevented the HPCI system from tripping automatically when a high level in the RPV is signaled. The affected instrument did not impact the HPCI system initiation capability, therefore the HPCI system safety function to start and provide cooling to the reactor vessel was not affected. In addition, the automatic restart (if no trip signals are present) of HPCI on low level following a turbine shutdown was unaffected. Licensed Operators always maintained the ability to manually trip HPCI if a high water level condition was observed and therefore the HPCI system was considered to be available.
This event is not considered to be risk significant.
Cause of the Event
The cause of this event was due to inadequate verification practices by the l&C technician for re-landing the lead lifted during the surveillance conducted on 8/3/04. A contributing cause to this event included the procedure used to re-land the lead on 8/3/04 did not contain an independent verification step required by station procedures.
Corrective Actions
The lifted lead was reconnected and the functional test of the ECCS compensated trip system was performed satisfactorily.
Additional corrective actions, including upgrading the functional testing procedures, are being evaluated in accordance with the corrective action program.
Previous Similar Occurrences There were no previous similar LERs identified involving a loss of HPCI high level trip function due to lifted leads.