05000301/LER-1992-007-01, :on 921026,inadvertent ESF Actuation Occurred as Result of Improper Surveillance Testing.Caution Label Installed in Vicinity of Undervoltage Relay Test Button
| ML20127N143 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 11/23/1992 |
| From: | Schweitzer J WISCONSIN ELECTRIC POWER CO. |
| To: | |
| Shared Package | |
| ML20127N137 | List:
|
| References | |
| LER-92-007-01, LER-92-7-1, NUDOCS 9212010010 | |
| Download: ML20127N143 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 3011992007R01 - NRC Website | |
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ABSTRACT:
On October 26, 1992, with Unit 2 in reduced inventory during its annual refueling and maintenance outage, Routino Maintenance Procedure (RMP) 74,
"'B' Train Degraded and Loss of Voltage Relay Test, Unit 2,"
was being performed.
During the performance of the procedure, personnel failed to completely perform the actions defined in a' step required by the procedure.
This procedure non-conformance resulted in the trip of the feeder breaker to 2A06, the "B" train 4160 volt safeguards bus.
This trip occurred at 1:16 a.m.
The loss of power to 2A06 caused a loss of power to 2B04, the associated "B" train 480 volt safeguards bus.
The loss of 2B04 resulted in the loss of power to the running "B" train residual heat-removal (RHR) pump.
In response to the loss of power to 2A06, the emergency diesel generator G02 automatically started and re-energized 2A06 and 2B04.
Additionally, at 1:17 a.m.,
the control room operators, upon recognizing that the "B" train RHR pump had been de-energized, restored RHR flow by starting the "A" train RHR pump.
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EVENT DESCRIPTION
On October 26, 1992, with Unit 2 in reduced inventory during its annual refueling and maintenance outage, Routine Maintenance Procedure (RMP) 74,
"'B' Train Degraded and Loss of V0ltag7 Relay Test, Unit 2,"
was being performed.
This RMP is performed monthly to test the degraded voltage and undervoltage relays associated with 2A06, the "B" train 4160 volt safeguards bus, and 2B04, the "B" train 480 volt safeguards bus.
During the portion of the procedure that tests the undervoltage relays for bus 2A06, the initial step requires the person performing the test to remove the cover to test switch 2-TSl/A06, open its left-most knife blade switch, and remove the 2A06 bus undervoltage test switch test point cover.
The technicians performing this step failed to open the knife blade switch, but initialed for completion of the stop.
This knife blade switch is required to be opened in order to defeat one of the undervoltage stripping functions to the 2A06 bus supply and tie breakers.
In order to test the undervoltage relays, a trip / test button is depressed on the undervoltage sensing relay to simulate an undervoltage condition on the bus.
This step was subsequently performed.
Since the undervoltage stripping function had not been defeated, depressing the trip / test button caused the supply breaker to 2A06 to actually trip, de-energizing the bus at 1:16 a.m. on October 26, 1992.
The loss of 2A06 also resulted in the de-energization of 2B04.
Following the de-energization of 2A06 and 2B04, control room personnel ocknowledged annunciators indicating the loss of these buses.- They also observed indications that neither RHR pump was running.
Prior to the ovent, the "B" train RHR pump had been running, but it is powered from 2B04.
Upon recognizing that the running RHR pump had been lost, the operator manually started the "A" train RHR pump at 1:17 a.m.,
restoring RHR flow.
There was no indication of any reactor coolant system temperature increatu during the one-minute period when neither RHR pump was running.
When 2A06 de-energized, thy associated emergency diesel gene"ator, G02, cutomatically started, as designed, and re-energized 2A06 and 2B04.
Once power was restored to 2A06, 2A06 relaying was returned to normal, all loads that had been lost were restored, and the emergency diesel generator was secured.
These actions were completed by 1:26 a.m. on October 26, 1992.
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COMPONENT AND SYSTEM DEdCRIPTION:
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2A06 is the "B" train 4160 volt safeguards equipment distribution bus for Unit 2.
It. is normally supplied from 2A04, with the emergency diesel generator, G02, supplying alternate emergency power.
In the event 2A06 experiences an undervoltage condition, the 2A06 supply breaker and the 2A05/2A06 bus tie breaker, if shut, will trip open and the emergency diesel generator, G02, will start.
When G02 reaches the proper frequency and voltage, the bus supply breaker from G02 will shut, re-energizing 2A06.
Both 4160 volt safeguards buses have two channels of undervoltage protection, but only one channel has to be actuated to initiate the protective feature.
These 4160 volt safeguards buses aleo have three channels of degraded voltage protection.
The actuation of two of threa channe:s will trip the associated bus supply breaker, but will not o;rectly start the diesel generator.
2A06 supplies power to the "B" train safety injection pump and 2X14, a 4160/480 volt staticn service transformer.
The output of 2X14 supplies 480 volt power to 2B04.
2B04 is the "B" train 480 volt safeguards bus.
This bus supplies safeguards power to two containment ventilation fans, two service water pumps, a containment spray pump, a component cooling water pump, a residual heat removal pump, a motor-driven auxiliary feedwater pump, battery charger D08, and MCC 2B42.
MCC 2B42 is a 480 volt motor control center that supplies power to motor-operated valves associated with safeguards systems.
In the event that either 480 volt safeguards bus, B03 or B04, experiences an undervoltage condition, most of the feeder breakers on the bus are tripped in order to expedite return of the bus to service once power has been restored.
Both B03 and B04 have three channels of undervoltage protection, but only two channels have to be actuated to initiate the protective feature.
CAUSE AND CORRECTIVE ACTION:
Following the event, a Human Performance Enhancement System (HPES) evaluation was conducted to determine the underlying causes of this event.
This evaluation determined that the event was caused when the two maintenance electricians assigned to perform the procedure, failed to completely perform a step within the procedure.
This allowed'the undervoltage stripping function to still be available to the supply breaker for 2A06.
The breaker then tripped when the undervoltage relay test button was subsequently depressed.
There le a caution label installed in the vicinity of the undervoltage relay test button that addresses the concerns about knife blade switch positioning.
These
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prior to performing the prceedure on Unit 2.
The two workers were subsequently counselled by the manager of the maintenance group c9ncerning this event.
Additionally, this evaluation dotcrmined that the procedure was not s
fully adequate.
The ster that was improperly performed directed the technician to, " Remove the cover to 2-TS1/A06 and open the left-most knife blade switch.
Also remove the test point cover."
The problem with this step is that it identifies three separate actions that must be performed, with only one sign-off block.
The procedure did, however, provide a caution statement immediately prior to the step that was incompletely performed.
This caution statement adequately addresses the concerns about the positioning of the knife blade cwitchen.
In order to correct the identified procedural problem, the routine maintenance procedures associated with this testing for both units will be revised to provide separate steps and sign-off blocks for each required action item.
The procedural revisions will also add verification requirements at critical steps within the procedures.
These procedural revisions will be in place by December 18, 1992.
In addition to the personnel aspects of the event, concerns were
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expressed concerning the timing of the testing.
The testing was performed with the unit in reduced inventory.
Reduced inventory is defined as a period when reactor vessel water level is less than 55 percent, and is considered one of the more sensitive periods of reactor refueling operations.
We believe that safeguards surveillance testing should not be conducted when in reduced inventory without some form of evaluation of tho safety significance of the testing taking place prior to its performance.
There are existing controls that could have prevented this procedure from being performed during reduced inventory, but these were not effectively utilized.
The performance of the testing on Unit 2 was not discussed during the daily outage planning meeting.
This meeting is held daily during the outage to review and discuss activities planned for the next 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period.
The performance of the testing was discussed immediately following the meeting's termination, but this l-resulted in the testing not being placed on the major items work list, and prevented a thorough review of the safety significance of this testing from being performed.
Discussion of the testing during the outage planning meeting may have precluded its performance when in reduced inventory, i
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In order to ensure that surveillance testing receives the proper safety review prior to its parformance during a unit refueling outage, all safety-related surveillance testing is now required to be placed on the major items work list.
Additionally, RMP 74 and its "A"
train counterpart, RMP 73, and the associated procedures for Unit 1 will be revised to preclude their performance when the respective unit is in reduced inventory.
These procedural revisions will be in place by DAcomber 18, 1992.
Finally, the outage planning and safety evaluation groups are currently evaluating methods to ensure that a proper review of maintenance and testing activities is conducted should such activities be required when the reactor is in a reduced inventory condition.
These methods will be implemented by March 31, 1993, prior to the 1993 Unit i refueling and maintenance outage.
REPORTABILITY
This Licensee Event Report is being submitted in accordance with the requirements of 10 CFR 50.73(2) (iv), "Any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESP), includ Mg the Reactor Protection System (RPS)."
A 4-hour NRC notification was made at 2:29 a.m. on October 26, 1992, in accordance with the requirements of 10 CFR 50.72(b) (2) (ii) and 10 CFR 50.72 (b) (2) (iii) (B).
The NRC Resident Inspector was also notified of this event.
BAFE'!:; ASSESSMENTt RMP 74 requires that both diesel generators be operable prior to the performance of the test.
This is done to ensure that a reliable emergency power source is available should an actual loss of a safeguards bus occur.
When 2A06 was de-energized during this event, the associated emergency diesel generator performed as designed, automatically starting and re-energizing the bus.
Additionally, both trains of the RilR system were operable to ensure that redundant decay heat removal capability was available.
This is required by Technical Specification Section 15.3.1.A.3.b.
When the "B" train RHR pump was lost following the de-energization of 2B04, the "A" train RHR pump was successfully started, restoring R11R flow within one minute.
Therefore, the health and safety of plant personnel and the-general public was not endangered during this event.-
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- - 4.c w =4 w nn SIMILAR OCCURRENCESI A review of previous Licenseo Event Reports was performed.
The following reports describe ESF actuations that resulted from personnel error LER 301/92-006-00 Inadvertent 2B04 Equipment Lockout During As-Built Wire Tracing LER 266/91-006-00 Inadvertent Start of G01 Emergency Diesel Generator LER 301/90-005-00 Inadvertent Relay Actuation causes Loss of Condensate Flow LER 301/90-004-00 Inadvertent ESF Actuation; Servico Water Low Flow Annunciation No Licenseo Event Reports were identified that described a loss of decay heat removal ability.
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