05000301/LER-1992-006-01, :on 921020,inadvertent ESF Actuation Occurred as Result of as-built Wire Tracing & Disconnected Output from 2B04 Lockout Relay.Cabling Reconnected on 921020
| ML20127M611 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 11/19/1992 |
| From: | Hennig B WISCONSIN ELECTRIC POWER CO. |
| To: | |
| Shared Package | |
| ML20127M617 | List:
|
| References | |
| LER-92-006-01, LER-92-6-1, NUDOCS 9211300320 | |
| Download: ML20127M611 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 3011992006R01 - NRC Website | |
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ABSTRACT:
On October 20, 1992, with Unit 2 shutdown for its annual maintenance and refueling outage, a pre-shift walkdown of the control boards was being performed by the Duty Shift Superintendent (DSS).
At 2:50 p.m.,
the DSS observed that the Unit 2 B04 non-safeguards-equipment lockout _on-the rear of main control board C01R was in the tripped position.- This equipment lockout is designed to trip following a "B" train safety injection signal, stripping non-safeguards loads from safeguards
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It is believed that.the trip of this-lockout was caused when-l a "B
train safety in-}ection relay. was. inadvertently bumped during as-built wire tracing that was being performed in the' Unit 2 safeguards racks.
The trip of this lockout is being reported because it is an-actuation of an -Engineered Safety Feature _ (ESF).
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Tlem Point Beach Nuclear Plant, Unit 2 o l5 j o [o lo l 31011 912 01Ol6 0!0 012 05016 raria w a=cs.o. m m on EVENT DESCRIPTIONt On October 20, 1992, with Unit 2 shutdown for its annual maintenance and
.. fueling outage, a pre-shift walkdown of the control boards was being performed by thn Dut Shift Superintendent (DSS).
At.' 50 p.m.,
the DSS observed that tne Uni, 2 B04 non-safeguards equipment lockout on the rear of main control biard C01R was in the tripped position.
This equipment lockout strips non-safeguards loads f'om 2B04, the "B" train 480 volt safeguards bus, following a "B" train safety injection signal.
This load stripping ensures that the emergency diesel generators supp1'r powel only to essor. 1.a1 safeguards equipment.
Therefore, the tripping of this equipment lockout was an unexpected actuation of an Engineered Safety Feature (ESF).
It is believed that the tripping of the lockout occurred when a "B"-train safety injection relay was inadvertently bumped during as-built wire tracing.
This wire tracing was taking place in the Unit 2 safeguards racks in the vicinity of the "B" train safety injection relay on the same day that the tripped lockout was discovered.
One of the loads from 2B04 that should be stripped following the trip of the equipment Inckout is non-safeguards motor control center MCC B21.
The stripping or this load should have resulted in the actuation of a control room annunciator.
This annunciator failed to actuate.
Furti.ar investigation determined that MCC B21, had not stripped off of 2B04 as required.
The failure of MCC B21 to strip necessitated-an inspection of the wiring associatet with the 2B04 lockout circuit.
The wiring inspection showed that the output wiring from the 2B04 lockout was not connected to th3 2B04. supply breaker 2B52-28C for MCC B21. 'The output wiring discrepancy was subsequently corre;ted.
Additionally, the lockout c ircuitcy and associated wiring was checked for each train on both Point Beach Nuclear Plant, Units 1 and'2.
The l-
'four no -safeguards lockout circuits were all wired-to their appropriate load-j.
COMPO W AND BYSTEM DESCRIPTION:
1 2B04 is the Unit 2 "B" train 480 volt safeguards bus This bus supplies safeguards power to safeguards loads including two containment ventila-
' tion fans two service water pumps, a containment spray pump, a compo-e nent cooling water pump, a residual heat removal pump, a motor-driven auxiliary feedwater. pump, battery charger D08, motor control center 2B42, and non-safeguards motor control conter B21.
2B04 is supplied l-
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=ac e m.om from 2A06, a 4160 volt safeguards bus.
In the event of a loss of power to 2A06, diesel generator G02 Will start and supply emergency power to reenergize the bus.
A lockout of the 480 volt safeguards buses occurs to assure that t
excessive loads are not present on the safeguards busos in the event a safeguards diesel generator is automatically cycled on, and to assure that two electrically separated, dedicated sources of power are available to each of the two saieguards trains.
A train-specific lockout will occur as a result of its train-related safety injection signal.
A safety injection signal will trip the 480 volt safeguards bus lockout relays (868-03 and 86u-04), which, in turn, causes all non-safeguards loads on buses B03 and B04 to strip, including the backup supply feeders to the two non-safeguards buses, B01 and B02, and the B03 to B04 bus tie breaker, if closed.
The bus lockout relays are tripped electrically and can be manually reset when the safety injection signal has cleared, been blocked, or been reset.
Tripping circuit continuity and power to each lockout relay is monitored by a local white lamp al.d a fuse monitoring relay which will annunciato " Common Critical control Power Failure" in the control room following a loss of DC control power.
CAUSES
1.
An eva: cation of this event.was performed and concluded that the ESF actuation was most probably caused when a "B" train safety injection relay was accidently bumpad by contractor personnel during as-built wire tracing in the Unit 2 safeguards racks earlier in the day on October 20, 1992.
2.
A sview of material history was performed in order to determine why non-safeguards MCC B21 was connected to thu 2B03 lockout circuit.
This review determined that power for MCC B21, during initial construction, was suoplied from 1801, a Unit 1, 480 volt non-safeguards bus.
It appears that a decision was subsequently made to power the motor control center from 2B03, the "A" train 480 volt safeguards bus.
However, supplying power to this MCC from 2B03 would have resulted in three motor control centers being powered from the same bus.
It was therefore decided to power MCC B21 from 2B04, the "B" train 480 volt safeguards bus.
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This condition has been determined to be a result of an error dur.ng init.tal construction.
CORRECTIVJ ACTIONS:
Immediate:
1.
Following discovery that the 2B04 equipment lockout had tripped, a check was conducted to determine which loads had been stripped off of 2B04.
This check revealed that all of the required loads had been properly stripped, with the exception of MCC B21.
Short-Term:
1.
A review of the procedure used during the wire tracing, Instrumentation and Control Procedure (ICP) 11.468, "As-Built Wire Tracing of the Safeguards Relay Racks Unit 2," was performed.
This review revealed that the procedure did provide adequate precaution statements concerning the need to use extreme caution to ensure that relays and switches are not accidently bumped, causing their contacts to change state.
No changes to this procedure are currently planned.
2.
Inspection of the 2B04 lockout circuitry revealed that the output from the 2B04 lockout relay was not connected to 2B52-28C, the 2B04 supply breaker to MCC B21.
This cabling was subsegunntly reconnected on October 20, 1992.
3.
The capability of the B03 and B04 lockout circuitry to perform their functions is tested during each unit's annual maintenance and refueling outage during the performance of Operations Refueling Test (ORT) 3,
" Safety Injection Actuation With Loss.of Engineered Safeguards AC."
This procedure tests both the B03 and B04 equipment lockouts simultaneously.
Plant personnel concluded that MCC B21 always tripped during ORT 3 because it was improperly 1
connected to the 2B03 equipment lockout circuitry.
Therefore, an "A" train safety injection signal would cause MCC B21, which is powered from the "B" train 480 volt safeguards bus, to trip.
This was subsequently confirmed during field inspections of the wiring of the 2003 lockout circuitry.
The wiring from the 2B03 lockout circuitry to the' supply breaker for MCC B21 was subsequently disconnected on October 21, 1992.
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In order to confirm that all of the equipment lockout circuitry was properly installed, an inspection of the B0; and B04 lockout circuits and associated wiring for both units was conducted.
All of the required equipment was verified to be connected to the appropriate lockout circuit.
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On October 24, 1992, following correction of the wiring discrepancy, a modified ORT 3 was performed that tested each train of the Unit 2 lockout circuitry separately.
This test was successfully completed on each train.
We currently plan to conduct a r,imilar test on both trains of the Unit i lockout circuitry during the 1993 maintenance and refueling outage.
REPORTABILITY
This Licensec Event Report is being submitted in accordance with the requirert..its of 10 CFA 50.73 (2) (iv), "Any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature (ESP), including the Reactor Protection System (RPS)."
A 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> NRC notification was made at 5:40 p.m. on October 20, 1992, in accor-dance with the requirements of 10 CFR 50.72 (b) (2) (ii).
The NRC Resident Inspectors were also informed of this event at 5:50 p.m. on October 20, 1992.
BAFETY ASSESSMENT During the time period when MCC B21 was connected to the 2B03 non-safeguards equipment lockout circuit, the actuation of both trains of safety injection still would have resulted in the stripping of MCC B21 from 2004.
A potential problem could have existed with the as-found condition of the 2B04 lockout circuit and associated wiring if G02, the emergency diesel generator, was the only power source supplying 2A06 and 2B04 and a safety injection actuation occurred with only the'"B" train being actuated.
This would have required G02 to carry all of the safeguards loads on 2A06 and 2B04, as well as MCC B21.
During power operation, G02 would not normally be the only power. source supplying 2A06 and 2B04.
The Point Beach Technical Specifications Section 15.3.7.B.1.d only allows such a condition for a period of seven days during power operation.
Otherwise, the affected unit would have.to be placed in hot shutdown.
The Point Beach Technical Specifications also prohibit taking a reactor critical if A05, A06, B03, and B04 are not energized from their normal power supplies.
Additionally, an evaluation performed by engineering personnel determined that emergency
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w oc w anu v mi diesel generator G02 would have been capable of supplying power to all of the "B" train safeguards loads and MCC B21.in the event such a condition had occurred.
Therefore, this event did not endanger the health and safety of plant personnel or the general public.
SIMILAR OCCURRENCES:
A review of Licenseo Event Reports was conducted.
The following Licenseo Event Reports describe ESF actuations that resulted from personnel error:
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; Service Water Low Flow Annunciation
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