AOP-8 Loss of C Bus

Question 1

What is the purpose of AOP-8, Loss of C Bus?

Answer 1

• Provides operator actions that must be accomplished subsequent to a loss of Bus 1C.
• Assumes that only Bus 1C is deenergized due to a fault, a failure to transfer, or a failure to load onto Emergency Diesel Generator (EDG) 1-1.
• The buses supplied by Bus 1C are assumed to be fault free.

Question 2

What are the AOP-8, Loss of C Bus, entry conditions?

Answer 2

Symptoms of loss of Bus 1C (eg, loss of power to all Bus 1C powered components) in conjunction with one or more of the following:

• EK-0515, “2400V BUS 1C AND/OR 1D HI/LO VOLTAGE UNDERVOLTAGE” (< 2375 V, 18 sec time delay)
• EK-0522, “BUS FAIL TO TRANSFER”
• EK-0521, “2400V STANDBY POWER NOT AVAILABLE”
• EK-0503, “2400V BUS 1C BKR 152-105 TRIP” (if closed)
• EK-0509, “2400V BUS 1C BKR 152-106 TRIP” (if closed)
• EK-0532, “BUS 1C OR 1D OVERCURRENT LOCKOUT”

Question 3

What automatic actions are expected with AOP-8, Loss of C Bus?

Answer 3

Emergency Diesel Generator 1-1 starts

Question 4

When and how would you trip the 1-1 EDG under AOP-8, Loss of C Bus?

Answer 4

Direct NPOs to Trip 1-1 EDG via Mechanical Overspeed Trip/Reset when:

Jacket water temperature greater than or equal to 195F on TI-1482, Diesel Generator K-6A Jacket Water Temp.

Lube oil temperature greater than or equal to 200F on TI-1478, Diesel Generator K-6A Lube Oil Temperature Indicator.

Question 5

What are the AOP-8, Loss of C Bus, immediate actions?

Answer 5

None

Question 6

Does Y-01 de-energize on a loss of C bus?

Answer 6

No, auto swaps to MCC-2 (Delta Bus).

AOP-8 Action: Verify Y-01 Energized, if not - enter AOP-16.

Question 7

Why does AOP-8, Loss of C Bus, have you secure a liquid batch if in progress?

Answer 7

Interlocks on P-40A, Dilution Water Pump, breaker close CV-1054 if pump not running.

Intent of this step is to terminate any batch releases to avoid exceeding the NPDES limits. This is necessary since P-40A, Dilution Water Pump is lost when Bus 1C deenergizes.

Question 8

What can happen to service water if P-7B is running?

Answer 8

On loss of C-Bus, P-7B looses power. Standby pump should start.

AOP-8, Loss of C Bus, has you check SW pumps and ensure those available are in service.

Question 9

What LCO’s are associated with AOP-8, Loss of C Bus, when the plant is in Mode 1-4?

Answer 9

T.S. 3.8.9 Distributing Systems - Operating

• Left Train and Right Train AC, DC, and Preferred AC bus electrical power distribution subsystems shall be OPERABLE.

T.S. 3.8.1 AC Sources Operating

• The following AC electrical sources shall be OPERABLE:
  
  • Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electrical Power Distribution System; and
  • Two Diesel Generators (DGs) each capable of supplying one train of the onsite Class 1E AC Electrical Power Distribution System.
    
    • 1 Hour do Offsite Source Check

T.S. 3.3.10 Engineered Safeguards Room Ventilation (ESRV) Instrumentation

• Two channels of ESRV Instrumentation shall be OPERABLE.
  
  • Immediately Initiate action to isolate the associated ESRV System.

T.S. 3.7.13 Engineered Safeguards Room Ventilation (ESRV) Dampers

• Two ESRV Damper trains shall be OPERABLE.
  
  • Immediately Initiate action to isolate associated ESRV Damper train(s).

Question 10

What LCO’s are associated with AOP-8, Loss of C Bus, when the plant is in Mode 5/6?

Answer 10

T.S. 3.8.2 AC Sources - Shutdown

The following AC electrical power sources shall be OPERABLE:

a. One qualified circuit between the offsite transmission network and the onsite Class 1E AC electrical power distribution subsystem(s) required by LCO 3.8.10, “Distribution Systems - Shutdown”; and
b. One Diesel Generator (DG) capable of supplying one train of the onsite Class 1E AC electrical power distribution subsystem(s) required by LCO 3.8.10.

T.S. 3.8.10 Distribution Systems - Shutdown

The necessary portion of AC, DC, and Preferred AC bus electrical power distribution subsystems shall be OPERABLE to support equipment required to be OPERABLE.

Question 11

Why do we Trip the EDG with the overspeed trip/reset lever versus turning it off?

Answer 11

The start/stop switches don’t have a pull to lock option. A standing start signal would restart the EDG.

Question 12

If C Bus is being supplied by the 1-1 EDG and offsite power is available the crew will transfer to that source. What happens if SIAS signal is present?

Answer 12

If a SIAS signal is present, failure to reset the SIAS will result in re-initiating a SIAS signal when the sequencer is reset during the transfer of Bus 1C to off-site power.

Question 13

What happens to MSRs on loss of C Bus? What steam load do they represent?

Answer 13

HP reheat inlet steam valves go closed. Loss of Load 3-5%.