Week 3: Safeguards and Standby Power

Question 1

What is an Auto Bus Transfer?

Answer 1

Normally the PA01 and PA02 buses are supplied by the Main Generator through the Unit Aux XFMR. If the Main generator breaker is opened, the buses are isolated from the Unit Aux XFMR and connected to the Startup XFMR.

Question 2

What is the function of load shedding and load sequencing?

Answer 2

To ensure safety related loads are automatically started to safely shutdown the plant or mitigate the effects of a major accident.

Question 3

What are the sets of conditions that will trigger the load shed/sequencing system?

Answer 3

Safeguards bus undervoltage
SIS
Undervoltage and SIS

Question 4

Describe the sequence of events resulting from an Undervoltage signal on a safeguards bus.

Answer 4

Associated DG starts
Loads are shed from the bus
10s after DG starts, DG breaker closes
Shutdown sequencer starts

Question 5

Describe the sequence of events resulting from a Safety Injection signal received by a safeguards bus.

Answer 5

All non-safety loads shed from bus (any safety-related loads remain on)
LOCA sequencer started

Question 6

Describe the sequence of events resulting from a Safety Injection signal received by a safeguards bus alongside an Undervoltage signal.

Answer 6

Associated DG starts
Loads are shed from the bus
10s after DG starts, DG breaker closes
LOCA sequencer starts

Question 7

What is the function of the Emergency Diesel Generators?

Answer 7

To provide a sufficient alternate source of 4160VAC power to the safeguards buses to carry the needed safety-related loads in the event that offsite power is lost.

Question 8

What subsystems comprise one train of an Emergency Diesel Generator?

Answer 8

Diesel engine
Starting air system
Intake/exhaust air system
Fuel oil system
Auxiliary heat removal system
Lube oil system
Generator