ESAS Flashcards
What are the major functions of ESAS?
- Monitors two parameters for indications of a major transient that challenges fuel cladding integrity and reactor building integrity
- Protection of the fuel cladding by injection of coolant at both high and low pressures.
- Maintenance of the reactor building integrity through building isolation and cooling of the building atmosphere.
- Control of fission products in the RB atmosphere; accomplished using RB spray. (As well, the spray serves cool the RB atmosphere to limit and reduce RB pressure.)
- Provides indications and alarms for monitoring of plant status during accident conditions. (Control Room, Remote Shutdown Dasey Panel, and SPDS
What are the ESAS trip setpoints and associated channels?
How many analog channels are there, what are their power sources and how do they generate their trip signal?
3 analog channels provide input to the digital channels for trip signal. When 2 of 3 channels reach appropriate setpoint, the applicable channels will de-energize to trip and send signal to the applicable digital channels for actuation. Analog channels 1, 2, 3 are powered from RS-1/2/3 respectively.
How many digital channels are there, what are their power sources and how do they generate their trip signal?
10 digital channels receive input from the analogs and are energized to trip. Each digital channel will actuate its associated equipment when applicable threshold is met (RCS pressure/RB pressure). Odd channels are powered from RS-1. Even channels are powered from RS-2.
How is ESAS de-energized?
Digitals are de-energized first to trip to prevent them from actuating since they are energized to trip.
How is ESAS reset?
Analogs are energized first prior to digitals. If digitals were energized first, they would actuate due to analogs being de-energized.
What are the design requirements for ESAS?
Single Failure – no single failure will prevent actuation or cause spurious actuation
Redundancy – redundant logic and actuation devices
Independence and separation – electrically independent, physically separated and electrically isolated
Manual trip – each digital channel has manual PB on C-04
Testing – means of testing
Loss of power – loss of power will trip analogs
Module withdrawal – withdrawal will result in a trip of affected string. Withdrawal of digital channel will not actuate but provides annunciator
Low pressure bypass – Bypass for controlled S/D
Which instruments input to ESAS? What are their ranges?
RCS Pressure Range is 0 - 2500 psig
Draw ESAS analog/digital drawing.
What is the purpose of the buffer amplifier?
The buffer amplifier is a DC voltage amplifier which electronically isolates the signal from the rest of the circuit and provides output to 2 bistables. It ensures electrical independence and separation and prevents faults occurring outside the ESAS cabinets from reflecting into an analog signal.
What is the purpose of bistables?
Bistables generate trip signals by opening contacts when reaching the bistable trip setpoint and sends a signal to the relevant digital channel. The bistable converts the analog input signal to a digital output.
What is the purpose of the logic buffers?
Provides the communication links between analog and digital channels. There are 5 logic buffer modules in each of the ESAS analog channels. Each logic buffer module contains a normally energized trip relay and is de-energized by contacts opening in the associated bistable. This closes 2 contacts when de-energized to energize the digital channel.
Describe the function and operation of the ESAS low RCS pressure bypass feature?
PBs on C04 are used for means of bypassing the 3 analog channel low RCS pressure actuation. When RCS pressure is below 1720 psig, the RCS low pressure bypass feature is enabled. Once RCS pressure reaches > 1750 psig, the bypass feature is disabled.
What occurs if a module upstream of the logic buffer is removed?
Depending on which module is removed affects what signal is sent. If buffer amplifier is removed then its applicable feeds are de-energized.
If logic buffer is removed, the affected digital channel is prevented from tripping.
Examples:
1) Removal of the RB buffer amplifier -> results in analog channel trip for digital channels ES channels 1 - 10.
2) Removal of RCS low pressure bistable results in analog channel trip for digital channels 1 - 4.
What would occur on loss of power to RS-1 for ESAS?
Analog channel 1 and odd digital channels would de-energize. This would result in a half trip ES condition for digital channels 2,4,6,8,10.
