CEDMCS- Control Element Drive Mechanism Control System Flashcards
What is used to control the fission rate of the reactor?
CEAs (control rods)
What does CEDMCS allow the movement of CEAs to achieve?
Power control and power distribution control so the reactor can be operated from full power to cold shutdown within acceptable limits
CEA movement controls the location of power in the core. What do these movements compensate for?
Minor variations in moderator temperature, boron concentration and axial xenon oscillations
After a reactor trip, CEDMCS provides signals to what systems?
Main turbine
Feedwater
Steam bypass control
ERFDADs
SRP multiplexer
For what purpose does CEDMCS provide CEA position signals?
CEA position indicates the reactivity control system maintained the plant within safety limits
What are the major components in the CEDMCS system?
Two independent power supplies-Motor Generators and control cabinets
Four reactor trip switchgear breakers
Four control cabinets
Two aux. relay cabinets
Where are the Motor generators in the CEDMCS system powered from?
NGN-L03 and NGN-L10
What is the output voltage of the Motor Generators in the CEDMCS system?
240VAC
What does the CEDM control system receive automatic CEA motion demands from?
Reactor Regulating System (RRS)
Manual signals from CEDMCS operators module
Reactor plant cutback
Plant computer
How many coil stacks does each power switch assembly (subgroup) control?
4 except subgroup 8 that powers 5 coil stacks
How does CEDMCS interface with NG?
NG powers the motor generators
How does CEDMCS interface with NN?
NN provides 120VAC to CEDMCS cabinets A, B, C, D.
How does CEDMCS interface with PN?
powers CEDMCS cabinets instrument buses for logic and relay power supplies
powers CEDMCS Aux. cabinets C5 and C6
What do the CEDMCS aux cabinets do?
receive and provide isolation for safety (class) inputs from reed switch position transmitters and plant protection system and send non-safety (non-class) outputs to cabinet 4 of CEDMCS
How does CEDMCS interface with QA?
QA powers cabinets A, B, C, D cooling fans, utility outlets and lighting
How does CEDMCS interface with HA?
Aux building HVAC cools CEDMCS cabinets on the 120ft
What is the required temp. range for the CEDMCS control and Aux. cabinets?
55-104*F
What cools CEDM coils and CEA reed switch position transmitters in containment?
HC (containment building HVAC)
How does CEDMCS interface with MT?
CEDMCS provides a contact to trip the turbine on a reactor trip
How does CEDMCS interface with RC?
RC sends Tc indication to CEDMCS
How does CEDMCS interface with MD (SRP plant multiplexer)?
CEDMCS sends a signal when reactor trips
How does CEDMCS interface with Reactor protection system?
CEDMCS provides CEA positions to CEA calculators and Core protection calculators
How does CEDMCS interface with Feed water control system?
provides a contact on reactor trip
limits the possibility of over cooling the reactor on a reactor trip
How does CEDMCS interface with reactor power cutback system?
CEDMCS receives signals to drop CEAs when a cutback is required
How does CEDMCS interface with Reactor regulating system?
sends signals to CEDMCS to regulate reactor coolant average temp. to a programmed setpoint
How does CEDMCS interface with steam bypass control system?
SBCS dumps steam directly to the condenser when the main turbine is unavailable
provides CEDMCS with an AWP (auto withdrawal prohibit) signal to prevent rods from withdrawing when there is excess energy
What is on each end of the motor generator sets?
an inertial flywheel is on each end
What is the amp draw on the Motor generators?
601 amps
What speed do the motor generators maintain? Does speed change under load?
constant speed of 1800 RPM and shaft speed remains constant regardless of load
What is the purpose of the inertial flywheels?
to maintain required output power and frequency during a one second loss of power
When do under-frequency relays drop out?
57 Hz
What is the normal frequency range of the MG sets?
> 58 Hz
How are the MG sets controlled?
from the respective control cabinet and in the remote control box on the opposing cabinet
What maintains the generator output voltage at a preset level?
voltage regulator
What must happen prior to CEAs being moved in Auto sequential, manual group, or manual sequential?
both MG sets must be running
If only one MG set is running, trying to move CEAs will cause what to happen?
a large reduction in voltage, causing CEAs to drop
Where are the MG sets located?
aux building 120 ft
Almost all controls for the MG sets are on the front of the control cabinets. Where are the three overload resets? Where are the two high vibration resets?
overload resets are in the back of the control cabinets
the vibration resets are on the MG sets locally
What is the purpose of the load contactor?
connects the generator to the load and actuates automatically by MG overload or under-frequency
On the MG control cabinets, what do the light colors indicate?
green: open switch
white: closed switch
red: alarm
What is the purpose of the RTSG (reactor trip switch gear)?
They provide a reliable flow path for electrical power to the CEDMs during normal steady state operations
Upon a signal from the Reactor Protective System, Supplementary Protection System, or Operator, trip open to remove motive power to the CEDMs
What are the RTSG breakers rated for?
600VAC, 800amps
Where can the RTSG breakers be opened?
control room
locally
At the Plant Protection System cabinets
At the Supplementary Protection Logic Assembly cabinets, during SPS testing
Where can the RTSG breakers be closed from?
locally, PPS cabinets, Supplementary Protection Logic Assembly cabinets
Where are the RTSG breakers located?
aux building 120ft
What is a CEDM (control element drive mechanism)?
controlled by CEDMCS, uses magnetic fields to operate a magnetic jack in order to move CEAs
What type of power is used to power CEDM coils?
DC
What converts the AC output of the MG sets to the DC input of the CEDM coils
SCRs (silicon controlled rectifiers) in the Power Switch Assemblies
How long is the Extension shaft assembly?
280 inches
A grooved drive shaft extends through the CEDM to the CEA. What is the purpose of the grooves?
act as rack teeth to allow the CEDM to engage the shaft
What are the four coils in each CEA coil stack assembly?
upper lift, upper gripper, lower lift, lower gripper
How do the coil stack assemblies operate?
they provide the magnetic flux that operates the coils on the mechanical latches of the CEDM. operating the coils in sequence allows the extension shaft to raise and lower
What subgroup is CEA1 programmed to operate with?
subgroup 8
Where are the CEDM coil stack assemblies located?
above the reactor head, outside of containment boundary
What mode selection is the reactor in when power is above 20% and CEAs are essentially fully withdrawn?
auto sequential
At what power percentage is the reactor normally tripped?
20%
What is the purpose of a power switch assembly?
power switch assemblies contain the SCRs (silicon controlled rectifiers) that turn the AC input to DC output and direct that DC output to the CEDM coils
each PSA has four breakers (except CEA 1), that are each 4 small breakers ganged together, supplying the individual coils
What is at the bottom of the PSA panel?
four electrical connectors for testing CEAS
In the CEDMCS cabinets, what is the purpose of the subgroup logic housing?
controls the operation of the two power switch assemblies
What happens where there is a low logic voltage signal? How long do you have to correct this before damage occurs?
initiates a continuous gripper high voltage annunciator
10 minutes
How are the intake and exhaust blowers on the CEDMCS cabinets controlled?
a toggle switch on the front and a breaker in the back of the cabinets
Which cabinet is CEA1 in?
SFN-C01B bay 2
Which cabinet is the hold bus in?
SFN-C01B
What is the purpose of the Hold Bus?
Maintenance is to be performed on the normal power switch
Served to hold a subgroup during a condition when the subgroup is experiencing a high gripper voltage condition from its normal power switch and needs to be disconnected to prevent damage to CEDM
What are the hold bus controls?
Subgroup selection thumbwheel, transfer toggle switch, and a reset toggle switch
How are the phase voltages monitored?
with a selector switch on the hold bus indicator panel along with a meter
What is the purpose of the CEA relay interface housing cards?
interface with the reactor cutback system
provide up-count and down-count signals for each increment of motion by the CEAs to the plant computer
What is the purpose of the totalizer panel assembly?
totalizers for CEDMs count the number of steps each CEA has taken up or down
What is the purpose of the ACTM cards?
control the voltages and monitoring of CEDMs
What is the auto feature associated with CEDMCS?
regulating groups of CEAs can automatically move to control RCS temp.
initiate a reactor power cutback
trip the reactor
If CEDMCS lost power, what impacts to plant operations would occur?
reactor trip
If NG was lost to CEDMCS, what would happen?
If just one power supply was lost, no CEA movement would be able to occur
If both power supplies were lost, all CEAs would drop and reactor would trip
If NN was lost to CEDMCS, what would happen?
loss of logic, all CEAs would drop
What would happen if CEDMCS lost connection with PN?
the RTSG breaker relative to the PN channel that is lost would open
2 of 4 RTSG breakers opening trips the reactor
What would happen if CEDMCS lost connection with HA?
if CEDMCS room temp cant stay lower than 104*F, plant will shutdown
OPS installs temporary ventilation
What would happen if CEDMCS lost connection with HC?
CEDM coils damaged
shutdown if no fans restored
What is the tech spec related to CEDMCS?
four RTSG breakers to be operable
What is the purpose of CEDMCS?
Develop the control voltages to withdraw, hold or insert CEAs in the core
Allow the CEAs to drop into the core on an interruption of power
How can the voltage setpoint of the MG set be adjusted?
Locally by the operator
How long is the time delay for the overvoltage relays for the MG sets? Why is it necessary?
3-5 seconds to prevent alarms due to momentary voltage transients
There are 89 CEAs in the core, with each being assigned to what three groups?
Shutdown Groups
Part-strength Groups
Regulating Groups
How far apart are the annular rings on the CEDM assembly?
3/4”
What is the purpose of the CEDMCS cabinets?
Houses the timing and control circuits that control the movements of the CEAs
What is contained in CEDMCS Cabinets C01A and C?
Sub-group logic and power switch assemblies
Concerning Cabinet C01B, which bay has the Hold Bus Power Supply?
Bay 2
How many breakers will the area operator operate when placing/removing a subgroup from the hold bus?
5
referring to the CEDMCS hold bus, what light comes on to indicate a transfer?
A red light. Another red light will indicate which subgroup is on the hold bus
What are the CEDMCS Control modes?
Auto Sequential Manual Sequential Manual Group Manual Individual Standby
What would happen if I had a loss of power output from the MG sets?
All CEAs will drop
What would happen if I had a loss of power from one or more of the power switch assemblies?
Would result in one or more CEA subgroups dropping into the core which will result in a reactor trip
