RPS Flashcards
What is the purpose of the RPS?
To initiate a reactor trip to ensure that the Technical Specification Safety Limits are not exceeded.
Linear Heat Rate - < 21kw/ft
DNB > 1.17/1.154/1.141
PCS Pressure < 2750 psia
What are the RPS Trips?
- Reactor High Power
- Reactor Power High Rate of Change
- Primary Coolant System Flow
- Steam Generator Level 1
- Steam Generator Level 2
- Steam Generator 1 Low Pressure
- Steam Generator 2 Low Pressure
- Pressurizer High Pressure
- Thermal Margin/Low Pressure
- Loss of Load
- Containment High Pressure
What are the RPS Power Supplies?
Channel A - Y10
Channel B - Y20
Channel C - Y30
Channel D - Y40
What are the two types of RPS Trip Units?
Bistable Trip Units
- 7 of the RPS Trips are from Bistable Trip Units
Auxiliary Trip Units
- 4 of the RPS Trips are from Auxiliary Trip Units
What is a Bistable Trip Unit?
Bistable Trip Unit
- The measured value is compared to a pre-determined or calculated set point
- Measured value > set point
- Bistable de-energizes
- Measured value > set point
What is an Auxiliary Trip Unit?
Auxiliary Trip Unit
- Digital Input
- Voltage Present = safe
- No Voltage Present = unsafe
- Trips
What are the RPS Bistable Unit Trips?
Can be identified on the RPS panel by the presence of potentiometer adjusting holes.
- Primary coolant system low flow
- Steam generator 1 low level
- Steam generator 2 low level
- Steam generator 1 low pressure
- Steam generator 2 low pressure
- Pressurizer high pressure
- Thermal margin/low pressure
What are the RPS Auxiliary Unit Trips?
Auxiliary Trip Units
- Reactor high power (variable high power trip)
- Reactor power high rate of change
- Loss of load
- Containment high pressure
What makes up the coincendence logic matrix?
Power Supplies?
Trip Inputs?
Six logic matrices, or “logic ladders
- Each ladder compares output of 1 RPS unit to another
- AB
- AC
- AD
- BC
- BD
- CD
Ladders are thus supplied by two different preffered AC busses
11 trips per channel = 22 per ladder
Each ladder powers 4 matrix relays which de-energize with a conicendent trip.
How does a logic ladder trip the reactor?
Clutch Power Supplies are fed by Y-30 and Y-40 through four large power “M” relays.
The M relays are controlled by four trip paths of six closed matrix relay contact pairs arranged in series (an OR arrangement).
If a coincedent trip occurs in a ladder, the associated M-relay opens and de-energizes both power supplies. Reactor is tripped.
What supplies Clutch DC Power Bus 1, 2, 3 and 4?
Clutch DC Power Bus 1
- Supply 1 (Y-30 via trip paths 1 & 2)
- Supply 3 (Y-40 via trip paths 3 & 4)
Clutch DC Power Bus 2
- Supply 2 (Y-30 via trip paths 1 & 2)
- Supply 4 (Y-40 via trip paths 3 & 4)
What is the M-Coil arc suppression?
When M relay contacts open, the magnetic field collapse in the coil induces a large voltage spike in the connected cables.
Could “weld” closed the matrix relay contacts.
Suppression network of capcitor/zehner diode shunts the spike.
What is the normal/tripped reading on the M-coil suppression network?
Normally indicates about 20 VAC - 100 VAC is dropped across capacitor, 20 across resistor which is indicated on voltmeter for that M-coil.
If reactor tripped, should read 0 VAC.
Not 20 if reset or 0 if tripped, investigate to ensure matrix relay functionality.
What are the K-relay power supplies?
K1 and K2 - DC Clutch Power Bus 1
K3 and K4 - DC Clutch Power Bus 2
What is the function of the K-relays?
When de-energized, K-Relays function to:
- CRDM Rundown - all but part-length
- Trip Reset - prevents reactor from auto resetting and damaging CRDM gears
- 30-Second Lockout - prevents manual reset for 30 seconds
- Turbine Trip - energize 20/AST Relay
- Reactor Trip signal to PPC/Datalogger
- EK-0972, “REACTOR TRIP”
What are the indications for Clutch Power supplies?
C-06, Channel A & D, bottom rack
Clutch power supplies are de-energized, i.e. after a reactor trip,
- “AC ON,” “AC TROUBLE,” “GROUND,” and “DC ON” lamps go dark
- “TRIP” lamp illuminates (red)
How does the manual reactor trip button on C-02 function?
C-02 Trip Button
De-energizes all four M relays, which de-energizes the four clutch power supplies
How does manual trip button 2 function?
Reactor Trip Button 2 on C-06
De-energizes the undervoltage coil on reactor trip breakers 42-1/RPS and 42-2/RPS, interrupting the voltage from Preferred AC Busses Y-30 and Y-40 to the clutch power supplies
How do you clear a reactor protective trip signal?
Bypass
Clear by correcting the conditon
How can you tell what has caused a trip?
Indicated by illuminated red lamps on the affected trip unit front panels, and by illuminated related annunciators.
What are the Reactor Protective System Trip Bypasses?
Reactor Protective System Trip Bypasses
There are three means of bypass:
- Trip Channel Bypass
- Automatic Bypass
- Only on Loss of Load and High Rate of Power Change
1. Zero Power Mode Bypass
How and when do you apply a trip channel bypass?
Trip Channel Bypass
- Manually implemented via keyswitch directly above the trip unit to be bypassed.
- Only 1 key for each trip; fits all four channels of that trip
Used:
- To prevent an inadvertent reactor trip when a trip unit is being serviced or calibrated
- To temporarily remove a trip unit from service when either it or its instrument channel is inoperable
How is the coincendence logic impacted when a trip channel is bypassed?
In BYPASS, the trip logic changes from 2/4 to 2/3 channels
- Yellow light above keyswitch illiminates
- If the supplying preferred AC buss is de-energize, no light
TS limit of 7 days for bypass
How is Automatic Bypass accomplished?
Automatic Bypass
Only available on Loss of Load and High Rate of Power Change
Loss of Load
- Enabled >15% power
- Disabled < 15% power
High Rate of Power Change
- Disabled < 10-4% power by one of two Source/Wide Range NIs
- Disabled > 15% power by power range NI
- Enabled between 10-4% power and 15% power
What is the function of the Zero Power Mode (ZPM) Bypass?
Zero Power Mode (ZPM) Bypass
- It is a manual bypass.
- Used when reactor shutdow to bypass certain reactor trip signals to allow control rod withdrawel.
What trips can be bypassed using the Zero Power Mode Bypass?
Trips bypassed via Zero Power Mode Bypass:
- PCS Low Flow
- SG 1 Low Pressure
- SG 2 Low Pressure
- Thermal Margin/Low Pressure
How do you insert a Zero Power Mode Bypass?
Inserting Zero Power Mode Bypass
- Manually inserted via 1 keyswitch for each RPS channel (four keyswitches total).
- +15V is applied to the output of the four bypassed trip units, ensuring that the trip unit outputs cannot de-energize.
How is Zero Power Mode Bypass automatically not allowed?
At >10-4% Power - ZPM Bypass is automatically removed.
In series with the bypass keyswitch are automatic removal contacts (one for each trip unit) that are operated by the associated Source/Wide Range NIs
- NI 1/3A removes the ZPM bypass from trip units in RPS Channels A & C
- NI 2/4A removes the ZPM bypass from trip units in RPS Channels B & D
How is the insertion/removal of a Zero Power Mode Bypass accomplished?
Lamp 1 on panel - availability of bypass
- Dark when test push button depressed if bypass available
- Illuminated when test push button depressed at > 10-4% power
Lamp 2 on panel - insertion of bypass
- Dark when test push button depressed if keyswitch in bypass
- Illuminated when test push button depressed and no bypass
Bottom-Line
- Lights dark if bypass inserted/available
- Lit if bypass not inserted/not available
What are the requirements prior inserting a zero power mode bypass?
Ensure operable both Wide Range NIs
Ensure power level less than 10-4% RTP
Verify primary system boron concentration greater than Cold Shutdown concentration
When testing removal of ZPM bypass, why is only 1 test pushbutton at a time depressed?
SOP-36 contains a Caution that states, “Zero Power Mode test buttons should be operated one at a time to prevent Reactor Protective System trips.”
How do you place an RPS unit in trip?
Loosen both hold down screws on desired trip unit
Pull RPS trip unit out at least two inches, using the handle on the front of the trip unit
Ensure the connections on the back of the trip unit are disengaged
Changes 2 out of 4 to 1 out of 3.
How do you tell if and where a ground is within the logic matrix?
Two rows of four lights.
If ground on positive side:
- Top lights go dark, bottom lights get brighter
If ground on negative side
- Bottom lights go dark, to lights get brighter
If a monitored parameter input signal fails high, how will trip unit react?
If trip unit designed to trip on high
- Only that channel (A,B,C,D) trips
- Logic becomes 1 out of 3, unless bypassed to become 2 of 3.
If trip unit desinged to trip on low
- That unit will not trip, but other three will.
How will a failure of a Preferred AC Bus impact RPS?
All parts of the affected RPS Channel will de-energize:
- Field Instrumentation
- All eleven trip units
- All three 28 VDC logic matrix power supplies( i.e. AB, AC, AD, etc)
- If Y-30 fails, then clutch power supplies 1 and 2 will lose their power, causing a half-trip
- If Y-40 fails, then clutch power supplies 3 and 4 will lose their power, causing a half-trip
Why are the Red Matrix lamps replaced via work order?
due to the potential for a shorted bulb to trip both auctioneered 28VDC Matrix Ladder power supplies and cause a plant trip
What supplies ATWAS Power?
ATWAS Power
Y-230
What are the ATWAS Solenoids?
ATWAS Solenoids
If DC control power is lost, then two solenoids, SV-0522G and SV-0522H, de-energize and open the normal air or backup nitrogen supply line to the air-to-open steam supply valve CV-0522B, which provides steam to the steam-driven auxiliary feedwater pump.
What is the ATWAS Setpoint?
ATWAS Setpoint
2 out of 4 on pressurizer pressure > 2375 psia
What is the function of ATWAS?
ATWAS Function
- Trip the reactor
- Initiate auxiliary feedwater
- Trip the main turbine
What are the 1 Hour or Less TS actions related to RPS?
One Hour or Less TS Actions
One or more ZPM Bypass Removal channels inoperable
- Immediately Remove the affected ZPM Bypasses.
OR
- Immediately Declare the affected trip units inoperable.
One or more Functions with two RPS trip units or associated instrument channels inoperable. Not applicable to high SUR or Loss of Load
- Within 1 hour, Place one trip unit in trip
One channel of Trip Initiation Logic inoperable.
- Within 1 hour, De-energize the affected clutch power supplies
Two channels of Trip Initiation Logic affecting the same trip leg inoperable
- Immediately De-energize the affected clutch power supplies.
