SRM Flashcards
What is the purpose of SRMs?
Provide indication of core neutron flux levels during shutdown, refueling and startup until IRMs are on scale
Provides high flux SCRAM during refuel outages
Under what modes are SRM’s normally used?
Shutdown, Refueling and startup
What is required for SRM to provide a high flux SCRAM?
Shorting links removed
How many SRMs are there and how many are required to be Operable?
4 total: 3 total are required to be operable (depending on mode)
How does an SRM function?
Current pulse is generated from the output of the detector and conditioned through: pulse preamplifier, pulse height discriminator log integrator log count rate amplifier
Displayed and sent to trip units
What is the SRM detector?
detects neutron flux in the core using a proportional range fission chamber:
Operating voltage of 350vdc;
Fill Gas - Argon
Proportional Range
What does the SRM detector send signals to?
Pulse Pre-amplifier
What is the Pulse pre-amplifier?
Located outside DW
Used to amplify detector pulses by sending 350vdc to detector, then:
receives detector signal, isolates high voltage, and passes the signal to the pulse height discriminator
What is the Pulse Height Discriminator?
It eliminates pulses from gamma and only passes pulses from neutron/fission events.
How does the Pulse Discriminator eliminate Gamma pulses?
Gamma pulses provide a much smaller signal which allws the discriminator to isolate the neutron pulses.
PHD only sends pulses with signal greater than specified amplitude
What is the Logarithmic Integrator?
Produces a current signal output equal to the log of input pulse rate
What signal conversion does the Logarithmic integrator perform?
It converts the signal from the pulse height discriminator using a logarithmic (base 10) conversion.
If Input 1000pulses - output proportional to 3
What is the Log Count Rate amplifier and when is it functioning?
when SRM switch is in “OPERATE” this receives the current signal from the log integrator and converts to voltage signal.
Voltage signal used for period amp, meters, trip units and recorder
What is the SRM Period Amplifier?
produces a signal that provides indication of reactor period. Done by looking at rate of change of counts and displaying period.
What is reactor period?
Measure of how long it will take for count rate to grow by factor of e.
Period = 1.44 x DT
When are SRM’s not needed?
When IRM’s are “firmly” on scale
In what region of the gas amplification curve do SRM’s operate?
Proportional Range
How does the SRM produce a count rate?
Proportional Range Fission Chamber coated in Uranium Oxide
What is the operating voltage of the SRM?
350vdc
Where are the SRM mechanical and electrical stops?
upper electrical stop : 18” above core mid-plane
Upper mechanical stop: 24” above core mid-plane
Lower Electrical Stop: just above lower mechanical stop
Lower Mechanical Stop: 24” below active fuel (under core plate)
Where are the SRM drive mechanism and motor?
Drive is undervessel, rack and pinion
motor is in DW outside Rx Pedestal
How does the SRM drive in and out?
Seal in - select SRM, press in button and it continues to get in signal until the “in” button is pressed again
Drive out - Select SRM, “out” button must be held the entire time it gets moved.
What are the power sources for the SRM Motors?
SRM 21/22 - MCC 28-1
SRM 23/24 - MCC 29-1
What provides the SRM detector with the required voltage?
What is the power supply for it?
What is the voltage supplied to it and what is sent to SRM detector?
HV Supply sends to SRM detector
The 24/48vdc battery system provides power to the HV supply (2A - SRM 21,22; 2B - SRM 23,24) via:
Pre-regulator maintains voltage at steady 20vdc, and then the voltage regulator supplies 15vdc to the HV supply and rest of SRM circuit
What is the SRM Signal Generator?
When SRM Mode Switch is in either 10 or 10^5 position, it sends test signals to the Pulse Height Discriminator for calibration purposes.
Which SRM Trips are seal in and where can they be reset?
Where are the trip lights present and how do they react to the trip signal clearing?
Seal in: Upscale Hi-Hi Upscale Hi Period Tip Voltage low INOP trip
Must be manually reset on back panel SRM cabinet. 902-5 panel lights auto clearn when trip signal no longer present
What are the SRM Mode Switch Modes?
Operate, Zero, Standby, 10, 10^5
What provides power to the SRM Select Matrix?
Instrument Bus
What provides power to the SRM Chart Recorder? Where is it?
ESS; 902-5 panel
What is the SRM INOP INHIBIT?
Red pushbutton on SRM backpanel - allows SRM MODE switch to other than OPERATE without initiating alarm or rod block
Rod blocks and alarms caused by Mode switch being “out of operate” are inhibited for as long as the “INOP INHIBIT” pushbutton is held in
There are ________ SRM Shorting Links. With all of them removed, signals from _________ will cause ________.
With ______ shorting links removed, all neutron monitoring systems are changed to ________ logic. The SRM ______ is operational but a _______ signal is required from each trip subsystem(train).
When all shorting links are installed, the SRM _______ is ________. The other neutron monitoring systems are in _______ logic.
4; Any Single SRM, IRM, or APRM Hi-Hi; Will Cause Scram.
2; coincident (1 out of 2 twice); SCRAM; Hi-Hi
SCRAM; Bypassed; Coincident (1 out of 2 twice)
What is the purpose of the SRM Bypass Switch?
Bypasses rod blocks, scrams, and alarms for SRM channel to be bypassed. ONLY ONE SRM MAY BE BYPASSED
The 902-5 retract permit light illuminates when?
When the retract permit light is off on the 902-36 panel
What causes a retract permit block?
All of the following: Detector not "full in" Indicated CPS <290 IRM on range 1 or 2 Rx Mode Switch not in Run
During startup, whn will an SRM withdrawal prevention interlock occur when withdrawing an SRM? What else will happen?
If withdraw results in <290cps. Rod block results
How does the period meter respond during subcritical rod pulls?
Deflects up and returns to infinity
What are the SRM Alarms/Trips/Interlocks?
SRM INOP SRM HI SRM HI-HI SRM Short Period SRM Downscale SRM Retract Permit (Detector Wrong Position)
What is the Signal for SRM Downscale and the resultant?
SRM Counts <6cps (4-8cps) - ALARM ONLY
What is the signal for SRM HI and the resultant?
8.85 E 4 CPS - Results in Rod Out Block
Bypassed when IRMs on Range 8 or above or Rx Mode in RUN
What is the Signal for SRM Short Period and result?
Alarm Only for period <20sec
What is the Signal for the SRM INOP and resultant?
HV Voltage Low
Module Unplugged
Function Switch out of Operate
Results in Rod Block Out Trip
Bypassed when all IRMs on Range 8 or above; OR Rx in RUN
What is the signal for the SRM Retract Permit (Detector Wrong Position) and resultant?
Failure to meet any ONE of the following: Detector fully inserted >290cps IRMs on range 3 or above Reactor Mode Switch in Run
Rod Out Block
What is the signal for an SRM Hi-Hi and resultant?
> = 2.7E5 CPS - Causes SCRAM - ONLY if all shorting links installed.
What happens to SRM with a loss of 24/48 Bus A? Bus B?
Loss of division SRM - causes rod block if Rx Mode not in RUN and IRM < range 8
Half Scarm on Div if 2 shorting links removed
Div SRM status lights lost
Meters and recorders go downscale
What happens to SRM with loss of ESS?
Recorder fail as is ONLY
What happens to SRM with loss of IB?
Loss of Drive Select Matrix - cannot move any SRMs
What are the power sources of the SRM motors and what happens if this power source is lost?
21/22 - 28-1; 23/24 - 29-1
Cannot move the detectors
For the SRM: what is the Detector Coating and Thickness?
Fill Gas and Pressure?
Voltage Supplied?
Ionization Gap?
Uranium Oxide - 3mg
Argon - 213 psi
Voltage is 350V-550V
Ionization Gap is 12.5mils
Where are the SRMs Located (Core Quadrant)?
21 | 23
______
24 | 22
