Nuclear Instrumentation Flashcards
LCO 2.1.1 “Reactor Core Safety Limits” requirement
- DNBR shall be maintained at or above the following correlation safety limits: XNB - 1.17, ANFP - 1.154, and HTP - 1.141
- LHR shall be maintained <= 21.0 kW/ft
LCO 2.1.1 “Reactor Core Safety Limits” applicability
Modes 1-2
LCO 2.1.1 “Reactor Core Safety Limits” required action if DNBR or LHR not within safety limits
WITHIN 1 HOUR restore compliance and be in Mode 3
LCO 3.2.1 “Linear Heat Rate” requirement
LHR shall be within limits specified in the COLR, and the incore alarm system or excore monitoring system shall be operable to monitor LHR
LCO 3.2.1 “Linear Heat Rate” applicability
Mode 1 with thermal power > 25% RTP
LCO 3.2.1 “Linear Heat Rate” required actions if LHR not within limits specified in the COLR, as determined by 4 or more coincident incore channels, excore monitoring system, or manual incore readings
WITHIN 1 HOUR restore LHR to within limits
LCO 3.2.2 “Total Radial Peaking Factor” requirement
Total Radial Peaking Factor shall be within the limits specified in the COLR
LCO 3.2.2 “Total Radial Peaking Factor” applicability
Mode 1 with thermal power > 25% RTP
LCO 3.2.3 “Quadrant Power Tilt” requirement
Quadrant Power Tilt shall be <= 0.05
LCO 3.2.3 “Quadrant Power Tilt” applicability
Mode 1 with thermal power > 25% RTP
LCO 3.2.4 “Axial Shape Index” requirement
The ASI shall be within limits specified in the COLR
LCO 3.2.4 “Axial Shape Index” applicability
Mode 1 with thermal power > 25% RTP
LCO 3.3.1 “Reactor Protective System Instrumentation” requirement
4 RPS trip units, associated instrument channels, and associated ZPM bypass removal channels shall be operable for each RPS trip function
LCO 3.3.1 “Reactor Protective System Instrumentation” applicability
- High Startup Rate Trip - Modes 1-2
- Loss of Load Trip - Mode 1 when thermal power >= 17% RTP
- All others - Modes 1-2, and Modes 3-5 with more than 1 full-length control rod capable of being withdrawn and PCS boron concentration less than refueling boron concentration
LCO 3.3.1 “Reactor Protective System Instrumentation” allows bypass of which trips, and when?
- High Startup Rate - when wide range power < 1E-4% RTP or > 13% RTP
- Low PCS Flow, Low S/G A Pressure Trip, Low S/G B Pressure Trip, and TM/LP Trip - when wide range power < 1E-4% RTP. Bypass shall be automatically removed when wide range power is >= 1E-4% RTP
LCO 3.3.1 “Reactor Protective System Instrumentation” required action if 1 or more ZPM bypass removal channels inoperable
IMMEDIATELY remove the affected ZPM bypasses or declare the affected trip units inoperable
LCO 3.3.1 “Reactor Protective System Instrumentation” required action if 1 or more functions with 2 RPS trip units or associated instrument channels inoperable
- WITHIN 1 HOUR place 1 trip unit in trip
- Not applicable to ZPM bypass removal function
LCO 3.3.7 “PAM Instrumentation” requirement
The PAM instrumentation for wide range flux and CETs (all 4 quadrants) shall be operable
LCO 3.3.7 “PAM Instrumentation” applicability
Modes 1-3
LCO 3.3.8 “Alternate Shutdown System” requirement
The alternate shutdown system function for 1 source range channel on C-150 shall be operable
LCO 3.3.8 “Alternate Shutdown System” applicability
Modes 1-3
LCO 3.3.9 “Neutron Flux Monitoring Channels” requirement
2 channels of neutron flux monitoring instrumentation shall be operable
LCO 3.3.9 “Neutron Flux Monitoring Channels” applicability
Modes 3-5
LCO 3.3.9 “Neutron Flux Monitoring Channels” required action if 1 or more required channel(s) inoperable
IMMEDIATELY suspend all operations involving positive reactivity additions
LCO 3.9.2 “Nuclear Instrumentation” requirement
2 source range channels shall be operable
LCO 3.9.2 “Nuclear Instrumentation” applicability
Mode 6
LCO 3.9.2 “Nuclear Instrumentation” required action if 1 source range channel inoperable
IMMEDIATELY suspend core alterations and suspend positive reactivity additions
LCO 3.9.2 “Nuclear Instrumentation” required action if 2 source range channels inoperable
IMMEDIATELY initiate action to restore 1 source range channel to operable status
How many excore NIs do we have, and what are there functions?
2 source range, 2 wide range, and 4 power range NIs to monitor neutron flux from the source range through 125% power
What is the purpose of the excore NIs channel range overlap?
To ensure flux is continually monitored
What are the excore NIs signals used for?
Used to process a reactor trip on SUR, VHPT, and TM/LP
How do the source range NIs function?
- Dual fission chamber detectors
- Output pulses are amplified, discriminated, and summed, then sent to the control room, C-150A, and containment
Which NIs go to C-150A through an optical isolator?
NI-1/3, SR/WR detector
What range is covered by the source range detectors?
6 decades from 0.1 to 10^5 CPS
What range is covered by the wide range detectors?
10^-8 to 200% power
When source range detectors read 3 CPS, what will the wide range detectors read?
10^-7
What are the power supplies for the source range/wide range NIs?
NI-1/3A - Y-30
NI-2/4A - Y-40
How does pulse discrimination work?
Neutron pulses are bigger than gammas, so the threshold voltage (bias) is set to pass only neutron pulses.
What is the function of campelling mode for the wide range detectors?
Between 0.05% and 0.1% power, wide range swaps from pulse mode to campbelling mode, which swaps from counting pulses to measuring current flow. When this swap occurs, SR/WR will indicate a step change of approximately 0.04% power.
What are the power supplies for the power range detectors?
NI-5/6/7/8 from Y-10/20/30/40 respectively
How are the power range detectors used in the rod drop alarm circuitry?
A summer sums the output of the upper and lower amplifiers and sends an output to the rod drop detection circuit. Upon detection of an 8% power drop in < 8 seconds, a relay activates a rod drop alarm
What is the function of the incore NIs?
- provide measured data that may be used in evaluating the neutron flux distribution in the core
- thermocouples at the top of each incore provide input the the PPC (CET)
Why aren’t incores used for control or safety function?
- self-powered rhodium detectors
- rhodium has a long half-life (41.8 seconds), so the effects of a step change in reactivity won’t be fully seen by the incores for 3-5 minutes
What is cold leg temperature shadowing?
As water surrounding the core lowers in temperature, it becomes more dense, which reflects more neutrons back into the core. This causes excores to read lower than actual power. Typically 0.5% power per degree F
How do we compensate for cold leg temperature shadowing?
Periodic calibration of the excores to match calorimetric power (heat balance)
What is control rod shadowing?
Excores only see neutron leakage from the core periphery. Anything that causes peripheral fuel assemblies to indicate a power level not representative of core average power will cause erroneous power level to be seen by the excores.
How do we compensate for control rod shadowing?
We operate with all rods full out at full power, and we periodically calibrate the excores to match calorimetric power
How does fuel burnout affect indicated power?
Fuel burnout causes flux to shift towards the outside of the core over core life. This causes power to indicate higher than actual if not adjusted for.
How do boron concentration changes affect NIs?
Boron concentration changes can result in rod movement, which changes axial neutron flux, ASI, local power densities, LHR, and cause xenon oscillations.
How do reactor poisons affect NIs?
Reactor poisons can shift core power, and thus neutron flux density, both axially and radially
What does the “High Voltage” light indicate on the power range drawers?
When lit, indicates a loss of high voltage (675 VDC) to the detector
What does the “15% Bypass” light indicate on the power range drawers?
When lit, indicates “Loss of Load” trip is bypassed for this channel (automatically bypassed < 15% power, and automatically removed > 15% power and rising).
What does the “Rod Drop” light indicate on the power range drawers?
When lit, indicates rod drop bistable has tripped, due to a sudden drop in power (>= 8% in <= 8 seconds)
What does the “Channel Deviation Level 1 (5%)” light indicated on the power range drawers?
When lit, indicates a 5% deviation between this channel’s power and the 4 channel’s average power.
What does the “Channel Deviation Level 1 (10%)” light indicated on the power range drawers?
When lit, indicates a 10% deviation between this channel’s power and the 4 channel’s average power.
What causes a rod withdraw prohibit?
- VHP Pre-Trip (2/4 13.5% above reset power level)
- High Power Rate Pre-Trip (1/4 1.5 DPM, between 10^-4% and 15% power)
- EM OFF
- Loss of Y-40 above 15% power
How do we enable/disable the ZPM Bypass?
- Key switch (1/4 with wide range NI < 10^-4% power)
- Automatically removed above 10^-4% power
What trips are removed when in ZPM Bypass?
- Low PCS Flow
- Low Pressure S/G 1
- Low Pressure S/G 2
- TM/LP
What is the system interrelationship between NIs and RPS?
- Power range instruments provide inputs for VHPT, TM/LP, disabling “Loss of Load”, and generator coastdown trip
- Wide range instruments provide input for high rate of change trip, and disabling ZPM bypasses > 10^-4%power
What is the system interrelationship between NIs and SPI Node/Host Computer?
- If SPI Node/Host Computer inoperable in Mode 1 > 25% power, then Excores shall be used to monitor LHR
- If SPI Node/Host Computer inoperable in Mode 1 > 25% power and exocore monitoring isn’t available, then manually reading incores shall be performed to monitor LHR
What is the system interrelationship between NIs and Heat Balance Calculation?
Heat Balance is used to check and calibrate power range NIs
When is a heat balance verification required to be performed?
If heat balance differs by more than 2% from any indicated nuclear power or delta T power channel on TMMs
When is it required to calibrate the power range NIs?
If heat balance differs by more than 1% from any indicated power channel on TMMs digital meters or status screen, or if desired
When is it required to calibrate the delta T power indication channels?
If heat balance differs by more than 1% from any indicated delta T power channel or TMM primary screen, or if desired
How is calibration of delta T power indication channels performed?
- (Heat Balance Power - Delta-T Power) x 0.01 = change in bias.
- If calculation results in a positive value, then the bias needs to be raised by that much, and vice versa for a negative value.
What trips must be bypassed prior to entering new bias terms in the TMM when calibrating Delta-T Power indication?
- VHPT
- TM/LP
How do you remove a source range/wide range NI from service?
- Place in bypass 1 affected channel High SUR Trip
- Place in trip any other affected channel High SUR Trip
How do you remove a power range NI from service?
Place in bypass 1 affected channel, and place in trip any other affected channel of TM/LP, Loss of Load, VHPT, and High Power Rate
