COLSS Flashcards
What is the purpose of Core Operating Limit Supervisory System (COLSS)?
Purpose:
* Assists in ensuring AOOs will not result in exceeding SAFDL’s and acceptable accident consequences, as long as CPCs trip as expected.
* COLSS provides alarms/indications. CPCs provide the trips.
What is the Linear Heat Rate Power Operating Limit (POL)? Why?
Linear Heat Rate LCO:
* Operating limit (POL) ensures 13.1 kW/ft Tech Spec limit is not exceeded.
* Ensures ≤ 2200°F peak fuel cladding temperature during a LOCA.
* Peak centerline temp safety limit (5080°F) based on preventing fuel centerline melt. (21 kW/ft Hi LPD trip bases)
What computers support COLSS?
Two computers / different Analog to Digital converters
* Core Monitoring Computer (CMC) - normally used to drive the output devices (meters).
* Plant Computer (PC) - back up to the CMC.
* Both part of Plant Monitoring System (PMS / RJ).
* If PMS is failed, COLSS is inoperable.
* Some inputs / input hardware is shared. Failures may affect both.
What is the purpose of the DNBR POL?
DNBR Margin LCO:
* Operating limit (POL) ensures the most rapid DNB Transient from an AOO does not result in **DNBR < 1.34. **
What does COLSS use CEA Positions for? How?
CEA Positions
* Radial Peaking Factor calculations
* Relative Power calculations (compensated for CEA Insertions and Fuel Burnup)
- **COLSS uses the lowest CEA position in a group, and deviation between highest and lowest CEA in a group. **
-
Signal from pulse counters (demanded position).
** Dropped rod (DRC): pulse counter position is reset to zero. **
o *COLSS thinks entire group is on the bottom and affected group has a deviation. (Conservative)
* If one rod slips or sticks (partial insertion): COLSS no longer knows the rod position.* (Non-conservative)
o Position must be manually entered into PMS.
What does the Power Limit Margin Meter display?
Power Limit Margin Indicator (one for CMC / one for PC output)
* Displays the margin to most restrictive power limit.
* Smoothed plant power compared to license power, DNBR POL and KW/FT POL.
* Most restrictive value (smallest margin) is displayed.
What does the Reactor Power Meter display?
Reactor Power Meter
* Displays the unsmoothed value of Plant Power.
* **Displays the larger of Calibrated ∆T Power or Turbine Power ** if inputs to the power calculations are valid.
What is the equation for JSCALOR?
Calculated Secondary Calorimetric
JSCALOR = (hSTM) (FW flow-BD flow) + (hBD) BD flow - (hFW ) FW flow + energy losses – energy gains
How does changing blowdown flow affect JSCALOR?
- Raising SGBD flowrate cause JSCALOR to drop. (COLSS sees some of FW entering the SG not being turned into steam.)
What is the equation for NKBDELT?
∆T Power Calculation
* COLSS uses Th, Tc, PPZR, and RCP mass flow rates for calculation of enthalpy difference. [Q = ṁ(Δh)]
* NKBDELT: uncalibrated ∆T power.
* ∆T power is then calibrated by the secondary calorimetric power (JSCALOR).
* Calibrated ∆T power then becomes JCPCAL.
(JCPCAL has a quicker response than JSCALOR).
What power calculation is normally used at steady state power operations?
JSCALOR: Used when steady state (more accurate)
* Not as accurate during a transient
* Used to calibrate excore NIs
How is turbine power calibrated?
COLSS correlates turbine first stage pressure (TFSP) to power.** It is calibrated to the secondary
calorimetric** (with the same time constants as for JCPCAL).
NKBTFSP = turbine power.
NKCBTFSP is NKBTFSP calibrated by the JSCALOR (secondary calorimetric) value.
What actions are required if JSCALOR is INOP? How long to complete?
- If JSCALOR inoperable - operate on plant power for 12 hours while not raising power. **> 12 hours, lower power to < 96.6%. **
What is the concern with fuel cladding exceeding 2200 F?
- Prevent fuel clad failure during a LOCA by maintain cladding ≤ 2200°F
o **2200°F **causes severe cladding failure by oxidation (zirc-water reaction)
How does COLSS calculate Steam Generator Blowdown Constants?
Secondary Calculations vs Blowdown Constant
* SGBD is manually entered
* ↑ SGBD flow = ↓ FF = ↓ JSCALOR
If Steam Generator Blowdown actual flow stops and constants are not updated in COLSS, is displayed power conservative or non-conservative?
- If actual SGBD flow stops and constants NOT updated, actual power will lower (less feed flow).
o JSCALOR will read lower than actual (non-conservative) (updates fully in 1 hour
How does COLSS respond to loss of pulse counters?
COLSS is INOP
Rod position (CEAs)
* If no rod position is available, COLSS is inoperable. (No substitution)
* Uses group position and group deviation is sent.
* Rod insertion will lower both POLs (radial peaking factors rise).
How does COLSS respond to a loss of In-Core Instruments exceeding the TRM limit?
Incore instruments
* If < TRM number of incores, COLSS is inoperable. (No substitution)
* Any tilt will lower both POLs.
* ASI higher in core (-ASI) will lower DNBR POL. (higher flux in hotter part of the core)
What input sensors can COLSS substitute?
Primary (RCS) sensors and Steam flow
What’s the purpose of Tcold Compensation in COLSS?
Tcold Compensation
* Corrects measured Tcold for sensor dynamics and inlet plenum mixing delays.
o Makes COLSS more responsive during a transient.
What is “Relative Power” in COLSS?
Relative Power
* Incore NI signal should represent the flux in its region in the core. May be affected by:
o CEA insertion in an instrumented F/A
o Instrumented F/A with a different exposure history than other F/As in its region. (higher flux for same power)
o Detector Burnup
* Compensated for by tracking the exposure of instrumented Fuel Assembly, by CEA position and exposure of detectors.
o Signal is modified based on assembly exposure (called the burnup file in COLSS).
o Rhodium decay and signal delay time.
How does a change in Tcold affect COLSS?
T-cold
* If one T-cold fails, COLSS will substitute the other detector (no effect on COLSS).
* ↑ T-cold = ↓ DNBR POL (~ 1% per 2°F ↑)
* Deviation from 555°F causes radial peaking factors to rise (causes KW/FT POL ↓)
T-cold vs. Plant power
* Same as Thot, but opposite direction [↑Tc = ↓NKBDELT]
If JSCALOR is reading less than actual reactor power, is this conservative or non-conservative?
Non-conservative
If Feedwater temperature goes up (stays within range), how does JSCALOR respond?
Feedwater temperature vs. plant power calculations
* One fails - JSCALOR is BAD (COLSS still operable).
* **↑ FW Temp (hFW ↑) **= ↓ JSCALOR (PP will indicate lower in ~ 1 hour)
How does COLSS select Plant Power (PP)?
Plant Power (PP)
* Larger of JCPCAL (calibrated 1° calorimetric power) or NKCBTFSP (calibrated Turb power) becomes plant power (PP)
How does COLSS respond to lowering Pressurizer Pressure?
* ↓ pressure = ↓ DNBR POL. (~ 1% per 20 psi ↓)
* Pressure has minimal effect on LPD POL (no change).
How does COLSS respond to Thot going up?
* ↑ Thot = ↑ NKBDELT
o Reflected in plant power (auctioneered high) until calibrated back down by JSCALOR (~ 1 hour).
* ↓ Thot = NKBDELT ↓ momentarily until calibrated up by JSCALOR
How does COLSS respond to RCP ΔP going up?
- ↑ RCP ΔP = power unaffected (NKCBTFSP would be higher)
- ↑ ΔP = ↓ DNBR POL
- Flow drops as you are closer to shutoff the head (↑ ΔP = ↓ flow)
How does COLSS respond to RCP ΔP going down?
- ↓ RCP ΔP = ↑ indicated power (until calibrated back down by JSCALOR)
How does COLSS calculate Azimuthal Tilt (AZTILT)?
Azimuthal Tilt (AZTILT) Calculation
* Uses incores NIs
* Calculations are performed at 5 levels in the core and averaged to give core AZTILT
* If the number of calculations is less than the Tech Spec value, COLSS will set AZTILT to BAD (COLSS is inoperable).
How will COLSS respond to a slipped CEA?
- AZTILT would rise if a rod is slipped, due to ICI seeing flux shift
- CEA NOT fully withdrawn will result in both POLs being lower (higher RPFs)
How does COLSS calculate Planar Radial Peaking Factor?
Planar Radial Peaking Factors (RPFs) Calculation
* Peaking factor for each of 20 axial levels in the core is computed using:
o CEA data
o RCSVAV (average inlet moderator specific volume based on T-cold).
o For each level, the peaking factor is determined from lookup tables
o** Any Tcold deviation from 555°F **will cause radial flux distribution to get worse.
* Incore information is NOT used to determine radial flux distribution
How does the DNBR POL change as ASI becomes more negative (power to the top of the core)?
DNBR POL will lower
- ASI higher in core (-ASI) will lower DNBR POL. (higher flux in hotter part of the core)
What mode of operation must COLSS be in to be OPERABLE
Scheduled
- COLSS is not operable in any mode but SCHEDULED.
How does COLSS respond to ASI becoming more positive (power moving down in the core)?
DNBR POL will rise (more margin)
