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Effects of loss of Y-10/20/30/40 on TMMs
- if power is lost you will lose TMM channel and associated RPS channel will trip
- if only lose power to the TMM w/ associated RPS channel still energized, the associated TM/LP trip setpoint fails low, and the VHPT and ASI alarm will trip
Function of the power peaking function generator in the TMM?
generates the power portion of the DNB penalty calculation for the TM/LP trip setpoint
Purpose of the thermal margin/ low pressure (TM/LP) trip
- ensures fuel protection during slow reactivity addition transients starting at low reactor power
- allows S/G tube plugging while maintaining 100% power
- MDNBR safety limit is 1.17(xnb fuel), 1.154(anfp) or 1.141(HTP fuel)
How many times and why do you press the "clr" key prior to taking the TMM to the "Data Modify" mode?
- 6 times minimum
- this clears the buffer
- when any TMM constant has been changed you must verify all other constants prior to exiting "Data Modify" mode
When is it not allowed to reset the VHPT setpoints?
during plant transients
EK-06D3/D4/D7/D8 "Nuclear (delta) T power deviation/ T-inlet off normal/calculator trouble channel A,B,C,D"
- 8 second time delay
- Nuclear-delta-T: 3% deviation
- Tc Max-543.5F
- Tc Min-525F
- calculator trouble
Delta T power (B) signal generation
- Inputs from Tc and Th-ave used to generate delta T power
- Bias term set in TMM adjusts for heat balance
- -only TMM parameter we adjust
When do you reset the VHPT setpoints during power escalation?
prior to escalations above 28.5% and prior to reaching the pre-trip setpoint (</= to 13.5% delta T power) during power escalation
penalty in the Pvar formula that causes the trip setpoint to rise due to an abnormal ASI
LOCA peaking function generator
- takes higher of delta T power or summed NI power via the LPD (low power density) block
- provides for adjustments to the ASI alarm setpoint based on LOCA considerations
- LOCA peaking function not used
What defines the operating envelope for the cores Axial Shape Index?
local power density function generator
Purpose of Axial Shape Index (ASI) alarm
- alerts operator that core axial flux shape is approaching the limits assumed in the safety analysis for T-inlet LCO technical
- assures core axial shape is maintained w/in the boundaries of the safety analysis
What criteria must be met to reset the VHPT setpoints during stable plant conditions?
- Rx power has not changed more than 1/2% for 10 minutes following a transient
- all control rods are withdrawn above PDIL
- PZR press is between 2010-2100 psia, is controlled, and is approaching NOP of 2060 psia
- Tave is within 3F of Tref and is controlled
- PZR level is controlled between 40-60% and is approaching normal programmed level
- Both S/G levels are between 60-70%
Purpose of the Thermal Margin Monitors?
- provides thermal margin/low pressure (TM/LP) trip setpoint to RPS
- prvides the Variable High Power trip (VHPT) signal to RPS
- provides an alarm when ASI is unacceptable prior to exceeding tech specs
- provides and alarm if any of the following exist:
- -delta T-nuclear power deviation
- -TMM calculator trouble
- -Tc alarm
When may calibration of TMM delta-T power be required?
- if heat balance differs by more than +/- 1% from indicated delta-T power on any TMM "primary screen" ORcalibration of delta-T power indication channels is desired
ASI alarm development
- TMM provides an alarm prior to the ASI exceeding TS limits
- uses excores to calculate ASI
- converts it over to an axial offset signal through the ASI function
- compares to the operating box created by the local power density function which takes the higher of NI/delta-T power
How does the VHPT setpoint change w/ power changes?
- Qtr follows power going down
- Qtr must be manually reset on power going up
- resetting VHPT setpoint
- -pushing VHPT reset ( 1for each channel) on C-02
- -can reset on each channel drawer
- TMM only recognizes reset once every 10 seconds
- Pvar is the low pressure trip limit
- Pvar calculated using Tc and Qdnb penalty
- higher of Pvar and Pmin (1760 psia) auctioneered to give you Ptrip
TM/LP trip and pre-trip alarm
- -higher of Pvar and Pmin(1760 psia)
- -setpoint displayed on C-12
- Ppre-trip=Ptrip + 50psia
- TM/LP setpoint low alarm is generated if the TM/LP setpoint drops to 1720 psia indicating a circuit failure
Axial Function Generator
- for a given ASI (Yi) the axial function will calculate Qa, which is used as a factor in computing the penalty factor Qdnb
- -ASI penalty portion of Qdnb
- a negative ASI will produce a greater DNB penalty into the Pvar equation than a positive ASI
Inputs for VHPT operation of VHP function generator
- takes higher of delta-T power and summed NI power
- Q is measured against 2 setpoints
- -Qptr-pretrip alarm=Q + 13.5%
- -Qtr-trip level=Q + 15%
Local Power Density Function Generator
- computes the maximum allowable ASIs(+/-) for the existing power level (QR2)
- QR2 takes higher of delta-T power and NI summed power through LOCA peaking function generator
- trip alarm is generated if ASI, Yi exeeds Yp or Yn
- -not a CR annunciator
- -reported on "status" screen of TMM
- pre-trip alrm is not used
Power Peaking Function (QR1)
- input is Q1, which is higher of delta-T power(B) or summed NI power
- power peaking function is shorted therefore Q1=QR1
- power portion of the DNB penalty
Where is delta-T power sent?
- to determine Tcal
- -has no effect because it is multiplied by a constant Kc=0
- sent to determine power peaking function which determines Qr1 for TM/LP setpoint calculation
- delta-T also sent to VHPT and ASI alarm calculation
- delta-T power indications on C-02 and C-27
Tc max and Tc min Alarm Setpoints
- Tc max=543.5F
- Tc min= 525F
- brings in alarms EK-06D3,4,7,8 annunciators
- alarms also brought in by a TMM calculator trouble alarm override (internal error logic)
Inputs for TM/LP trip portion of the TMM?
- higher of the 2 Tc signals
- -provides input to Pvar setpoint calculation
- -provides input to calculate delta-T power (B)
- 2 Th are measured and averaged
- -average signal sent to determine delta-T power (B) signal
Power supplies for the Thermal Margin Monitors?
- 2 battery backup systems
Inputs to the Thermal Margin Monitors?
- Tcold X2
- Thot X2
- NI power range
Purpose of Variable High Power Trip (VHPT)?
- provides capability to limit transients quickly beginning @ low power levels, w/out operator action
- functions to trip the reactor when the greater of NI power or delta-T power exceeds a preset high power trip value
What must be done to enter new bias terms into the TMM?
- bypass VHPT
- bypass TM/LP
- record date and time in SOP-35 att 4
- press clear on TMM at least 6 times to clear out the numbers in the memory
Outputs from the Thermal Margin Monitors
- nuclear power/ VHPT setpoint and pretrip alarm
- TM/LP pretrip alarm setpoint
- TM/LP setpoint and VHP trips to RPS channels
- TM/LP setpoint low alarms (1720 psia)
- multifunction alarms on EK-06D
ASI function generator
- provides relationship between Ye (input) and Yi (output) using the shape annealing factor S.A.F.
- S.A.F. corrects for bleedover or shine on the excore NIs
- output of ASI function is sent to the axial function generator and to the ASI alarm comparators (via LPD block)
- function of LPD block is to disable the ASI alarm (15% ascending, 14.5% descending)
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