Reactor Protective System Flashcards
Discuss the function of Reactor Protection System.
- Ensure TS Safety Limits are not exceeded by tripping the Reactor whenever any of the Limiting Safety System Settings (LSSS; RPS Trip setpoints) are exceeded. Required by 10CFR50 APP-A
- Protects Specified Acceptable Fuel Design Limits during Normal and AOO’s
- DNBR for cladding protection
o Thermal Power, Pressure, Tcold - Peak Linear Heat Rate for Fuel Protection (KW/FT – Peak Fuel Centerline Temp)
- Limits RCS <2750 psia during AOOs
- RPS has redundancy such that a single failure will NOT cause nor prevent a Reactor Trip
- Protects plant equipment (RCPs)
What Reactor Trips ensure that SAFDLs are not exceeded?
- TM/LP & Low Power Density in conjunction with T/S’s
- Variable High Power & PDIL’s
Discuss the RCS Pressure Safety Limit.
- RCS Pressure must NOT exceed 2750 psia – RCS integrity protection
Mode 1, 2: Be in Mode 3 with pressure 2750 within 1 hour
Mode 3, 4, 5: be <2750 psia within 5 min
Discuss how DNBR protection is achieved.
Combination of Power, Tc, and Ppzr shall NOT exceed limits of curve – DNBR protection
* RCS Cold Leg Temp
* Thermal Power
* RCS Flow
* ASI
What are the RPS Color designators.
RPS Color Designators
A Channel - Red
B Channel - Yellow
C Channel - Green
D Channel - Blue
Discuss Q Power.
- The value of Q power is the auctioneered high value of either LRNI power or ∆ T power
- The calculated value of Q power is then sent to each RPS channel
Why does Q power look at two signals?
- NI Power is inaccurately low during C/D events since colder water tends to shield the Ex-core detectors
- Delta T power is too slow to protect against a CEA ejection accident, and not accurate at low power.
What are the Inputs in the Q Power calculation?
∆T power & Linear Range NI’s
1) ∆ T power:
- Calculated ∆ T power is derived from:
a) Average Hot Leg Temp; and
b) Maximum Cold Leg Temp.
RPS ∆ T = Thot avg - Tcold max
- Thot has a range of 515°F – 665°F. This is important when considering failures!! Since ∆T is derived from (Average Thot - Maximum Tc), a failed high Th would cause the calculated ∆T to increase, most likely shifting the auctioneered high value of Qpwr to be generated from ∆T power.
- Tcold range 465 – 615°F. This is important when considering failures!! Since ∆T is derived from (Average Thot - Maximum Tc), a failed high Tc would cause the calculated ∆T to decrease, most likely shifting the auctioneered high value of Qpwr to be generated from the LRNI’s.
2) Linear Range NI Power:
* 4 Linear Range Nuclear Instrument channels, each consisting of an upper and a lower detector feed each channel of Q power
What is the Basis for the Variable High Power Trip?
The Variable High Power Level trip provides reactor core protection against positive reactivity excursions that are too rapid for a High Pressurizer Pressure or TM/LP trip to protect against.
The following events require Variable Power Level - High trip protection:
* Uncontrolled CEA withdrawal event
* Excess load
* [Unit 2, Excess feedwater heat removal event]
* CEA ejection event
* Main steam line break (MSLB) (backup protection)
What are the Setpoints for the Variable High Power Trip?
Setpoint:
Variable (calculated by CPC-2) within Max 107 % and Min 15% power
(CWP on Pretrip ~ 2% less than trip setpoint)
9.61% Trip above last reset
7.61% Pre-Trip (trip setpoint - 2%)
5.61% Manual Reset lights (trip setpoint – 4 %)
What are the Blocks or Interlocks associated with the Variable High Power Trip?
Setpoint ranges from 15% minimum to 107% maximum
Setpoint automatically follows power down, but must be manually adjusted as power is increased by pressing the Hi Power Reset Pushbuttons on the RTGB or on the RPS Cabinets
VHP Trip Reset Button lights up when power is within 4% of setpoint - indicates setpoint needs to be reset
What is the Pre-Trip Setpoint for the Variable High Power Trip?
Pretrip when power is within 2% of the setpoint
2/4 Pretrips generate a CEA Withdrawal Prohibit signal.
What is the Basis for the High Startup Rate Trip?
The High Rate of Power Change trip is NOT credited in the accident analysis as providing primary protection for any limiting case AOO or Postulated Accident (PA).
Equipment protection trip to protect core, used only at low power levels to protect the reactor against an uncontrolled CEA withdrawal or boron dilution incident when the reactor is critical but at low power.
What are the Setpoint for the High Startup Rate Trip?
Setpoints:
Trip < 2.49 dpm
Pretrip ~ 1.3 dpm
Provides CWP (CEA Withdrawal Prohibit)
Auto blocked if:
< 10-4% power decreasing
> 15% power increasing
What is the Pre-Trip Setpoint for the High Startup Rate Trip?
Pretrip lights enabled at 1.3 DPM (between enabled ranges of >10 –4 % and <15%)
2/4 Pretrips generate a CEA Withdrawal Prohibit
What is the Basis for the Thermal Margin/Low Pressure Trip?
The TM/LP trip prevents exceeding the DNBR SL during AOOs and aids the ESFAS during certain accidents. The following events require TM/LP protection:
* Excess load (inadvertent opening of a steam generator ADV)
* RCS depressurization (inadvertent safety or PORVs opening)
* Steam generator tube rupture
* LOCA accident
TM/LP is also utilized to trip on asymmetric steam generator pressure conditions (ASGT).
What is the Setpoint for the Thermal Margin/Low Pressure Trip?
Trip setpoint is variable and compares pressure setpoint (derived by the Core Protection Calculator) vs. actual PZR pressure. The calculated pressure setpoint is compared to actual RCS pressure. If RCS pressure is less than the setpoint, a RX trip signal would be generated.
Minimum setpoint: {1887 psia} [1900 psia]
What are the Blocks or Interlocks associated with the Thermal Margin/Low Pressure Trip?
The Zero Power Mode Bypass key block bypasses this trip when {≤ 1%} [≤ 0.5%] WR power
What is the Pre-Trip Setpoint for the Thermal Margin/Low Pressure Trip?
Pre-trip 50 psi higher than setpoint.
2/4 Pretrips generate a CEA Withdrawal Prohibit
What are the inputs to the Thermal Margin/Low Pressure Trip Setpoint?
1) Max Cold Leg temperature
2) QPwr
3) ASI - modifies signal through shape annealing.
4) Assymetric S/G trip – If present will drive pressure trip setpoint to ≥ 2500 psia.
Asymmetric SG Transient (ASGT) – Part of TM/LP (DNBR)
Basis: Protects against secondary system malfunctions that create asymmetric Tc tempsresulting in significant radial peaking.
Most limiting event is the Loss of Load caused by the slow closure of one MSIV
* (PSG A – PSG B) > 135 psid [120 psid] sets TM/LP input to 2500 psia = TM/LP trip (on affected channel) since normal RCS pressure is 2250 psia.
What failures could cause a Thermal Margin/Low Pressure Trip to be generated?
A TM/LP trip will be generated if:
1) S/G pressure inst fails (High or low) – (ASGT)
2) Failed upper or lower NI detectors (High or low) – would impact penalties for ASI
3) Failed upper or lower NI detectors (High failures only) – would raise calculated value of Qpwr.
4) Failed Thot high – Would raise calculated value of Qpwr due to ∆T power increasing.
Failed Tcold high – Would raise calculated value of TM/LP setpoint
What is the Basis for the Local Power Density Trip?
The Local Power Density - High trip ensures that excessive axial peaking, such as that due to axial xenon oscillations, will not cause fuel damage. It ensures that neither a DNBR less than the SL nor a peak linear heat rate that corresponds to the temperature for fuel centerline melting will occur. This trip is the primary protection against fuel centerline melting.
Input:
Core Protection Calculator-2 contact. CPC-2 calculates both ASI (Y) and ASI limits (Yn & Yp).
Setpoint:
Trip: Variable, ITS Figure 3.3.1-3 (this is two pages)
Pre-Trip: Variable
(CWP on Pretrip)
Bypassed <15% power via Lin 1 bistable
What is the Setpoint for the Local Power Density Trip?
Setpoint is Variable with power (As determined by Core Protection Calculator #2)
Basically this trip is based on actual ASI as determined by Q-power vs. ASI setpoint as determined by LRNI’s. To calculate the trip setpoint, CPC-2 looks at Q-power that is sent to core protection calculator -2 and it develops a limit curve that ASI must be within. If ASI is not within these limits, a Rx trip is generated.
CPC-2 looks at actual ASI versus an ASI Limit curve which is developed by CPC-2 with inputs from Qpower.
What are Blocks or Interlocks associated with the Local Power Density Trip?
Enabled > 15% by the Linear PR Safety LRNI #1 Bistable
Auto Bypass disabled at <15%
What is the Pre-Trip Setpoint for the Local Power Density Trip?
Variable setpoint.
2/4 Pretrips will cause a CEA Withdrawal Prohibit
What failures could generate a Local Power Density Trip?
Failed upper or lower detector – Would drive either HIGH OR LOW (ASI)
Failed T-hot HIGH (to 665°F) - ASI limits
What is the Basis for the RCS Low Flow Trip?
The low reactor coolant flow trip is provided to prevent violation of the DNB SAFDL during the Loss of Coolant Flow and Loss of AC Power AOOs
Assists ESFAS in accident analysis for seized/sheared rotor shaft [U2 only – certain MSLB events] and thus limit fuel pin damage due to DNB along with peak RCS pressure.
Input S/G D/P (RCS side)
Setpoint: {>95%} [>95.4%] of 375,000gpm
Manual Key Bypass {< 1%} [.5] via ZPMB, Auto removal on power rising
What is the Setpoint for the RCS Low Flow Trip?
Trip is set at {95%} [95.4%] of RCS design flow (375,000 gpm)
DP across each SG is summed to provide RCS flow indication
What are Blocks or Interlocks Associated with the RCS Low Flow Trip?
Zero Power Mode Bypass key block bypasses trip when {≤ 1%} [≤ 0.5%] WR power
Bypass is auto removed when power rises above permissive.
What is the Pre-Trip Setpoint for the RCS Low Flow Trip?
Pre-trip at {96%} [97%] flow
What is the Basis for the High Pressurizer Pressure Trip?
The Pressurizer Pressure - High trip, in conjunction with pressurizer safety valves and main steam safety valves (MSSVs), provides protection against overpressure conditions in the RCS during the following events:
* Loss of condenser vacuum with a concurrent loss of offsite power
* Loss of condenser vacuum with a concurrent loss of one 6.9 kV bus
* Loss of External Load/Turbine trip
* CEA withdrawal
* Loss of feedwater flow
Input: NR Pressurizer Pressure
Setpoint: {2400} [2370] psia
Sends a signal to open PORVs
What is the Setpoint for the High Pressurizer Pressure Trip?
Trip is set at 2/4 NR Pressurizer Pressure instruments sense {≥ 2400 psia} [≥ 2370 psia]
What is the Pre-Trip Setpoint for the High Pressurizer Pressure Trip?
Pretrip set @ {2350 psia} [2327 psia]
What is the Basis for the Low Steam Generator Level Trip?
The Steam Generator Level - Low trip ensures that low DNBR, high local power density, and the RCS pressure SLs are maintained during normal operation and AOOs, and, in conjunction with the ESFAS, the consequences of the Feedwater System pipe break accident will be acceptable.
Input:
Low select of either S/G A or B Narrow Range Levels
Setpoint: 35% NR Level
What is the Setpoint for the Low Steam Generator Level Trip?
Trip is set at ≤ 35% level on Narrow Range level on the auctioneered low A or B S/G
Each RPS channel looks at both SG’s and uses the lowest level (auctioneered low)
An individual RPS Channel Trip will occur if:
* Any single ‘A’ train S/G level instrument senses level ≤ 35%; or
* Any single ‘B’ train S/G level instrument senses level ≤ 35%
An actual RX Trip would occur if:
* Any 2 RPS Channels have a S/G level instrument that senses level ≤ 35%
Setpoint ensures enough inventory in SG’s at time of trip for 10 min margin before AFW is required
What is the Pre-Trip Setpoint for the Low Steam Generator Level Trip?
Pre-trip at 40%
