Term
Reactor Coolant Temperature Instrumentation
Purpose |
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Definition
1. Provide signals which are processed for:
Monitoring, Control, Reactor Protection and ESFAS Actuation
2. RCS Temperature is sensed at each hot and cold leg by two different systems:
Wide Range RC Temp Instrumentation
- RCS temp indication during heatup, cooldown, Natural Circulation and Post Accident Conditions
- Input to POPs, temperature indication (Train A Loop 21, Train B Loop 22)
- Input to RVLIS for density compensation ( Train A Loop 22, Train B Loop 24)
Narrow Range RC Temp Instrumentation
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RCS temp indication and alarms during normal operations
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Tave protection against excessive RCS cooldown
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Delta T protection against DNBR
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Signals to various control and protection circuits
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Term
Reactor Coolant Temperature Instrumentation
Design Basis |
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Definition
Prevent or supress conditions which could result in exceeding acceptable fuel design limits.
Develops signals that are used by RPS: OPΔT and OTΔT
These signals provide:
Rod Stops
Runbacks
Reactor Trips |
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Term
Resistance Temperature Detector (RTD)
Operating Principle and Failure Modes |
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Definition
- Operate on the principle that resistance to current flow in a metal will change with temperature
- This change in resistance is proportional to temperature and can be measured with simple electronic circuits.
Failure Modes:
Open Circuit- infinite resistance; RTD fails HIGH temp output
Short Circuit- zero resistance; RTD fails LOW temp output |
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Term
Narrow Range HL RTD
Description |
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Definition
Dual element – Weed-type RTDs
RTDs are NOT in direct contact with reactor coolant. (Three per hot leg, located within 120° of each other)
RTD response time constant ~ 4 seconds
Sampling used to overcome the effects of streaming, appearance of RTD is scoop with 5 holes, mixes RCS in scoop to ensure accurate temp reading. This is required to overcome the laminar flows in RCS HL.
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Term
Narrow Range CL RTD
Description |
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Definition
•Dual element – Weed-type RTDs
One for protection and control
One spare
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RTDs are located in each RCP’s discharge line (one per cold leg)
•No sampling is required, because the RCPS adequately mix RCS coming into the RX.
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Term
| Wide Range RTDs Description: |
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Definition
•RTDs are not in contact with reactor coolant
•RTD response time is slower than NR, i.e. not used for protection function
Functions:
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SPDS & computer
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HSd Pnl 213 indication
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CR indication
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RVLIS (WR T) Tr A from Loop 22, Tr B from Loop 24, used for density compensation with RCPs running
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POPS (WR T) Tr A from Loop 21, Tr B from Loop 22, used for OHA to prompt arming – disarming POPS (312oF)
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Term
Coolant Tave
Tave Channel Range |
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Definition
Tave Channel Range: 530-630°F
(T hot= 530-650°F)
(T cold= 510-630°F)
T hot- T cold = Tave
2
Remember, T hot is the average of the 3 T hot RTDs on the loop. |
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Term
Isolation Amplifier: Purpose |
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Definition
Electrical separation point in circuit, physically separates two sections.
For our circuits it separates the Safety Related and Non Safety Related Parameters which are fed from channels
Will not allow a fault from the NSR circuit create a fault in the SR circuit. |
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Term
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Definition
Turns off one input from four separate loops, i.e. prevents a failed instrument reading from going into the auctioneer. Operators can choose an instrument to be disregarded (left out) when there are indications that one instument has failed.
For Tave, this will only protect the control circuit. The control circuit is downstream of the channel defeat. |
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Term
| Tave Deviation: Definition |
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Definition
| The difference in temperature between Auctioneed Tave and T reference (program Tave) |
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Term
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Definition
Used to record one loop's temperature for event review (rebuilding accident post event)
Operator can choose one Coolant loop to record via bezels. |
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Term
Coolant Tave:
Safety Related Circuit |
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Definition
Outputs on the safety related circuit:
- OTΔT
- OPΔT
- P-12
- MSIL
- Steam Dumps
- HI/LO Tave Alarm
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Term
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Definition
ΔT is a measure of core thermal power, Range 0-100°F
ΔT= T hot - T cold
§Each loop’s ΔT is sent to an auctioneering circuit which selects the highest calculated loop ΔT
§The highest auctioneered loop ΔT is used for various alarm functions
§Rod Insertion Limit alarms
§Loop ΔT / High ΔT deviation alarms
§Individual loop ΔT’s are used for indication and protective functions
§Indication and recording
§High ΔT auctioneering circuit
§Comparison to the OTΔT setpoint
§Comparison to OPΔT setpoint
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Term
OTΔT
Purpose and Background |
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Definition
Purpose: Protect the core against DNB
Background: Status of Nucleate Boiling cannot be directly measured
§Margin to DNB is reduced by:
•Raising coolant TAVE
•Lowering coolant pressure
•Core Axial Flux (ΔI) outside of normal range
•Core thermal power
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Lowering RCS flowrate
§All can be directly measured
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Term
3 Factors Considered in the OTΔT Setpoint and
General Trends when these factors are raised/lowered: |
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Definition
Factors considered in the development of the OTΔT trip setpoint influence DNBR:
•RCS Pressure
•Coolant TAVE
•Core flux distribution
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1 setpoint developed for per coolant loop & compared to actual ΔT in that loop
Normal Value: 76.8°F(when considering program Tave (63)x 1.22)
You start out with a setpoint equal to 122% of the 100% power
ΔT. Then you reduce or raise that setpoint based on:
§TAVE deviation from 100% value:
§Hotter = closer to DNB therefore lower setpoint
§Colder = further from DNB therefore higher setpoint
§Pressure deviation from nominal value:
§Higher = further from DNB therefore higher setpoint
§Lower = closer to DNB therefore lower setpoint
§ DI Φ deviation from design values (too high or too low).
§Higher penalty for Top Peaked because you’re closer to DNB at
the top of the core already.
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Term
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Definition
| Prevent excessive heat generation in the fuel |
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Term
3 Factors Considered in the OPΔT Setpoint and
General Trends when these factors are raised/lowered: |
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Definition
Factors Considered:
§Loop TAVE
§Rate of change of loop TAVE
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Flux distribution (SET TO ZERO)--
There is NO POWER in OPΔT!!!!
Normal Value: 76.8°F(when considering program Tave (63)x 1.09)
The setpoint for OPΔT is 109% of full power ΔT:
§Minus a correction for the rate of change of TAVE (when rising)
§Minus a correction for the magnitude of the change in TAVE
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The OPΔT setpoint cannot be raised >109% of normal power ΔT
Impact (reduced setpoint) when temp is above normal Tave
OPΔT does not give more margine for the setpoint, when Tave gets colder.
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Term
OTΔT and OPΔT
Logic and Plant response prior to hitting trip set point |
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Definition
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When two-out-of-four (2/4) loops have reached the calculated trip setpoint, a reactor trip signal will be generated
§Prior to reaching the trip setpoint, OTΔTor the OPΔT rod withdrawal stop and turbine runback signals are generated
§The pretrip setpoint for this function is 3% below the trip setpoint
§Requires two-out-of-four (2/4) channels to exceed the pretrip setpoint
§This function attempts to correct the plant conditions to prevent a reactor trip
§Automatic and manual Control Bank withdrawal is blocked
§The turbine EHC circuit receives a signal to runback the turbine at 10%/min until condition clears
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Term
| RCS Temp Instrumentation Interfaces with ESFAS: |
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Definition
§Two-out-of-four (2/4) low loop TAVE signals less than 543oF generate the P-12 ESFAS interlock signal
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P-12 allows the manual block of the High Steamline Flow Safety Injection
§Safety Injection, Steamline Isolation, and Feedwater Isolation are generated by 2/4 High Steamline Flow signals, coincident with either
§2/4 Low Steamline Pressure signals, or
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2/4 low loop TAVE signals less than 543oF
§Auctioneered high TAVE (554oF) coincident with a Reactor Trip (P-4) creates a Feedwater Interlock which closes the Main Feedwater Control Valves (BF-19s) and Main Feedwater Bypass Valves (BF-40s)
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Term
Temp Instrumentation Failures:
NR HL RTD Fail High
Tave |
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Definition
§Narrow Range Hot Leg RTD Failure HIGH
§The loop average THOT will be HIGHER
•(range 530 – 650oF for each of the 3 RTDs)
§TAVE and ΔT outputs to their auctioneering units will be HIGHER
§Failed HIGH TAVE will impact
§Rod Control
§With CR in auto (>15% power) – rods step in at 72 steps per minute
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Rod insertion continues until either Rx trip occurs OR
operator action is taken
§Failed HIGH TAVE will impact (continued)
§As rods insert actual RCS Temp will lower, steam pressure lowers, generator output lowers
§RCS volume lowers due to contraction, PZR level and pressure will lower.
§A PZR low pressure reactor trip may occur with no operator action taken.
§PZR Level
•Pzr level setpoint ( Unit 2: 22.3 – 59% from 547 – 576.2oF) will rise and due to lowering PZR level, charging flow will start raising to make up for perceived deviation in program and actual level.
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Term
Temp Instrumentation Failures:
NR HL RTD Fail Low |
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Definition
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Term
Temp Instrumentation Failures:
ΔT Failure |
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Definition
§Provide one OTΔT and OPΔT reactor trip input, and one OTΔT and OPΔT rod stop/turbine runback trip signal
§Since the required 2/4 is not satisfied, no trip or runback will actually occur
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Term
Instrument Failure Response
Narrow Range Hot Leg RTD Failure LOW |
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Definition
§Narrow Range Hot Leg RTD Failure LOW
§The LOW failure has no result in control effect, since the auctioneering circuit will effectively “screen out” this signal.
§Control Console alarms will actuate for:
§RC TAVE HI-LO and
§RC LOOPS ΔT DEV
The low failure will cause ΔT to be low:
•Effectively blocks OTΔT and/or OPΔT trip signal from being developed from that loop
§OTΔT setpoint will rise
§OPΔT setpoint will not rise, but would be blocked from lowering
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Term
Instrument Response:
Narrow Range Cold Leg RTD Failure HIGH |
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Definition
Narrow Range Cold Leg RTD Failure HIGH
§Cold leg RTD failure high will result in a high TAVE but a lowΔT
§Control system response and secondary plant response will be the same as the hot leg RTD failure high
§Individual loop ΔT for the affected loop will be low, so the OTΔT and OPΔT trip setpoints may not be reached
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Term
Instrument Response:
Narrow Range Cold Leg RTD Failure LOW
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Definition
Narrow Range Cold Leg RTD Failure LOW
§No control functions would be affected
§The indication of this failure is the RC TAVE HI-LO and RC LOOPS D/T DEV Control Console alarms
§ΔT for the affected loop would rise, causing the associate OPΔT trip signal from that loop to be generated
§The reduced TAVE in that loop results in OTΔT trip setpoint being raised and depending on where in the allowable calibration band the instrumentation is, the OTΔT Rod Block, Runback and Trip setpoint for that loop may also be exceeded.
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