Excore Nuclear Instrumentation System

Purpose:

 Protect the reactor by monitoring neutron flux and generating reactor trip input signals to the Reactor Protection System (RPS) during various operational conditions.

Excore NIs Design Basis:

Source Range-Safety Related

Excore NIs Design Basis:

Intermediate Range-Safety Related

Protection against reactivity excursions from an inadvertent Boron Dilution accident.

Excore NIs Design Basis:

Power Range- Safety Related

Provide high flux trips that protect against reactivity excursions caused by:

Excore NIs Design Basis:

Source, Intermediate and Power Range- NSR

Source Range Nuclear Instruments

Source Range Detectors N31 and N32

Location, Type and Power Supply

Located in detector wells on opposite sides of the core at 0o  and 180o ; core centerline and approximately ¼ core height, ensures detector is located in area of maximum flux during reactor startup Detector wells are shared with the intermediate range detectors (N35, N36)

Type

Boron Trifluoride (BF3) gas filled proportional counters

Without a preamplifier the long cable length and very low signal strength would result in signal loss.

Excore NIs Components- Isolation Amplifier

Isolate the non-safety related outputs from the safety related circuitry

Excore NIs SR Components:

Pulse Shaper

Excore NIs SR Components:

Pulse Driver

Excore NIs SR Components: 

Log Pulse Integrator

Excore NIs SR Components:

Level Amp

Amplifies Log Pulse Integrator Output

Test Signal (0 to 106 cps, variable)

Feeds:

1. Isolation Amplifier with all NSR loads
2. Bistable- SR Hi Flux S/D
3. Bistable- 1/2 >105  cps Rx Trip
4. Local Indication

Gas Filled Detector Six Regions

Region, Description and Location

I Recombination Region: ion pairs recombine before reaching detector anode (Inner chamber of IR detector)

II Ionization Region: all ion pairs reach detector anode (outer chamber of IR detector; PR detector)

III Proportional Region: motion of ions causes additional ionization of the gas, proportional to the ionizing event (SR detector)

IV Limited Proportional Region: Motion of the ions causes additional ionization of the gas, NOT proportional to the ionization event (none)

V Geiger-Mueller Region: Single Ionization event causes all the gas molecules to ionize (GM "frisker" detector)

VI Continuous Discharge Region: Continuous discharge between anode and cathode, regardless of ionizing events (none)

• E-13 SR High Flux at S/D- SR indication > 0.5 decade above bkgrnd
• E-5 SR Det Volt Trbl- SR volts <100 VDC below normal
• E-21 SR High Flux at S/D Blocked- High Flux at S/D switch Block position
• E-29 SR and IR Trip Bypassed-SR or IR Level Trip switch in Bypass position
• A-5 NIS Channel in Test- SR operation selector switch not in normal position
• F-25 SR High Flux Rx Trip- SR Indications >106  cps with level trip switch in normal and/or Hi Level Trip unblocked

• Manual Block of Hi Flux Trip enabled wjen 1/2 IR channels above P6(1x10-10Amps)
• SR Detector auto deenergized when 2/4 PR Channels above P10 (10% Power)
• SR Detectors manual unblock enabled when 3/4 channels below P10 (10% power)
• Hi Flux Trip unblocked and SR detectors auto energized when 2/2 IR channels below P6 (7x10-11Amps)

SR Instruments-

Impacts of Rx Power vs Instrument Failures-Table

Rx Pwr:         Below P6     >P6 (not Blocked)   >P6 and Block or >P10

Lvl Trip Sw:  Norm/Bypass       Norm/Bypass         Norm/Bypass

Loss Instr    Rx Trip/No Trip       Rx Trip/No Trip      NoTrip/No Trip

Power:

Loss Cntrl    Rx Trip/Rx Trip      Rx Trip/Rx Trip       NoTrip/No Trip

Power:

Excore NIs IR Detectors N35 and N36:

Location, Type, Power Supply

Located in detector wells on opposite sides of the core at 0o  and 180o ; core centerline and approximately ¼ core height, ensures detector is located in area of maximum flux during reactor startup Detector wells are shared with the isource range detectors (N31, N32)

Type

Compensate Ion Chambers (CIC)

Excore NIs IR

Overcompensated vs Under Compensated

Over Compensated: Occurs when the Compensation voltage is too high. This causes the indicated value to be lower than actual neutron population. On S/D, may cause the IR current to decrease below the P6 setpoint earlier than normal. If both IRs set wrong, would cause the SR detectors to energize at a higher than normal flux level. On S/U if both iRs set wrong, could cause High SR Trip before recieving permissive to block the SR trip. Also results in false high, SUR indication. 

Under Compensated: Occurs when the Compensation voltage is too low. This causes the indicated value to show higher than actual neutron population. On S/D may cause the IR current to stay above the P6 setpoint, preventing the SR detectors and HVPS from automatically energizing. SRs can be manually unblocked. On S/U could allow block of SR trip early. Indicated SUR will be less than actual SUR.

At 10-11 amps, curve flattens out due to circuit "live zero" when set properly, IR is set slightly undercompensated.

Excore NIs IR Components:

IR Det Volt Loss and IR Compensating Volt Loss Bistables

Both Fed from CIC

IR DET Volt Loss will generate alarm if the detector volts see more than 100 volt loss.

IR Compensating Volt Loss will generate an OHA if the detector see <50% of normal voltage (E-14 and E-22)

Excore NIs IR Components:

Log Current Amp

Provides amplified output proportional to the logarithum of the input. (Fed by Operation Selection Inputs and Amp Idling  Current (live zero) which prevents 0 input to amp during absence of detector output.

Feeds the following:

• Isolation Amplifier- NSR loads
• 10-10Amps Bistable (P6 SR Block Permissive)
• Current = 25% Power to Level Trip Bypass and IR High Flux Rx Trip
• Current =20% Power to Level Trip Bypass and IR High Flux Rod Stop

• E-30, IR High Flux Rod WDRWL Stop, IR indication >20% power and IR Trip Unblocked
• E-6, IR Det Volt Loss, IR 100 volts below normal voltage setpoint
• E-14, IR N35 Compensating Volt Loss, Compensation Voltage <10% normal voltage (-100VDC)
• E-22 IR N36 Compensating Volt Loss, Compensation Voltage <10% normal voltage (-100VDC)
• A-5, NIS Channel in test, IR operation selector switch is not in normal position
• F-17 IR Flux Hi, > 25% power and IR High Flux Trip
• E-29 SR & IR Trip Bypassed, IR level Trip Bypass switch in Bypass Position

IR Detectors:

Impacts of RX Power vs Instrument Failures-Table

Rx Pwr:         Below P10     >P10 (not Blocked)   >P10 (Blocked)*

Lvl Trip Sw:  Norm/Bypass       Norm/Bypass         Norm/Bypass

Loss Instr    Rx Trip/No Trip       Rx Trip/No Trip      NoTrip/No Trip

Power:

Loss Cntrl    Rx Trip/Rx Trip      Rx Trip/Rx Trip       NoTrip/No Trip

Power:

* If >P10 and IR trip is blocked- SSPS internal circuitry inhibits the IR High Flux Trip and Rx IR Rod Stop, independent of status of IR drawer 120 VAC Instrument and Control Power.

The IR instrumentation is required in Mode 1 (<P10) and Mode 2

One IR Channel INOP-

• Mode 1 (<P10) and 2(>P6) Restore to Operable prior to increasing power >10% (NOTE: TS 3.04 is applicable, so if power is >5%, do not increase power above 5%
• Mode 2 (<P6) Restore to operable prior to increasing power above P6 setpoint.

Two IR Channels INOP-

• Mode 1 (<P10) and 2, enter TS 3.03
• Mode 1 (>P10) The provisions of TS 3.03 are not applicable.

The SR instruments are require in Mode 2 (<P6, with Rx Trip System Brkrs in Closed Position and CRD system capable of rod withdrawl) through Mode 6. In mode 6 each SR must have continuous visual indication, in the MRC and one must have audible indication is the containment and MCR.

1 SR Channel INOP

• Above P6- observation may continue
• Mode 2 <P6, Restor inop channel to Operable prior to increasing thermal power above P6
• Mode 6 Immediately suspend core alternations or positive reactivity changes

2 SR Channel INOP 

• Mode 3-5 Verify SDM within 1 hour and once per 12 hrs thereafter
• Mode 6, Immediately suspend core alterations or positive reactivity changes and determine RCS B- conc. at least once per 12 hrs thereafter (TS 3.03 is NOT APPLICABLE)

The PR instruments are required in Mode 1 and 2 (The High Flux Low Set Point Trip is required in Mode 1 below P10, and Mode 2) The provisions of TS 3.04 do not apply to PR instrumentation.

1 PR Instrument INOP

• Place INOP Channel in tripped condition within 6 hrs
• Perform QPTR every 12 hrs or reduce power <75% and PR Trip setpoints to <85% within 4 hrs (inoperable Channel can be bypassed for upto 4 hours for testing of other channel)

2 PR Instruments INOP 

• Enter TS 3.03

Excore NIs PR 

Location, Type and Power Supply

Location: Surround the RX at 45, 135, 225 and 315°, upper and lower detector at each location.

Type: 

Power Supply:

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Excore NIs- PR

Quadrant Power Tit Ratio (QPTR)

QPTR is defined as the ration of the maximum upper excore detector calibrated output to the average of the upper excore detector calibrated output or the ratio of the maximum lower excore detector calibrated output, whichever is greater. The upper and lower current comparators perform  the same function as the process computer in calculating QPTR. If a 2% or greater deviation exists (QPTR > 1.02) then the upper or lower current comparator will generate an alarm to indicate QPTR > 1.02.

Excore NIs PR-

Permissives Table

P6 SR Permissive:

Initiates: 1/2 IR Channels > 10-10 amps

Resets: 2/2 IR Channels <7 x 10-11 amps

Function:

Allows Manual Block of SR High Flux Trip

Automatically re-energizes SR detectors when reset

P10 At Power Permissive:

Initiates: 2/4 PR Channels > 10% Power

Resets: 3/4 PR Channels<10%

Function: 

De-energize SR High Voltage

Blocks SR High Flux Trip

Inputs to P7

Allows Manual Block of IR High Flux Trip

Allows Manual Block of PR (Low Set point) High Flux Trip

P7 Low Power Permissive:

Initiates:1/2 Inputs P10 and P13

Resets: Both P10 and P13 clear

Function:

Unblocks 6 Rx Trips when above P-7

2/4 RCS Low Flow

RCP Bus Underfrequency

RCp Bus Undervoltage

Pzr Low Pressure

Pzr High Level

2/4 RCP Breakers Open

P-8 Low Flow:

Initates: 2/4 PR Channels > 36% power

Resets3/4 PR Channels <36%

Function:

When >P-8, 1/.4 RCS Low Flow

When <P8 and > P7, 2/4 RCS Lower

P-9

Initates: 2/4 PR Channels>49% power

Resets: 3/4 PR Channels < 49%

Function:

When above P9, Enables auto Rx Trip when we have a turbine trip

When below P-9, Disables turbine trip.

• E-15, PR Hi RNG Flux High, 1/4 PR channels > 109%
• E-38, Upper Sect Dev. ABV 50% Pwr, Upper Detector deviation ratio of 1.02 with any channel > 50%
• E-23, PR Lo RNG Flux Hi, 1/4 PR Channels > 25% with PR low Set Point Rx trip not blocked
• E-46, Lower Sect Dev. ABV 50% Pwr, Lower Detector deviation ratio of 1.02 with any channel > 50%
• E-31, PR Overpwr Rod Stop, 1/4 PR Channels > 103%
• E-47, PR Neut Flux Rate Hi, 1/4 PR channels change +/- 5% with 2 sec time constant
• E-39, PR Channel Deviation, 4% difference between highest and lowest PR Channel outputs
• E-7, PR Det Volt Loss, PR 100 volts below normal voltage set point
• A-5, NIS Channel in Test, PR operation selctor switch not in Normal position
• F-1, PR Hi Rng Flux Hi, 2/4 PR channels > 109%
• F-9, PR Lo Rng Flux Hi, 2/4 PR Channels > 25% with PR low setpoint Rx Trip not blocked
• F-33, PR Flux Rate High, 2/4 PR Channels change +/- 5% with 2 sec time constant

Excore NIs PR Components-

Channel and Rate Drawer

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Loss of Power disables to the Comparator Channel Defeat switch and will not function

Indications:

• -5 to 5 decade Meter- Indicates the SUR of this channel selected via the Channel selector switch.
• Channel Deviation Light- Lit when a 4% deviation exists between the highest and lowest of all 4 PR channel output levels (OHA E-39)
• Comparator Defeat-lit when Comparator Channel Defeat Switch is not in Normal Position
• Instrument and Control Power Lights- Lit when power is available.
• Rate Channel Test- Lit when Rate Test switch is not in normal position
• Comparator Channel Defeat Knob- Takes PR channel out of the comparator circuitry (4% difference between channels)
• SUR-Channel Selector Knob- Selects a channel to indicate SUR
• SUR Rate Test Knob- Inserts a 1.0 or 5.0 dpm test signal to the meter

Excore NIs PR Components

Detector Current Comparator Drawer

Powered from D 115 VAC VIB. Loss of Power disables the Upper and Lower Section defeat switches. The Rod Stop Bypass and Powere Mismatch Bypass switches are unaffected by a loss of power and are still functional.

Indications:

• All Channels below 50% FP- Lit when all 4 PR upper detector currents are below 50% of the 100% current value for that detector
• Channel Defeat- Lit when upper section defeat switch is not in normal position
• Upper Selection Deviation- Lit when 1 detector current in upper plane of the core reads 1.02 different from the average of the 4 detector currents in the same plane (QPTR) OHA E-38
• All Channels below 50% FP- Lit when all 4 PR lower detector currents are below 50% of the 100% current value for that detector
• Channel Defeat- Lit when lower section defeat switch is not in normal position
• Upper Selection Deviation- Lit when 1 detector current in lower plane of the core reads 1.02 different from the average of the 4 detector currents in the same plane (QPTR) OHA E-46
• Section Knobs (Upper/Lower)- defeats an upper section detector current input to the comparator circuitry
• Rod Stop Bypass (N41/N43 and N42/N44)- Removes the selected channel from the Rod Stop (C-2) circuitry (RP4 Blue Light)
• Power Mismatch Bypass- Removes the selected channel from the Rod Control System input

Excore NIs PR Components:

Power Range A Drawer

Loss of either control or instrument power to PR drawers will result in tripping all bystables in the associated drawer.

Indications:

• Fuses- Lit when the instrument power is lost, all lights are dark when control power is lost.
• Control Power On- Lit regardless of power level unless control power is lost
• Loss of Dector Voltage- Lit when detector voltage 100 volts below normal.
• Overpower Trip High Range- Lit with Channel above 100%
• Overpower Rod Stop-Lit with Channel above 102% (C-2)
• Overpower Trip Low Range- Lit with channel above 25%
• Power Above Permissive P10- Lit with Channel above 10%,P-10
• Power Above Permissive P-6- Lit with Channel above 36%, P-6
• Positive Rate Trip- Indicates channel level rises >5% with 2 sec time constant
• Negative Rate Trip- indicates channel level lower >5% with 2 sec time constant
• Power Above P9- Lit with Channel above 49%, P9
• Rate Mode Knob- resets + and - rate trip

Excore NIs PR Components

Power Range B Drawer

Loss of either control or instrument power to PR drawers will result in tripping all bystables in the associated drawer.

Indications:

• Amp Meters- indicate actual detector current (unnormalized)
• Operation Selector-Allows testing of either or both detectors
• Operation Selector-Gain- adjusts the level of the drawer output not the level of the detector current (normally adjusted during Calometric BOS)
• Detector A/B Test signal- Inserts variable test signal whent he operation selector switch is selected to the specific detector
• Range Milliamps Knob- ranges detector current meter.
• Instrument power on- lit regardless of power level, unless power is lost
• Channel On Test- lit when operation selector switch is not in normal.

Excore NIs PR Components:

Circuitry

Detector Outputs

Upper and Lower Detector share PR Det Volt Loss Bystable, which monitors the high voltage supply (100 VDC below normal, OHA E-7)

1. Each detector feeds its own Detector Current
2. Each detector feeds its own Isolation Amplifier for Δi to OTΔT and OPΔT Circuits
3. Each detector feeds its own Isolation Amplifier for NR-45, Upper (lower) detector current recorder, P-250, Percent Δi meter. Upper (lower) current comparator defeat switch, Comparator and OHAs E-38 Upper Detector Deviation High (>2% Difference from avg of four) or E-46 Lower Detector Deviation High (>2% Difference from avg of four) 
4. Both detectors feed the Summing and Level Amp Gain Pot.

Excore NIs PR Components

Circuitry

Detector Outputs-Bistables

• Low Range Hi Flux (25%)-OHA E-23 (1/4) OR Rx Trip (2/4)
• P10, PR and IR High Flux Trip Block (10%)-(2/4)
• High Range Hi Flux Trip(109%)- OHA E-15 (1/4) OR Rx Trip (2/4)
• High Range Hi Flux Rod Stop C-2 (103%)- OHA E-31 (1/4) OR Rod Stop (1/4), has the Rod Stop Bypass Switch
• P8, 3 Loop Flow (36%)
• P9, Turb/Rx Trip (49%)

Rate Comparator Feeds 2 Bistables and Local Indication

• Local Indications (0-120% Local indication)
• High Positive Flux Rate (+-5% sec TC)-OHA E-47 (1/4) OR  Rx Trip (2/4)
• High Negative Flux Rate (+-5% sec TC)-OHA E-47 (1/4) OR  Rx Trip (2/4)

Excore NIs PR Components

CircuitryDetector Outputs-

Isolation Amplifiers fed from Summing and Level Amp Gain Pot

Isol Amp-> Power Mismatch Bypass Switch-> feeds and auctioneered high circuit (compares 4 PR instruments) and sends signal to Rod Control (Power Mismatch) and AFD. 

Isol Amp-> MCB Meter, NR45, Plant Process Computer, SPDS

Isol Amp-> Channel Comparator Defeat Switch -> Comparator (looks at all 4 PR instruments) and will initiate OHA E-39 Channel Deviation Alarm when >5% Difference between two channels

This Isol Amp also feeds the Overpower Recorder (0% to 200%)