Nuclear Instrumentation

Question 1

Describe Nuclear Instruments.

Answer 1

*12 [14] detectors total
*Monitors core power over 10 decades from shutdown (2 * 10 –8) to 200% power
*Encased in polyethylene to thermalize neutrons (detects fast leakage from core)

Question 2

Discuss the Fission Chamber Nuclear Instruments.

Answer 2

WR Log Safety Channels - Ionization Region (4)
o {U1 ONLY: Extended Range for 0-1000 cps}
o {BDAS}
o [U2 ONLY: Channels A and B Wide Range Safety Channels to provide another indication on the HSCP. WR Channels A and B make sense with the Excores powered from MC and MD]

WR Log Excore Appendix R Channels - Ionization Region (2)
o Each unit has 2 Excore App-R instruments with indication in the control room and at the HSCP.
o 2 Excore Neutron Monitoring Channels Fission Chambers (Same as WR)

Question 3

Discuss the Uncompensated Ion Chamber Nuclear Instruments.

Answer 3

Linear Power Range Safety Channels - Ionization Region (4)
Linear Power Range Control Channels - Ionization Region (2)
o 2 Linear Power Range Control Channels - Uncompensated Ion Chambers (N2 gas, B coated wire)

[BF3 Proportional Counter]
Unit 2 Only Log Startup Channel – Proportional Region (2)
o [2 Logarithmic Startup Channels (SR) - BF3 Proportional Counter – (BF3 gas) – 0-10,000 cps]
o [BDAS]
o [Manually energize on shutdown <10-5% power. Auto de-energizes at 10,000 cps ~10-4% on up-power.]

Question 4

Discuss Nuclear Instrument Detector Ranges.

Answer 4

Detector Ranges
* Wide Range_________2 * 10-8% - 200% Power
* Linear Range________0% - 200% Power
* Source Range_______{0-1000 cps – WR safety extended range} [0 – 10,000 cps]

Question 5

How do Nuclear Instruments differentiate between neutron and gamma radiation?

Answer 5

Gammas eliminated by Pulse Height Discriminator below 410-3% (low power)
Campbelling discrimination >410-3%: Uses square root compensation to widen the gaps between the pulses to make them easier to detect and discriminate. Ac voltage squared is proportional to power.

Question 6

Discuss the regions of the Gas Amplification curve.

Answer 6

Recombination Region
* Applied voltage is too low so electrostatic force is too low and Ion Pairs Recombine before collection

Ionization Region - WR and Linear
* Applied voltage is strong enough to cause the ion pairs to move to the electrodes
* Each event will cause a fixed number of ion pairs and all will be collected

Proportional Region - [BF3 Start-up Channels]
* Applied voltage results in an electrostatic force strong enough to accelerate the ion pairs thus causing Secondary Ionizations of the detector gas. More Ions are collected (Gas Amp) than were originally produced by the event but the number produced is still directly ~ to power

Limited Proportional Region
* The higher applied voltage causes even more Gas Amp - Ion pairs are no longer ~ to power

Geiger Mueller Region, Friskers; Unit 1 CIAS Monitors
* Applied voltage is high enough to cause ALL gas in tube to ionize for a single radiation event, Avalanche of secondary ionizations causes’ detector saturation-cannot immediately detect another incident radiation event

Continuous Discharge Region
* Applied voltage is so high-current arcing continuously between electrode-no measurement possible

Question 7

Describe the Wide Range Log Safety Channel Nuclear Instruments.

Answer 7

4 Fission Chamber instruments operating in the Ionization Region.

Range: 2x10-8 % - 200 % Power

Question 8

What do the Wide Range Log Safety Channel Nuclear Instruments provide power level input to?

Answer 8

• High SUR RX trip.
• LOG bistable: (10 -4% power)
• Zero Power Mode Bypass (ZPMB) bistable {< 1.0%} [0.5%]
• Swap from pulse height discrimination to Campelling Mode @ 4*10-3%

Unit 1 Only:
* CTMT audible count rate circuit – in RPS Cabinet Channel ‘D’
* Extended / Source Range Power Bistable – swaps from CPS to % power @ ~1000cps (~10-7%)

Question 9

Describe the Linear Range Safety Channel Nuclear Instruments.

Answer 9

4 Uncompensated Ion Chamber instruments operating in the Ionization Region.

Range 0-200% Power

Question 10

What do the Linear Range Safety Channel Nuclear Instruments provide power level input to?

Answer 10

• Q power signal development
• LPD trip setpoint calculation circuit
• TM/LP trip setpoint calculation circuit.
• Allows the calculation of azimuthal tilt ratio (aka quadrant power tilt ratio). Azimuthal tilt is determined by comparing one channel against the other three channels.
• Unit 1 only - Inputs to a Comparator Averager which compares each of the eight safety-related lower and upper safety detectors against the average of all eight. Located behind ‘A’ RPS.

This resulting quadrant power azimuthal tilt ratio is compared against high and high-high limits to alarm a subchannel deviation condition. Alarm at 2% deviation

Question 11

Describe the Linear Range Control Channel Nuclear Instruments.

Answer 11

2 Uncompensated Ion Chamber instruments operating in the Ionization Region.

Range: 0-200% Power

Question 12

What do the Linear Range Control Channel Nuclear Instruments provide power level input to?

Answer 12

Reactor Regulating System

Question 13

Describe the WR Log Excore Appendix R Channel Nuclear Instruments.

Answer 13

2 Fission Chamber instruments operating in the Ionization Region.

Question 14

Describe the Unit 2 BF3 Proportional Counters.

Answer 14

• Unit 2 Only Log Startup Channel – Proportional Region (2)
• Boron Dilution Alarm System
• Audible Count Rate – TS requires audible in Control Room

Question 15

Describe the Zero Power Mode Bypass Bistable.

Answer 15

LED lit / bistable is enabled: {< 1.0%} [<0.5%] power.
Auto removed {>1.0%} [>0.5%]
ZPMB Key Switch – which allows for CEA testing while shutdown

When bistable is enabled, and key is placed in Bypass:
* TM/LP & RCS Low Flow Trips are bypassed
* Blocks ∆T power input to RPS Q power auctioneering circuits in CPC-2

Question 16

Describe the Log Bistable.

Answer 16

LED lit > 1 x 10-4 % power (T/S value)
Auto enables High SUR reactor trip. Disabled at 15% by LIN 1

Question 17

Describe the Unit 1 Extended/Source Range Bistable.

Answer 17

• At >1000 cps - Swaps RTGB displays from CPS to % Power (~10-7%)
• At <1000 cps - Swaps RTGB displays from % Power to CPS
• Sums both detector outputs for higher sensitivity.
• Status indicated by split lamp light on RTGB

Question 18

Describe the Unit 1 Audible Count Rate.

Answer 18

• {1 CR speaker and 12 RCB speakers}
• {Channel Select switch – A, B, C, D,}. {Rate Scaler switch – 1, 10, 102, 103, off}
• {Located on RPS channel D}

Question 19

When does pulse discrimination swap to Campbell mode?

Answer 19

> 4X10-3 %

Question 20

Discuss the Trip Reset Pushbutton.

Answer 20

Resets (turns off) LED lights after the condition no longer exists

Question 21

Describe the effects of a Wide Range Log Safety NI Failure.

Answer 21

HIGH
If power is <15%:
* Removes Hi SUR block for < 10-4% power
* Zero Power Mode Bypass (Delta T input to Qpwr, TM/LP and Low RCS Flow trips are enabled for this RPS channel)
* SUR channel trips and will clear
* Delta T power will cause VHP and TM/LP channel trips if at low power (due to Tc & Th instrument range difference),
* CWP channel logic for High SUR Trip now in 1/3
* Unit 1 ONLY High Audio Counts if in SU Range and selected.

If power is >15%:
* SUR channel trips are blocked – Lin 1 block

LOW
* Applies channel High SUR < 10-4% power block.
* Permissive to allow manually enabling the ZPMB.
* CWP logic for Hi SUR Trip now in 2/3 logic.
* Unit 1 ONLY Loss of Audio Counts if in SU Range and that channel selected.

Question 22

Describe where Excore Nuclear Instruments can be read.

Answer 22

Unit 1
* Primary Alarm Panel: (Wide Range Recorder; Source Range Recorder)
* RTGB 104: (Wide Range Meter; Source Range Meter; SUR Meter; Boron Dilution Monitor)
* Hot Shutdown Panel: (WR Meter; Source Range Meter)

Unit 2
* RTGB 204: (Wide Range Meter; Source Range Meter; SUR Meter)
* Hot Shutdown Panel: (Wide Range Meter; Source Range Meter)
* PACB-2 (Wide Range Meter)

Question 23

Describe Unit 1 Boron Dilution Alarm System (BDAS).

Answer 23

• Input (CPS) provided by Excore Detectors only.
• Monitors Flux Level and causes a red light on the RTGB and an Annunciator alarm to alert the operator to a possible dilution event in progress
• Switch inside the module selects Setpoint in multiples of 1.5, 2.0, 2.5, 3.0, & 4.0 x current Count Rate

Question 24

Describe the Unit 2 Logarithmic Startup Channels.

Answer 24

• Provide reliable and accurate flux monitoring low in the power range on Unit 2
• Used for Boron Dilution Alarm System
• Used for Audio Count Rate
• BF3 Proportional Counter (4 detector tubes/assembly); uses Pulse Height Discriminator - Gammas produce a small pulse, and neutron-induced reactions produce a large pulse
• Principles of Operation
  – Outer cylinder is cathode; inner wire is anode
  – Cylinder contains BF3 gas
  – Incident thermal neutron hits B-10 atom, causes ions
  – These ions strike and ionize gas atoms
  – Charged ions collect on electrodes (current flow)
• To prolong detector life, the applied voltage is automatically removed at 10,000 CPS by the Source Range Bistable, actuates high counts alarm at 10,000 CPS. If not done the detector becomes saturated and detector damage or burnout could occur
• SU Channel Hi Volt Removal (Off-Auto-On/Reset) - Must be manually energized when power drops below 10-5% [Provides input to BDAS]
• [Audible Count Rate Circuitry, Switch for Ch A or B, Scaler switch (1, 10, 100, 1000)]
• Located on the RRS Cabinets on the back of RTGB-205

Question 25

Describe the effect of a failure of the Unit 2 Logarithmic Startup Channels.

Answer 25

Failed High:
* Possible total loss due to HV cutout.
* Possible Boron dilution alarm (BDAS) alarm on high cps.
* Possible High audio counts if selected during startups.

Failed Low:
* Loss of Boron dilution alarm (BDAS) alarm on that channel
* Loss of Audio Counts if selected during startups

Question 26

Describe Nuclear Instrument Power Supplies.

Answer 26

WIDE RANGE SAFETY CHANNELS (4)
* 120VAC Instrument Buses MA, MB, MC & MD

LINEAR POWER RANGE SAFETY CHANNELS (4) - Feeding RPS
* 120VAC Instrument Buses MA, MB, MC & MD

EXCORE NEUTRON FLUX MONITORING SYSTEM (APP. “R”) (2)
* 120VAC Instrument Buses MC & MD

LINEAR POWER RANGE CONTROL CHANNELS (2)
* RRS 1(2) 120V AC power supply MCC-A6 (B6)

[BF3 LOG STARTUP CHANNELS (UNIT 2 ONLY) (2)]
* [RRS 1(2) 120V AC power supply via MCC-2A6(2B6)]

Question 27

Describe Reactor Startup as it applies to Nuclear Instruments.

Answer 27

• NI/Delta T calibrations (30%, 45%, 50%, 80%, and 98%) and whenever >2% mismatch
• If >5% mismatch, notify RE
• Unit 1: {Use 4 WR Log Safety NI’s & 2 WR Excore Channels until the power range is reached and the 4 Linear Power Range Safety Channels are used}
• Unit 2: [Use 4 WR Log NI’s’, 2 BF3 Startup NI’s & the 2 App-R Excore Channels until the power range is reached and the 4 Linear Power Range Safety Channels are used]
• {Unit 1: Above 1000 cps, WR Log NI’s shift from CPS to % (extended range to WR) – causes CPS light to go out, % light to go on, and recorder to shift}
• [Unit 2: HV relays should de-energize BF3 detectors at 10,000 CPS]
• At 10-4%  - SUR trip auto energizes and PDIL lines come on
• At 5x10-4%  - stabilize power and record critical data and {ensure all CPS lights are out}
• At 4x10-3%  - WR Log NI’s shift gamma discrimination from Pulse Height Mode to Campbelling Mode
• At 0.1%, observe Linear PR indication and verify NI overlap (2 decades)
• At 1.0  [0.5  ] Zero Power Mode Bypass interlock removed
• At 15%  - Lin 1 bistable enabled

Question 28

Describe Reactor Shutdown as it applies to Nuclear Instruments.

Answer 28

• At 15% ↓, LIN 1 Bistable is off and Hi SUR Trip is enabled and LOL and LPD Trips are disabled
• At 11% ↓, auto CEA control is blocked (Low Power Auto Motion Inhibit from RRS
• At 4x10-3% ↓ - WR Log NI’s shift gamma discrimination from Campbelling Mode to Pulse Count Mode
• Observe negative SUR (Br-87)
• {Below 1000 CPS, WR Log NI’s shift from % to CPS (extended range)}
• [Operator must manually energize BF3 detectors below 10,000 CPS]
• Below 10-4%, SUR trip is disabled

Question 29

Describe Wide Range NI Channel Malfunction.

Answer 29

• Place the affected channel Hi SUR trip bistable in BYPASS or TRIP within 1 hour
• {Can only leave in BYPASS for 48 hours – then must place in TRIP}
• {Switch WR Recorder and Audible Count Rate to an operable channel}

Question 30

Discuss Linear Range Safety NI Channel Malfunction (actions for affected channel).

Answer 30

• Place the Hi Pwr, TM/LP, and LPD trip bistables in BYPASS or TRIP within1 hr
• If >15% power, place LOL trip bistable in BYPASS or TRIP within 1 hour
• With power between 10-4 and 15%, place the HI SUR trip bistable in BYPASS or TRIP within 1 hr
• {Can only leave bistables in BYPASS for 48 hours – then must place in TRIP}
• {Place toggle switch for Comparator Averager in OFF at rear of Channel A RPS cabinet for affected channel only, clears Hi and Hi-Hi Deviation alarms}
• Declare failed channel OOS
• If >75% power, notify RE to perform Tq once per 12 hours using incores

Question 31

Discuss Linear Range Control NI Channel Malfunction (actions for affected channel).

Answer 31

• Remove failed channel’s input to the Power Ratio Calculator (PRC) by using the switches located inside the PRC panel in the rear of Channel D RPS cabinet
• Clears the Deviation alarm
• Removes the failed input from Actual ASI Indication as displayed on the PRR

Question 32

Describe where each NI can be read.

Answer 32

Unit 1
WR Log Safety
RTGB (CPS/%, DPM) & (CPS/%-R- 1 pen), PAP A&B (CPS/%-R- 2 pens, red=%, blue=CPS) - CH A&B

Linear PR Safety
RTGB (Q, ASI, & ASI red/green pen), RPS (%, lin, DPM)

Linear PR Control
RTGB (lin-R blue-1, red-2; ASI blue pen), RRS (lin-U&L)

Excores
RTGB (CPS, %, DPM); HSCP (CPS, %); PAP (CPS, %)
Startup N/A

Unit 2
WR Log Safety
RTGB (%, DPM) & (%-R); HSP (A&B only, %)

Linear PR Safety
RTGB (Q, ASI, & ASI red/green pen), RPS (%, lin, DPM)

Linear PR Control
RTGB (%-R blue-1, red-2; ASI blue pen), RRS (lin-U&L)

Excores
RTGB (CPS, %, DPM); HSCP (CPS, %), PACP (%-rec)

Startup
RTGB (CPS), RRS (CPS)

Question 33

Describe Remote Shutdown NI Instrumentation.

Answer 33

Unit 1
HSP - App. R Neutron Detectors (Excores)

Unit 2
RSP - App. R Neutron Detectors (Excores)
WR Log (Ch. A & B only) - NOT qualified or Tech Spec