Incore Detection and QSPDS Flashcards
Discuss Incore Instrumentation.
- Consists of 45 [56] fixed incore detector assemblies
- 4 levels. Instruments are self powered.
- Physically fragile (particularly as compared to Excores) - small ceramic covered inconel wires susceptible to breaking resulting in a higher failure rate – particularly during inserting and removing.
- Response “slower” -Slight delay in response to neutron flux level changes.
- Linear Correlation 15-100%
- Use of data – inputs to BEACON™. Beacon Monitoring System - scans incore data looking for peaking factors during power maneuvers.
Discuss ICIS Functions.
- Determination of gross power distribution in the core from 15-100% power
- Fuel burn up estimation date for each fuel assembly
- Excore NI correction (shape annealing) data
- Provide CET data for subcooled margin calculation
- Data for core power distribution calculations
- Notification of abnormal core flux conditions
- Monitoring of LHR
Discuss ICIS Interfaces.
- QSPDS-uses CET data for subcooled margin information and core exit temps
- Beacon Monitoring System-scans Incores data for peaking factors during power changes
- RPS ASI-RE calibrates the RPS ASI to Incores ASI monthly
- TS core physics parameter data-peaking factors, LHR calculations, power distribution data
- DCS-provides a method for data retrieval and alarm indications
Discuss Fixed Incores Detector Assemblies.
The incore instrumentation system (ICIS) consists of {45} [56]) fixed incore detector assemblies with the following in each assy:
* 4-40 cm long Rhodium Self Powered Neutron Detectors (DCS)
* 1 Self Powered Chromel - Alumel CET (QSPDS & DCS)
* Each detector is positioned at 20%, 40%, 60%, & 80% of Core Height
* Response Time of the detector is governed by the Half Life of Rhodium 104 which is 42s
* Can last for 3 cycles, highly accurate
Discuss ICIS theory of operation.
- Similar to Excores (indirectly count neutrons, correlate data to reactor power).
- Self-powered because the interaction results in a highly energetic charged particle.
- Rhodium 103 + Neutron forms Rhodium 104 which Beta-decays by emitting 2.4 Mev Beta
- Correlation to power is fairly linear over the range of interest (~15-100%). Gammas contribute only a small amount to total signal and are accounted for at factory.
What constitutes an OPERABLE Incore Detector System?
An OPERABLE Incores Detector System includes:
* During start-up testing following each refueling, you need:
≥ 75% of all detectors operable AND
≥ 4 detectors per upper and > 4 detectors per lower quadrant
≥10 detectors per combined (upper and lower) quadrant
- After start-up testing is complete, you need:
≥ 50% of all detectors operable AND
≥ 4 detectors per upper and > 4 detectors per lower quadrant &
≥10 detectors per combined (upper and lower) quadrant
Which detectors should be providing LHR determination?
Unit 1
* < 15% Excore Only
* 15 – 85% Excore or Incore
* >85% Incore only
Unit 2
* < 15% Excore Only
* 15 – 100% Excore or Incore
What is the impact of a loss of Incore Detectors?
If the Incore Detection System is not available to monitor the LHR:
Monitor the LHR using the Excore Detectors; AND
Unit 1 – Reduce Rx Power to ≤ 85% within 4 hours
Unit 2 – Operation can continue for up to 31 days from the last flux map at a power level as determined by Plant Physics Curve Book Figure C.3. Usually this will not require a down-power.
What is the impact of a loss of DCS?
If the DCS System is not available to monitor the LHR:
Unit 1: If DCS cannot be restored within 24 hours, place the Unit in Mode 3.
Unit 2: If DCS cannot be restored within 72 hours, place the Unit in Mode 3.
What are QSPDS Indications?
Has a 2-Channels flat panel display system that allows for monitoring of:
* Subcooled and saturation margins
* Rx vessel level indication
* Core exit temperatures
* Backup RCS temperature and pressure indications
What are the QSPDS Power Supplies?
QSPDS A – Instrument Bus {MC} [MC-1]
QSPDS B – Instrument Bus {MD} [MD-1]
What are QSPDS Inputs?
- Core Exit Thermocouples: A Train – 22 [28] per channel, B Train – 23 [28] per channel
- Tcold – 2/channel (A & B safety instruments)
- Thot – 2/channel (A & B safety instruments)
- Pzr Pressure – 1/channel
- Heated & Unheated Junction Thermocouples – Two channels. 16 per channel (8 heated & 8 unheated)
Describe Reactor Vessel Level Monitoring System (RVLMS).
Provides visual indication of inventory above the fuel assemblies (upper plenum)
One assembly contains one unheated and one heated thermocouple (8 assemblies/channel)
Normal temperature difference is between 75 - 100 °F
Level loss (shown as core uncovering) determined by either:
o 200ºF (T between the heated and unheated thermocouples (UHJTC).
o 700ºF on UHJTC.
> 200°F delta turns background RED, indicating an alarm
UHJTC > 700°F indicates “Failed Sensor” – Background turns White
If a HJTC fails low its segment will indicate Failed Sensor – Background turns White.
In EOP-03, LOCA, Safety Function Status Tree check for RCS Inventory Control, either representative CET temperature or RVLMS can be used to provide satisfactory indication of RX Vessel level.
If HPSI throttling criteria met:
a) RVLMS sensors 4-8 are covered
OR
b) Less than 20° F ∆ between Thot and REP CET
If HPSI throttling criteria is not met:
a) RVLMS Sensors 7-8 are covered
OR
b) REP CET temperatures < 22° F superheated
Describe Saturation Margin Calculation.
Both Pressure and temperature margins automatically calculated by QSPDS.
Receives temperature inputs are from:
* Max hot and cold leg temperatures.
* Max of the top 3 UHJTCs in the vessel head.
* Representative CET temperature.
* Pressure input is from pressurizer pressure instruments.
List QSPDS Inputs/Ranges.
INPUT RANGE
Pressurizer Pressure: PT 1107 and 1108 0-3000 psia
Cold Leg: TT1122-CA, CB; TT 1112-CA, CB {212 - 705°F} [50 - 750°F]
Hot Leg: TT1122-HA, HB; TT 1112-HA, HB {212 - 705°F} [50 - 750°F]
Max UHJTC 32-2300°F
CET (representative) 32-2300°F
