Instrumentation systems of PWR - 北海道大学roko.eng.hokudai.ac.jp/studentadm/chiba_data/others/nre_g...Coolant temperature Coolant flow rate Pressure Reactivity - To monitor operation

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Instrumentation systemsof PWR

Ex-core/In-core measurement systems

- Thermal power produced by nuclear fissionsis proportional to neutron flux level.

- With NIS, neutron flux level is measured to monitor a reactor power.

Nuclear instrumentation system (NIS)

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Coolant temperatureCoolant flow ratePressureReactivity

- To monitor operation condition and to control a nuclear power plant, various state variables should be measured.

Process instrumentation system

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Measurement range is divided into three sub-ranges.These sub-ranges overlap with each other.

– Start-up range– Intermediate power range– Power range


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Power level




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Power level




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Measurement range extends over 11 orders from start-up state to full power state.

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10-7 10-6 10-5 10-3 1 1010-8 10-4 10-2 10-1 100Power

(% or rated power)

Start-up channel

Power channel

Start-up range Intermediate power range

Power range

Neutron source range

BF3 detector Fission chamber

-ray compensated ionization chamber

Uncompensated ionization chamber

Measurement ranges of NIS

Each of these neutron detectors will be explained later.

Intermediate power channel

Power range detector

Reactor Vessel

Power range detector Power range

detector


Four independent detectors for the power.

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Ex-core neutron detectors (top view)


Reactor Vessel

Startup and intermediate ranges detectors

Power range detector Power range

detector


Startup and intermediate ranges detectors

Four independent detectors for the power range and two independent detectors for the other two ranges.

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Ex-core neutron detectors (top view)

Reactor vessel

Sealed plug

Cable connection box

Position in operation

Position in non-operation

Positioning device

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Ex-core neutron detectors (side view)

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10 7 4B n Li He

235U n

BF3 neutron detector

Fission chamber

Fission fragments

Ionization

Ionization

Pulsed signal

BF3：boron trifluoride

Neutrons are detected as “CPS”.

Start-up range neutron detectors

10 7 4B n Li He

n Ionization

nn

Current signal

TimeNeu

tron

flux

leve

lBF3 is used as an interaction material to neutrons.

Ionization chamber for intermediate/power ranges

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We want to detect neutrons leaked from a reactor core to measure neutron flux level in a reactor core.

Activated materials

pressure vessel

Reactor

Ionization chamber

Neutrons

-ray Compensated Ionization Chamber (CIC)

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Some materials surrounding ex-core ionization chambers are activated by neutron exposure during a long-term power operation.

Activated materials

pressure vessel

Reactor

Ionization chamber

Neutrons


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-rays emitted from activated materials ionize gaseous components contained in an ionization chamber.

Activated materials

pressure vessel

Reactor

Ionization chamber

-rays

Neutrons


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Therefore, the ionization current contains some contributions induced by -rays as well as ones induced by neutrons. This contribution is not negligible in the intermediate power range and must be removed from the ionization current. Activated

materials

pressure vessel

Reactor

Ionization chamber

-rays

Neutrons


Q1. Answer how to do that?Hint: only -rays can directly ionize gaseous components; neutrons cannot.

10 7 4B n Li He

I n I

Detector Signal I n

High voltage (+)

High voltage (-)

Plates coated with 10B

I n

(Background)

Common electrode

The current caused by ionization by (10B,n) reactions and background gamma-rays

I

n

n

The current caused by ionization by background gamma-rays

Principle of -ray compensation

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In a high power range, the contribution from -rays is negligible.

-ray Uncompensated Ionization Chamber (UIC)

Activated materials

pressure vessel

Reactor

Ionization chamber

-rays Neutrons

- Measurement with in-core neutron detectors is carried out to calibrate ex-core neutron detectors.

- Measurement is scheduled once a month.

- Movable small-sized neutron detector (fission chamber detector) is inserted into a guide tube in a fuel assembly.

Fission chamber detector

Driving wire Connector

Guide tube

Reactor vessel

Driving mechanism

In-core neutron detectors

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○A、B、C、D Guide tube positions: 35○CAL Calibration guide tube position

Guide tube

Guide tube for control rod

Fuel assembly

The number of detectors is limited, so it is impossible to measure at all the positions simultaneously. Measurements are carried out several times, but measurement at the calibration position is done at every time.

Positions of in-core neutron detectors

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Measurement by thermocouples

- Thermocouples are installed at the upper structure of a reactor core to measure coolant temperature at outlets of fuel channels to know radial power distributions.

- Chromel-Alumel thermocouple (CA thermocouple) is used.

- Used as a backup system for checking the validity of the ex-core and in-core measurements.

T/C In-core thermocouple detector at 26 locations

In-core coolant temperature measurement

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Resistance Temperature Detector (RTD：測温抵抗体) is used to measure primary coolant temperature. The RTD uses a property that specific resistance of metal changes with temperature.

Specific resistance of Pt

Temperature [℃]Spec

ific

elec

tric

resi

stan

ce

Rapid response RTD

Heat-conducting plate

Temperature detector

Insulation tube

Protective tube

Temperature measurement of primary coolant

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T/C RTDCost Low High

Precision Low HighResponse Rapid SlowRange <1500℃ <600℃

Robustness Strong Weak

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Comparison between T/C and RTD

Orifice flowmeter (Known): Gravitational

constant: Density: Cross-section area

of flow

(Unknown): Velocity: Pressure

By measuring , mass flow rate can be obtained.

Flow rate measurement based on Bernoulli’s principle

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1pg 2p

gh

1v

2v

Energy conservation law

Mass conservation law

Difference of water level Mass flow rate

2 2 2 2

2

1

2

1

g hG A v AAA


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(Known): Gravitational

constant: Density: Cross-

section area of flow


Q2. Derive the mass flow rate from known parameters and .

∆ can be represented by and .

1pg 2p

gh

1v

2v

Energy conservation law

Mass conservation law

Difference of water level Mass flow rate

2 2 2 2

2

1

2

1

g hG A v AAA


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(Known): Gravitational

constant: Density: Cross-

section area


2 2

∆

Direct method

： Coolant mass flow rate [kg/sec]： Outlet coolant enthalpy [J/kg]

： Inlet coolant enthalpy [J/kg]

It is difficult to measure the flow rate of the primary coolant precisely.

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Power evaluation

＝ (Thermal power output of steam generators)＋ (Electrical power consumed in primary coolant pumps)＋ (Heat loss of primary coolant side)

Thermal power output of steam generators＝

： Flow rate of feedwater into steam generators [kg/sec]： Steam enthalpy (saturated steam) [J/kg]： Enthalpy of feedwater [J/kg]

* Heat loss of the primary coolant loop can be evaluated through a detailed measurement experiment about heat balance.

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Power evaluation

Indirect method

Controllers and process instrumentationof PWRs

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reactor power control

feedwater control

steam dump control

Average coolant temperature

water level control

electric power control

condenser

feedwater pump

pressure control

pump speed control

coolant pump

pressurizer water level

control rod driving mechanism

feedwater control valve

condenserdump valve

neutron flux

reactor

heater

spray

L.P. turbine

H.P. turbine

First stage pressure

steam generator

pressurizer

T temperature

P pressureL water level

F flow rate

R rotation speed

f frequencyvolume control tank

generator

makeup water control

charging pump

governor valve

AFC

CP control rod position

Instrumentation systems of PWR - 北海道大学roko.eng.hokudai.ac.jp/studentadm/chiba_data/others/nre_g...Coolant temperature Coolant flow rate Pressure Reactivity - To monitor operation

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