NUCLEAR REACTORS WORLD NEEDS POWERCANDU6 – CANadian Deuterium Uranium

Presented byAshok Sharma 11166Chitha Sai Teja 11223Hitesh Sahu 11311

Teaching AssistantMr. Ranjeet

Submitted toProf. Ashok KhannaProf. Prabhat Munshi

OUTLINE

• Why Nuclear Reactors?

• Reactor Generations

• What is CANDU6?

• Explained Different Processes

• Components of CANDU6

• Safety Precautions

• CANDU Reactor- An International View

• Canadian Nuclear Industry – At a Glance

WHY NUCLEAR REACTORS?

•Electricity is fundamental to our lifestyle and economic growth

•Nuclear is clean, safe, reliable and

economical for base load electricity

production

•Climate change due to global warming

has led to a sea-change increase in

public support

WHY NUCLEAR REACTORS? COND…

Nuclear is Clean

REACTOR GENERATIONS

WHAT IS CANDU6?

The CANDU (short for CANada Deuterium Uranium) reactor is a Canadian-invented, Pressurized Heavy Water Reactor. The acronym refers to its deuterium-oxide (heavy water) moderator. It uses natural uranium as fuel. CANDU reactors were first developed in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited (AECL), the Hydro-Electric Power Commission of Ontario (now Ontario Power Generation), Canadian General Electric (now GE Canada), and other companies. All power reactors built in Canada are of the CANDU type

HOW CANDU REACTOR WORKS

In the reactor, neutrons emitted in the fission reaction are slowed down by the heavy water, which acts as a coolant carrying the heat energy produced in the nuclear reaction from the uranium rods to the heat exchanger and then to the turbines to produce electric power. The products of fission are hot because the smaller atoms produced when a large atom breaks up, it has a great deal of kinetic energy.

BEFORE REACTION

The stored energy is brought into the generating system in the form

of uranium rods.

The fuel is put into the section of the reator called the calandria.

In this process of nuclear fission some energy is stored in the

uranium, and some transformed into heat

AFTER REACTION

The heat heats up the uranium fuel bundles which in turn heats up

the heavy water coolant and flows to the heat exchangers.

Here, some of the heat is transferred to a separate flow of ordinary

water boiling and transforming into steam.

BEFORE GENERATION

In the heat exchangers some of the energy released from the

uranium fuel has been transformed into steam.

It flows from the heat exchangers to blades of the turbines.

This transfer has created the energy to transform into the format of

motion.

AFTER GENERATION

Not all the energy from the uranium is transformed into the electricity. Some of this energy stays in the steam passing the turbine blades, then is divided.

Some of it returns to the heat exchangers in the form of preheated steam. Here it reduces the reactors own energy consumption by helping to maintain the steam cycle.

The remainder is transferred one more time, it heats another flow of ordinary water which discharges into lakes or rivers beside the generating station.

COMPONENTS OF CANDU6

Reactor Assembly

Pressure Tubes

Fuel

On-Power Refuelling

Heat-Transport System

Moderator System

Reactivity Devices

SCHEMATIC OF A CANDU NUCLEAR POWER PLANT

CANDU-6 PLANT

Reactor ContainmentBuilding

Turbine Building

Reactor

1. Reactor face

2. Reactor coolant pump

3. Steam generator

4. Fuelling machine

carriage

5. Moderator heat

exchanger

6. Dousing water system

7. Dousing water tank

5

1

3

2

4

6

7

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CANDU-6 REACTOR

Natural-uranium fuel

Heavy-water coolant

Heavy-water moderator

Separate coolant and moderator

Pressure tubes

Small, simple fuel bundle

On-power refueling

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CANDU CORE DESIGN

CANDU-6

Reactor

Vault

Pressure Tubes

(Fuel

Channels)

Calandria

Heavy-Water Moderator

(between & around fuel

channels)

Feeders

REACTOR ASSEMBLY

The reactor assembly contains the reactor core and the reactivity control devices. Major components of the reactor assembly are:

• Calandria Vessel

• End-Shields

• Shield Tank

• Fuel Channels

• Reactivity Control Devices

CALANDRIA VESSEL

• Low-pressure tank

• Includes calandria tube and supports pressure tubes

• Contains heavy water moderator

• Contains reactivity control devices and shutdown systems

• Embedded in light-water reactor vault (which provides radiation shielding)

CANDU 6 Calandria with Pressure Tubes Installed

CALANDRIA, SHOWING FUEL CHANNELS

PRESSURE-TUBE CORE DESIGN

• Sub-divided reactor coolant system, no large pressure vessel.• Cool moderator separated from hot

coolant.• Zr-2.5%Nb pressure tubes constitute CANDU

‘pressure vessel’.• Individual pressure tubes are replaceable.• Modular component – allows scaling of

reactor size.• Zirconium alloy provides neutron economy.

• Interstitial reactivity devices (between fuel channels).

MAIN CANDU REACTOR SYSTEMS

• Reactor Assembly

• Fuel and Fuel Channels

• Heat Transport System

• Moderator System

• Reactivity Devices (Control & Safety Systems)

Steam Generators

CANDU 6 HEAT TRANSPORT SYSTEM

STEAM GENERATOR

Tube Bundles

Reactor Face

End Fittings

and Feeders

CANDU-6 HEAT-TRANSPORT SYSTEM DESIGN

Reactor Coolant Parameters

Outlet header pressure 10 MPa

Outlet header temperature 310ºC

Outlet header steam quality (max.) 4.0%

Inlet header temperature 266ºC

Secondary Side Conditions

Steam pressure 4.7 MPa

Steam quality <0.25% moisture

Feedwater temperature 187ºC

CANDU FUEL

• Natural uranium (~0.7% 235U).

• High-density uranium oxide (UO2) fuel pellets in Zircaloy-4 cladding.

• Short (0.5 m) fuel elements arranged in cylindrical fuel bundles.

CANDU 37–ELEMENT FUEL BUNDLE

Uranium Fuel

Pellets

Zircaloy Fuel

Sheath

CANDU-6 REACTOR ASSEMBLY (SIDE VIEW)

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Fuel

Channel

12 Bundles per

Channel

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1 BASIC CELL OF CANDU REACTOR

D2O

Primary

Coolant

Gas Annulus

Fuel Elements

Pressure Tube

Calandria Tube Moderator

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ON-POWER REFUELLING

• Refuelling for long-term maintenance of reactivity: required because reactivity eventually decreases as fuel is irradiated (fission products accumulate and total fissile content decreases).

• In CANDU 6, average refuelling rate ~ 2 channels per Full-Power Day (FPD), using the 8-bundle-shift refuelling scheme (8 new bundles pushed in channel, 8 irradiated bundles pushed out).

• 4-bundle-shift and 10-bundle-shift refuelling schemes have also been used in other CANDUs.

• Selection of channels is the job of the station physicist.

FUELLING MACHINES AT BOTH ENDS OF THE REACTOR REMOVE SPENT FUEL, INSERT NEW FUEL

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Fuelling machines at both ends of the reactor

remove spent fuel, insert new fuel

MODERATOR SYSTEM

• Low-temperature (< 80oC), low-pressure system.

• Independent of reactor coolant system.

• Normal heat removal is ~4-5% of full power.

• Contains reactivity devices located outside of high-pressure heat transport system.

• Potential heat sink if Emergency Core Cooling is unavailable during a Loss-of-Coolant Accident (LOCA).

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MODERATOR SYSTEM

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CANDU REACTIVITY DEVICES

• All reactivity devices are located or introduced into guide tubes permanently positioned in the low-pressure moderator environment.

• These guide tubes are located interstitially between rows of calandria tubes (see next Figure).

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CANDU-6 REACTOR(700-MWECLASS)

Ion Chambers

Interstitial

Guide Tubes

for Reactivity

Devices (Zone

Controllers,

Adjusters, …)

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CANDU REACTIVITY DEVICES

For Regulation (Control):• 14 liquid-zone-control compartments (H2O

filled)• 21 adjuster rods• 4 mechanical control absorbers• Moderator poisonFor Emergency Shutdown:• 2 Shutdown Systems: SDS-1 & SDS-2

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CANDU SPECIAL SHUTDOWN SYSTEMS

Two independent, fully

capable shutdown

systems:

SDS-1 (cadmium rods

enter core from top)

SDS-2 (injection of

gadolinium neutron

“poison” from side.

SAFETY PRECAUTIONS

The main safety precaution that is taken is to ensure that the core does not melt. It has three steps for shutting down the system.

The heavy water moderator can be dumped by gravity into a storage tank under the reactor vessel. This will stop the fission reaction because the neutrons won’t be slowed down.

Boron can be injected into the moderator absorbing the neutrons so the chain reaction is suppressed.

The Cadmium control rods are held above the reactor core by electromagnetic clutches. They automatically fall if the power fails, this stopping the chain reaction since cadmium absorbs the neutrons.

CANADIAN REACTOR AN INTERNATIONAL VIEW

CANDIAN NUCLEAR INDUSTRY

Canada has been a nuclear industry leader since 1940’s

Exported seven CANDU reactors in the past 12 years

World’s largest exporter of isotopes & uranium

$5 billion/year industry

30,000 workers, 150 companies

20 CANDU reactors in Canada

Over 50% of generation in Ontario is nuclear

17% of generation across Canada is nuclear

FUTURE PROGRESS

Nuclear Renaissance is here:

• 440 nuclear power plant units operating worldwide

• 30 nuclear power plant units under construction

• 200 plants planned or proposed

World Nuclear Association predicts that by 2030 there will be

between 700 and 1500 nuclear plants worldwide

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THANK YOU