The document discusses the CANDU6 nuclear reactor. It begins by explaining the need for nuclear power to provide reliable base load electricity. It then describes the key components and design features of the CANDU6, including its use of natural uranium fuel and heavy water moderator, pressure tube core design, and ability to refuel online. Safety systems are highlighted which can dump the moderator or inject boron to stop the reaction. The Canadian nuclear industry is said to be a world leader in CANDU reactor exports and isotope/uranium production.

1. NUCLEAR REACTORS
WORLD NEEDS POWER
CANDU6 – CANadian Deuterium Uranium
Presented by
Ashok Sharma 11166
Chitha Sai Teja 11223
Hitesh Sahu 11311
Teaching Assistant
Mr. Ranjeet
Submitted to
Prof. Ashok Khanna
Prof. Prabhat Munshi

2. 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

3. 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

4. WHY NUCLEAR REACTORS? COND…
Nuclear is Clean

5. REACTOR GENERATIONS

6. 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

7. 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.

8. 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

9. 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.

10. 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.

11. 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.

12. COMPONENTS OF CANDU6
 Reactor Assembly
 Pressure Tubes
 Fuel
 On-Power Refuelling
 Heat-Transport System
 Moderator System
 Reactivity Devices

13. SCHEMATIC OF A CANDU NUCLEAR
POWER PLANT

14. CANDU-6 PLANT
Reactor Containment
Building
Turbine Building
Reactor

15. CANDU-6 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
15

16.  Natural-uranium fuel
 Heavy-water coolant
 Heavy-water moderator
 Separate coolant and moderator
 Pressure tubes
 Small, simple fuel bundle
 On-power refueling
16
CANDU CORE DESIGN

17. CANDU-6
Reactor
Vault
Feeders
Pressure Tubes
(Fuel
Channels)
Calandria
Heavy-Water Moderator
(between & around fuel
channels)

18. 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

19. 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)

20. CANDU 6
Calandria with
Pressure Tubes
Installed

21. CALANDRIA, SHOWING FUEL CHANNELS

22. 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).

23. MAIN CANDU REACTOR SYSTEMS
• Reactor Assembly
• Fuel and Fuel Channels
• Heat Transport System
• Moderator System
• Reactivity Devices (Control & Safety Systems)

24. CANDU 6 HEAT TRANSPORT SYSTEM
Steam Generators

25. STEAM GENERATOR
Tube Bundles

26. Reactor Face
End Fittings
and Feeders

27. 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

28. 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.

29. CANDU 37–ELEMENT FUEL BUNDLE
Uranium Fuel
Pellets
Zircaloy Fuel
Sheath

30. CANDU-6 REACTOR ASSEMBLY (SIDE VIEW)
30
Fuel
Channel
12 Bundles per
Channel

31. 31
1 BASIC CELL OF CANDU REACTOR
D2O
Primary
Coolant
Gas Annulus
Fuel Elements
Pressure Tube
Calandria Tube
Moderator

32. 32
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.

33. FUELLING MACHINES AT BOTH ENDS OF THE
REACTOR REMOVE SPENT FUEL, INSERT NEW FUEL
33
Fuelling machines at both ends of the reactor
remove spent fuel, insert new fuel

34. 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).
34

35. MODERATOR SYSTEM
35

36. 36
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).

37. 37
CANDU-6
REACTOR
(700-MWE
CLASS)
Interstitial
Guide Tubes
for Reactivity
Devices (Zone
Controllers,
Adjusters, …)
Ion Chambers

38. 38
CANDU REACTIVITY DEVICES
For Regulation (Control):
• 14 liquid-zone-control compartments (H2O
filled)
• 21 adjuster rods
• 4 mechanical control absorbers
• Moderator poison
For Emergency Shutdown:
• 2 Shutdown Systems: SDS-1 & SDS-2

39. 39
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.

40. 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.

41. CANADIAN REACTOR
AN INTERNATIONAL VIEW

42. 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

43. 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

44. 44
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