This document provides information on various topics related to nuclear power plants, including: 1. It describes the basic components of a nuclear power plant including the nuclear fuel, moderators, control rods, shielding, and coolant. 2. It discusses different types of nuclear reactors including boiling water reactors, pressurized water reactors, CANDU reactors, and fast breeder reactors. 3. It covers safety systems in nuclear power plants including control of the fission reaction, cooling of the reactor core, and containment of radioactive materials. Emergency core cooling systems and containment buildings are described.

1. UNIT – III NUCLEAR POWER PLANTS

2. Atomic Structure

3. Atomic Number
The number of protons in the nucleus.
Mass Number
Total number of nucleons in the nucleus.
Isotopes
Mass number different forms is different and atomic number is same.
Binding Energy
Energy released at the moment of combination of two nucleons to form
nucleus of an atom.
1 eV = 1.602 x 10-9J
Radioactivity
It is phenomenon of spontaneous emission of powerful radiations exhibited by
heavy elements.

4. Nuclear Fuels
•Uranium-233
•Uranium-235
•Plutonium-238
•Plutonium-239
•Plutonium-241
•Neptunium-237
•Curium-244
The most often used fuels are Uranium-235 and Plutonium-239.
Uranium-233 was also used in India and USA.

5. 92U238
• 92 represents number of protons or electrons
• 238 represents mass number
• 146 represents number of neutrons
• U represents Uranium

6. Uranium-235
General Facts
• The most often isotope of Uranium found in Nature is U-238,
U-235 is only found in low proportions (0.71%).
• U-235 is created from U-238 via isotope separation.
• The critical mass for an sphere of U-235 is about 50 kg (17 cm
of diameter).
Fission Process
• One slow neutron strikes a U-235 atom; the result is U-236.
• U-236 is highly unstable and it fissions. There are twenty
different fission processes, the products masses always add up
236.
• Example: U-235 + 1 neutron -> 2 neutrons + Kr-92 + Ba-142 +
ENERGY

7. Plutonium-239
General Facts
• Plutonium is very rare in nature.
• For military purposes,Uranium-238 is used .(used in nuclear bombs)
• It has a reasonably low rate of neutron emission due to
spontaneous fission.
• It is usually contaminated with Plutanium-240 which is more
unstable (4%-7% of plutanium-240 is considered bomb-grade). This
is the reason why plutonium-based weapons must be implosion-
type.
• The critical mass for an unreflected sphere of Plutonium is 16 kg.
Fission process: When Platinium-239 absorbs a slow neutron it
becomes Platinium-240, which decays fast via different processes
emitting at least two neutrons.

9. Nuclear Fission
• Nuclear fission is the
process of splitting a
nucleus into two nuclei
with smaller masses.
• Fission means “to
divide”

10. Nuclear Fission

11. Nuclear Fusion
• Nuclear fusion is the
combining of two nuclei
with low masses to form
one nucleus of larger
mass.
• Nuclear fusion reactions
are also called
thermonuclear reactions.

12. Chain Reaction
• A chain reaction is an
ongoing series of fission
reactions. Billions of
reactions occur each
second in a chain
reaction.

13. Uranium enrichment methods
• Natural uranium primarily consist of a mixture
of two isotopes of uranium.
• Only 0.7% of natural uranium is fissile or
capable of undergoing fission in which the
energy is produced in a nuclear power reactor
• Enrichment is the process of extract U-235

14. Gas Centrifuge
•4 to 5 meters Tall
•20 cm diameter
•50000-70000 rpm
•The motor rotates the Uranium
in the feed

15. Gaseous Diffusion

16. Thermal Diffusion

17. Nuclear power plant

19. Components
of
Nuclear
power
Plant

20. Fuel:
The fissionable material used in the reactor is called as fuel. The commonly
used fuels are Uranium, Plutonium or Thorium. It can be U-235, U-238, Pu-
236 or Th-232. Uranium is mostly preferred as it has high melting point.
Moderators:
Only neutrons of a fairly low speed should be used to have controlled chain
reaction. To slow down the speed fast moving neutrons produced during the
fission process, moderators are used. Moderator reduces the speed of the
neutron by absorbing its energy but not absorb neutron. Graphite, Heavy water
and Beryllium are common moderators.
Control Rods:
These rods absorb neutrons and stop the chain reaction to proceed further.
These are made up of steel containing a high percentage of material like
cadmium or boron which can absorb neutrons. When control rods are
completely inserted into the moderator block then all the neutrons is absorbed
and reaction comes to halt.

21. Shielding:
Shielding prevents radiations to reach outside the reactor.
Lead blocks and concrete enclosure that is strong enough of
several meters thickness are used for shielding.
Coolant:
The coolant is substance in a pipe to the steam generator
where water is boiled. This is where heat-exchange process
occurs. Heat is absorbed by the coolant that is produced in the
reactor. Typical coolants are water, carbon dioxide gas or
liquid sodium.
Turbines:
Steam produced in the boiler is now passes to a turbine. The
force of the steam jet causes the turbine to rotate. Heat energy
(steam) is converted to mechanical energy (moving turbine).

23. Types of Reactors
Boiling Water Reactor - BWR
Pressurized Water Reactor- PWR
CANada Deuterium-Uranium reactor – CANDU
Fast Breeder Reactor – FBR or BR
Gas Cooled Reactor - GCR
Liquid Metal Cooled Reactor - LMFBR

24. Boiling Water Reactor - BWR

25. • Boiling water reactors have a closed water-steam
cycle.
• In the cooling water system, the coolant water flows
through the reactor core, where the heat in the fuel
elements,
• Produced through nuclear fission, heats the water to
around 286 degree Celsius so that it boils in the
reactor pressure vessel.
• There is relatively low pressure in the reactor
pressure vessel (about 70 bar).
• Boiling and evaporation of the coolant water in the
reactor pressure vessel is the main feature
distinguishing the BWR from a pressurised water
reactor (PWR).

26. Pressurized Water Reactor- PWR

27. CANDU( CANADIAN-Deuterium-
Uranium) reactor

29. Fast Breeder Reactor – FBR or BR

30. GAS COOLED FAST BREEDER REACTOR

31. SODIUM COOLED FAST BREEDER REACTOR

32. LEAD COOLED FAST BREEDER REACTOR

33. MOLTEN SALT REACTOR

34. VERY HIGH TEMPERATURE REACTOR

35. SELECTION OF THE SITE FOR THE
NUCLEAR POWER STATION

38. • Reactor protection system (RPS) - A reactor protection
system is designed to immediately terminate the
nuclear reaction. By breaking the chain reaction, the
source of heat is eliminated.
• Control rods - Control rods are a series of rods that can
be quickly inserted into the reactor core to
absorb neutrons and rapidly terminate the nuclear
reaction.
• Safety injection - boric acid, which acts as a neutron
poison and rapidly floods the core in case of problems
with the stopping of the chain reaction.
Nuclear Power Plant Safety

39. SAFETY IN NUCLEAR POWER PLANTS
• 1. Control of fission Reaction
• 2. Cooling of the reactor core
• 3. Containment of the radioactive fission
products

40. • 1. Control of Reactor:
– Control neutrons by neutron absorbers like boron
and cadmium
– For shutting down the reactor control rods are fully
inserted in the reactor
– Secondary shutdown system also provided which
may either another set of control rods.
– Hence the case of power failure the rods drop due to
gravity or liquid poision injected due to accumulator
gas pressure.

41. • 2. Maintenance of Core Cooling:
– If the reactor is shut down , some heat is liberated
due to decay of fission products
– To achieve reliable cooling two more coolant circuits
are provided
– Coolant pumps are provided with the battery backup
from diesel generators
– All the reactor having emergency cooling circuit.

42. • 3. Containment of radioactivity:
– Radio active materials produced in the core of
reactor.
– In fission products remain it contains
– Atleast three successive barriers are provided
• Ist barrier- fuel clad – fuel is enclosed
• 2nd barrier- leak tight coolant circuit
• 3rd barrier - containment building barrier

43. ENGINEERED NUCLEAR POWER PLANT
SAFETY FEATURES

44. Emergency core cooling system - ECCS
• Emergency core cooling systems (ECCS) are designed to
safely shut down a nuclear reactor during accident
conditions.
• High pressure coolant injection system - HPCI consists of a
pump or pumps that have sufficient pressure to inject
coolant into the reactor vessel while it is pressurized.
• Automatic Depressurization system - DS consists in the
case of Boiling water reactors of a series of valves which
open to vent steam several feet under the surface of a large
pool of liquid water
• Low pressure coolant injection system - LPCI consists of a
pump or pumps that inject coolant into the reactor vessel
once it has been depressurized.

45. EMERGENCY CORE COOLING SYTEM OF PWR

46. EMERGENCY CORE COOLING SYTEM OF BWR

47. Ventilation and radiation protection
• In case of a radioactive release, most plants
have a system designed to remove
radioactivity from the air to reduce the
effects of the radioactivity release on the
employees and public. This system usually
consists of containment ventilation that
removes radioactivity and steam from primary
containment. Control room ventilation
ensures that plant operators are protected.