Nuclear power plant

2. NUCLEAR POWER PLANT
A nuclear power plant works in a similar way as a thermal power plant.
The difference between the two is in the fuel they use to heat the water in
the boiler(steam generator).
 Inside a nuclear power station, energy is released by nuclear fission in
the core of the reactor.
1 kg of Uranium U235 can produce as much energy as the burning of
4500 tones of high grade variety of coal or 2000 tones of oil.

3. FUEL OF NUCLEAR POWER PLANT
Uranium-235 use as fuel for nuclear power plants. its properties are
follows:
General
 Symbol 235U
 Names:uranium-235, U-235
 Protons 92
 Neutrons 143
Data Nuclide
 Natural abundance 0.72%
 Half-life 703,800,000 years

4. NUCLEAR FISSION PROCESS
• In the nucleus of each atom of uranium-235 (U-235) are 92 protons
and 143 neutrons, for a total of 235. The arrangement of particles
within uranium-235 is somewhat unstable and the nucleus can
disintegrate if it is excited by an outside source. When a U-235
nucleus absorbs an extra neutron, it quickly breaks into two parts.
This process is known as fission (see diagram below). Each time a
U-235 nucleus splits, it releases two or three neutrons. Hence, the
possibility exists for creating a chain reaction.

5. NUCLEAR CHAIN REACTION

6. CONTROLLED NUCLEAR FISSION
To maintain a sustained controlled nuclear reaction, for every 2 or 3
neutrons released, only one must be allowed to strike another
uranium nucleus. If this ratio is less than one then the reaction will
die out; if it is greater than one it will grow uncontrolled (an atomic
explosion). A neutron absorbing element must be present to control
the amount of free neutrons in the reaction space. Most reactors are
controlled by means of control rods that are made of a strongly
neutron-absorbent material such as boron or cadmium.

7. NUCLEAR FISSION IN REACTOR
 U235 splits into two fragments (Ba141 & K92) of approximately
equal size.
 About 2.5 neutrons are released. 1 neutron is used to sustain the chain
reaction. 0.9 neutrons is absorbed by U238 and becomes Pu239. The
remaining 0.6 neutrons escapes from the reactor.
 The neutrons produced move at a very high velocity of 1.5 x 107
m/sec and fission other nucleus of U235. Thus fission process and
release of neutrons take place continuously throughout the remaining
material.

8. NUCLEAR FISSION IN REACTOR(CONTINUE)

9. COMPONENTS OF NUCLEAR POWER PLANT

10. NUCLEAR REACTOR
• A nuclear reactor is a key device of nuclear power plants. Main
purpose of the nuclear reactor is to initiate and control a
sustained nuclear chain reaction.

11. STEAM GENERATORS
• Steam generators are heat
exchangers used to convert feed
water into steam from heat produced
in a nuclear reactor core. They are
used in pressurized water
reactors (PWR) between the primary
and secondary coolant loops.

12. PRESSURIZER
• Pressure in the primary circuit is maintained by a pressurizer,
a separate vessel that is connected to the primary circuit (hot leg) and
partially filled with water which is heated to the saturation
temperature (boiling point) for the desired pressure by submerged
electrical heaters. Temperature in the pressurizer can be maintained at
345 °C (653 °F), which gives a sub cooling margin (the difference
between the pressurizer temperature and the highest temperature in the
reactor core) of 30 °C.

13. REACTOR COOLANT PUMP
• Reactor coolant pumps are used to pump primary coolant around the
primary circuit. These pumps are powerful, they can consume up to 6
MW each and they can be used for heating the primary coolant before
a reactor start-up.

14. SAFETY SYSTEMS
• According to the U.S. Nuclear Regulatory Commission primary
objectives of nuclear reactor safety systems are to shut down the
reactor, maintain it in a shutdown condition and prevent the
release of radioactive material. Reactor safety systems consist of:
• Reactor Protection Systems
• Essential service water system
• Emergency core cooling systems
• Emergency power systems
• Containment systems

15. STEAM TURBINE
• A steam turbine is a device that extracts thermal
energy from pressurized steam and uses it to
do mechanical work on a rotating output shaft.

16. GENERATOR
• A generator is a device that converts mechanical energy of
the steam turbine to electrical energy.

17. CONDENSER & FEED WATER SYSTEM
• A condenser is a heat exchanger used to condense steam from last
stage of turbine.
• . Condensate-Feed water Systems have two major functions. To
supply adequate high quality water (condensate) to the steam
generator and to heat the water (condensate) to a temperature close
to saturation.

19. WORKING OF STREAM POWER PLANT
• The water in the core is heated by nuclear fission and then pumped
into tubes inside a heat exchanger. Those tubes heat a separate water
source to create steam. The steam then turns an electric generator to
produce electricity.
• The core water cycles back to the reactor to be reheated and the
process is repeated.

20. SAFETY SYSTEMS OF NUCLEAR POWER PLANT
I. Shutdown systems
II. Cooling the fuel
 the heat transport system
 the steam system
 the condenser cooling system

21. SHUTDOWN SYSTEMS
All nuclear power reactors in Canada have
two independent, fast-acting and equally
effective shutdown systems. The first
shutdown system is made up of rods that
drop automatically and stop the chain
reaction if something irregular is detected.
The second system injects a liquid, or
poison, inside the reactor to immediately
stop the chain reaction. Both systems
work without power or operator
intervention. However, they can also be
manually activated. These systems are
regularly and safely tested.

22. DECAY HEAT
Due to shutdown, the amount of energy produced by the reactor
decreases rapidly. The nuclear fuel will, however, continue to produce
some heat and must be cooled. That heat, called decay heat, represents
a small fraction of the heat produced during normal operation.

23. MAIN COOLING SYSTEMS
Fuel cooling involves three main systems:
• the heat transport system
• the steam system
• the condenser cooling system

24. HEAT TRANSPORT SYSTEM
The heat transport system brings the heat produced by the reactor to
the steam generators. This system is made up of very robust pipes,
filled with heavy water - a rare type of water found in nature. Pipes
and other components are maintained and inspected regularly, and
replaced if necessary. Inspections include measuring pipe wear and
tear and identifying any microscopic cracks or changes well before
they become a problem.

25. STEAM SYSTEM
 The second system, the steam system, uses normal water. The heat
from the reactor turns this water into steam to run the turbines and
generators.
 That steam is then cooled and condensed using a third system that
pumps in cold water from a body of water such as a lake or reservoir.
This is called the condenser cooling system.
 Like other components, the steam and condenser cooling systems are
regularly inspected.
 These inspections take place throughout the life of the nuclear
facilities to confirm that aging equipment is functioning as originally
designed.

26. SHUTDOWN COOLING SYSTEM
A simpler cooling system is used when the reactor is shut down for an
extended period, for example during a planned outage. It requires little
power to function and is connected directly to the heat transport
system. It allows the primary coolant system to be partly drained to
perform inspection and maintenance work (e.g., inspection of the
steam generator tubes or replacement of pump components).
MULTIPLE POWER SUPPLIES
Cooling systems need electricity to operate. Under normal operation,
they get their electricity from the same power grid as the rest of us.
Nuclear power plants in Canada are also equipped with multiple
sources of backup power if they get disconnected from the grid.
Sources of backup power include onsite power - that is, the power
produced by the plant itself.
In addition, the following are available:
Emergency power generators
 two or three standby power generators
 two or three emergency power generators
 emergency batteries

27. ADVANTAGES &DISADVANTAGES
ADVANTAGES
 Produces no polluting gases.
 Does not contribute to global
warming.
 Very low fuel costs.
 Low fuel quantity reduces
mining and transportation
effects on environment.
 High technology research
required benefits other
industries.
 Power station has very long
lifetime.
DISADVANTAGES
 Waste is radioactive and safe
disposal is very difficult and
expensive.
 Local thermal pollution from
wastewater affects marine life.
 Large-scale accidents can be
catastrophic.
 Public perception of nuclear
power is negative.
 Costs of building and safely
decommissioning are very high.
 Cannot react quickly to changes
in electricity demand.