Nuclear Power Plant - M.Tech

SNIST (JNTUH) – M.Tech (Therm.Engg)
NUCLEAR POWER PLANT
Dr. SIRIVELLA VIJAYA BHASKAR
Professor in Mechanical Engineering
Sreenidhi Inst. of Science &
Technology, Hyderabad, TS

Syllabus: NUCLEAR POWR PLANT
Nuclear Power Plant:
Nuclear physics
Nuclear Reactor
Classification
Types of reactors
Site selection
Method of enriching uranium.
Application of nuclear power plant.

Nuclear Physics: Atomic Structure
Atomic Model:
 An element is defined as a substance
which cannot be decomposed into other
substances
 The smallest particle of an element which
takes part in chemical reaction is known as
an 'atom'.
The word atom is derived from Greek
word 'Atom' which means indivisible and for a
long time the atom was considered as such.

Atomic Structure
Dalton's atomic theory states that
(i) all the atoms of one element are
precisely alike, have the same mass
but differs from the atoms of other
elements
(ii) the chemical combination consists of the
union of a small fixed number of atoms of
one element with a small fixed number of
other elements.

Nuclear Fission
 Nuclear Fission is the splitting of a heavy,
unstable nucleus such as U233, U235, PU239
into two lighter nuclei.
6
proton
neutron
Kr=Krypton
Energy
U-235 nucleus
Kr-92 nucleus
Ba-141 nucleus
Barium

Nuclear Fusion
 Fusion is the process where two lighter
nuclei combine together
 In both process, vast amounts of energy will
be released
7

Tarapur Atomic Power Station
(TAPS) was the first nuclear power
plant in Maharashtra, India.
The construction of TAPS was
started in 1962 and the plant went
operational in 1969.
Nuclear/Atomic Power Plant: History
First Electricity Production: 20 December, 1951 in Arco, Idaho,
USA.
First Commercial Use: June 26, 1954 at Obninsk, Russia.
Present Scenario: 442 nuclear power plant units in 31 countries
produce electricity about 384 GW.
Under Construction: 66 plants with a capacity of 65 GW are in 16
countries.

Nuclear/Atomic Reactor
Working Principle :
❖ When a neutron strikes an atom of Uranium, Plutonium the Ur or Pl
splits into two lighter atoms and releases heat energy simultaneously
❖ More energy is released each time another atom splits. This is called
a chain reaction.
U235 + n → fission + 2 or 3 n + 200 MeV (Mega Electron Volt)
If each neutron releases two more neutrons, then the number of
fissions doubles each generation. In that case, in 10 generations there
are 1,024 fissions and in 80 generations about 6 x 10 23 (a mole)
fissions.

NR: Working Principle
• It is a process of splitting up of nucleus of fissionable material
like uranium into two or more fragments with release of
enormous amount of energy.
• The nucleus of U235 is bombarded with high energy neutrons
U235+0n1 Ba141+Kr92+2.50n1+200 MeV energy.
Ba = Barium Kr=Krypton
• The neutrons produced are very fast and can be made to fission
other nuclei of U235, thus setting up a chain reaction.
• Out of 2.5 neutrons released one neutron is used to sustain the
chain reaction.
1 eV = 1.6X10-19 joule.
1 MeV = 106 eV

proton
neutron
U-235 nucleus
Nuclear chain reaction: Neutrons released in
fission trigger the fissions of other nuclei
NUCLEAR CHAIN REACTION

NR Working Principle
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.
A large amount of energy(200 Million
electron volts, Mev) is produced.
Note : Moderators are
to the
high
provided
neutrons
velocities
them.
slow down
thefrom
but not to absorb

❖ A nuclear power plant works in a similar way as a thermal
power plant (TPP). The difference between the two is: a fuel
will be used to heat the feed water in TPP. But in case of
nuclear power plant, thermal 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 tonnes of high grade variety of coal or 2000
tonnes of oil.
Nuclear/Atomic Power Plant…

NPPs in Operation…
PWRs in Diablo Canyon-CA, USA
Diablo Canyon - CA
PWR: Pressurized Water Reactors
Kudankulam nuclear plant
Tamilnadu, India

Components and Working of Nuclear Power Plant
The main components
of a nuclear power
plant are :
1. Nuclear reactor
2. Heat exchanger
(steam generator)
3. Steam turbine
4. Condenser
5. Feed pump
6. Electric generator.
Figure 1: Nuclear Power Plant

 In a nuclear power plant the reactor performs the same
function as that of the furnace of steam power plant (i.e.,
produces heat).
 The heat liberated in the reactor as a result of the nuclear
fission of the fuel is taken up by the coolant circulating
through the reactor core.
 Hot coolant leaves the reactor at the top and then flows
through the tubes of steam generator and passes on it heat
to the feed water.
 The steam so produced expands in the steam turbine,
producing work and thereafter is condensed in the
condenser.
 The steam turbine in turn runs an electric generator
thereby producing electrical energy.
 In order to maintain the flow of coolant, condensate and
feed water pumps are provided as shown in Fig. 1.

Advantages of Nuclear power plant:
1. Space required is less when compared with other power plants.
2. Nuclear power plants can meet the large power demands at a
reasonable cost.
3. They give better performance at high load factors (80 to 90%)
4. A nuclear power plant uses much less fuel than a fossil-fuel
plant. 1 metric tonne of uranium fuel = 3 million metric tonnes
of coal = 12 million barrels of oil.
5. Since the fuel consumption is very small as compared to
conventional type of power plants, therefore, there is saving in
cost of the fuel transportation.
6. The nuclear power plants, besides producing large amount of
power, produce valuable fissible material which is produced
when the fuel is renewed

Advantages of Nuclear power plant:
7. The operation of a nuclear power plant is more reliable.
8. Nuclear power plants are not affected by adverse weather
conditions.
9. Bigger capacity of a nuclear power plant is an additional
advantage.
10. The expenditure on metal structures piping, storage
mechanisms is much lower for a nuclear power plant than a
coal burning power plant.

Disadvantages/Limitations of Nuclear power plant:
1. The capital cost of a nuclear power station is always high.
2. The danger of radioactivity always persists in the nuclear
stations (inspite of utmost pre-cautions and care).
3. These plants cannot be operated at varying load efficiently.
4. Maintenance cost of the plant is high (due to lack of
standardisation and high salaries of the trained personnel in
this field of specialisation).
5. The disposal of fission products is a big problem. If it is
disposed properly, that will adversely affect the
environment
6. Working conditions in nuclear power station are always
detrimental to the health of workers

Nuclear Reactor
A nuclear reactor is an apparatus in which nuclear fission is
produced in the form of a controlled self-sustaining chain
reaction.
In other words, it is a controlled chain-reacting system
supplying nuclear energy.
It may be looked upon as a sort of nuclear furnace which
burns fuels like U285, U283 or Pu2s9 and, in turn,
produces many useful products like heat, neutrons and
radioisotopes.
Nuclear Reactors are classified according to the chain
reacting system, use, coolants, fuel material etc.

Classification of Reactors-High level

1.On the basis of neutron
energies
Intermediate/
epi-thermal
reactors
Reactors in
which the
velocity of
neutrons is kept
between the
limits of fast and
Fast reactors
In these
reactors Fast
fission is caused
by high energy
neutrons.
Slow/thermal
reactors
If in a reactor
fission process
is maintained
due to slow
neutrons
capture, the
reactor is known
as slow reactor.
Classification of Reactors

2.On the basis of fuel state
LIQUID
FUEL
GAS
FUEL
SOLID
FUEL
3.On the basis of fuel material
a.Natural uranium with U-235 contents … occurs in nature
b.Enriched uranium with more than 0.71% of U-235 … man made
c.Pu-239,Pu-241 or Pu-239 …. man made
d. U-233 …. man made

i. Water (H₂o)
moderated reactors
ii. Heavy water (D₂o)
reactors
iii. Graphite moderated
reactors
iv. Beryllium or beryllium
oxide moderated
reactors
4.On the basis of Moderator
aka..D2O-deuterium oxide
10% heavier than H2O
H2 replaced by D2

 Pressurised Water Reactor(PWR)-It is a light water
cooled and moderated reactor. It uses enriched
uranium as fuel.
 Boiling water reactor(BWR)-In this type of
reactor, enriched uranium is used as fuel and
water is used as coolant, and moderator.
 CANDU(Canadian-deuterium-uranium)reactor:
It uses heavy water (99.8% D₂O) as moderator and
coolant as well. It differs from light water reactor as the
later uses the same water as coolant and moderator both
while in CANDU reactor moderator and coolant are kept
separate.
5.On the basis of Coolant used
A. Water or other liquid cooled reactors

In such type of reactor, the coolant used can be air,
hydrogen, helium or carbon dioxide. The moderator used
is graphite.
There are two types of gas cooled reactors:
1.The gas cooled graphite moderator reactor(GCGM)
uses natural uranium fuel and graphite as
moderator.
2.The high temperature gas cooled reactor(HTGC)
uses enriched uranium carbide mixed with thorium
carbide as fuel and graphite as moderator.
Sodium–graphite reactor(SGR) is one of the typical liquid metal
reactor in which sodium works as coolant and graphite
works as moderator.
C.Liquid Metal Cooled Reactors
B. Air, Carbon or Helium/Gas Cooled Reactor

1)Research reactors-to produce neutron for research work.
2)Power reactor- to produce heat
3)Breeder reactor- to produce fissionable material
(i.e..U-238 & Th 232 to Pu-239 and U233) besides
power production.
4)Production rector- to produce isotopes.
6.On the basis of principal product

i. Cubical
ii.Cylindrical
iii.Octagonal
iv.Spherical
v. Slab
vi.Annulus (ring-shaped)
7.On the basis of construction of cores

1. Reactor core
2. Reflector
3. Control mechanism
4. Moderator
5. Coolants
6. Measuring instruments
7. Shielding
NUCLEAR REACTOR– Principal
Components

Reactor Core : This is the main part of reactor which contain the
fissionable material called reactor fuel. Fission energy is
liberated in the form of heat for operating power conversion
equipment. The fuel element are made of plate of rods of
uranium.
Reactor reflector :The region surrounding the reactor core is
known as reflector. Its function is to reflect back some of the
neutron that leak out from the surface of core.
Reactor Core  Where the nuclear fission process takes place.

Control rods :The rate of reaction in a nuclear reactor is
controlled by control rods. Since the neutron are responsible for
the progress of chain reaction, suitable neutron absorber are
required to control the rate of reaction.
• For starting the reactor
• To keep the production at a steady state
• For shutting down the reactor under normal or emergency
conditions
Cadmium and Boron are used as control rods.
Control rods :
Control rods limit the
number of fuel atoms that
can split. They are made of
boron or cadmium which
absorbs neutrons

• Moderator :The function of a reactor is to slow down the fast
neutron. The moderator should have
• High slowing down power
• Non corrosiveness
• High melting point for solids and low melting point for
liquids.
• Chemical and radiation stability.
• High thermal conductivity
• Abundance in pure form.
The commonly used moderator are :
o Ordinary water
o Heavy water
o Graphite.
Moderator : This reduces the speed of fast moving neutrons.

• Coolant :The material used to carry the intense heat
generated by fission as fast as liberated is known as reactor
coolant. The coolant generally pumped through the reactor in
the form of liquid or gas. It is circulated throughout the
reactor so as to maintain a uniform temperature.
.
• Measuring Instruments: Main instrument required is for
the purpose of measuring thermal neutron flux which
determines the power developed by the reactor.
• Shielding: The large steel recipient containing the core, the
control rods and the heat-transfer fluid.
All the components of the reactor are container in
a solid concrete structure that guarantees further
isolation from external environment. This structure
is made of concrete that is one-metre thick,
covered by steel.

energy is released
very quickly
the rate of fission
increases rapidly
Nuclear bomb
Uncontrolled nuclear reaction
The chain reaction is not
slowed down

Types of Nuclear Reactors:
1. Pressurised Water Reactor (PWR)
2. Boiling Water Reactor (BWR)
3. CANDU (Canadian-Deuterium-Uranium) Reactor
4. Gas-Cooled Reactor
5. Liquid Metal Cooled Reactor
6. Breeder Reactor

✓Heat is produced in the reactor due
to nuclear fission and there is a chain
reaction.
✓The heat generated in the reactor is
carried away by the coolant (water
or heavy water) circulated through
the core.
✓The purpose of the pressure equalizer
is to maintain a constant pressure of
14 MN/m2. This enables water to
carry more heat from the reactor.
✓ The purpose of the coolant pump is
to pump coolant water under
pressure into the reactor core.
Pressurised Water Reactor (PWR)

PWR: Pressurized Water Reactor

Schematic diagram of a PWR nuclear power plant
control rods
fuel
rods
reactor
pressure
vessel
water
Pump
(cool) pump
(high water
pressure)
(Low water
pressure)
coolant out
coolant in
steam condenser
steam (low
pressure)
turbine
steam
generator
reactor
core
water
(hot)
electric
power
steam (high pressure)
primary loop secondary loop
generator

turbine steam (low
pressure)
steam coolant in
generator steam condenser
fuel rods • They are surrounded by a
moderator (water or graphite) to
slow down the neutrons released.
• They contain the nuclear fuel:
uranium (U-235)
control rods
 They control the rate of reaction by
moving in and out of the reactor.
• Move in: rate of reaction Down
• Move out: rate of reaction up
• All are moved in: the reactor is
shut down
 They are made of boron or
cadmium that can absorb neutrons.
pump

steam (high pressure)
turbine
electric
power
generator
The steam drives a turbine, which turns
the generator.
Electricity is produced by the Generator
Two separate water systems are used to avoid
radioactive substances to reach the turbine.

•The energy released in fissions heats up the water
around the reactor.
•The water in the secondary loop is boiled to steam.
water
(hot)
water
(cool)
steam
generator

Dark Blue: Primary circuit water
Red: Secondary circuit water

 The pressurized water reactor belongs to the light water type:
the moderator and coolant are both light water (H2O). It can be
seen in the figure that the cooling water circulates in two loops,
which are fully separated from one another.
 The primary circuit water (dark blue) is continuously kept at a
very high pressure and therefore it does not boil even at the
high operating temperature. (Hence the name of the type.)
 The primary circuit water transferred its heat to the secondary
circuit water in the small tubes of the steam generator, it cools
down and returns to the reactor vessel at a lower temperature.
 Since the secondary circuit pressure is much lower than that
of the primary circuit, the secondary circuit water in the steam
generator starts to boil (red).

Pressurized Water Reactor
 The steam goes from here to the turbine, which has high and
low pressure stages. When steam leaves the turbine, it
becomes liquid again in the condenser, from where it is
pumped back to the steam generator after pre-heating
 Normally, primary and secondary circuit waters can’t mix.
 In this way it can be achieved that any potentially radioactive
material that gets into the primary water should stay in the
primary loop and cannot get into the turbine and condenser.
 This is a barrier to prevent radioactive contamination from
getting out.
 In pressurized water reactors the fuel is usually low (3 to 4
percent) enriched uranium oxide, sometimes uranium and
plutonium oxide mixture (MOX).
 In today's PWRs the primary pressure is usually 120 to 160
bars, while the outlet temperature of coolant is 300 to 320 °C.
 PWR is the most widespread reactor type in the world: they
give about 64% of the total power of the presently operating
nuclear power plants.

Dimensions of a typical
PWR reactor pressure vessel:
Height : 15 m (49 ft)
Diameter : 5 m (16 ft)
Wall : 25 cm (10 in) thick steel
Containment : 1 m thick concrete (steel lined)
Core loading : 82 tons of UO2
Pressure (Pri.) : 2250 psig (158 Atmos )
FYI: Pressurized Water Reactor

Arrangements of RPV,
Steam Generators,
Primary pumps,
Pressurizer, etc.
RPV: Reactor Pressure Vessel

PWR in Operation…
PWRs in Diablo Canyon - CA , the USA
Diablo Canyon - CA
PWR: Pressurized Water Reactors
Kudankulam nuclear plant
Tamilnadu, India

Advantages Pressurized Water Reactor
• PWR reactors are very stable and easier to operate.
• PWR reactors lifetime is longer and safer control over
power level.
• Because PWR reactors use enriched uranium as fuel,
they can use ordinary water as a moderator rather than
the much more expensive heavy water as used in a
pressurized heavy water reactor.
• PWR turbine cycle loop is separate from the primary
loop, so the water in the secondary loop is not
contaminated by radioactive materials.
• Water is used in reactor is cheap and easily available.
• Small number of control rods are required

Disadvantages Pressurized Water Reactor
• Requires high strength piping and a heavy pressure vessel and
hence increases construction costs.
• Most pressurized water reactors cannot be refueled while
operating. This decreases the availability of the reactor—it has to go
offline for relatively long periods of time
• The high temperature water coolant with boric acid dissolved in it is
corrosive to carbon steel
• Natural uranium is only 0.7% uranium-235, the isotope necessary for
thermal reactors. This makes it necessary to enrich the uranium fuel,
which increases the costs of fuel production.
• If heavy water is used, it is possible to operate the reactor with
natural uranium, but the production of heavy water requires large
amounts of energy and is hence expensive.
• Because water acts as a neutron moderator, it is not possible to build
a fast neutron reactor with a PWR design. A reduced moderation
water reactor may however achieve a breeding ratio greater than
unity, though this reactor design has disadvantages of its own.

Boiling Water Reactor (BWR)
➢The water is circulated through the
reactor where it converts to water
steam mixture.
➢The steam gets collected above the
steam separator.
➢This steam is expanded in the turbine
which turns the turbine shaft.
➢The expanded steam coming out of
the turbine is condensed and is pumped
back as feed water by the feed water
pump into the reactor core.
➢Also the down coming recirculation
water from the steam separator is fed
back to the reactor core.

BWR: Boiling Water Reactor
 In a boiling water reactor, light water (H2O) plays the
role of moderator and coolant, as well.
 Part of the water boils away in the reactor pressure
vessel, thus a mixture of water and steam leaves the
reactor core.
 The so generated steam directly goes to the turbine,
therefore steam and moisture must be separated (water
drops in steam can damage the turbine blades).
 Steam leaving the turbine is condensed in the condenser
and then fed back to the reactor after preheating.
 Water that has not evaporated in the reactor vessel
accumulates at the bottom of the vessel and mixes with
the pumped back feed water.

BWR: Boiling Water Reactor
 The BWR uses demineralized water (light water) as a coolant and
neutron moderator.
 Heat is produced by nuclear fission in the reactor core, and this
causes the cooling water to boil, producing steam.
 The steam is directly used to drive a turbine, after which it is cooled
in a condenser and converted back to liquid water.
 This water is then returned to the reactor core, completing the loop.
The cooling water is maintained at about 75 atm (7.6 MPa, 1000-
1100 psi) so that it boils in the core at about 285°C (550°F).
 In comparison, there is no significant boiling allowed in a PWR
because of the high pressure maintained in its primary loop -
approximately 158 atm (16 MPa, 2300 psi).

Advantages Boiling Water Reactor
• The reactor vessel and associated components operate at a
substantially lower pressure compared to a PWR.
• Pressure vessel is subject to significantly less irradiation
compared to a PWR, and so does not become as brittle with
age.
• Operates at a lower nuclear fuel temperature.
• Fewer components due to no steam generators and no
pressurizer vessel.
• Lower risk (probability) of a rupture causing loss of coolant
compared to a PWR
• Can operate at lower core power density levels using natural
circulation without forced flow.
• A BWR may be designed to operate using only natural
circulation so that recirculation pumps are eliminated entirely.
• BWRs are overrepresented in imports, if the importing nation
doesn't have a nuclear navy

Disadvantages Boiling Water Reactor
• Requires more instrumentation in the reactor core.
• Much larger pressure vessel than for a PWR of same
power
• This means that shielding and access control around the
steam turbine are required during normal operations due
to the radiation levels arising from the steam entering
directly from the reactor core.
• Elaborate safety precautions needed which are costly.
• Boiling limits power density , only 3 to 5% by mass can
be converted to steam per pass through the boiler.

Comparison of PWR and BWR
PWR BWR

CANDU(CANADIAN DEUTERIUM URANIUM)
Key
1 Fuel bundle 7
Heavy water
pump
2
Calandria
(reactor core)
8
Fueling
machines
3 Adjuster rods 9
Heavy water
Moderator
4
Heavy Water
pressure
reservoir
10 Pressure tube
5
Steam
Generator
11
Steam going
to Steam
turbine
6
Light water
pump
12
Cold water
returning
from turbine

CANDU (Canadian Deuterium Uranium ) Reactors
 The CANDU reactor is a Canadian-invented, pressurized
heavy water reactor developed initially in the late 1950s
and 1960s by a partnership between Atomic Energy of
Canada Limited (AECL), Canadian General Electric (now
known as GE Canada), as well as several private
industry participants.
 "CANDU", stands for "CANada Deuterium Uranium".
 This is a reference to its deuterium-oxide (heavy water)
moderator and its use of uranium fuel (originally, natural
uranium).
 All current power reactors in Canada are of the CANDU
type.
 The reactors are used in nuclear power plants to
produce nuclear power from nuclear fuel

CANDU (Canadian-Deuterium-Uranium ) Reactors
• Heavy water is used as moderator and coolant
as well as neutron reflector.
• Natural Uranium(0.7% 235U) is
used as fuel.
• In CANDU reactor the
moderator and coolant
are kept separate.
• The "whole idea" of the CANDU
design is that the uranium does not
have to be enriched, but simply
formed into ceramic natural
uranium-dioxide fuel.
• This saves on the construction of
an enrichment plant, and on the
costs of processing the fuel.

Description of CANDU Reactors
 Reactor vessel and core: The reactor vessel is a steel
cylinder with a horizontal axis ; the length and diameter
of a typical cylinder being 6 m and 8 m respectively. The
vessel is penetrated by some 380 horizontal channels
called pressure tubes because they are designed to
withstand a high internal pressure. The channels contain
the fuel elements and the pressurised coolant flows
along the channels and around the fuel elements to
remove the heat generated by fission. Coolant flows in
the opposite directions in adjacent channels..

 Fuel: In a CANDU reactor the fuel is normal (i.e.,
unenriched) uranium oxide as small cylinder pellets.
The pellets are packed in a corrosion resistance
zirconium alloy tube, nearly 0.5 long and 1.3 cm
diameter, to form a fuel rod. The relatively short rods are
combined in bundles of 37 rods, and 12 bundles are
placed end to end in each pressure tube. The total mass
of fuel in the core is about 97,000 kg.
The CANDU reactor is unusual in that refueling is
conducted while the reactor is operating.
 Control and protection system: There are the various
types of vertical control system incorporated in the
CANDU reactor :
— A number of strong neutron absorber rods of
cadmium which are used mainly for reactor shut-down
and start-up.

— In addition to above there are other less strongly,
absorbing rods to control power variations during reactor
operation and to produce an approximately uniform heat
(power) distribution throughout the core. In an
emergency situation, the shutdown rods would
immediately drop into the core, followed, if necessary by
the injection of a gadolinium nitrate solution into the
moderator.
 Steam system:
— The respective ends of the pressure tubes are all
connected into inlet and outlet headers.
— The high temperature coolant leaving the reactor
passes out the outlet header to a steam generator of the
conventional inverted U-tube and is then pumped back
into the reactor by way of the inlet header.

Advantages of CANDU reactor
1. Heavy water is used as moderator, which has higher
multiplication factor and low fuel consumption.
2. Enriched fuel is not required.
3. The cost of the vessel is less as it has not to withstand
a high pressure.
4. Less time is needed (as compared to PWR and BWR)
to construct the reactor.
5. The moderator can be kept at low temperature which
increases its effectiveness in slowing down neutrons.

 It requires a very high standard of design,
manufacture and maintenance.
 The cost of heavy water is very high.
 There are leakage problems.
 The size of the reactor is extremely large
as power density is low as compared with
PWR and BWR.
Disadvantages of CANDU reactor

NPPs in Operation
CANDU Reactors at Pickering, Canada
CANDU at Qinshan, China

GAS COOLED REACTORS
• Uses graphite as a neutron moderator and
carbon dioxide as coolant
• The GCR was able to use natural uranium as fuel.
• Two main types of GCR:-
1. Magnox reactors developed by United Kingdom.
2. UNGG (Uranium Naturel Graphite Gaz) reactors developed
by France.
• The main difference between these two types is in
the fuel cladding (shielding) material.
• Both types used fuel cladding materials that were
unsuitable for medium term storage under water,
making reprocessing an essential part of the nuclear
fuel cycle.

 it features a fast-neutron spectrum and closed fuel cycle for efficient
conversion of fertile uranium and management of actinides.
 The reference reactor design is a helium-cooled system operating
with an outlet temperature of 850°C using a direct Brayton cycle
gas turbine for high thermal efficiency.
 Several fuel forms are being considered for their potential to
operate at very high temperatures and to ensure an excellent
retention of fission products: composite ceramic fuel, advanced fuel
particles, or ceramic clad elements of actinide compounds.
 Core configurations are being considered based on pin- or plate-
based fuel assemblies or prismatic blocks, which allows for better
coolant circulation than traditional fuel assemblies.
GAS Cooled Reactor

GAS Cooled Reactor
 The reactors are intended for
use in nuclear power plants to
produce electricity, while at the
same time; producing
(breeding) new nuclear fuel,
respectively.

Liquid Metal Cooled Reactor
• Liquid metal reactor also called as Sodium graphite reactor
• Sodium works as a coolant and graphite works as moderator.
• Sodium boils at 880deg C, sodium is first melted by electric heating
system and be pressurized to 7 bars. The liquid sodium is then
circulated by the pump.

Liquid Metal Cooled Reactor or Sodium Graphite Reactor (SGR)

Working of SGR
(i) The primary circuit has liquid sodium which circulates through the fuel
core and gets heated by the fissioning of the fuel. This liquid sodium gets
cooled in the intermediate heat exchanger and goes back to the reactor
vessel.
(ii) The secondary circuit has an alloy of sodium and potassium in liquid form.
This coolant takes heat from the intermediate heat exchanger which gets
heat from liquid sodium of primary circuit. The liquid sodium-potassium
then passes through a boiler which is once through type having tubes only.
The steam generated from this boiler will be superheated. Feed water from
the condenser enters the boiler, the heated sodium-potassium passing
through the tubes gives it heat to the water thus converting it into steam.
The sodium-potassium liquid in the second circuit is then pumped back to
the intermediate heat exchanger thus making it a closed circuit.

Advantages of SGR
1. The sodium as a coolant need not be
pressurised.
2. High temperature can be achieved in the cycle
and that means high thermal efficiency at low
cost and low cost power.
3. The low cost graphite moderator can be used as
it can retain its mechanical strength and purity at
high temperatures.
4. Excellent heat removal.
5. High conversion ratio.
6. Superheating of steam is possible.
7. The size of the reactor is comparatively small.

Disadvantages of SGR
1. Sodium reacts violently with water and actively
with air.
2. Thermal stresses are a problem.
3. Intermediate system is necessary to separate
active sodium from water.
4. Heat exchanger must be leak proof.
5. It is necessary to shield the primary and
secondary cooling system with concrete block
and as sodium becomes highly radioactive due
to neutron bombardment.
6. The leak of sodium is very dangerous as
compared with other coolants.

BREEDER REACTOR
• A breeder reactor is a nuclear reactor that consumes
fissile and fertile material at the same time as it creates
new fissile material.
• Breeders can be designed to utilize Thorium, which is
more abundant than Uranium.
• Production of fissile material in a reactor occurs by
neutron irradiation of fertile material, particularly
Uranium-238 and Thorium-232.

Breeder Reactor
 If fission is initiated with U235 it not only gives off heat but
also free neutrons.
 Under certain conditions if U238 is placed in the reactor
these free electrons may convert U238 into plutonium.
 This process is known as breeding. These reactors are
therefore known for their better utilization.

Working of Fast Breeder
Reactor
 In its simplest form a fast breeder reactor is a small
vessel in which necessary amount of enriched plutonium
is kept without using moderator.
 A fissible material, which absorbs neutrons, surrounds
the vessel. The reactor core is cooled by liquid metal.
 Necessary neutron shielding is provided by the use of
light water, oil or graphite.
 Additional shielding is also provided for gamma rays. It is
worth noting that when U235 is fissioned, it produces heat
and additional neutrons.
 If some U238 is kept in the same reactor, part of the
additional neutrons available, after reaction with U235,
convert U238 into fissible plutonium).

Breeder Reactor
 This reactor uses highly enriched fuel and liquid metal cooled.
 No moderator is used in FBR.
 U235 core is completely surrounded by U238 and thus absorbs
excess neutrons and therefore it is converted into plutonium.
 The coolant is possibly liquid sodium or an alloy of sodium or
potassium.
 Plutonium and other isotopes are produced in such reactions can
further be used.
 Advantages:
 No moderator is required
 High Breeding is possible
 Fuel burn up is high since there is no absorption risk.
 Disadvantages:
 Control becomes difficult at extreme temperatures, since no moderator.
 Power is not as high as that of thermal reactors
 Liquid sodium is corrosive
 Highly Enriched fuel is needed.

Types of breeder reactors
• The fast breeder reactor or FBR.
Initial fuel charge of plutonium, requires only natural
(or even depleted) uranium feedstock as input to its
fuel cycle. This fuel cycle has been termed the
plutonium economy.
• The thermal breeder reactor.
Initial fuel charge of enriched uranium,
plutonium, requires only thorium as input to its
fuel cycle. Thorium-232 produces Uranium-233
after neutron capture and beta decay.

Nuclear Plant Site Selection
• Proximity to load center
• Population distribution
• Land Use: not agricultural
• Meteorology: wind direction
• Geology: bearing capacity of soil
• Seismology: low seismic activity
• Hydrology: Near a water source

1. Proximity to load center
 Electrical power can be transmitted over considerable
distances by power-transmission lines, but, because of the
capital cost of the lines and rights-of-way and transmission
losses, an economic penalty is incurred which increases with
increasing distance between the generating station and the
load center.
 It is apparent, therefore, that the closer the power-plant site
can be located to the load center (while meeting other
requirements such as reasonable land cost, adequate cooling
water, local zone restrictions, accessibility for fuel shipment,
etc.), the lower can be the cost of power delivered to the
consumer.

2. Population Distribution
 Since power reactors must be located reasonably close to
load centers, the population distribution around the site is a
necessary consideration in the evaluation of a nuclear power-
plant site.
 The distances, the site meteorological conditions and the
amount of radioactive material which could be released from
the plant during a major accident are used to evaluate the
suitability of the site from the standpoint of safety to the
public.
 In addition to the permanent population surrounding a site, it
is also necessary to consider part-time peaks in population,
such as during the day or on weekends in recreational areas,
and seasonal variation in population, particularly in resort
areas. Consideration also should be given to estimates of
future increases or changes in population distribution.
Reasonable thinly populated area is preferred

3. Land Use
 The use to which the land surrounding a nuclear-plant site is
being put, even though it may not be densely populated, may
have an effect on the suitability of the site for a nuclear plant.
 For example, if land is used for agriculture, ingestion of food which
has been contaminated by fallout after an accident might
conceivably result in a greater radiation dose to the public than
might be received from direct exposure to radioactive materials
transported downwind from the plants.
 Of similar concern, but possible as a result of normal operation,
is the chance that certain marine life, stationary shellfish in
particular, can concentrate the small quantities of radioactivity
normally released into the cooling water discharged from the
plant.
 Over a long period of time, the concentration of radioactivity
conceivable could build up to levels approaching maximum
permissible concentrations.

 Meteorology is of concern both for normal discharges of
gaseous radioactive wastes and for the much less likely
releases of larger quantities of airborne radioactive material
which might result from an accident. A number of
meteorological variables are normally evaluated for the site to
determine appropriate atmospheric dilution factors.
 Among these variables are wind-direction frequencies, in
conjunction with the population distribution ; wind velocities and
the frequencies of each velocity increment ; frequency and
duration of calms ; atmospheric lapse rate (the decrease of
an atmospheric variable with a change of altitude);
frequency and duration of inversion conditions- Atmospheric
dilution is increased, and thus the meteorological conditions
are more favourable, the more unstable the atmosphere and
the greater the wind velocity.
4. Meteorology

 Other meteorological conditions of concern are the following :
precipitation, since it may significantly increase deposition of
radioactive materials from the atmosphere, i.e., "rain-out”;
possible effects of topography on the local meteorology;
seasonal variations in meteorological conditions; and the
frequency and severity of storms, particularly tornadoes and
hurricanes, which could severely damage the plant.
 Meteorological information collected at the plant site provides
the greatest assurance that it is representative of actual site
conditions, provided that sufficiently accurate instrumentation
is used and the data are collected over a long enough period
of time to be statistically valid.
4. Meteorology …

5. Geology
 Investigation of the site geology is necessary to
determine the bearing capacity of the soil and the types
of foundations which must be used for the major portions
of the plant.
 Test borings are usually made for this purpose, just as
for any other large structures. Of particular concern for
nuclear plants, because of the implications for public
safety, is the possibility of sudden earth movement which
could severely damage the plant.
 Earth slides due to soil instability, subsidence due to
removal of oil or water from subsurface formations,
and ground displacements during earthquakes along
geologic faults traversing the site each receives very
careful consideration.

6. Seismology
 Seismology is of particular concern is areas of high seismic
activity because of the possibility that the forces which can be
produced by earthquakes could be sufficient to damage the
reactor system and rupture the containment structure.
 Careful consideration is given to the general seismic history of
the area, including a description of all earthquakes which
have been observed at the site, their magnitude or intensity,
and the frequency spectrum for which structures should be
analyzed.
 Conservative earthquake design factors, usually
substantially greater than those required by the Uniform
Building Code, are used for critical equipment and
structures in areas of high seismic activity.
 In coastal areas the possibility of tsunamis may have to be
considered.

7.Hydrology
 Present-day type of nuclear plants require substantially
greater quantities of cooling water than do modern fossil
steam plants because of their higher turbine heat rates. In
areas of limited water supply, cooling towers can be used but
at some cost penalty.
 An additional consideration for nuclear plants is that there be
sufficient water flow for the discharge of low-level radioactive
liquid wastes.
 This usually imposes no limitation because of the small
quantities of wastes to be discharged and because it is
possible to dilute or clean up the wastes to nearly any
required concentration. If necessary, it is possible to collect
and ship these wastes off site.

 Another area of concern is the possibility of flooding, which
could cause damage to the plant and equipment and cause
plant shutdown.
 Seismic sea waves and hurricanes may increase the
possibility of flooding at coastal sites. Seiches (Periodic
surface oscillations) could result in flooding adjacent to large,
enclosed bodies of water.
 The flooding history of the site must be determined to permit
adequate site evaluation and plant design.
 The characteristics of the ground water and the level of the
water table at the site must be evaluated to ensure that
contamination of local water sources by the discharge of liquid
radioactive wastes does not occur.
 It there is any possibility of significant discharge of radioactive
contamination to ground water, the absorption characteristics
of the soil and the drainage characteristics of the ground
water.

Uranium …
 Low Enriched Uranium (LEU):
0.72-20% 235 U
 LEU is primary fuel for nuclear
reactors (PWR & BWR)
 High Enriched Uranium (HEU)
>20% 235 U.
 HEU is used primarily in
weapons.
 Atomic weapons of WWII used
HEU of about 93.5% 235 U
Uranium:
 51st most abundant element found
in earth crest
 Melting point : 38180 C
 0.7 % 235 Uranium and 99.3% of U-238
(isotope) is naturally occurring

Enriching Uranium
 Natural uranium contains 0.7% of the U-235 isotope. The
remaining 99.3% is mostly the U-238 isotope which does
not contribute directly to the fission process (though it
does so indirectly by the formation of fissile isotopes of
plutonium).
 Isotope separation is a physical process to concentrate
(‘enrich’) one isotope relative to others.
 Uranium-235 and U-238 are chemically identical, but
differ in their physical properties, notably their mass.
 The nucleus of the U235 atom contains 92 protons and
143 neutrons, giving an atomic mass of 235 units. The
U-238 nucleus also has 92 protons but has 146 neutrons
– three more than U235 – and therefore has a mass of
238 units

Enrichment of Uranium
Thermal Diffusion
Diffusion
Gaseous Diffusion
Centrifuge  Gaseous Centrifuge
Electromagnetic Separation
Laser Separation

Thermal Diffusion
 Thermal diffusion utilizes the transfer of heat across a thin liquid or
gas to accomplish isotope separation.
 Pressurized liquid uranium hexafluoride (UF6) is used
 By cooling a vertical film on one side and heating it on the other side,
the resultant convection currents will produce an upward flow along
the hot surface and a downward flow along the cold surface.
 Under these conditions, the lighter 235 U gas
molecules will diffuse toward the hot surface,
and the heavier 238 U molecules will diffuse
toward the cold surface.
 These two diffusive motions combined with the
convection currents will cause the lighter
235 U molecules to concentrate at the top of
the film and the heavier 238 U molecules to
concentrate at the bottom of the film

Thermal Diffusion: High Level Description
 Thin film of UF6 in liquid form
 Heat applied to top side of film and bottom
side cooled
 Works based on convection currents due
to heat difference
 235 collects at top of film and 238 collects
at bottom
 Also used for weapons production in WWII

Gaseous Diffusion
 UF6 at 135 F becomes gas
 It involves forcing uranium hexafluoride gas under pressure through
a series of porous membranes or diaphragms.
 As U-235 molecules are lighter than
the U-238 molecules they move faster
and have a slightly better chance of
passing through the pores in the
membrane.
 The UF6 which diffuses through the
membrane is thus slightly enriched,
while the gas which did not pass
through is depleted in U-235.
This process is repeated many times in a
series of diffusion stages called a
cascade.

The large Georges BesseI enrichment plant at Tricastin
in France was shut down in 2012

Gaseous Centrifuge
Principle: Rotation of cylinders creates a strong centrifugal force which
moves the heavier gas molecules containing U 238 to outside of
cylinder and lighter U235 molecules collect closer to the center.
 Centrifugal force in a cylinder spinning
rapidly on its vertical axis would
separate a gaseous mixture of two
isotopes. This is because the lighter
U-235 isotope would be less affected
by the action and could be drawn off
at the top center of the cylinder.
 A cascade system composed of
thousands of centrifuges could
produce a rich mixture.

Electromagnetic Separation
Based on principles of mass spectrometer: charged
particles follow a circular path in unified magnetic field
In the electromagnetic isotope
separation process (EMIS),
metallic uranium is first
vaporized, and then ionized to
positively charged ions.
The cations are then
accelerated and subsequently
deflected by magnetic fields onto
their respective collection targets
(like mass spectrometry) .

Laser Separation
Separation of Isotopes by Australian project : Laser
Excitation (SILEX)
The SILEX technology can be utilised in 2 steps of the
Nuclear Fuel Cycle to produce:
natural grade uranium via re-enrichment of tails
inventories; and
enriched uranium for use as fuel in nuclear power
reactors.

Present Source of Enrichment Process
Source: World Nuclear Association

Application of Nuclear Power Plant
A nuclear power station is ideally suited under the following
situations :
(i) In an area with potential for industrial development, but
limited conventional power resources, nuclear power
generation appears as an only alternative.
(ii) If the existing power grid is to be firmed up or additional
power demand is to be met while all available hydro power
resource have been exploited, and coal is scarce or
expensive to transport, a nuclear power station may be
END

Nuclear Power Plant - M.Tech

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