NUCLEAR POWER PLANT

POWER PLANT ENGINEERING
S.BALAMURUGAN - M.E
ASSISTANT PROFESSOR
MECHANICAL ENGINEERING
AAA COLLEGE OF ENGINEERING & TECHNOLOGY
UNIT 3 – NUCLEAR POWER PLANTS

• Number of Electron = Number of
Proton, Atom is Neutral Element
• Addition of number of electrons
to Neutral Element, Negatively
Charged Atom
• Any Subtraction of the electrons
in the Neutral Element,
Positively Charged Atom
• This atom is known as Ion. The
process of charging the atom is
termed as Ionization.
ME 6701 POWER PLANT ENGG. S.BALAMURUGAN AP/MECH AAACET

ISOTOPES – Not Stable, Disintegrates at fixed rate – Radioactive Isotope
Instability – Parent Nucleus 2 or more Nuclei + Emission of Particles,
High Velocity Emission of Particles (RADIATION)

• Fission reactions. Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller
parts (lighter nuclei). The fission process often produces free neutrons and photons (in the form of gamma
rays), and releases a large amount of energy.
• 235U (n, 3 n) fission products
• Fusion reactions. Occur when, two or more atomic nuclei collide at a very high speed and join to form a
new type of atomic nucleus. The fusion reaction of deuterium and tritium is particularly interesting because
of its potential of providing energy for the future.
• 3T (d, n) 4He
• Nuclear decay (Radioactive decay). Occurs when an unstable atom loses energy by emitting ionizing
radiation. Radioactive decay is a random process at the level of single atoms, in that, according to quantum
theory, it is impossible to predict when a particular atom will decay. There are many types of radioactive
decay:
• Alpha radioactivity. Alpha particles consist of two protons and two neutrons bound together into a
particle identical to a helium nucleus. Because of its very large mass (more than 7000 times the mass of
the beta particle) and its charge, it heavy ionizes material and has a very short range.
• Beta radioactivity. Beta particles are high-energy, high-speed electrons or positrons emitted by certain
types of radioactive nuclei such as potassium-40. The beta particles have greater range of penetration than
alpha particles, but still much less than gamma rays. The beta particles emitted are a form of ionizing
radiation also known as beta rays. The production of beta particles is termed beta decay.
• Gamma radioactivity. Gamma rays are electromagnetic radiation of an very high frequency and are
therefore high energy photons. They are produced by the decay of nuclei as they transition from a high
energy state to a lower state known as gamma decay. Most of nuclear reactions are accompanied by
gamma emission.
• Neutron emission. Neutron emission is a type of radioactive decay of nuclei containing excess neutrons
(especially fission products), in which a neutron is simply ejected from the nucleus. This type of radiation
plays key role in nuclear reactor control, because these neutrons are delayed neutrons.

• The component parts of nuclei are neutrons and protons, which are collectively
called nucleons.
• The mass of a nucleus is always less than the sum masses of the constituent
protons and neutrons when separated.
• The difference is a measure of the nuclear binding energy which holds the nucleus
together.
• According to the Einstein relationship (E=m.c2) this binding energy is proportional
to this mass difference and it is known as the mass defect.
• During the nuclear splitting or nuclear fusion, some of the mass of the nucleus gets
converted into huge amounts of energy and thus this mass is removed from the
total mass of the original particles, and the mass is missing in the resulting
nucleus.
• The nuclear binding energies are enormous, they are on the order of a million times
greater than the electron binding energies of atoms.

EINSTEIN’S FAMOUS EQUATION
•Einstein equation, mass and energy are in fact the
same thing.
•Converting one into the other doesn’t therefore violate
either of the two conservation laws.
•Both quantities are conserved, although the state of
the mass/energy may have changed.
•Each atom of a substance can be thought of as a little
ball of tightly packed energy that can be released
under certain circumstances.
• Speed of light = 3 x 10 8 m/s
• Energy (Form – Heat & Light) = Unit – Joules
• Electrical Devices Rated in Watts = Joules / S (J/S)
• Bulb – 100 W = Bulb use energy at a rate of 100
joules every second
• Mass – Measure of Bodies inertia, Resistance to
Acceleration

Half Life - It is the time required for a quantity to reduce to half its initial value

Fusion
For most of their lives, stars fuse elemental hydrogen into helium in their cores.
Two atoms of hydrogen are combined in a series of steps to create helium-4.
These reactions account for 85% of the Sun’s energy. The remaining 15% comes
from reactions that produce the elements beryllium and lithium.

Ternary fission is a rare type of
fission(0.2-0.4%) in which three
charged products are produced.
Beta decay is a type of radioactive
decay in which a beta ray(energetic
electron) or positron or
antineutrino or neutrino are
emitted from an atomic nucleus.
Atomic Mass Unit (a.m.u) standard unit of mass that quantifies mass on an
atomic or molecular scale, 1 AMU = 1.66 × 10-24g
Mass of Electron (me) = 9.1 x 10-28 g
Mass of Proton = 1837 me =
1837 x 9.1 x 10−28
1.66 × 10−24 = 1.00758 a.m.u
Mass of neutron = 1839 me =
1839 x 9.1 x 10−28
1.66 × 10−24 = 1.00893 a.m.u
Radius of Nucleus = 1.57 x 10-3 x 3 𝑨 , 𝑨 = 𝑵𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝑵𝒖𝒄𝒍𝒆𝒐𝒏𝒔 𝒊𝒏 𝑵𝒖𝒄𝒍𝒆𝒖𝒔

Electron volt is defined as the amount of energy one electron gains by moving
through a potential difference of one volt.
(It is the amount of kinetic energy gained by an electron as it passes through an
electric potential difference of 1 Volt).

Gaseous diffusion, gas centrifugation
MOX Fuel – Mixed Oxide Fuel formed by Mixing Uranium & Plutonium Oxide

Mining – Depending on the depth and concentration of the uranium source,
and the conditions of the surrounding rock, mining companies will extract
uranium ore in one of three ways: open pit mining, underground mining
or in-situ recovery.
Milling – To extract the uranium, the ore is crushed in a mill and ground to a
fine slurry. The slurry is then leached in sulfuric acid, which produces a
solution of uranium oxide (U3O8). The concentrate of this solution is called
yellowcake.
Refining – A series of chemical processes separate the uranium from
impurities, producing high-purity uranium trioxide (UO3).
Conversion – UO3 is converted to uranium dioxide (UO2) for use in heavy
water reactors, UO3 to uranium hexafluoride (UF6) for enrichment, before it
can be used in light water reactors.
Enrichment (Gas Centrifugation)– Uranium-235 is the uranium isotope
that can be used in fission, but it makes up only 0.7% of naturally occurring
uranium, which is not concentrated enough for light water reactors. So,
enrichment processes increase the concentration of U-235 to about 3% –
5%. After undergoing enrichment, the UF6 is chemically transformed back
into UO2 powder.
NUCLEAR FUEL CYCLE

Fuel manufacturing – Natural or enriched UO2 powder is pressed into
small cylindrical pellets, which are then baked at high temperatures,
and finished to precise dimensions.
Electricity generation – Fuel is loaded into a reactor, and nuclear
fission generates electricity. After fuel is consumed, it is removed from
the reactor and stored onsite for a number of years while its
radioactivity and heat subside.
Optional chemical reprocessing – After a period of storage, residual
uranium or by-product plutonium, both of which are still useful sources
of energy, are recovered from the spent fuel elements and reprocessed.
Disposal – Depending on the design of the disposal facility, the nuclear
fuel may be recovered if needed again, or remain permanently stored.
At some point in the future the spent fuel will be encapsulated in sturdy,
leach-resistant containers and permanently placed deep underground
where it originated.
NUCLEAR FUEL CYCLE

To produce 1 kg of enriched uranium with 5% of 235U, about 10 kg of natural
uranium is required with a byproduct of about 9 kg of depleted uranium.
Therefore annual natural uranium consumption of 3000MW reactor is about 250
tonnes of natural uranium (to produce of about 25 tonnes of enriched uranium).

ESSENTIAL COMPONENTS OF NUCLEAR REACTOR
Reactor Core
• It consists of assemblage of fuel
elements, control rods, coolant &
moderator.
• Right circular cylinder – Dia of 0.5 m to
15 m. Pressure Vessel houses the
reactor core.
• Fuel rods or plates are cladding with
stainless steel or zirconium or aluminium
to provide corrosion resistance &
Retention of Radioactivity
• Enough space is provided between fuel
rods to allow free passage of the coolant
Reflector
• Placed around the core to reflect back
some of the neutrons that leak out from
the surface of the core. It is made up of
the same material as the moderator.

Control Rod
• It works on the simple principle of absorbing the excess
neutrons. Material – Boron steel, Cadmium strips
• For starting the reactor – to bring the reactor up to its normal operating level
• For maintaining at that level – Keep Power production at a steady level
• For Shutting the reactor down under normal or emergency conditions
Moderator
• To slow down the neutrons from the high velocities & high energy level
By scattering collisions with nuclei of the light elements – Hydrogen,
graphite, H20, D20 & Beryllium
• To slow down the neutrons but not absorb them
Properties of Moderator
• Highly slowing down power
• High melting point for solids & Low melting point for liquids
• High thermal conductivity
• Chemical & Radiation stability

Coolants – CO2, Helium - He, Mercury - Hg
• To remove the intense heat produced in the reactor & to bring out for being
utilized.
Properties
Low melting point, High boiling point, Non Corrosiveness
High Specific Heat (reduces pumping power & thermal stresses)
Chemical & Radiation stability
Shielding
• Protect the walls of the reactor vessel from radiation damage
• Protect operating personnel from exposure to radiation
First - Thermal Shield – Steel Lining
External – Biological Shield – Thick Concrete
Nuclear Radiations – Alpha, Beta, Thermal neutrons (Slow), Fast neutrons &
Gamma Rays.
Harmful - Fast neutrons & Gamma Rays.

NUCLEAR POWER PLANT

• Enriched Fuel is used,
• Natural Convection or Forced Circulation (Constant pressure irrespective of load to avoid
accident)
• Under Part loading, some steam is by-passed
• Heat Exchanger is eliminated, Gain in cost & thermal Efficiency
• Low pressure vessel in the reactor, Thicker Vessel not required, reduces cost
• The disadvantage of this concept is that any fuel leak can make the water radioactive and
that radioactivity can reach the turbine and the rest of the loop.
• Wastage of steam resulting in lowering of thermal efficiency in Part load condition.
63 Fuel Tubes, 140 Tonnes of Uranium
70 Bar, 290° C

Circulation Ratio =
𝑅𝑒𝑐𝑖𝑟𝑐𝑢𝑙𝑎𝑡𝑒𝑑 𝐶𝑜𝑜𝑙𝑎𝑛𝑡
𝑆𝑎𝑡𝑢𝑟𝑎𝑡𝑒𝑑 𝑉𝑎𝑝𝑜𝑢𝑟 𝑃𝑟𝑜𝑑𝑢𝑐𝑒𝑑
= 6-10 (BWR)

•Enriched Fuel is used
•Light water used as Coolant , Moderator & Reflector – Cheap & Easily available
•Steam in the turbine not Radioactive, Secondary circuit, Freedom to inspect & maintain the
turbine, Feed heater & condenser
•Pressurizer maintain the water at 155 Bar pressure, so it will not boil , (Boiling Point 345°C)
•Pressurizer - Electrical heating coils in the pressurizer boil some water to form steam that
collects in the dome. As more steam is forced into the dome by boiling, its pressure rises &
pressurizes the entire circuit. The pressure reduced by providing spraying water on the
steam
•Capital cost High – Pressure Vessel
•Severe Corrosion Problem
•It is imperative to shutdown the reactor for fuel charging
264 Fuel Tubes, 80-100 Tonnes of Uranium

HEAVY WATER
Deuterium Oxide D2O
• It is produced from natural water
• Natural water contains 0.015% of deuterium oxide,
about one part in 6500
Deuterium Production method
• Distillation of water – Ordinary water is slightly lighter
than heavy water. USA – World war II, Cost of
Production - $ 390 / kg
• Steam – Hydrogen Exchange – When hydrogen & steam
passed together in a gaseous phase over a catalyst, an
interchange takes place where by deuterium is
concentrated in the water.
• By product – Hydrogen

PRESSURIZED HEAVY WATER REACTOR - CANDU REACTOR
• Fuel – Natural Uranium (0.7% U235) – 97000kg,
• Fuel pellets – 0.5 cm long 1.3 cm dia, Packed in Zirconium Alloy – Corrosion resistance
• Heavy water (D2O) Rs.500/kg – Moderator, Coolant & Reflector, Moderator & Coolant Kept Separate
• Reactor vessel – Steel Cylinder with Horizontal axis, Length – 6m Dia - 8m, low pressure than
PWR & BWR
• 480 Horizontal channels, 12 Bundles & 37 pellets – pressure tubes (Designated to with stand
high internal pressure)
• Coolant Leaving the reactor – 10 Bar & 370°C Steam Generator (265° C)
• 5% heat generated by fast neutrons escaping to the Moderator, Removed by circulation
through Heat Exchanger

Cadmium rods are used to startup or
shut-down the reactor (Neutron
absorber)
Emergency Situation
• Shutdown rods immediately drop
into the core
• By injecting of a gadolinium
nitrate solution into the
moderator
The purpose of the annulus gas system is to
provide thermal insulation between the hot
coolant channels and the relatively cool calandria
tubes and surrounding moderator, To reduce heat
losses from the channels.

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.
1. 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.
2. Gadolinium Nitrate is forced through the seven injection nozzles by the helium
pressure so that it is sprayed into the centre of the reactor core. The poison tanks
each contain a polyethylene ball which floats on the surface of the Gadolinium
Nitrate. Once the Gadolinium Nitrate is injected, the ball will be forced onto the
lower seat in the Gadolinium Nitrate tank which prevents the helium gas from over
pressurizing the calandria.
3. Boron can be injected into the moderator absorbing the neutrons so the chain
reaction is suppressed.
4. 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.

FERTILE MATERIALS
• Some of the materials are not fissionable
• But it can be converted into Fissionable, Fertile Materials
92U238 + 0n1 92U239 + Ƴ (Half life- 92U239 - 23.5 minutes )
92U239
-1e0 + 93Np239 (Half life - 93Np239 - 2.3 days )
93Np239
-1e0 + 94Pu239 (Half life – 94Pu239 – 24000 years)
90Th232 + 0n1 90Th233 + Ƴ (Half life- 90Th233 - 23.3 minutes)
90Th233
-1e0 + 91Pa233 (Half life - 91Pa233 - 27.4 days )
91Pa233
-1e0 + 92U233 (Half life – 92U233 – 1,60,000 Years)

INDIA’S 3 STAGE NUCLEAR PROGRAMME
Problem – Choice of reactor &
fuel. The choice between natural
uranium against enriched
uranium depends on availability
of natural uranium resources in
the country
• 1st Stage – Natural Uranium
fuelled reactor established in
our country, Produce
Fissionable material (Pu239)
• 2nd Stage – Plutonium from 1st
stage used as fuel in Fast
Breeder Reactor, Add U238 or
U233 which produce P239 or
U233
• 3rd Stage – U233 from 2nd Stage
used as fuel, Thorium
converted into Fissile U233
(U233 – Best fissile material
for Breeder reactors)
1000 MW Nuclear Power Plant,
• 1st Stage, Produce 380 kg of P239 per year
with an annual feed of 150 tonnes of
natural uranium
• 2nd stage, With the feed of 380 kg of P239, it
will produce 170 kg of U233 per year

Gas Cooled Reactor
• Natural Uranium – Fuel
• Coolant – Air, hydrogen, Helium & Carbon di oxide, Corrosion Problem Eliminated
• Coolant Pressure – 7 Bar & Temperature - 336° C
• Moderator – Graphite (Remains same – Irradiation at High Temperature)
• Fuel – Natural Uranium, U235 with an alloy of magnesium (MAGNOX)
• If helium is used instead of CO2, then leakage of gas is major problem
• Gas Coolant has low heat transfer capacity, High mass flow rate is required, Power density
low, Large Vessel Required.
Types of Gas Cooled Reactor
• High Temperature Gas Cooled Reactor (30 Bar & 800°C)
• Advanced Gas Cooled Reactor (648°C – Stainless Steel Cladding fuel due to High temp.)
Stainless steel absorbs neutrons – Enriched fuel is used

LIQUID METAL COOLED REACTOR
• Graphite – Moderator, Sodium – Coolant
• Sodium – At 1 Bar, Boiling point 880°C – Freezing point 95°C – Neutron Absorption
cross – section of sodium is low – Best suited to thermal reactor
• Sodium is melted by Electric heating system – Pressure increases to 7 Bar
• Primary Circuit – Coolant absorbs the heat from fuel core – Gets cooled in the
Intermediate Heat Exchanger
• Secondary Circuit – Alloy of Sodium & Potassium - Absorbs the Heat from Primary
circuit– Once through type Boiler – Water from condenser converted to Steam
• Shielding – Reactor vessel, Primary loop & intermediate heat exchanger –
• Liquid metal covered with Inert gas (helium) – To prevent contact with air

BREEDER REACTOR
• Fuel – Enriched Uranium (15 % ), the fuel is a mix of oxides of plutonium and uranium
• Small Core – Power Density high
• Small vessel – Chain Reaction sustained by fast moving neutrons (with out using
Moderator)
• Fertile Material + Neutron = Fissile Material
• Coolant – Liquid metal – Sodium
• Handling of Sodium is difficult – Highly Radioactive

TYPES OF NUCLEAR WASTE
• High Level Waste (3%) – Spent fuel containing 95% of radioactivity
in the nuclear waste
• Intermediate Waste (7%) – Used filters, steel components from
within the reactor & some effluents from reprocessing containing 4%
of radioactivity in the nuclear waste
• Low level waste (90%) – Lightly contaminated items like tools &
clothing containing only 1% of radioactivity in the nuclear waste.
• Both LLW and ILW from a nuclear power station will be isolated from
the environment for typically 300 years so that their radioactivity will
reduce with time to natural levels.
• HLW is highly radioactive. After being extracted from the spent fuel, it
typically needs a period of 20 to 50 years to cool down.
• Technology has been developed to pack the waste in glass in a
process known as vitrification.
• The packaged vitrified waste can then be stored underground in a
stable geological formation to isolate it and prevent its movement for
over thousands of years. Furthermore, the radioactivity will fall over
time and after several thousand years it will fall to natural levels

• Spent fuel is processed at facilities in Trombay near Mumbai, at
Tarapur on the west coast north of Mumbai, and at Kalpakkam on the
southeast coast of India.
• Plutonium will be used in a fast breeder reactor (under construction) to
produce more fuel, and other waste vitrified at Tarapur and Trombay.
• Interim storage for 30 years is expected, with eventual disposal in a deep
geological repository in crystalline rock near Kalpakkam.
NUCLEAR WASTE PROCESSING IN INDIA

NUCLEAR WASTE - PROCESSING
• Highly reactive materials created during production of
nuclear power.
• Core of the nuclear reactor or nuclear weapon
• Uranium, plutonium, high reactive elements from fission
• Long lives> 100000years
Management of high level waste in India following three stages
Immobilization- Vitrified borosilicate glasses
Engineered interim storage of vitrified waste for passive
cooling & surveillance over a period of time
Ultimate storage / disposal of the vitrified waste a deep
geological depository
deep geological depository requirements
• remoteness from environment
• absence of circulating ground water

Joule Heated Ceramic Melter (JHCM)

SAFETY MEASURES FOR NUCLEAR POWER PLANT
• Ensure the safety of neighboring communities
• To prevent abnormal incidents, if occurs to prevent the
spreading of abnormal incidents
Basic Safety Functions in Reactor
• To control reactivity
• To cool the fuel
• To contain radioactive substance
Aseismic measures taken by a nuclear power plant
Assuring safety at design stage
• Detailed study in the site & its surroundings
• Conformation of safety against Tsunami
• Geological structure of site
Assuring safety at construction & operation stage
• Ground with sufficient Bearing Resistance
• Automatic shut down of reactor at certain level of Earth
quake is detected

NUCLEAR POWER PLANT

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