Nuclear power plant

Introduction to Nuclear Power
• It is the use of Nuclear Fission reactions to
Generate Power
• Nuclear energy is the world's largest source of
emission-free energy
• Most efficient Power Source per Unit Area
• Used in 31 Countries (approx 441 reactors)1
• Accounts for about 16% of all electricity
generated world wide (approx 351 Gigawatts)
1. 2003 Figures

The major benefits of Nuclear Power include:
• No Green House Gas emissions
• No Air Pollutants such as CO,SO2,NO,Hg or
particulate matter, thus ensuring “Nil”
contribution to Acid Rain, Global Warming etc.
• Relatively low risk of “Work Related Injury”
• Efficiency per capita fuel unit is very high

Developed Countries are shifting to Nuclear Power

US 97
North America Region 109
France 63
Germany 21
U. K. 12
Western Europe Region 126
Japan 44
Asia Region 66
Eastern Europe Region 11
Former Soviet U. Region 34
World Nuclear Power Production in Gigawatts

India Nuclear Power Production in MW
Plants under operation MWe
14 reactors at 6 sites viz., Tarapur, Rawatbhata, Kalpakkam
Narora, Kakrapar and Kaiga
2720
Plants under construction
2x500 at Tarapur 1000
Plants likely to commence in the current
financial year
2x220, 2x1000, 1x500 2940
Future Plans
2x220,4x500,10x500,6x1000 13440
Total 20100

Advantages over coal
• One gram of fissionable uranium can produce a
million times more heat than one gram of coal.
• For 400MW of electricity, only 20 kg of uranium
fuel is required per day. In comparison, a coal
burning thermal power station of the same
capacity would require about 4000 tonnes of
coal daily

Disadvantages
• The problem of radioactive waste is still an unsolved
one.
• High risks
• Nuclear power plants as well as nuclear waste could be
preferred targets for terrorist attacks.
• Radioactive waste is produced can be used for the
production of nuclear weapons.
• Uranium is a scarce resource

The Underlying Principle
“Nuclear Fission”
• In Physics, “fission” is a nuclear process, i.e., it
occurs in the nucleus of an atom. Fission occurs
when the Nucleus splits into two or more smaller
nuclei plus some by-products. These by-products
include free neutrons and photons (usually
gamma rays). Fission releases substantial
amounts of energy (the strong nuclear force
binding energy).
• The use of this energy for generation of electricity
is the essence of nuclear power generation.

• Radioactivity was discovered by Sir James Chadwick (1932)
• Later Enrico Fermi experimented and Physicist Lise Meitner
and Otto Frish discovered Chain Reactions
• Chicago Pile
– The first controlled chain reaction was conducted
in December 1942, resulted in heat Generation of
2 kW using Uranium
• The Manhattan Project:
– Atomic bomb
– Nagasaki & Hiroshima

•Fission can be induced
by several methods,
including bombarding
the nucleus of a fissile
atom with a free
neutron moving at the
right speed
•Neutron + U-235 -->
fission products + more
neutrons + energy
•The process releases a lot of energy compared to chemical reactions.
•Energy released by a fission event is approximately 200 MeV.

How does fission work
• A neutron hits a uranium nucleus.
• The nucleus becomes unstable and needs to release
energy.
• The nucleus breaks releasing energy, neutrons and 2
smaller atoms.
• The 2 smaller atoms formed are called fission fragments.

• When the neutrons are released during fission, they
go on to hit 2/3 other uranium nuclei.
• This continues and is called a chain reaction
• In a nuclear reactor the chain reaction is controlled.
• As the control rods are removed the chain reaction
increases, and if we want to slow the reaction
control rods are inserted.

Block Schematic for Nuclear Power Plant

A Nuclear Power Plant is basically a Thermal Power Plant in which
steam is produced in a Nuclear Reactor rather than in a Conventional
Boiler

Nuclear Power Plant - Working
Components of a Nuclear Power Plant

Basic Reactor Model
Pump
1.Fuel
3.Controlrod
5.Steamgenerator
4. Coolant
6.
8.
7.
Turbine
Generator

Major components of Nuclear Reactor
TYPE DESCRIPTION
Fuel These are Fissile Elements like U235’ PU239 arranged in the form of Bundled rods
Control Rods /
Nuclear Poison
A control rod is of chemical elements capable of absorbing many neutrons without fissioning
themselves (E.g. silver, indium and cadmium)
Control rods are usually inserted into guide tubes within a fuel element. A control rod is
removed from or inserted into the central core of a nuclear reactor in order to control the
neutron flux — increase or decrease the number of neutrons which will split further uranium
atoms. This in turn affects the thermal power of the reactor, the amount of steam produced,
and hence the electricity generated.
Moderator Moderator is a medium which reduces the speed of fast neutrons, thereby turning them
into thermal neutrons capable of sustaining a nuclear chain reaction involving U235.
Commonly used moderators include regular (light) water, used in roughly 75% of the world‘s
reactors, solid graphite (20%) and heavy water (D2O) (5%). Beryllium has been used in some
experimental reactor types, and hydrocarbons have been suggested as a possibility.
Coolant Coolant is a medium used to transfer heat generated in the Nuclear Reactor’s core to the heat
exchanger to produce Steam for driving Steam Turbines. Light Water, Heavy Water, Carbon
Dioxide, Nitrogen, Molten Sodium etc. are some commonly used coolants

Nuclear Power Reactor - Fuel
Uranium Fuel Cycle

Types of Nuclear Reactor
1. The Boiling Water Reactor (BWR): This is the simplest of all reactors.
Water absorbs heat from the reactions in the core and is directly driven to the
turbines. After condensing the water is pumped back to the reactor core

2. Pressurized water reactors, (PWR): In this type of reactor, the heat is dissipated
from the core using highly pressurized water (about 160 bar) to achieve a high
temperature and avoid boiling within the core. The cooling water transfers its heat to the
secondary system in a steam generator

3. Pressurized Heavy Water Reactor (PHWR), : In this type of reactors, fuel
bundles are inserted into the Heat Exchanger where a heavy water moderator is
circulated to provide cooling in addition to moderating neutrons. This heavy water
is then circulated to the steam generator to transfer its heat and then pumped back
to the reactor. The steam is a secondary circuit as above and is used to drive a
turbine assembly before condensing and re-use

4. The Gas Cooled Reactor (GCR) : It uses CO2 gas to remove heat from the core.
This is then piped through the steam generator where heat is removed from the
gas and it can then be re-circulated to the reactor. As usual steam generated is
used to drive the turbine and generate electricity, condensed then recirculated.
Graphite is used as a moderator to allow energy production by un-enriched
uranium.

5. The Light Water Graphite Reactor (LWGR): Here Graphite replaces heavy
water as moderator. Light water is used to remove heat from the core for transfer
to steam drums. The steam evolved in these is used subsequently to power
turbines.

6. The Fast Breeder Reactor (FBR): It uses a Plutonium fuel rather than Uranium.
The Pu is surrounded by rods of U-238 which absorb neutrons and are transmitted
into Pu-239 which undergoes fission to generate energy. As the plutonium in the
core becomes depleted it creates or breeds more plutonium from the Uranium
around it.

Nuclear Waste management
• Radioactive wastes from the nuclear reactors
and reprocessing plants are treated and
stored at each site
• High level waste is currently kept in storage
facilities and will finally be put into specially
engineered underground repositories.
• Research on final disposal of high-level and
long-lived wastes in a geological repository is
in progress .

Technology advancements in nuclear power reactors

Generation II reactor
• A generation II reactor is a design classification
for a nuclear reactor, and refers to the class of
commercial reactors built up to the end of the
1990s.
• Prototypical generation II reactors include the
PWR, CANDU, BWR, AGR, and VVER.
(2,5)

Generation III reactors
• Advanced Boiling Water Reactor (ABWR) — A GE design that
first went online in Japan in 1996.
• Advanced Pressurized Water Reactor (APWR) — developed by
Mitsubishi Heavy Industries.
• Enhanced CANDU 6 (EC6) — developed by Atomic Energy of
Canada Limited.
• VVER-1000/392 (PWR) — in various modifications into AES-91
and AES-92.
(2,5)

Generation IV reactor
• Generation I V reactors(Gen IV) are a set
of theoretical nuclear reactor designs
currently being researched.
• commercial construction before 2030,
with the exception of a version of the
Very High Temperature Reactor (VHTR)
called the Next Generation Nuclear
Plant (NGNP).
• Research into these reactor types was
officially started by the Generation IV
International Forum (GIF)
(2,5)

Goals of Gen IV
• Improve nuclear safety.
• Improve proliferation Resistance.
• Minimize waste and natural resource
utilization.
• Decrease the cost to build and run such
plants.
• Increase life time of nuclear reactors.

Reactor types
Thermal reactors
• 1. Very-high-
temperature
reactor (VHTR)
• 2. Supercritical-
water-cooled
reactor (SCWR)
Fast reactors
• 1. Gas-cooled fast
reactor (GFR)
• 2. Sodium-cooled
fast reactor (SFR)
• 3. Lead-cooled fast
reactor (LFR)

• VHTR:- Concept uses a graphite-moderated core with a once-
through uranium fuel cycle, using helium or molten salt as the
coolant.
• SCWR:- Concept that uses supercritical water as the working fluid.
It could operate at much higher temperatures than both current
PWRs and BWRs.
• MSR:- Nuclear reactor where the coolant is a molten salt. Nuclear
fuel dissolved in the molten fluoride salt as UF4 or ThF4.

• FR:- Fast-neutron spectrum and closed fuel cycle. The reactor is
helium-cooled. Based on Brayton cycle gas turbine.
• SFR:- Builds on two closely related existing projects, the liquid
metal fast breeder reactor and the Integral Fast Reactor.
• LFR:-fast-neutron-spectrum lead or lead/bismuth eutectic (LBE)
liquid-metal-cooled reactor with a closed fuel cycle.

Advantages
• Nuclear waste that lasts a few centuries
instead of millennia.
• 100-300 times more energy yield from
the same amount of nuclear fuel.
• The ability to consume existing nuclear
waste in the production of electricity.

Facts of disaster
• 6-7 % heat still decay out from core even in shutdown condition
which is must to remove.
• In emergency shutdown back up gens ets take 60-75 seconds to
achieve full load.
• Test was conducted with night shift workers instead of trained
day shift workers.
• Production of xenon reduced the stable power level required
for test causing withrawal of more control rods.
• Human error by Er. Toptunov who inserted control rods in the
core.

• To increase power output control rods were removed
instantly in large number causing rise in temperature
and hence massive power spike occurred which
damaged the fuel rods also .
• As power was around 700 mw actual test begins and
turbine generator went off and ext. gensets resumed
the working of ECCS.
• Due to some alarm triggering 4 of 8 main circulation
pumps went off air causing serious steam voids in
coolant process thus increasing the temperature of
core.

• To reduce the increased power output control rods
are allowed to get in the core which was already
damaged. So only1/3 part of rods was in the core.
• Consequently power output rose up to 33GW(10
times of peak output).
• Hydrogen blast took place first blowing off the
secondary containment and then flammable graphite
blasted with huge impact involving radioactive core
also.

Fukushima Daiichi Event
Unit 1
439 MW
11 March 2011
(2,5)

Fukushima Event
 The Fukushima nuclear facilities were damaged in a
magnitude 8.9 earthquake on March 11 (Japan time),
centered offshore of the Sendai region, which
contains the capital Tokyo.
 Plant designed for magnitude 8.2 earthquake. An
8.9 magnitude quake is 7 times in greater in
magnitude.
 Serious secondary effects followed including a
significant tsunami, significant aftershocks and a
major fire at a fossil fuel installation.

Waste Management
Disposal of waste of nuclear power plant
Nuclear power plant wastes can be classified
• Low level radioactive waste
• High level radioactive waste

Waste Management
• It includes cooling water pipes,radiation
suits,discarded fuel elements cans and gloves
• Low level radioactive waste are easy to
dispose off
• Low level radioactive wastes are stored under
sea bed and large stable geologic formations
on land
Low level radioactive waste

Waste Management
High level radioactive waste
• It includes materials from the core of the nuclear reactor.
• Plutonium, Uranium, Control rods and other radioactive
elements made during fission
• Difficult to dispose

Waste Management
• These radioactive materials are stored in shielded storage
vaults
• Shielded vaults are stored in deep salt mines
• Sometimes high level nuclear waste can be sunk to the
bottom of the sea & oceans
• Fired into the sun or into a long term stable orbit.
• Transmutation
High level radioactive waste disposal

• Necessary to guard personnel and delicate instruments
• Materials used are lead, Concrete, Steel and cadmium
• Water is used to slow down fast neutrons
• Boron and steel are employed for absorption of thermal
neutrons
• Heavy metals like lead is required to act as thermal shield and
to absorb gama rays
Waste Management
Shielding of Nuclear reactor

Nuclear power plant

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Nuclear power plant