Transcript LECTURE 7 ELECTRIC POWER INDUSTRY ECE 371 Sustainable Energy Systems NUCLEAR POWER  The essence of the nuclear technology is the same as steam cycle of fossil-fueled.

LECTURE 7
ELECTRIC POWER
INDUSTRY
ECE 371
Sustainable Energy Systems
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NUCLEAR POWER

The essence of the nuclear technology is the
same as steam cycle of fossil-fueled plants


The difference is that heat is created by nuclear
reaction
Nuclear plant have the advantage of essentially
being carbon-free source of power

If carbon associated with the plant construction is
ignored
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NUCLEAR POWER

The world’s first nuclear-powered electric
generating plant was constructed by Soviet
Union in 1954 – 5 MW

The first US PWR was constructed and placed
in service by Westinghouse at Pennsylvania in
1957

The first US BWR was constructed and placed
in service by GE at California in 1957 – 5 MW
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NUCLEAR POWER

The following figure shows the number of
nuclear plant orders placed annually
1973: Arab Oil Embargo
1979: Three Mile Island #2
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NUCLEAR REACTION

It is a reaction that changes the number of
protons or neutrons in the nucleus of an atom

There are several kinds of nuclear reactions

Fragmentation of large nuclei into smaller ones


Nuclear fission
Building up of small nuclei into larger ones

Nuclear fusion
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NUCLEAR FISSION

It is a nuclear reaction in which nucleus of an
atom splits into smaller parts

This process often release neutrons


Self-sustaining chain reaction, if slowed (concept of
“moderator” invented by Fermi)
It also releases enormous amount of energy in
the form of heat
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NUCLEAR FISSION

In 1939 Hahn and Strassman in Berlin
bombarded a Uranium-235 isotope with
neutrons and demonstrated nuclear fission for
the first time
Barium
Krypton
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NUCLEAR FISSION

The number of protons in a nucleus determines
the elements

The number of neutrons determines the isotope

Example

Uranium nucleus has 92 protons
If it has 143 neutrons, it is Uranium-235
 If it has 146 neutrons, it is Uranium-238

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NUCLEAR FISSION

The naturally mined uranium contains 0.7% of
U-235 and 99.3% of U-238

Separation is difficult

Bohr found that nuclear fission was much more
likely to occur in Uranium-235 isotope than in
Uranium-238

The process of “enrichment” was developed to
increase concentration of U-235 in the mixture
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NUCLEAR POWER PLANT

In a nuclear power plant, a nuclear reactor
produces and controls the release of energy
from splitting the atoms of elements such as
uranium and plutonium

The energy released as heat from the continuous
fission of the atoms in the fuel is used to make
steam
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NUCLEAR POWER PLANT
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CORE

Reactor core is the portion of the nuclear
reactor which contains the nuclear fuel where
the nuclear reaction takes place

The main function of a core is to create an
environment which establishes and maintains
the nuclear chain reaction

It provides a means for controlling the neutron
population and removing the energy released
within the core
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MODERATOR

Moderator is a material which slows down the
released neutrons from the fission process

Slow moving neutrons are much more likely to
be absorbed by uranium atoms to cause fission
than fast moving neutrons

Newly released neutrons after a nuclear fission
move at 300,000 km/sec
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MODERATOR

It must be slowed down or “moderated” to
speeds of a few km/sec

This is necessary to cause further fission and
continue the chain reaction
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MODERATOR

The most commonly moderators are

Water - H2O
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Light water reactor
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Heavy water D2O (formed by a heavier isotope of
hydrogen with atomic mass 2)
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Heavy water reactor
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Not efficient – it slows neutrons and also absorbs them
Efficient
Graphite
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FUEL
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The most common fuel is
Uranium-235
 Plutonium-239
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Light water reactors use uranium oxide (UO2)
pellets which are arranged in zirconium alloy
tubes to form fuel rods (melting point of UO2 is
2800oC)
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FUEL
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Pellets are 1 cm in diameter and 1.5 cm long
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FUEL
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The fuel rods are placed in fuel assemblies in the
reactor core
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CONTROL ROD

It is made of neutron-absorbing material
Cadmium
 Hafnium
 Boron


Rods are used to control the rate of reaction

They are inserted or withdrawn from the core to
decrease or increase the rate of fission
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CONTROL ROD
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CONTROL ROD

Inserting the rod slows down the reaction by
absorbing the neutrons and reducing the
available neutrons for fission

Withdrawing them has the opposite effect

Allowing the rate of fission to grow beyond a
certain point can be very dangerous (Chernobyl)
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COOLANT

It is a liquid or gas circulating around or through
the core
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It carries the heat away from the reactor

It generates steam in the steam generator
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The most common coolant is pressurized water
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STEAM GENERATOR

It is a heat exchanger

Uses heat from the core which is transported by
the coolant
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Produces steam for the turbine
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CONTAINMENT

It is the structure around the reactor core

It protects the core from outside intrusion

Protects outside environment from effects of
radiation in case of a malfunction

Typically it is a meter thick concrete and steel
structure
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SPENT FUEL POOL

It stores the spent fuel from the nuclear reactor

About 1/4 to 1/3 of the total fuel is removed
from the core every 12 to 18 months and
replaced with the fresh fuel

The removed fuel rods still generate a lot of heat
and dangerous radiation
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SPENT FUEL POOL
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The fuel bundles freshly removed from the core
are separated for several months for initial
cooling

Then they are sorted in other parts of the pool
for final disposal

Metal racks keep the fuel in safe positions to
avoid the possibility of a nuclear chain reaction
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SPENT FUEL POOL

The spent fuel is typically stored underwater for
10 to 20 years before being sent for disposal or
reprocessing
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LOCATION OF NUCLEAR
PLANTS IN U.S.
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NUCLEAR SHARE OF
ELECTRICITY PRODUCTION
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LIGHT WATER REACTORS

There are 2 types of Light Water Reactors (LWR)
Boiling Water Reactors (BWR)
 Pressurized Water reactors (PWR)
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BWR
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1000 psi, 285oC
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PWR
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2300 psi, 315oC
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LIGHT WATER REACTORS

PWRs are more complicated, but

They operate at higher temperatures than BWR


More efficient
They are safer

Fuel leak would not pass any radioactive contaminants into
the turbine and condenser
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HEAVY WATER REACTORS

In HWRs some of the hydrogen atoms in the
water is replaced by deuterium (D2O)
Hydrogen with an added neutron
 Deuterium in heavy water is more efficient in slowing
down neutrons
 Ordinary uranium that is mined can be used without
enrichment (only 0.7% of it is U-235)
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NUCLEAR FUEL CYCLE
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The nuclear fuel cycle is shown below
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NUCLEAR FUEL CYCLE
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After 40 years the reactor will have to be
decommissioned

Radioactive components will also have to be
transported to a secure disposal site

Reactor waste contain plutonium which has a
half-life of 24,390 years
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NUCLEAR FUEL CYCLE

Plutonium makes nuclear waste dangerously
radioactive and toxic

Removing plutonium from nuclear waste before
disposal is possible
It can be used for nuclear weapons (dozens per year
from 1 reactor)
 It can be used as a reactor fuel

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NUCLEAR FUEL CYCLE
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