chapter 4 nuclear power station

Chapter 8
Nuclear Power station
• The Motivation for Nuclear Energy
• Neutron Reactions, Nuclear Fission and Fusion
• Nuclear Reactors
• Nuclear Fuel Cycle
• Nuclear Energy Systems: Generation IV
• Storage and Disposal of Nuclear Wastes
By: Prof. Ghada Amer

Chapter 8
• Chain Reactions and Nuclear Reactors

The Motivation for Nuclear Energy
• The generation of electricity from fossil fuels, particularly natural
gas and coal, is a major and growing contributor to the emission of
carbon dioxide – a greenhouse
• At least for the next few decades, there are only a few realistic
options for reducing carbon dioxide emissions from electricity
generation:
 increase efficiency in electricity generation
 expand use of renewable energy sources such as wind, solar,
biomass, and geothermal;
 capture carbon dioxide emissions at fossil-fueled (especially coal)
electric generating plants and permanently sequester the carbon;
and
 increase use of nuclear power.
Nuclear Energy - Prof. Ghada Amer5/14/2018 3

• In certain report from the MIT, in USA in 2015 they wrote “In
our view, it is likely that we shall need all of the above
options and accordingly it would be a mistake at this time to
exclude any of these four options from an overall carbon
emissions management strategy.
Nuclear Energy - Prof. Ghada Amer
Rather we seek to explore and
evaluate actions that could be taken to
maintain nuclear power as one of the
significant options for meeting future
world energy needs at low cost and in
an environmentally acceptable
manner.
5/14/2018 4

A Brief History of Nuclear Power
• The first nuclear reactors were all designed to produce plutonium for
nuclear weapons programmes.
• ‘‘In the post war era, as Britain still had to import relatively expensive oil,
policy makers thought that nuclear energy could be a cheap alternative.
• The shift from military to peaceful uses of nuclear power gained power in
1953 when President Eisenhower proposed his ‘‘Atoms for Peace’’
programme, suggested nuclear materials be used to provide ‘‘ample electrical
energy in the power-starved areas of the world’’.
• This was beneficial to governments who were keen to develop their nuclear
weapons programme away from the glare of public examination.
• The optimism and almost euphoria about the possible manifold peaceful uses
of the atom captured the imagination of writers and scientists, with claims
we would see:
‘‘nuclear powered planes, ships, trains . . . nuclear energy would naturally
modify crops and preserve grains and fish’’. (Scurlock 2007)
• The cold war enabled nuclear power to be constructed as vital for national
security.

• The initial reactors were of elementary
design, graphite blocks into which
uranium fuel was placed and plutonium
chemically extracted from the spent fuel
to be used in atomic bombs.
• The world’s first nuclear reactor, built as
part of the Manhattan project, it
achieved criticality in December 1942.
• As a result of the research conducted
during the Manhattan project,
researchers in the West and the USSR
realised that the heat generated from
nuclear fission could be attached to
generate electricity for power hungry
nations, as well as to provide force for
submarines and aircraft carriers.

• The remarkable proposition was that the
UN commission would in effect own and
control the nuclear fuel cycle, from
uranium mining through to reprocessing,
and in effect release uranium to nations
who wanted to build nuclear power plants
for electricity production only.
• As part of this international control of
nuclear technology, the US release a report
suggested, should license its control on
nuclear weapons sharing knowledge with
nations but not proceeding with weapons
development.
• It seemed to be a win-win situation.
Countries could take advantage of the
promise of cheap base load electricity from
nuclear power plants and the international
community could nip proliferation risks in
the bud.

• BUT!! This small window of opportunity that existed for
international cooperation on nuclear matters was firmly shut,
leading to the nuclear arms race and the cold war, the
outcomes of which ring down to the present day.
• The US Congress in 1946 passed the report, which firmly denied
foreigners’ (even wartime allies) access to US nuclear data.
Individual countries had to
pursue their own nuclear
weapons and nuclear energy
programmes with all the
attendant costs and risks of
‘‘going it alone’’.

Expansion of Nuclear Power
• The large scale use of nuclear power during the 1950s and 1960s was
concentrated in the USA, UK, Russia and Canada.
• Then expanded later 1960s and 1970s (Sweden, Japan, West
Germany).
• It was also touted as a solution to the urban pollution caused
primarily by coal-fired power stations.
• As a result, the federal government financed and built a number of
demonstration reactors to prove to the Energy companies that
nuclear was feasible.
• A pamphlet published by the nuclear company Westinghouse in the
1960’s captures the prevailing optimism about the promise of
nuclear power:
‘‘It will give us all the power we need and more. That’s what it’s all
about. Power seemingly without end. Power to do everything that man
is intended to do. We have found what may be called lasting youth’’.

• In 2016, nuclear power supplied 20% of United States and
17% of world electricity consumption.
• Experts project worldwide electricity consumption will
increase substantially in the coming decades, especially in
the developing world, accompanying economic growth and
social progress.
• However, official forecasts call for a mere 10% increase in
nuclear electricity generating capacity worldwide by 2020.
• These projections entail little new nuclear plant
construction and reflect both economic considerations and
growing anti-nuclear sentiment in key countries.
• The limited prospects for nuclear power today are
attributable, ultimately, to four unresolved problems:

1. Costs: nuclear power has higher overall lifetime costs compared to
natural gas with combined cycle turbine technology (CCGT) and coal, at
least in the absence of a carbon tax or an equivalent “cap and trade”
mechanism for reducing carbon emissions;
2. Safety: nuclear power has perceived adverse safety, environmental, and
health effects, heightened by the 1979 Three Mile Island and 1986
Chernobyl reactor accidents, but also by accidents at fuel cycle facilities
in the United States, Russia, and Japan. There is also growing concern
about the safe and secure transportation of nuclear materials and the
security of nuclear facilities from terrorist attack;
3. Proliferation: nuclear power entails potential security risks, notably the
possible misuse of commercial or associated nuclear facilities and
operations to acquire technology or materials as a precursor to the
acquisition of a nuclear weapons capability. Fuel cycles that involve the
chemical reprocessing of spent fuel to separate weapons-usable
plutonium and uranium enrichment technologies are of special concern,
especially as nuclear power spreads around the world

4. Waste: nuclear power has unresolved challenges in long-term
management of radioactive wastes. The United States and other
countries have yet to implement final disposition of spent fuel or high
level radioactive waste streams created at various stages of the
nuclear fuel cycle. Since these radioactive wastes present some danger
to present and future generations, the public and its elected
representatives, as well as prospective investors in nuclear power
plants, properly expect continuing and substantial progress towards
solution to the waste disposal problem. Successful operation of the
planned disposal facility at Yucca Mountain would ease, but not solve,
the waste issue for the U.S. and other countries if nuclear power
expands substantially.

Chapter 8

Nuclear Reactions
• Nuclear reactions deal with interactions between the nuclei
of atoms including of nuclear fission and nuclear fusion
• Both fission and fusion processes deal with matter and energy
• Fission is the process of splitting of a nucleus into two
"daughter" nuclei leading to energy being released
• Fusion is the process of two "parent" nuclei fuse into one
daughter nucleus leading to energy being released

• Nuclear reactions are different from chemical reactions
Chemical
Reactions
Mass is
conserved
(doesn’t
change)
Small
energy
changes
No changes in the
nuclei; involve
ONLY valance
electrons
Nuclear
Reactions
Small
changes in
mass
Huge
energy
changes
protons, neutrons,
electrons and
gamma rays can be
lost or gained

Mass Defect
• Some of the mass can be converted into
energy
• Shown by a very famous equation!
E=mc2
Energy
Mass
Speed of light Nuclear Energy - Prof. Ghada Amer5/14/2018 16

Nuclear Reactions
• Two types:
–Fission = the splitting of nuclei
–Fusion = the joining of nuclei (they fuse
together)
• Both reactions involve extremely large
amounts of energy
Albert Einstein’s
equation E = mc2
illustrates the energy
found in even small
amounts of matter

Nuclear Fission:
• Is the splitting of one heavy nucleus into two or more smaller nuclei, as
well as some sub-atomic particles and energy.
• A heavy nucleus is usually unstable, due to many positive protons
pushing apart.
• When fission occurs:
1.Energy is produced.
2.More neutrons are given off.
• Neutrons are used to make nuclei unstable
– It is much easier to crash a neutral neutron than a positive
proton into a nucleus to release energy.
There are 2 types of fission that exist:
1. Spontaneous Fission
2. Induced Fission

FYI: The penetrating power of radiation.

Spontaneous Fission
• Some radioisotopes contain nuclei which are highly unstable and
decay spontaneously by splitting into 2 smaller nuclei.
• Such spontaneous decays are accompanied by the release of
neutrons.
Induced Fission
• Nuclear fission can be induced by bombarding atoms with
neutrons.
• The nuclei of the atoms then split into 2 equal parts.
• Induced fission decays are also accompanied by the release of
neutrons.

U
235
92n
1
0
The Fission Process
A neutron travels at high speed towards a uranium-235 nucleus.

U
235
92n
1
0
The Fission Process
A neutron travels at high speed towards a uranium-235
nucleus.

U
235
92n
1
0
The neutron strikes the nucleus which then captures
the neutron.
The Fission Process

U
236
92
The nucleus changes from being uranium-235 to
uranium-236 as it has captured a neutron.
The Fission Process

The uranium-236 nucleus formed is very unstable.
The Fission Process
It transforms into an elongated shape for a short time.

The Fission Process

It then splits into 2 fission fragments and releases
neutrons.
141
56Ba
92
36Kr
n
1
0
n
1
0
n
1
0
The Fission Process

neutrons.
141
56Ba
92
36Kr
n
1
0
n
1
0
n
1
0
The Fission Process

neutrons.
141
56Ba
92
36Kr
1
n
1
0
n
1
0
The Fission Process

Energy from Fission
Both the fission fragments and neutrons travel at high
speed.
The kinetic energy of the products of fission are far
greater than that of the bombarding neutron and
target atom.
EK before fission << EK after fission
Energy is being released as a result of the fission reaction.

Energy from Fission
U
235
92
+Cs
138
55
+ n
1
0
2n
1
0
+Rb
96
37
Element Atomic Mass (kg)
235
92U 3.9014 x 10-25
138
55Cs 2.2895 x 10-25
96
37Rb 1.5925 x 10-25
1
0n 1.6750 x 10-27

Energy from Fission
Calculate the total mass before and after fission takes place.
The total mass before fission (LHS of the equation):
The total mass after fission (RHS of the equation):
3.9014 x 10-25 + 1.6750 x 10-27 = 3.91815 x 10-25 kg
2.2895 x 10-25 + 1.5925 x 10-25 + (2 x 1.6750 x 10-27) = 3.9155 x 10-25 kg

The total mass before fission =
The total mass after fission =
3.91815 x 10-25 kg
3.91550 x 10-25 kg
total mass before fission > total mass after fission
mass difference,
m = total mass before fission – total mass after fission
m = 3.91815 x 10-25 – 3.91550 x 10-25
m = 2.65 x 10-28 kg
This reduction in mass results in the release of
energy.

The energy released can be calculated using the equation:
E = mc2
Where:
E = energy released (J)
m = mass difference (kg)
c = speed of light in a vacuum (3 x 108 ms-1)
E
m c2

Energy from Fission
E = mc2
U
235
92 +Cs
138
55+ n
1
02n
1
0 +Rb
96
37
Calculate the energy released from the following fission
reaction:
m = 2.65 x 10-28 kg
c = 3 x 108 ms-1
E = E
E = 2.65 x 10-28 x (3 x 108)2
E = 2.385 x 10-11 J
• The energy released from this fission reaction does not seem a
lot. This is because it is produced from the fission of a single
nucleus.
• Large amounts of energy are released when a large number of
nuclei undergo fission reactions.Nuclear Energy - Prof. Ghada Amer5/14/2018 38

Fission
produces
a chain
reaction

 Each uranium-235 atom has a mass of 3.9014 x 10-25 kg.
 The total number of atoms in 1 kg of uranium-235 can be found
as follows:
 No. of atoms in 1 kg of uranium-235 = 1/3.9014 x 10-25
 No. of atoms in 1 kg of uranium-235 = 2.56 x 1024 atoms
If one uranium-235 atom undergoes a fission reaction
and releases 2.385 x 10-11 J of energy, then the amount
of energy released by 1 kg of uranium-235 can be
calculated as follows:
total energy = energy per fission x number of atoms
total energy = 2.385 x 10-11 x 2.56 x 1024
total energy = 6.1056 x 1013 J

Nuclear Fusion
In nuclear fusion, two nuclei with low mass numbers combine to
produce a single nucleus with a higher mass number.
H
2
1
+He
4
2
+ n
1
0
H
3
1
+ Energy
H
2
1
H
3
1

H
2
1
H
3
1
Nuclear Fusion

Nuclear Fusion

He
4
2
n
1
0
Nuclear Fusion

Energy from Fusion
Element Atomic Mass (kg)
2
1H 3.345 x 10-27
3
1H 5.008 x 10-27
4
2He 6.647 x 10-27
1
0n 1.6750 x 10-27
H
2
1
+He
4
2
+ n
1
0
H
3
1 +Energy

Calculate the following:
• The mass difference.
• The energy released per fusion.
The total mass before fusion (LHS of the equation):
The total mass after fission (RHS of the equation):
3.345 x 10-27 + 5.008 x 10-27 = 8.353 x 10-27 kg
6.647 x 10-27 + 1.675 x 10-27 = 8.322 x 10-27 kg
H
2
1
+He
4
2
+ n
1
0
H
3
1 +Energy

m = total mass before fission – total mass after fission
m = 8.353 x 10-27 – 8.322 x 10-27
m = 3.1 x 10-29 kg
E = mc2m = 3.1 x 10-29 kg
c = 3 x 108 ms-1
E = E
E = 3.1 x 10-29 x (3 x 108)2
E = 2.79 x 10-12 J
H
2
1
+He
4
2
+ n
1
0
H
3
1 +Energy
The energy released per fusion is 2.79 x 10-12 J.Nuclear Energy - Prof. Ghada Amer5/14/2018 55

Chapter 8

What is a nuclear reactor?
• A nuclear reactor is a system that contains and controls
sustained nuclear chain reactions.
• Reactors are used for generating electricity, moving aircraft
carriers and submarines, producing medical isotopes for
imaging and cancer treatment, and for conducting research.
• Fuel, made up of heavy atoms that split when they absorb
neutrons, is placed into the reactor vessel (basically a large
tank) along with a small neutron source.
• The neutrons start a chain reaction where each atom that
splits releases more neutrons that cause other atoms to split.
• Each time an atom splits, it releases large amounts of energy in
the form of heat.
• The heat is carried out of the reactor by coolant, which is most
commonly just plain water. The coolant heats up and goes off
to a turbine to spin a generator or drive shaft. Nuclear reactors
are just exotic heat sources.

Nuclear Reactor Main components
• The core of the reactor contains all of the nuclear fuel and generates
all of the heat. It contains low-enriched uranium (<5% U-235), control
systems, and structural materials. The core can contain hundreds of
thousands of individual fuel pins.

• The coolant is the material that passes through the core,
transferring the heat from the fuel to a turbine.
It could be:
 water,
 heavy-water,
 liquid sodium,
 helium, or something else.
In the US fleet of power reactors, water is the standard.

• The turbine transfers the heat from the coolant to
electricity, just like in a fossil-fuel plant.
• The containment is the structure that separates the
reactor from the environment. These are usually
dome-shaped, made of high-density, steel-reinforced
concrete. Chernobyl did not have a containment to
speak of.

• Cooling towers are needed by some plants to dump the excess
heat that cannot be converted to energy due to the laws of
thermodynamics. These are the hyperbolic icons of nuclear
energy. They emit only clean water vapor.

• The image above shows a nuclear reactor heating up water
and spinning a generator to produce electricity.
• It captures the essence of the system well. The water coming
into the condenser and then going right back out would be
water from a river, lake, or ocean.
• It goes out the cooling towers. As you can see, this water does
not go near the radioactivity, which is in the reactor vessel.

Fuel pins
• The smallest unit of the reactor is the fuel pin.
• These are typically uranium-oxide (UO2), but can take on
other forms, including thorium-bearing material.
• They are often surrounded by a metal tube (called the
cladding) to keep fission products from escaping into the
coolant.

Fuel assembly
• Fuel assemblies are bundles of fuel pins.
• Fuel is put in and taken out of the reactor in
assemblies.
• The assemblies have some structural material to
keep the pins close but not touching, so that
there’s room for coolant.

Full core
• This is a full core, made up of several hundred assemblies. Some
assemblies are control assemblies.
• Various fuel assemblies around the core have different fuel in
them.
• They vary in enrichment and age, among other parameters.
• The assemblies may also vary with height, with different
enrichments at the top of the core from those at the bottom.

Types of Reactors
• There are many different kinds of nuclear fuel
forms and cooling materials can be used in a
nuclear reactor. As a result, there are
thousands of different possible nuclear reactor
designs.
• Here, we discuss a few of the designs that have
been built before, but don’t limit your
imagination; many other reactor designs are
possible. Dream up your own!

Pressurized Water Reactor (PWR)
• The most common type of reactor.
• The PWR uses regular old water as a coolant.
• The primary cooling water is kept at very high pressure so it does not
boil.
• It goes through a heat exchanger, transferring heat to a secondary coolant
loop, which then spins the turbine.
• These use oxide fuel
pellets stacked in
zirconium tubes.
• They could possibly
burn thorium or
plutonium fuel as
well.
5/14/2018 67

Pros:
• Strong negative void coefficient — reactor cools down if water
starts bubbling because the coolant is the moderator, which is
required to sustain the chain reaction
• Secondary loop keeps radioactive stuff away from turbines,
making maintenance easy.
• Very much operating experience has been accumulated and
the designs and procedures have been largely optimized.
Cons:
• Pressurized coolant escapes rapidly if a pipe breaks,
necessitating lots of back-up cooling systems.
• Can’t breed new fuel — susceptible to "uranium shortage"

Boiling Water Reactor
• Second most common, the BWR is similar to the PWR in many ways.
However, they only have one coolant loop.
• The hot nuclear fuel boils water as it goes out the top of the reactor,
where the steam heads over to the turbine to spin it.

Pros:
• Simpler plumbing reduces costs
• Power levels can be increased simply by speeding up the jet pumps,
giving less boiled water and more moderation. Thus, load-following is
simple and easy.
• Very much operating experience has been accumulated and the designs
and procedures have been largely optimized.
Cons:
• With liquid and gaseous water in the system, many weird transients are
possible, making safety analysis difficult
• Primary coolant is in direct contact with turbines, so if a fuel rod had a
leak, radioactive material could be placed on the turbine. This
complicates maintenance as the staff must be dressed for radioactive
environments.
• Can’t breed new fuel — susceptible to "uranium shortage"
• Does not typically perform well in station blackout events, as in
Fukushima.

Canada Deuterium-Uranium Reactors (CANDU)
• CANDUs are a Canadian design found in Canada and around the world.
• They contain heavy water, where the Hydrogen in H2O has an extra
neutron (making it Deuterium instead of Hydrogen).
• Deuterium absorbs many fewer neutrons than Hydrogen, and CANDUs
can operate using only natural uranium instead of enriched.

Pros:
• Require very little uranium enrichment.
• Can be refueled while operating, keeping capacity factors high
(as long as the fuel handling machines don’t break).
• Are very flexible, and can use any type of fuel.
Cons:
• Some variants have positive coolant temperature coefficients,
leading to safety concerns.
• Neutron absorption in deuterium leads to tritium production,
which is radioactive and often leaks in small quantities.
• Can theoretically be modified to produce weapons-grade
plutonium slightly faster than conventional reactors could be.

Sodium Cooled Fast Reactor
• These reactors are cooled by liquid sodium metal.
• Sodium is heavier than hydrogen, a fact that leads to the neutrons moving
around at higher speeds (hence fast). These can use metal or oxide fuel,
and burn a wide variety of fuels.

Pros:
• Can breed its own fuel, effectively eliminating any concerns about uranium
shortages
• Can burn its own waste
• Metallic fuel and excellent thermal properties of sodium allow for passively
safe operation — the reactor will shut itself down safely without any backup-
systems working (or people around), only relying on physics.
Cons:
• Sodium coolant is reactive with air and water. Thus, leaks in the pipes results in
sodium fires. These can be engineered around but are a major setback for
these reactors.
• To fully burn waste, these require reprocessing facilities which can also be used
for nuclear proliferation.
• The excess neutrons used to give the reactor its resource-utilization capabilities
could covertly be used to make plutonium for weapons.
• Positive void coefficients are inherent to most fast reactors, especially large
ones. This is a safety concern.
• Not as much operating experience has been accumulated. We have only about
300 reactor-years of experience with sodium cooled reactors

High Temperature Gas Cooled Reactor (HTGRs)
• HTGRs use little pellets of fuel backed into either hexagonal compacts or
into larger pebbles (in the prismatic and pebble-bed designs).
• Gas such as helium or carbon dioxide is passed through the reactor
rapidly to cool it. Due to their low power density, these reactors are seen
as promising for using nuclear energy outside of electricity: in
transportation, in industry, and in residential regimes. They are not
particularly good at just producing electricity.

Pros:
• Can operate at very high temperatures, leading to great thermal
efficiency (near 50%!) and the ability to create process heat for things like
oil refineries, water desalination plants, hydrogen fuel cell production,
and much more.
• Each little pebble of fuel has its own containment structure, adding yet
another barrier between radioactive material and the environment.
Cons:
• High temperature has a bad side too. Materials that can stay structurally
sound in high temperatures and with many neutrons flying through them
are hard to come by.
• If the gas stops flowing, the reactor heats up very quickly. Backup cooling
systems are necessary.
• Gas is a poor coolant, necessitating large amounts of coolant for
relatively small amounts of power. Therefore, these reactors must be
very large to produce power at the rate of other reactors.
• Not as much operating experience

Molten Salt Reactor
• Molten Salt Reactors (MSRs) are nuclear reactors that use a fluid fuel in the form of very
hot fluoride or chloride salt instead of the solid fuel used in most reactors.
• Since the fuel salt is liquid, it can be both the fuel (producing the heat) and the coolant
(transporting the heat to the power plant).
• There are many different types of MSRs, but the most talked about one is definitely the
Liquid Fluoride Thorium Reactor (LFTR).
• This MSR has Thorium and Uranium dissolved in a fluoride salt and can get planet-scale
amounts of energy out of our natural resources of Thorium minerals, much like a fast
breeder can get large amounts of energy out of our Uranium minerals.
• There are also fast breeder fluoride MSRs
that don’t use Th at all.
• And there are chloride salt based fast
MSRs that are usually studied as nuclear
waste-burners due to their extraordinary
amount of very fast neutrons.
5/14/2018 77

Pros:
• Can constantly breed new fuel, eliminating concerns over energy
resources
• Can make excellent use of thorium, an alternative nuclear fuel to
uranium
• Can be maintained online with chemical fission product removal,
eliminating the need to shut down during refueling.
• No cladding means less neutron-absorbing material in the core,
which leads to better neutron efficiency and thus higher fuel
utilization
• Liquid fuel also means that structural dose does not limit the life
of the fuel, allowing the reactor to extract very much energy out of
the loaded fuel.

Cons:
• Radioactive gaseous fission products are not contained in small pins, as
they are in typical reactors. So if there is a containment breach, all the
fission gases can release instead of just the gases from one tiny pin. This
necessitates things like triple-redundant containments, etc. and can be
handled.
• The presence of an online reprocessing facility with incoming pre-
melted fuel is a proliferation concern. The operator could divert Pa-233
to provide a small stream of nearly pure weapons-grade U-233. Also,
the entire uranium inventory can be separated without much effort. In
his autobiography, Alvin Weinberg explains how this was done at Oak
Ridge National Lab: "It was a remarkable feat! In only 4 days all of the
218 kg of uranium in the reactor were separated from the intensely
radioactive fission products and its radioactivity reduced five billion-
fold."
• Very little operating experience, though a successful test reactor was
operated in the 1960s

The Nuclear Fuel Cycle

The Front End of the Cycle
For Light Water Reactor Fuel

Uranium
• URANIUM is a slightly radioactive metal that occurs throughout the
earth's crust.
• It is about 500 times more abundant than gold and about as common as
tin.
• It is present in most rocks and soils as well as in many rivers and in sea
water.
• Most of the radioactivity associated with uranium in nature is due to
other materials derived from it by radioactive decay processes, and
which are left behind in mining and milling.
• Economically feasible deposits of the ore, pitchblende, U3O8, range from
0.1% to 20% U3O8. Nuclear Energy - Prof. Ghada Amer5/14/2018 83

Uranium Mining
 Open pit mining is used where deposits are close to the surface
 Underground mining is used for deep deposits, typically greater than
120m deep.
 In situ leaching (ISL), where oxygenated groundwater is circulated
through a very porous ore body to dissolve the uranium and bring it to
the surface.
ISL may use slightly acidic or alkaline solutions to keep the uranium in
solution. The uranium is then recovered from the solution.
• The decision as to which mining method to use for a particular deposit
is governed by:
1. the nature of the ore body,
2. safety and
3. economic considerations.
In the case of underground uranium mines, special precautions, consisting
primarily of increased ventilation, are required to protect against
airborne radiation exposure.Nuclear Energy - Prof. Ghada Amer5/14/2018 84

Uranium resources in Egypt
1-‫أبو‬‫زنيمة‬‫احدى‬‫مدن‬‫جنوب‬‫سيناء‬
2-‫جبل‬‫قطار‬
3-‫المسيكات‬-‫العرضية‬-‫وتقع‬‫جنوب‬‫طريق‬‫ق‬‫نا‬-
‫سفاجا‬
4-‫جبل‬‫أم‬‫آر‬-‫تقع‬‫هذه‬‫المنطقة‬‫على‬‫بعد‬180‫كم‬
‫جنوب‬‫شرق‬‫أسوان‬
5-‫الصحراء‬‫الشرقية‬
6-‫الصحراء‬‫الغربية‬-‫اكتشفت‬‫في‬‫الواحات‬
‫البحرية‬‫بعض‬‫تمعدنات‬‫اليورانيوم‬‫في‬‫جب‬‫ل‬
‫الهفهوف‬
7-‫سيناء‬
5/14/2018 85

Processing: from ore to “yellow cake”
• Once uranium ore has been extracted in an underground or open-pit
mine, it is transported to a processing plant.
• This step allows us to obtain concentrated uranium, or "yellow cake".
Purification and concentration of uranium ore
• Once the ore has been removed from the mine, it is processed in one
of the following ways, depending on its grade:
5/14/2018 86

1- Dynamic treatment
• High-grade ore (uranium content > 0.10%) is
transported to a processing plant, where it is
 crushed
 ground mechanically processed and
 purified with chemical solutions extracted from the
resulting liquor using organic solutions or ion exchange
resins
 washed and filtered
 precipitated and dried.

2- Acid heap leaching
• Many companies has been using this modern method for the
extraction of uranium from low-grade ores ( < 0.10%) since 2009.
• This process is called “heap” leaching because the ore is stacked up.
• It is the first time that leaching has been used in uranium mining.
The steps in the process are as follows:
1. The ore is crushed to reduce it to particles of appropriate size
2. The particles are aggregated in an agglomerator using water and
acid to enhance the permeability and stability of the heaps.
3. The ore is heaped up by stackers at the leach pads
4. An acid solution percolates through the ore heap for about 3
months
• The uranium-bearing solution drains from the heap and is collected.
The uranium is extracted from the solution using a solvent in a
chemical treatment plant.

• After drying, a solid, concentrated uranium is obtained
called "yellow cake" (due to its color and its doughy texture
at the end of the procedure) containing around 75% uranium,
or 750 kilograms per metric ton.
• The "yellow cake" is packaged and put into barrels, then sent
to conversion facilities for further chemical processing.

Uranium Metallurgy
“Yellowcake” Nuclear Energy - Prof. Ghada Amer5/14/2018 91

Enriching Uranium for Reactor Fuel
• Increase the concentration of fissionable U-235 isotope
• Enrichment requires a physical process since
U-235 and U-238 have the same chemical properties
• Physical processes require gases for separation
• Uranium and its oxides are solids
• Must convert uranium to Uranium hexafluoride (UF6)
• Enriched UF6 must be converted back to solid
uranium or uranium oxide

Enrichment
The two methods of uranium enrichment are:
• Gaseous diffusion (older)
• Centrifugation (newer)
Both use small differences in the masses (< 1%) of the U-235F6 and
U-238F6 molecules to increase the concentration of U-235.

F6
F6

Loading uranium
hexafluoride containers
Gaseous diffusion plant
Paducah, Kentucky

Centrifuge Enrichment
Feed
Enriched
exit
Depleted
exit
U235F6is lighter and
collects in the center
(enriched)
U238F6 is heavier and
collects on the outside
walls
(Depleted/Tails)
Feed to
Next Stage

1. Proven technology: Centrifuge is a proven enrichment process,
currently used in several countries.
2. Low operating costs: Its energy requirements are less than 5% of
the requirements of a comparably sized gaseous diffusion plant.
3. Modular architecture: The modularity of the centrifuge
technology allows for flexible deployment, enabling capacity to be
added in increments as demand increases.Nuclear Energy - Prof. Ghada Amer
The gas centrifuge process has
three characteristics that make it
economically attractive for
uranium enrichment:
5/14/2018 97

Fuel Fabrication
• Reactor fuel is generally in the form of ceramic pellets.
• These are formed from pressed uranium oxide which is sintered
(baked) at a high temperature (over 1400°C).
• The pellets are then encased in metal tubes to form fuel rods,
which are arranged into a fuel assembly ready for introduction
into a reactor. Nuclear Energy - Prof. Ghada Amer5/14/2018 98

UF6 Gas to UO2 Powder to Pellets

Fuel Pellets

Nuclear Fuel Assembly
Fuel
Pellet

Fuel Assemblies are Inserted in Reactor Vessel

Chapter 8
• Chain Reactions and Nuclear Reactors
• Nuclear Reactor Safety

Top 10 Nuclear Generating Countries, 2014
5/14/2018 104

Source: Energy Information Administration
Energy Source
% of U.S.
Electricity
Supply
% of U.S.
Energy
Supply
%
Imported
Oil 3 39 51
Natural Gas 15 23 16
Coal 51 22 0
Nuclear 20 8 0
Hydroelectric 8 4 0
Biomass 1 3 0
Other Renewables 1 1 0
We Will Need More Energy
But Where Will It Come From?
• Oil:
– U.S. imports 51% of its oil supply
– Susceptible to supply disruptions and price fluctuations
• Natural Gas:
– Today’s fuel of choice
– Future price stability?
• Coal:
– Plentiful but polluting
• Renewables:
– Capacity to meet
demand?
– Still expensive
• Nuclear:
– Proven technology
– Issues remain

The Evolution of Nuclear Power
Early Prototype
Reactors
Generation I
- Shipping port
- Dresden, Fermi I
- Magnox
Commercial Power
Reactors
Generation II
- LWR-PWR, BWR
- CANDU
- VVER/RBMK
1950 1960 1970 1980 1990 2000 2010 2020 2030
Generation IV
- Highly
Economical
- Enhanced
Safety
- Minimal
Waste
- Proliferation
Resistant
- ABWR
- System 80+
- AP600
- EPR
Advanced
LWRs
Generation III
Gen I Gen II Gen III Gen III+ Gen IV
Near-Term
Deployment
Generation III+
Evolutionary designs
offering improved
economics
Atoms for
Peace
TMI-2 Chernobyl
LWR: light-water reactor
PWR: Pressurized Water Reactors
BWR: Boiling Water Reactor
CANDU: Canada Deuterium Uranium Reactors
ABWR :advanced boiling water reactor

Generation IV Nuclear Energy Systems
• Six ‘most promising’ systems that offer significant
advances towards:
– Sustainability
– Economics
– Safety and reliability
– Proliferation resistance and physical
protection
• Summarizes R&D activities and priorities for the
systems
• Lays the foundation for Generation IV R&D
program plans
http://nuclear.gov/nerac/FinalRoadmapforNERACReview.pdf

IV Reactor types
• Many reactor types were considered initially; however, the list was
downsized to focus on the most promising technologies and those that
could most likely meet the goals of the Gen IV initiative.
• Three systems are nominally thermal reactors and three are fast
reactors.
• The Very High Temperature Reactor (VHTR) is also being researched
for potentially providing high quality process heat for hydrogen
production.
• The fast reactors offer the possibility of burning actinides to further
reduce waste and of being able to "breed more fuel" than they
consume.
• These systems offer significant advances in sustainability, safety and
reliability, economics, proliferation resistance (depending on
perspective) and physical protection.

A Long-Term Strategy for Nuclear Energy
1- Generation IV Thermal Reactors
• A thermal reactor is a nuclear reactor that uses slow or thermal
neutrons.
• A neutron moderator is used to slow the neutrons emitted by
fission to make them more likely to be captured by the fuel.
• Advanced, high burnup fuels
• High efficiency, advanced energy products
• Available by 2020

Thermal Systems
Example: Very High Temperature Reactor (VHTR)
– Thermal neutron spectrum and once-through cycle
– High-temperature process heat applications
– Coolant outlet temperature above 1,000oC
– Reference concept is 600 MWh with operating efficiency greater
than 50 percent
• Advanced Energy Production
– High efficiency electricity generation
– High efficiency hydrogen production via thermochemical water
cracking or high temperature electrolysis

Water
Oxygen
Hydrogen
Heat
O2
SO2
2H2O
H2
H2SO4
H20+SO2+½O2
H2SO4
HI
I2 + SO2 +2H2O
2HI + H2SO4
2HI H2 + I2
I2
900-1,100oC
5/14/2018 112

Generation IV Fast Reactors
• Fast neutron systems
• Proliferation-resistant closed fuel cycles
• Minimize long-term stewardship burden
• Available by 2030 to 2040

Molten Salt Reactor - MSR
• Molten/liquid fuel
reactor
• High outlet temperatures
• Operates at atmospheric
pressure
• Flexible fuel: no covering

Supercritical Water-Cooled Reactor - SCWR
• LWR operating above the critical pressure of water, and producing
low-cost electricity.
• The U.S. program assumes:
– Direct cycle,
– Thermal spectrum,
– Light-water coolant and moderator,
– Low-enriched uranium oxide fuel,
– Base load operation.
25 MPa (supercritical)
500C (supercritical)
280C (subcritical)
Subcritical pressure
Subcritical temperature
500C (supercritical)
280C (subcritical)
Subcritical pressure
Subcritical temperatureNuclear Energy - Prof. Ghada Amer5/14/2018 115

Fast Systems
Example: Gas-Cooled Fast Reactor (GFR)
– Fast neutron spectrum and closed fuel
cycle
– Efficient management of actinides and
conversion of fertile uranium
– Coolant outlet temperature of 850oC
– Reference concept is 600 MWth with
operating efficiency of 43 percent;
optional concept is 2,400 MWth
• Advanced Energy Production
– High efficiency electricity generation
– Good efficiency for hydrogen production
via thermochemical water cracking or
high temperature electrolysisNuclear Energy - Prof. Ghada Amer5/14/2018 116

Lead Cooled Fast Reactor - LFR
• Deployable in remote
locations without supporting
infrastructure (output,
transportation)
• High degree of proliferation
resistance
• 15 to 30-yr core lifetime
• Passively safe under all
conditions
• Capable of self-autonomous
load following
• Natural circulation primary
• Fuel cycle flexibility
• Options for electricity,
hydrogen, process heat &
desalination
• Licensable through testing of
demonstration plant

System
Neutron
Spectrum
Coolant Temperature (°C) Fuel Cycle Size (MW)
VHTR Thermal Helium 900–1000 Open 250–300
SFR Fast Sodium 550 Closed
30–150, 300–
1500, 1000–
2000
SCWR Thermal/fast Water 510–625
Open/
closed
300–700, 1000–
1500
GFR Fast Helium 850 Closed 1200
LFR Fast Lead 480–800 Closed
20–180, 300–
1200, 600–1000
MSR Fast/thermal
Fluoride
salts
700–800 Closed 1000
5/14/2018 118

http://www.nuclear.gov/AFCI_RptCong2003.pdf
January 2003
Advanced Fuel Cycle Initiative
The Path to a Proliferation-Resistant Nuclear
Future
• Develop fuel cycle technologies that:
– Enable recovery of the energy value from
commercial spent nuclear fuel
– Reduce the toxicity of high-level nuclear
waste bound for geologic disposal
– Reduce the inventories of civilian
plutonium in the U.S.
– Enable more effective use of the currently
proposed geologic repository and reduce
the cost of geologic disposal

Advanced Fuel Cycle Technologies
Application to Fast Reactors
Spent Fuel From
Commercial Plants
Direct
Disposal
Conventional
Reprocessing
PUREX
Spent
Fuel
Pu Uranium
MOX
LWRs/ALWRs
U and Pu
Actinides
Fission Products
Repository
Repository
Less U and Pu
(More Actinides
Fission Products)
Advanced, Proliferation-Resistant
Recycling
ADS Transmuter
Trace U and Pu
Trace Actinides
Less Fission Products
Repository
Gen IV Fast Reactors
Once Through
Fuel Cycle
European/Japanese
Fuel Cycle
Advanced Proliferation Resistant
Fuel Cycle
Gen IV Fuel Fabrication
LWRs/ALWRs
Gen IV Thermal Reactors
Advanced Separations

• The current methods of storage are
running out of space and are not
intended for long-term use
• The USA government was required by
the Nuclear Waste Policy Act of 1982 to
provide long-term storage for waste
• So far, the USA federal government has
scrapped Yucca Mountain, and it is
considering alternative storage methods
• The US has more than 64,000 metric
tons of nuclear waste “Enough to cover
a football field about 6.4008 m deep”
• The half-life of the fuel is more than 1
million years
• Legal requirements: Nuclear Waste
Policy Act of 1982
Fast Facts
Nuclear Energy - Prof. Ghada Amer5/14/2018122

USA Current Storage Locations

Nuclear Waste…Why?
•Most opponents of nuclear power point to two main arguments:
 meltdowns and
 nuclear waste.
•Nuclear waste is any form of byproduct or end product that
releases radioactivity.
•How to safely dispose of nuclear waste is essential for:
1. the continued operation of nuclear power plants,
2. safety of people living around dump sites, and
3. prevention of proliferation of nuclear materials to non-nuclear
states.
5/14/2018 124

Nuclear Waste Classifications
• Nuclear waste is separated into several classifications.
1. Low level waste is not dangerous but sometimes requires
shielding during handling.
2. Intermediate level waste typically is chemical sludge and other
products from reactors.
3. High level waste consists of fissionable elements from reactor
cores and transuranic wastes.
“Transuranic waste is any waste with transuranic alpha emitting
radionuclides that have half-lives longer than 20 years”

1. Low Level Waste (LLW)
• Low level waste is any waste that could be from a high activity area.
• 90% volume of waste
• It does not necessarily carry any radioactivity.
• Split into four categories: A, B, C, and GTCC.
2. Intermediate Level Waste (ILW)
• Intermediate level waste requires shielding when being handled.
• Dependent on the amount of activity it can be buried in shallow
repositories.
• Not recognized in the United States.

3. High Level Waste (HLW)
• High level waste has a large amount of radioactive activity and is
thermally hot.
• 95% of radioactivity
• Current levels of HLW are increasing about 12,000 metric tons per
year.
• Most HLW consists of Pu-238, 239, 240, 241, 242, Np-237, U-236
4. Transuranic Waste (TRUW)
• Transuranic waste consists of all waste that has radionuclides above
uranium.
• TRUWs typically have longer half-lives than other forms of waste.
• Typically a byproduct of weapons manufacturing.
• Only recognized in the United States.

Nuclear Fuel Cycle
Most nuclear waste comes from the byproducts of the
nuclear fuel cycle. The cycle typically is split into three
sections:
1. front end,
2. service period, and
3. back end.
There can be intermediate stages that include the
reprocessing of nuclear waste elements.
5/14/2018 128

Creation of Nuclear Waste
•Nuclear waste is generated at all points of the
fuel cycle.
•Front end waste consists primarily of low level
alpha emission waste.
•Service period waste typically includes LLW and
ILW such as contaminated reactor housings and
waste from daily operation.
•Back end waste normally is the most radioactive
and includes spent fuel rods and reactor cores.

Front End Waste
• Front end waste consists mostly of
LLW and ILW.
• The primary front end waste is
depleted uranium and radium.
– (Depleted uranium)DU has
several uses due to its high
density (19,050 kg/m3).
– Mix with uranium to form
reactor fuel

Service Period Waste
• Consists of mostly ILW.
• Mostly waste produced at the plant
during normal operation.
• Spent fuel rods are the most
dangerous waste produced during
the service period.

Back End Waste
• Nuclear waste developed during
the back end of the fuel cycle is
the most dangerous and
includes most of the HLW
produced.
• Most back end waste emits both
gamma and beta particles.
• Also uranium-234, neptunium-
237, plutonium-238 and
americium-241are found in back
end waste.
Spent nuclear fuel in a cooling pond in North
Korea.

Waste Management (LLW)
• There are several
options available for
the disposal of LLW due
to its lack of
radioactivity.
• Waste Isolation Pilot
Plant
• On-site disposal
Map of WIPP Facility

Treatment (LLW)
• Filtration
• Ion Exchange
• Evaporation
• Burning
• Compaction
• Solidification
Typical LLW treatment facility.

Waste Management (HLW)
• Most common utilized option are
reactor pools and dry cask storage.
• Other Options for waste
management include:
– Deep Geological Storage
– Transmutation
– Reuse
– Launching it into space
Locations of storage sites for nuclear
waste in the U.S.

Treatment
• Most common initial treatment
of waste is vitrification.
– Waste is first mixed with sugar
and then passed through a
heated tube to de-nitrite the
material.
– This material is then fed into a
furnace and mixed with glass.
– The molten glass mixture is
poured into steel cylinders and
welded shut.

• Mid level active waste is commonly treated with ion exchange
 Process reduces the bulk volume of radioactive material.
 Typically, mixed with concrete for a solid storage form.
• Synroc is a new method for storing nuclear waste developed in
1978 by Ted Ringwood. “Attempts to hold radioactive material in a
crystalline matrix”.
• Currently in use for military waste management at Savannah River
Site.
• Can hold 50%-70% volume of waste.
5/14/2018 Nuclear Energy - Prof. Ghada Amer 137

• Spent fuel rods are stored
in cooling ponds
• On-site at the reactors
• Protects surroundings from
radiation
• Absorbs heat generated
during radioactive decay
Spent Fuel Pools

Spent Fuel Storage Pools

• They were only intended as a temporary solution
• They are quickly reaching full capacity
Problems with Spent Fuel Pools

• Two options for storage:
horizontal and vertical
• Surrounded by inert gas,
steel, and concrete
• Must be licensed by the NRC
– 22 different licensed designs
• 9,000 metric tons are stored
this way
Dry Cask Storage

Dry Cask Storage on
Reactor Sites

• Even advocates admit
this is only viable for a
certain number of years
– right now they are
licensed for 50 years
• Transportation to offsite
is difficult
• Potential terrorist target
Problems with Dry Cask Storage

Deep Geological Repository
• Most common method for
handling nuclear waste.
• Typically kept separate
from actual plants and
buried far below ground.
• First used in 1999 in the
US.
• Current research is
focusing on Yucca
Mountain.
Yucca Mountain Site

• So far, rate payers have
paid in $27 billion to the
Nuclear Waste Fund
• The government has spent
$8 billion of this money
• The site was required by
law and contract to begin
collecting waste in 1998
Government Failure:
Yucca Mountain

• Two billion years ago, uranium
in Gabon was caught in a
chain reaction
• Plutonium was produced and
trapped in the rock
• Since then, the radioactivity
has moved only slightly and
the plutonium has devolved
into nonreactive substances
Precedent for Yucca Mountain

• Only 3% high level waste remains
• Results are mostly Plutonium and
some Uranium-235
• Current capabilities: 1/3 of the
world’s fuel
Reprocessing

Reprocessing – Closed Fuel Cycle
• Recovers of uranium and plutonium from spent fuel
• Reduces volume and radioactivity of waste
• France, the UK, Japan, and Russia currently reprocess spent fuel

Solidifying high-level waste in borosilicate glass
for long term storage in a repository

• In spent fuel, Plutonium is trapped in
bulky assemblies, but after
reprocessing it is stored in powdered
form
• Plutonium after reprocessing is
significantly less radioactive
• It is hard to keep track of all of the
material at a reprocessing facility
• Some storage and disposal is still
required
• Would divert funds from a
permanent storage facility
• Incredibly high price tag – perhaps
$100 billion to reprocess the existing
spent fuel
Problems with Reprocessing

• After reprocessing,
there is little security
threat
• The resulting Plutonium
can be used in MOX fuel
but not as easily in
weapons
Counter Argument to the Security
Threat from Reprocessing

Transport of Spent Fuel

Reuse of Nuclear Waste
• Research is being performed to find uses for
nuclear waste.
• Caesium-137 and strontium-90 already used
in industrial applications.
• Some waste can be used for radioisotope
thermoelectric generators (RTGs).
• Overall can reduce total HLW but not
eliminate it.

Launch it into Space
• Near infinite storage
space
• Completely removes
waste from biosphere
• Technical risks and
problems
• Political
entanglements

Conclusions
• HLW is most dangerous
byproduct of nuclear
power.
• Borosilicate glass most
common storage.
• Several venues being
researched for the safe
disposal of HLW.

Refernces
1) Introduction to Nuclear Materials: Fundamentals and Applications,
First Edition. K. Linga Murty and Indrajit Charit. # 2013 Wiley-VCH
Verlag GmbH & Co. KGaA. Published 2013 by Wiley-VCH Verlag GmbH
& Co.
2) “Nuclear Reactor Types” Provided by the IEE “The Institution of
Electrical Engineers” Savoy Place, London, November 2005, ISBN 0
85296 581 8.
3) https://en.wikipedia.org/wiki/Nuclear_power
4) Atoms for Peace: a pictorial history of the IAEA (book, August
2007)
5/14/2018 Nuclear Energy - Prof. Ghada Amer 156

Thanks for your attention
Good Luck!

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