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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
• Nuclear Reactor Safety
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 2
4/19/2018 Nuclear Energy - Prof. Ghada Amer 3
o The neutrons start a chain reaction where each
atom that splits releases more neutrons that cause
other atoms to split.
o Each time an atom splits, it releases large amounts of
energy in the form of heat.
o The heat is carried out of the reactor by coolant,
which is most commonly just plain water.
o The coolant heats up and goes off to a turbine to
spin a generator or drive shaft.
o 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 4
• 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 5
• 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 6
• 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 7
• 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 8
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 9
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 10
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 11
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!
Nuclear Energy - Prof. Ghada Amer4/19/2018 12
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.
Nuclear Energy - Prof. Ghada Amer
• These use oxide fuel
pellets stacked in
zirconium tubes.
• They could possibly
burn thorium or
plutonium fuel as
well.
4/19/2018 13
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"
Nuclear Energy - Prof. Ghada Amer4/19/2018 14
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 15
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 16
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 17
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 18
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 19
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
Nuclear Energy - Prof. Ghada Amer4/19/2018 20
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 21
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
Nuclear Energy - Prof. Ghada Amer4/19/2018 22
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).
Nuclear Energy - Prof. Ghada Amer4/19/2018 23
Molten Salt Reactor
• 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.
Nuclear Energy - Prof. Ghada Amer
• 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.
4/19/2018 24
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 25
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.
• Very little operating experience, though a successful test reactor
was operated in the 1960s
Nuclear Energy - Prof. Ghada Amer4/19/2018 26
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
• Nuclear Reactor Safety
The Nuclear Fuel Cycle
Nuclear Energy - Prof. Ghada Amer4/19/2018 28
The Front End of the Cycle
For Light Water Reactor Fuel
Nuclear Energy - Prof. Ghada Amer4/19/2018 29
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 Amer4/19/2018 30
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 Amer4/19/2018 31
Uranium resources in Egypt
Nuclear Energy - Prof. Ghada Amer
1-‫أبو‬‫زنيمة‬‫احدى‬‫مدن‬‫جنوب‬‫سيناء‬
2-‫جبل‬‫قطار‬
3-‫المسيكات‬-‫العرضية‬-‫وتقع‬‫جنوب‬‫طريق‬‫ق‬‫نا‬-
‫سفاجا‬
4-‫جبل‬‫أم‬‫آر‬-‫تقع‬‫هذه‬‫المنطقة‬‫على‬‫بعد‬180‫كم‬
‫جنوب‬‫شرق‬‫أسوان‬
5-‫الصحراء‬‫الشرقية‬
6-‫الصحراء‬‫الغربية‬-‫اكتشفت‬‫في‬‫الواحات‬
‫البحرية‬‫بعض‬‫تمعدنات‬‫اليورانيوم‬‫في‬‫جب‬‫ل‬
‫الهفهوف‬
7-‫سيناء‬
4/19/2018 32
Processing: from ore to “yellow cake”
Nuclear Energy - Prof. Ghada Amer
• 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:
4/19/2018 33
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 34
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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 35
Nuclear Energy - Prof. Ghada Amer4/19/2018 36
• 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 37
Uranium Metallurgy
“Yellowcake” Nuclear Energy - Prof. Ghada Amer4/19/2018 38
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 UF6
• Enriched UF6 must be converted back to solid
uranium or uranium oxide
Nuclear Energy - Prof. Ghada Amer4/19/2018 39
Enrichment
The two method 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.
Nuclear Energy - Prof. Ghada Amer4/19/2018 40
F6
F6
Nuclear Energy - Prof. Ghada Amer4/19/2018 41
Loading uranium
hexafluoride containers
Gaseous diffusion plant
Paducah, Kentucky
Nuclear Energy - Prof. Ghada Amer4/19/2018 42
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
Nuclear Energy - Prof. Ghada Amer4/19/2018 43
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:
4/19/2018 44
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 Amer4/19/2018 45
UF6 Gas to UO2 Powder to Pellets
Nuclear Energy - Prof. Ghada Amer4/19/2018 46
Fuel Pellets
Nuclear Energy - Prof. Ghada Amer4/19/2018 47
Nuclear Fuel Assembly
Fuel
Pellet
Nuclear Energy - Prof. Ghada Amer4/19/2018 48
Fuel Assemblies are Inserted in Reactor Vessel
Nuclear Energy - Prof. Ghada Amer4/19/2018 49

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4 chapter 4 nuclear power station 4-2

  • 1. 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 • Nuclear Reactor Safety
  • 2. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 2
  • 3. 4/19/2018 Nuclear Energy - Prof. Ghada Amer 3 o The neutrons start a chain reaction where each atom that splits releases more neutrons that cause other atoms to split. o Each time an atom splits, it releases large amounts of energy in the form of heat. o The heat is carried out of the reactor by coolant, which is most commonly just plain water. o The coolant heats up and goes off to a turbine to spin a generator or drive shaft. o Nuclear reactors are just exotic heat sources.
  • 4. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 4
  • 5. • 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 5
  • 6. • 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 6
  • 7. • 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 7
  • 8. • 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 8
  • 9. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 9
  • 10. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 10
  • 11. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 11
  • 12. 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! Nuclear Energy - Prof. Ghada Amer4/19/2018 12
  • 13. 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. Nuclear Energy - Prof. Ghada Amer • These use oxide fuel pellets stacked in zirconium tubes. • They could possibly burn thorium or plutonium fuel as well. 4/19/2018 13
  • 14. 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" Nuclear Energy - Prof. Ghada Amer4/19/2018 14
  • 15. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 15
  • 16. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 16
  • 17. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 17
  • 18. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 18
  • 19. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 19
  • 20. 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 Nuclear Energy - Prof. Ghada Amer4/19/2018 20
  • 21. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 21
  • 22. 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 Nuclear Energy - Prof. Ghada Amer4/19/2018 22
  • 23. 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). Nuclear Energy - Prof. Ghada Amer4/19/2018 23
  • 24. Molten Salt Reactor • 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. Nuclear Energy - Prof. Ghada Amer • 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. 4/19/2018 24
  • 25. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 25
  • 26. 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. • Very little operating experience, though a successful test reactor was operated in the 1960s Nuclear Energy - Prof. Ghada Amer4/19/2018 26
  • 27. 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 • Nuclear Reactor Safety
  • 28. The Nuclear Fuel Cycle Nuclear Energy - Prof. Ghada Amer4/19/2018 28
  • 29. The Front End of the Cycle For Light Water Reactor Fuel Nuclear Energy - Prof. Ghada Amer4/19/2018 29
  • 30. 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 Amer4/19/2018 30
  • 31. 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 Amer4/19/2018 31
  • 32. Uranium resources in Egypt Nuclear Energy - Prof. Ghada Amer 1-‫أبو‬‫زنيمة‬‫احدى‬‫مدن‬‫جنوب‬‫سيناء‬ 2-‫جبل‬‫قطار‬ 3-‫المسيكات‬-‫العرضية‬-‫وتقع‬‫جنوب‬‫طريق‬‫ق‬‫نا‬- ‫سفاجا‬ 4-‫جبل‬‫أم‬‫آر‬-‫تقع‬‫هذه‬‫المنطقة‬‫على‬‫بعد‬180‫كم‬ ‫جنوب‬‫شرق‬‫أسوان‬ 5-‫الصحراء‬‫الشرقية‬ 6-‫الصحراء‬‫الغربية‬-‫اكتشفت‬‫في‬‫الواحات‬ ‫البحرية‬‫بعض‬‫تمعدنات‬‫اليورانيوم‬‫في‬‫جب‬‫ل‬ ‫الهفهوف‬ 7-‫سيناء‬ 4/19/2018 32
  • 33. Processing: from ore to “yellow cake” Nuclear Energy - Prof. Ghada Amer • 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: 4/19/2018 33
  • 34. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 34
  • 35. 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 35
  • 36. Nuclear Energy - Prof. Ghada Amer4/19/2018 36
  • 37. • 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 37
  • 38. Uranium Metallurgy “Yellowcake” Nuclear Energy - Prof. Ghada Amer4/19/2018 38
  • 39. 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 UF6 • Enriched UF6 must be converted back to solid uranium or uranium oxide Nuclear Energy - Prof. Ghada Amer4/19/2018 39
  • 40. Enrichment The two method 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. Nuclear Energy - Prof. Ghada Amer4/19/2018 40
  • 41. F6 F6 Nuclear Energy - Prof. Ghada Amer4/19/2018 41
  • 42. Loading uranium hexafluoride containers Gaseous diffusion plant Paducah, Kentucky Nuclear Energy - Prof. Ghada Amer4/19/2018 42
  • 43. 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 Nuclear Energy - Prof. Ghada Amer4/19/2018 43
  • 44. 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: 4/19/2018 44
  • 45. 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 Amer4/19/2018 45
  • 46. UF6 Gas to UO2 Powder to Pellets Nuclear Energy - Prof. Ghada Amer4/19/2018 46
  • 47. Fuel Pellets Nuclear Energy - Prof. Ghada Amer4/19/2018 47
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