Unit 6: Nuclear Energy

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PHY 305
 Lecture 14

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 I. Introduction to Nuclear Energy

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❑ Nuclear energy is the energy in the nucleus, or core, of an atom. Nuclear energy can be used to
create electricity, but it must first be released from the atom.

❑ The nucleus contains protons and neutrons, held together by the strong force (the strong force
becomes ineffective at distances greater than 10-15 m).

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❑ Nuclear energy can be produced in two ways: fission – when nuclei of atoms split into several
parts – or fusion – when nuclei fuse together.

❑ The nuclear energy harnessed around the world today to produce electricity is through nuclear
fission, while technology to generate electricity from fusion is at the R&D phase.

❑ Fission, a nucleus much heavier than iron splits into two lighter ones. The binding energy
per nucleon of the fragments is greater than that of the original nucleus, so energy is
released.

❑ Fusion occurs when nuclei much lighter than iron join to form a heavier one. Once again the
increased binding energy per nucleon results in energy release.

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Nuclear fission: is a reaction where the nucleus of
an atom splits into two or more smaller nuclei, while
releasing energy.

For instance, when hit by a neutron, the nucleus of

an atom of uranium-235 splits into a barium nucleus
and a krypton nucleus and two or three neutrons.

These extra neutrons will hit other surrounding

uranium-235 atoms, which will also split and
generate additional neutrons in a multiplying effect,
thus generating a chain reaction in a fraction of a
second.

❑ Each time the reaction occurs, there is a release

of energy in the form of heat and radiation.

❑ The heat can be converted into electricity in a Ensure Access to Affordable, Reliable,
nuclear power plant, similarly to how heat from Ensure Access
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fossil fuels such as coal, gas and oil is used to Sustainable, and Clean Energy for All
generate electricity.
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Nuclear fusion is the process by which two light atomic nuclei combine to form a single heavier one while
releasing massive amounts of energy. Fusion reactions take place in a state of matter called plasma — a
hot, charged gas made of positive ions and free-moving electrons that has unique properties distinct from
solids, liquids and gases.

Nuclear fusion and plasma physics research are carried out in

The sun, along with all other stars, is powered by more than 50 countries, and fusion reactions have been
a reaction called nuclear fusion. If this can be successfully achieved in many experiments, albeit without
replicated on earth, it could provide virtually demonstrating a net fusion power gain. How long it will take
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limitless clean, safe and affordable energy to to recreate Ensure
the process
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Inside nuclear power plants, nuclear
reactors and their equipment contain
and control the chain reactions, most
commonly fuelled by uranium-235, to
produce heat through fission. The
heat warms the reactor’s cooling
agent, typically water, to produce
steam. The steam is then channeled to
spin turbines, activating an electric
generator to create low-carbon
electricity.

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Pressurized water reactors are the most used in
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world.

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 Mining, enrichment and disposal of uranium
❑ Because nuclear fuel can be used to create nuclear weapons as well as nuclear
reactors, only nations that are part of the Nuclear Non-Proliferation Treaty (NPT) are
allowed to import uranium or plutonium, another nuclear fuel. The treaty promotes the
peaceful use of nuclear fuel, as well as limiting the spread of nuclear weapons.

❑ A typical nuclear reactor uses about 200 tons of uranium every year. Complex
processes allow some uranium and plutonium to be re-enriched or recycled. This
reduces the amount of mining, extracting, and processing that needs to be done.

Isotopes have different numbers of neutrons in the nucleus

❑ Uranium is a metal that can be found in rocks all over the world. Uranium has several naturally occurring isotopes, which
are forms of an element differing in mass and physical properties but with the same chemical properties. Uranium has
initially two isotopes: uranium-238 and uranium-235. Uranium-238 makes up the majority of the uranium in the world but
cannot produce a fission chain reaction, while uranium-235 can be used to produce energy by fission but constitutes less
than 1 per cent of the world’s uranium.

❑ To make natural uranium more likely to undergo fission, it is necessary to increase the amount of uranium-235 in a given
sample through a process called uranium enrichment. Once the uranium is enriched, it can be used effectively as nuclear
fuel in power plants for three to five years, after which it is still radioactive and has to be disposed of following stringent
guidelines to protect people and the environment. Ensure Access to Affordable, Reliable,
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❑ Used fuel, also referred to as spent fuel, can also be recycled into other types of fuel for use as new fuel in special nuclear
power plants.
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Nuclear fuel is extremely dense.

It’s about 1 million times greater than

that of other traditional energy sources
and because of this, the amount of used
nuclear fuel is not as big as you might
think.

All of the used nuclear fuel produced by

the U.S. nuclear energy industry over the
last 60 years could fit on a football field
at a depth of less than 10 yards!

That waste can also be reprocessed and

recycled, although the United States
does not currently do this. However,
some advanced reactors designs being
developed could operate on used fuel. Ensure Access to Affordable, Reliable,
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When the fuel is removed from the reactor
it is still radioactive. Spent fuel is stored at
power plants under water in spent fuel
pools or in dry casks.

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 Radioactive material and waste

❑ However, the byproduct of nuclear energy is radioactive material. Radioactive material is a collection of unstable atomic
nuclei. These nuclei lose their energy and can affect many materials around them, including organisms and the
environment. Radioactive material can be extremely toxic, causing burns and increasing the risk for cancers, blood
diseases, and bone decay.

❑ Used fuel and rods of nuclear poison are extremely radioactive. The used uranium pellets must be stored in special
containers that look like large swimming pools. Water cools the fuel and insulates the outside from contact with the
radioactivity. Some nuclear plants store their used fuel in dry storage tanks above ground.

❑ Radioactive waste is what is left over from the operation of a nuclear reactor. Radioactive waste is mostly protective
clothing worn by workers, tools, and any other material that have been in contact with radioactive dust. Radioactive
waste is long-lasting. Materials like clothes and tools can stay radioactive for thousands of years. The government
regulates how these materials are disposed off, so they don't contaminate anything else.

❑ The storage sites for radioactive waste have become very controversial in the United States. For years, the government
planned to construct an enormous nuclear waste facility near Yucca Mountain, Nevada, for instance. Environmental
groups and local citizens protested the plan. They worried about radioactive waste leaking into the water supply and
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the Yucca Mountain environment, about 130 kilometers (80 miles) from the large
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Although the government began investigating the site in 1978, it stopped planningand
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Mountain in 2009.
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LOW LEVEL WASTE: HIGH LEVEL WASTE:

❑Includes items that have become contaminated ❑Spent (used) reactor fuel that can no longer
with radioactive material. This is typically create electricity because fission has
contaminated protective clothing and shoe covers, slowed but is still thermally hot and highly
wiping rags, mops, filters, reactor water treatment radioactive, emitting beta and gamma
residues radiation. Waste materials remaining after
spent fuel is reprocessed
❑Also includes medical tubes, injection needles, lab
animal carcasses and tissues ❑MUST BE STORED ON-SITE in specially
designed pools made of reinforced
concrete with 40 feet of water or in dry
❑Can be stored on site until quantities are sufficient
casks
to send to a low-level waste disposal site in
appropriate containers where it is buried.

❑Burial sites must be far from ground or surface

water (or lined with an impermeable layer to
prevent contamination via leaks) and in seismically
stable areas

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Nuclear waste

The operation of nuclear

power plants produces waste
with varying levels of
radioactivity. These are
managed differently
depending on their level of
radioactivity and purpose.

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 II. Nuclear Energy Trends

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As the world attempts to transition its energy systems away from
fossil fuels towards low-carbon sources of energy, we have a
range of energy options: renewable energy technologies such as
hydropower, wind and solar, but also nuclear power.

Nuclear energy and renewable technologies typically emit very

little CO2 per unit of energy production thus limiting the levels of
local air pollution, in comparison to fossil fuels.

But whilst some countries are investing heavily in increasing their

nuclear energy supply, others are taking their plants offline. The
role that nuclear energy plays in the energy system is therefore
very specific to the given country.

How much of our energy comes from nuclear power? How is its
role changing over time?

In this unit, we look at levels and changes in nuclear energy Ensure Access to Affordable, Reliable,
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to other sources of energy.

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Nuclear energy – alongside hydropower – is one
of our oldest low-carbon energy technologies.

Nuclear power generation has been around since

the 1960s, but saw massive growth globally in
the 1970s, 80s and 90s. In the interactive chart
shown we see how global nuclear generation has
changed over the past half-century.

Following fast growth during the 1970s to 1990s,

global generation has slowed significantly. In
fact, we see a sharp dip in nuclear output
following the Fukushima tsunami in Japan in
2011, as countries took plants offline due to
safety concerns.

But we also see that in recent years, production Ensure Access to Affordable, Reliable,
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Why did the nuclear power
generation drop in Japan?

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The global trend in nuclear energy generation
masks the large differences in what role it plays at
the country level.

Some countries get no energy at all from nuclear –

or are aiming to eliminate it completely – whilst
others get much of their power from it.

This map shows the amount of nuclear energy

generated by country. We see that France, the USA,
China, Russia and Canada all produce relatively
large amounts of nuclear power.

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This map shows the share of primary energy
that comes from nuclear sources.

In 2023, just over 9.11% of global primary

energy came from nuclear power.

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In the previous slides, we looked at the role of nuclear
in the total energy mix. This includes not only
electricity, but also transport and heating. Electricity
forms only one component of energy consumption.

Since transport and heating tend to be harder to

decarbonize – they are more reliant on oil and gas –
nuclear and renewables tend to have a higher share in
the electricity mix versus the total energy mix.

This interactive chart shows the share of electricity

that comes from nuclear sources.

Globally, around 10% of our electricity comes from

nuclear. But some countries rely on it heavily: it
provides more than 70% of electricity in France, and
more than 40% in Sweden.

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 III. Safety

Two centuries ago, we discovered how to use the energy from fossil fuels to make our work
more productive. It was the innovation that started the Industrial Revolution. Since then, the
increasing availability of cheap energy has been integral to the progress we’ve seen over the
past few centuries. It has allowed work to become more productive, and people in
industrialized countries are much richer than their ancestors, work much less, and enjoy
much better living conditions than ever before.

Energy access is therefore one of the fundamental driving forces of development. The
United Nations rightly says that “energy is central to nearly every major challenge and
opportunity the world faces today.”
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PHY 305
But while energy from fossil fuels brought many benefits it unfortunately also has major negative consequences.
There are three main categories of negative consequences.

1. The first is air pollution: at least five million people die prematurely every year as a result of air pollution. Fossil fuels
and the burning of biomass – wood, dung, and charcoal – are responsible for most of those deaths. Eliminating fossil
fuels could cut premature deaths from air pollution by around two-thirds. That’s three to four million deaths per year.

2. The second is accidents. This includes accidents that happen in the mining and extraction of the fuels (coal, uranium,
rare metals, oil and gas) and it includes accidents that occur in the transport of raw materials and infrastructure, the
construction of the power plant, or their deployment.

3. The third is greenhouse gas emissions: fossil fuels are the main source of greenhouse gases, the primary driver of
climate change. In 2018, 87% of global CO2 emissions came from fossil fuels and industry.

All energy sources have negative effects. But they differ enormously in size: as we will see, in all three aspects, fossil fuels are
the dirtiest and most dangerous, while nuclear and modern renewable energy sources are vastly safer and cleaner.

From the perspective of both human health and climate change, it matters less whether we transition to nuclear power or
renewable energy, and more that we stop relying on fossil fuels. Ensure Access to Affordable, Reliable,
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 How do fossil fuels, nuclear energy and renewables stack up in terms of safety?

Death rate for nuclear includes an estimated

4000 deaths from the 1986 Chernobyl disaster in
Ukraine (based on estimates from the WHO);
574 deaths from Fukushima (one worker death,
and 573 indirect deaths from the stress of
evacuation); and estimated occupational deaths
(largely from mining and milling)

We see massive differences in the death rates of

nuclear and modern renewables compared to
fossil fuels.

Nuclear energy, for example, results in 99.8%

fewer deaths than brown coal; 99.7% fewer than
coal; 99.6% fewer than oil; and 97.5% fewer than
gas. Wind, solar and hydropower are yet the Ensure Access to Affordable, Reliable,
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Nuclear energy and renewables are far, far safer than fossil fuels
Looking at deaths per terawatt-hour:

Energy Resource Deaths/year

Coal 25 people would die prematurely every year;

Oil 18 people would die prematurely every year

Gas 3 people would die prematurely every year
Nuclear In an average year nobody would die. A death rate of 0.07 deaths per terawatt-hour means it
would take 14 years before a single person would die. As we will explore later, this might even
be an overestimate.

Wind In an average year nobody would die – it will take 29 years before someone died
Hydropower In an average year nobody would die – it will take 42 years before someone died
Solar In an average year nobody would die – only every 53 years would someone die.
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It’s reported that in the days which
followed the Chernobyl disasters,
residents in surrounding areas were
uninformed of the radioactive material in
the air around them.

In fact, it took at least three days for the

Soviet Union to admit an accident had
taken place and did so after radioactive
sensors at a Swedish plant were triggered
from dispersing radionuclides.

It’s estimated that the delayed reaction

from the Soviet government and poor
precautionary steps taken (people
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In the case of Fukushima year 2011, the
Japanese government responded quickly to
the crisis with evacuation efforts extending
rapidly from a three kilometre (km), to 10km,
to 20km radius whilst the incident at the site
continued to unfold. In comparison, the
response in the former Soviet Union was one
of denial and secrecy.
A massive earthquake off the coast of Japan caused a
tidal wave that broke down the seawall surrounding
the power plant. The earthquake and tsunami cut off
supply of electricity to the plants cooling systems. The
fuel overheated and caused explosions. There were
releases of radiation into the environment. People
were evacuated and many were exposed to radiation

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Three Mile Island

The worst nuclear accident in the United

States. No deaths or injuries were directly
linked to the accident.

The Three Mile Island nuclear power

plant, near Harrisburg, Pennsylvania, is
capable of generating 892 net
megawatts of electricity. That is enough
to power more than 800,000 homes and
businesses. In 1979, part of the Three
Mile Island facility suffered a meltdown
and was never reopened.

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What is nuclear radiation?

• Radiation is energy moving through space in the

form of waves and particles. It is emitted by
unstable isotopes

• It can be ionizing or non-ionizing

• Ionizing radiation can knock electrons from an

atom, creating ions.

→ Alpha and beta particles /ions + gamma rays

are emitted from ionizing radioactive materials

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Types of ionizing radiation

1- Beta particles (electrons/positrons) are 3- Gamma rays are waves of energy without
small but can be stopped by aluminum mass or charge. They travel the farthest but
metal. They can travel several meters but can be stopped by lead, water or concrete
deposit less energy than alpha particles

2- Alpha particles are not very

penetrating but can damage very delicate ** A positron is a particle of matter with the same mass as an
tissue. They deposit the most energy. electron but an opposite charge.
However, A piece of paper or your skin
can stop them.

Because these radiations create ions, ionizing radiation can cause

chemical changes in living cells, possibly leading to cancer

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Exposure to radiation
• The unit used to measure ionizing radiation in the US is the millirem (mrem). The
international unit is the millisievert (mSv). Both measure the risk that the radiation will cause
damage to a person

• We use the curie (Ci) or becquerel (Bq) to measure the amount of radioactivity in a substance.
• We use the rad or gray (Gy) to talk about the energy in radiation absorbed by a person

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 IV. Public Opinion

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PHY 305
Public opinion on nuclear energy
tends to be very negative.

Many people still remember the

two major nuclear disasters in
history: Chernobyl and Fukushima.

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Even though nuclear energy is safer, cleaner, and more efficient than coal, oil, and natural gas, it continues to be
abandoned in the United States. Popular culture has played a large role in the way nuclear energy and weapons
are perceived to the general public.

One of the most recognizable instances of nuclear is in television on The Simpsons. The two-unit nuclear reactor
is notorious for being badly run. It is famous for its safety violations, spillage of radioactive waste, constant
flashing lights, and creation of mutants.

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This characterization of nuclear energy is
important because it shows how negatively
it is perceived by people. Comedians are
allowed to show power plants like this
because that is how people think they are
run.

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