Nuclear energy
Review: Elements and Isotopes

Elements are defined by the number of
protons in the nuclei of their atoms
– Eg all carbon atoms have 6 protons
Remember, isotopes are variations of atoms
of an element
 They vary in number of neutrons

– Eg Carbon-12 has 6 protons and 6 neutrons,
while Carbon-14 has 6 protons and 8 neutrons
– Many elements have isotopes some are stable
(never change), some are radioactive (unstable,
change over time)
Radioisotopes
Radioactive isotopes experience
radioactive decay (the loss of alpha or
beta particles over time)
 As a result of radioactive decay, atoms of
one element physically change into
another element.

– Eg Carbon-14 decays to Nitrogen-14 by loss of
negative beta particles

Radioactive half life= the amount of time
it takes for 50% of the radioactive isotope
in a substance to decay.
Practice:
Plutonium-239 has a half-life of 24,000
years. How much of a 4 gram sample will
remain after 96,000 years?
a. 1g
b. 0.5g
c.
0.25g
d. 0.125g
e. 0.625g
Geological dating with radioactive isotopes


Carbon-14 can be used to
estimate the age of plant and
animal remains
All living things utilize C-14 and
incorporate it into their tissues
– After death, C-14 changes into N14
– Geologists can determine the age
of a set of remains by comparing
the ratio of C-14 to N-14
– Carbon dating is useful for remains
between 1,000 and 50,000 years
old
Geological dating with Uranium



Uranium-238 is a very
common radioisotope
that decays to a stable
isotope of lead
It has a half life of 4.5
billion years
This is very useful for
dating rock formations
that are billions of years
old
– Eg if there are equal
parts lead and
uranium in a rock, it
is 4.5 billion years
old
The discovery of radioactive atoms





1896 a French physicist
discovered that uranium
containing minerals
spontaneously & continuously
gave off energy (radiation)
1898 a British physicist showed
radiation to consist of high
energy particles
In 1919 same British guy
bombarded N nuclei with alpha
particles and turned it into O
In 1938 German scientists hit
uranium with neutrons, splitting
U into barium and krypton, and
lots of energy…FISSION!
This led to a realization of the
potential power of fission and a
subsequent race for a bomb and
energy development (Einstein
came to US during WWII to warn
of impending German innovation)
Nuclear energy
Nuclear reactions differ from combustion
reactions
 Combustion (fossil fuels):

– atoms do not change, they are rearranged.
– The mass of the reactants is equal to the mass
of the products.
– Energy is given off as heat when chemical
bonds are broken.

Nuclear reaction:
– Changes occur within the nuclei of atoms.
– Atoms actually transform into atoms of
another element.
– Small amounts of matter are transformed into
large amounts of energy.
Types of nuclear reactions




Fission: larger atoms are split
into 2 smaller atoms of different
elements (this is the type of
reaction used to create
commercial energy and atomic
bombs)
Fusion: 2 smaller atoms combine
to make one larger atom of a
different element (this is what
powers the sun and stars)
In both reactions the end product
mass is less than the mass of the
starting material. The remainder
is converted to energy.
Fission produces 2-3 million
times more energy than
combustion of fossil fuels.
NUCLEAR ENERGY
 Nuclear
power plants use U-235, a
radioactive isotope of uranium.
– Mined uranium oxide consists of about
99.3% non-fissionable uranium-238 and
0.7% fissionable uranium-235.
– The concentration of uranium-235 is
increased through an enrichment
process (removing some of the U-238)
to result in 97% U-238 oxide and 3% U235 oxide fuel.
– Enrichment is very energy intensive, but
the energy payoff is even greater
Electricity


After enrichment, U235 is transformed into
uranium dioxide to
form small fuel pellets
These pellets are
placed into fuel rods,
which in turn are
grouped into fuel
assemblies (~100
rods), of which there
may be 1000s per
reactor core
Nuclear power plant
NUCLEAR WASTE
NUCLEAR WASTE
Math Practice
1.
After 100 million years, only 1/32 of the original amount
of a particular radioactive waste will remain. The half-life
of this radioactive waste is how many million years?
a. 10
b. 20
c. 30
d. 40
e. 50
2.
You have 180g of a radioactive substance. It has a halflife of 265 yrs. After 1,325 yrs, what mass remains?
Nuclear waste

Low level
– Radioactive solids, liquids, or gases that give
off small amounts of ionizing radiation
– Sources include power plants, hospitals,
research labs, and industries
– Low Level Radioactive Waste Policy Act 1980 &
1985
 All
states must be responsible for disposal of nondefense related waste produced w/in their borders.

High level
– Radioactive solids, liquids, or gases that
initially give off large amounts of ionizing
radiation
– Sources include anything that was inside the
reactor core (metals, water, gases, spent fuel)
Nuclear Waste Policy Act 1982

Stated that there must be a permanent site for
storing high level waste by 1998
– That was not met; postponed to 2010 at earliest

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

1987 Congress identified Yucca Mountain in
Nevada as the best potential site
Feasibility studies were carried out for over a
decade
In 2002 it was officially approved by Congress
Rescinded by Obama in 2009
NUCLEAR ENERGY
 Scientists
disagree about the best
methods for long-term storage of highlevel radioactive waste:
– Bury it deep underground.
– Shoot it into space.
– Bury it in the Antarctic ice sheet.
– Bury it in the deep-ocean floor that is
geologically stable.
– Change it into harmless or less harmful
isotopes.
The risks of nuclear energy



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Meltdown: this is when the actual metal around
the reactor core melts from the heat of fission;
radiation is emitted into the atmosphere in one
large dose
Acute radiation syndrome= too many body cells
are killed by the radiation dose to be repaired.
Daily radiation for workers (carcinogenic over
time)
Radiation into groundwater from stored waste
Small scale persistent radiation to nearby
communities
Radiation and health

We are exposed to natural (background
radiation) and artificial radiation every day
– 300 millirems per year from space/the
atmosphere, the soil (radon), foods we eat
(radioactive potassium)
– 60 millirems from manmade radiation
(radiowaves, hospitals, industries, housing
materials, microwaves, cell phones, tobacco,
television, smoke detectors, etc.)
Radiation is often ionizing, which is very
disruptive to living cells
 Chronic exposure to radiation can lead to
cancer and thyroid problems

NUCLEAR
ENERGY

A 1,000
megawatt nuclear
plant is refueled
once a year,
whereas a coal
plant requires 80
rail cars a day.
Figure 16-20
NUCLEAR ENERGY
 Building
more nuclear power plants
will not lessen dependence on
imported oil and will not reduce CO2
emissions as much as other
alternatives.
– The nuclear fuel cycle contributes to CO2
emissions.
– Wind turbines, solar cells, geothermal
energy, and hydrogen contributes much
less to CO2 emissions.
NUCLEAR
ENERGY
In 1995, the World
Bank said nuclear
power is too costly
and risky.
 In 2006, it was
found that several
U.S. reactors were
leaking radioactive
tritium into
groundwater.

Figure 16-19