Chapter 7: The Fires of Nuclear Fission
What is nuclear fission?
Is using nuclear energy
safe for humans and the
environment?
Is nuclear energy better
to use than electric
generated energy?
What happens to the
waste of nuclear fission?
What do you think of when you hear “nuclear energy”?
What is Fission and How Does it Produce Energy?
Nuclear fission is the splitting of a
large nucleus into smaller ones with
the release of energy.
Energy is released because the sum
of the masses of these fragments
is less than the original mass.
This 'missing' mass (about 0.1
percent of the original mass) has
been converted into energy
according to Einstein's E=mc2
equation.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
This equation dates from the early years of the 20th century and is
one of the many contributions of Albert Einstein (1879–1955).
It summarizes the equivalence of energy, E, and mass, m.
The symbol c represents the speed of light, 3.0 ×108 m/s.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
Consider this: c2 is equal to 9.0 × 1016 m2/ s2
When mass is in kg, the energy units are kg∙ m2/s2,
which is equivalent to 1 Joule.
The large value of c2 means that it should be possible to
obtain a tremendous amount of energy from a small
amount of matter - whether in a power plant or in a
weapon.
7.2
What is Fission and How Does it Produce Energy?
E = mc2
For 1.0 kg of U-235:
E = (1.0 x 10-3 kg)(3 x 108 m/s)2
E = (1.0 x 10-3 kg)(9.0 x 1016 m2/s2)
E = 9.0 x 1013 kg m2/s2 = 9.0 x 1013 J
Don’t
forget to
cube or
square
where
needed
This is equivalent to
33,000 tons of TNT
7.2
TNT, or trinitrotoluene (discovered in 1863 by Alfred Nobel)
became the standard of explosive power as a result of the birth of
nuclear weapons-they needed to be compared to some substance of
known explosiveness.
CH3
O2N
NO2
TNT
NO2
The TNT molecule is
very unstable and when
explodes, 2 moles of TNT
rearrange to form 15 moles of
hot gas (3 mol N2, 7 mol CO, 5
mol H2O) plus some carbon.
About 1 g of TNT will
produce about L of hot gas –
a 1000 times increase in
volume.
1 kg of U-235, where only about 0.1% mass is converted
to energy is equivalent to 33,000 tons of TNT
7.2
What is special about the mass number of U-235?
When a massive nucleus like U-235 undergoes fission, the
net yield of energy is a result of the sum of the fragments
being slightly less than the mass of the uranium nucleus.
If the mass of the fragments is equal to or greater than that
of iron at the peak of its binding energy curve, the nuclear
particles (daughters) will be more tightly bound than the
uranium nucleus was, and that mass decrease is converted
to energy according to E = mc2.
For elements with lower mass numbers than iron,
fusion may lead to energy release
7.5
Still, the only person to
win two unshared
Nobel Prizes was
Linus Pauling, the
American chemist who
won for his chemistry
work and also a Nobel
Peace Prize for his
objection to nuclear
testing.
Marie Sklodowska Curie won two Nobel Prizes—one
in chemistry, the other in physics—for her research on
radioactive elements.
7.5
Radioactivity
Include alpha, beta, and gamma rays.
7.5
U-238 Radioactive Decay Series
Radioactive isotopes
undergo decay until
they reach a stable
species.
All isotopes of all
elements with atomic
number 84 (Po) and
higher are radioactive.
7.5
A Chain Reaction with U-235
Visit Figures Alive! For more information on
nuclear fission and chain reactions!
7.5
Schematic of a
Nuclear Reactor
A nuclear
reactor is a
device in which
nuclear chain
reactions are
initiated,
controlled, and
sustained at a
steady rate (as
opposed to a
nuclear explosion,
where the chain
reaction occurs in
a split second).
7.3
Basics of a Nuclear Reactor
Actual size of
fuel pellet
An awesome
source of
electrical
energy— but
what to do with
the spent nuclear
fuel?
Reactor core
Cooling tower
7.3
Storage of nuclear waste
Thousands of canisters of spent
nuclear fuel rods submerged in water
Encapsulating reprocessed
HLW in glass canisters
(vitrification).
Two cooling towers at the Byron
nuclear plant in Illinois
This image shows a fuel
assembly submerged in
an active reactor core
7.6
On 26 April 1986, reactor # 4 at the
Chernobyl Nuclear Power Station, 100
km north from Kiev, blew up during a
routine daily operation. Nearly nine tons
of radioactive material - 100 times as
much as the Hiroshima bomb - were
hurled into the sky. Winds over the
following days, mostly blowing north and
west, carried, fallout into Belarus, as well
as Russia, Poland and the Baltic region.
Control rods were made of graphite
(unlike those used in the U.S.)
which caught on fire.
7.6
Chernobyl-What Happened: April 26, 1986
While performing a safety test on Reactor 4, technicians allowed a power
surge that reached 120 times the rated capacity of the reactor.
The surge, or "slow nuclear explosion", ripped open the core, including
cooling water pipes, and caused a huge steam explosion.
The 4,000 ton concrete covering over the reactor was blown away.
Fires broke out in many places all over the site.
Fifty different radioactive isotopes were released, with half-lives spanning
from two hours to 24,000 years.
These isotopes were shot 1.5 miles into the sky.
7.6
Chernobyl: Social and Environmental Consequences
Over 1,000 injuries and thirty-one deaths of firefighters and others who
reported to scene of accident.
150,000 people evacuated from their Ukraine homes.
Radioactive cloud released over a large part of Europe. Health threatening
levels of radioactive materials were found in at least twenty nations, and as
far away as 2,000 km from Chernobyl. Estimated 250 million people were
exposed to unhealthy amounts of radiation.
Estimates of future cancers from the accident range anywhere from 7,500 to
1 million.
Radioactive particles in the environment and in the food chain.
Large amount of uncertainty and fear in the population.
7.6
Chernobyl: Political Consequences
Distrust of government.
Soviet Union cover up: Sweden and Poland were the first
nations to bring attention to the accident.
Other nations attempted to downplay the health effects of the
accident in their own nations.
Public opposition to building
additional nuclear power plants
increased significantly worldwide.
7.6
rad = “radiation absorbed dose” – absorption of 0.01 J of
radiant energy/kg tissue
rem = “roentgen equivalent man” = Q x (number of rads)
where Q is a relative biological effectiveness factor
1 Sv = 100 rem
7.7
Half-life: the time required for the level of radioactivity to fall to
one-half of its value.
7.8
Half-life: the time required for the level of radioactivity to fall to
one-half of its value.
7.8
7.9
Proposed High Level Nuclear
Waste Storage in Yucca
Mountain, Nevada
7.9
A worker in one of the Yucca mountain tunnels
7.9
Nuclear Weapons
The isotopes U-235 and
U-238 behave essentially
the same in all chemical
reactions, so the separation
of these two isotopes is
extremely difficult and relies
on advanced technology that
is not readily available.
Building and deploying a nuclear weapon is a very
difficult operation to carry out.
7.10
Risks and Benefits of Nuclear Power
Break into groups to discuss, then debate.
How would you compare its safety with
coal power generation?
7.11