Transcript of Nuclear Energy. A little review… Radioactive isotopes: Unstable isotopes that undergo radioactive...
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- Nuclear Energy
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- A little review Radioactive isotopes: Unstable isotopes that
undergo radioactive decay: Spontaneous release of material and
energy from nucleus. Original element (parent) changes to a new
element (daughter) or isotope Types of radiation = only dangerous
if emitted inside body bc cant penetrate skin = electrons that can
slightly penetrate skin (tritium) = most harmful Half life: Average
rate of radioactive decay ( amount of time it takes for of the
original parent to decay)
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- Calculating half life If 100.0 g of carbon-14 decays until only
25.0 g of carbon is left after 11, 460 y, what is the half- life of
carbon-14? Given: initial mass of sample = 100.0 g final mass of
sample = 25.0 g total time of decay = 11 460 y Unknown: number of
half-lives = ? half-lives half-life = ? y 11,460 years/ 2 = half
life of 5730 years
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- Thallium-208 has a half-life of 3.053 min. How long will it
take for 120.0 g to decay to 7.50 g? Given: half-life = 3.053 min
initial mass of sample = 120.0 g final mass of sample = 7.50 g
Unknown: number of half- lives = ? half lives total time of decay =
?
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- Fraction remaining 7.5 g / 120 g =.0625 or 1/16 SO HOW MANY
HALF LIVES WILL IT TAKE? 1/2 * 1/2 = 1/4 * 1/2 = 1/8 *1/2 = 1/16 so
that was 4 half lives Time of decay = 4 x 3.053min = 12.21
minutes
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- Gold-198 has a half-life of 2.7 days. How much of a 96 g sample
of gold-198 will be left after 8.1 days? Given: half-life = 2.7
days total time of decay = 8.1 days initial mass of sample = 96 g
Unknown: number of half- lives = ? half-lives final mass of sample
= ? g 8.1 days / 2.7 days = 3 half lives 96/2 = 48 / 2 = 24 / 2 =
12 g
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- Nuclear Fission Fission: nuclear reaction that uses neutrons,
which are shot at an atomic nucleus leading to the break down and
subsequent energy release. Utilizes energy from radioactive
isotopes. Uranium 235 Chain reaction that can continuously create
heat, which can boil water to create heat, which can boil water to
create steam create steam
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- The typical Nuclear Fission Reaction
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- 1 Neutron + 235 U 236 U 141 Ba + 92 Kr + 3 Neutrons
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- The 3 neutrons keep the energy going
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- Nuclear reactor Fuel rods are pellets of uranium in the core
Which heats water during reaction Control rods are there to absorb
excess neutrons slowing reaction preventing overheating and
meltdown.
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- Fig. 16-16, p. 372 Small amounts of radioactive gases Uranium
fuel input (reactor core) Control rods Containment shell Heat
exchanger Steam Turbine Generator Waste heat Electric power Hot
coolant Useful energy 25%30% Hot water output Pump Coolant Pump
Moderator Cool water input Waste heat Shielding Pressure vessel
Coolant passage Water Condenser Periodic removal and storage of
radioactive wastes and spent fuel assemblies Periodic removal and
storage of radioactive liquid wastes Water source (river, lake,
ocean)
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- Nuclear power in the US Nuclear power in the US RED = nuclear
sites Black = recorded earthquakes in US
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- Nuclear Waste After three or four years in a reactor, spent
fuel rods are removed and stored in a deep pool of water contained
in a steel-lined concrete container.
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- After spent fuel rods are cooled considerably, they are
sometimes moved to dry-storage containers made of steel or
concrete
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- Fig. 16-18, p. 373 Decommissioning of reactor Fuel assemblies
Reactor Enrichment of UF 6 Fuel fabrication (conversion of enriched
UF 6 to UO 2 and fabrication of fuel assemblies) Temporary storage
of spent fuel assemblies underwater or in dry casks Conversion of U
3 O 8 to UF 6 Uranium-235 as UF 6 Plutonium-239 as PuO 2 Spent fuel
reprocessing Low-level radiation with long half-life Geologic
disposal of moderate & high-level radioactive wastes Open fuel
cycle today Closed end fuel cycle Triuranium octoxide Uranium
hexafloride
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- Why not more nuclear energy? After more than 50 years of
development and enormous government subsidies, nuclear power has
not lived up to its promise because: Multi billion-dollar
construction costs. Higher operation costs and more malfunctions
than expected. Poor management. Public concerns about safety and
stricter government safety regulations. Oyster Creek Example Oyster
Creek Example Oyster Creek Example
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- Nuclear Energy When a nuclear reactor reaches the end of its
useful life, its highly radioactive materials must be kept from
reaching the environment for thousands of years. Plutonium,
uranium, cesium, tritium Several reactors in the United States are
closing down early
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- Nuclear Waste Scientists disagree about the best methods for
long-term storage of high-level radioactive waste (uranium and
plutonium) 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
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- Chernobyl Nuclear Disaster The worlds worst nuclear power plant
accident occurred in 1986 in Ukraine. The worlds worst nuclear
power plant accident occurred in 1986 in Ukraine. The disaster was
caused by poor reactor design and human error (disconnected control
rods and cooling water). The disaster was caused by poor reactor
design and human error (disconnected control rods and cooling
water). By 2005, 56 people had died from radiation released. By
2005, 56 people had died from radiation released. 4,000 more are
expected from thyroid cancer and leukemia.
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- 3 Mile Island Disaster March 28, 1979 at 3 mile island nuclear
plant in PA a closed cooling water valve led to the overheating of
the reactor core and led to partial meltdown. Structure became
highly radioactive and unknown amount entered nearby environment No
documented evidence of adverse health effects but claims of
increased infant mortality and cancers.
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- Fukushima Nuclear Disaster March 11, 2011 the Great East Japan
Earthquake, measuring a 9.0 on the Richter Scale Led to coastline
movement of a few meters and a half meter of subsidence. Secondary
impact was a giant 15 foot tsunami Led to the malfunction of the
nuclear reactor power supply and the cooling station. Largest
discharge of nuclear waste into ocean (cesium) Cesium contamination
covering 4500 miles 2 and 250 miles around site considered too
radioactive for humans and evacuated Increased exposure limits from
1 mSv to 20 mSv to downgrade impact
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- Future of 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. o
May increase risk of cancer, but tritium is one of the least
dangerous radio nuclides
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- Fig. 16-19, p. 376 Trade-Offs Conventional Nuclear Fuel Cycle
AdvantagesDisadvantages Large fuel supply Cannot compete
economically without huge government subsidies Low environmental
impact (without accidents) Low net energy yield High environmental
impact (with major accidents) Emits 1/6 as much CO 2 as coal
Catastrophic accidents can happen (Chernobyl) Moderate land
disruption and water pollution (without accidents) No widely
acceptable solution for long-term storage of radioactive wastes and
decommissioning worn-out plants Moderate land use Low risk of
accidents because of multiple safety systems (except for 15
Chernobyl-type reactors) Subject to terrorist attacks Spreads
knowledge and technology for building nuclear weapons
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- A 1,000 megawatt nuclear plant is refueled once a year, whereas
a coal plant requires 80 rail cars a day.