Transcript Chapter 16 – Nuclear Energy

Chapter 16 – Nuclear Energy
Pages 250 – 263
Mrs. Paul
Environmental Science
Parts of an Atom
• 3 parts:
– 1. Protons: positively charged particles in nucleus.
– 2. Neutrons: particles in nucleus with no charge.
– 3. Electrons: negatively charged particles that
orbit the nucleus.
• Nucleus: cluster of protons and neutrons in
the center of the atom.
• Atoms usually have the same number of
electrons and protons = no charge.
Atoms and Isotopes
• Properties of atom determined by number of
protons.
• Atomic number: number of protons.
– Ex: oxygen = 8; uranium = 92
• Atomic mass: protons + neutrons
– Ex: oxygen = 16 (8 protons; 8 neutrons)
• Isotopes: atoms of the same element that
have different atomic masses (due to different
numbers of protons).
Radioactivity
• Some isotopes are unstable.
• Unstable atoms may change number of
protons or neutrons in nucleus to become
stable.
• Radioactive atoms: Atoms that decay and emit
particles and energy from their nuclei.
• Radiation: alpha particles, beta particles and
gamma rays given off in the decaying of
unstable nuclei.
• Radioactive particles:
– 1. alpha particles: large particles made of 2 protons
and 2 neutrons.
– 2. beta particles: high speed electrons
• Losing alpha particles changes an atoms atomic
mass, causing it to become a different element
(radioactive decay).
• Half-life: amount of time in which half the atoms
in a sample of a radioactive element decay.
Fission: Splitting Atoms
• Only about 17 % of the world’s electricity
comes from nuclear power.
• Nuclear power plants are powered by nuclear
energy: energy inside the nucleus of an atom.
An Atom!!
• Forces holding the nucleus together are
STRONG!
• Atoms of uranium (an element) are used as
fuel in nuclear power plants.
• Nuclear Fission: splitting of an atom’s nucleus.
– Nucleus is hit with neutrons (neutral atomic
particles).
– This causes neutrons and energy to be released
from uranium’s nucleus as it splits.
– Causes a chain reaction making other atoms
undergo fission.
Nuclear Fission
• Example: atomic bomb is uncontrolled fission reaction.
How Nuclear Energy Works
• Nuclear reactor surrounded by thick pressure
vessel filled with cooling fluid.
– Pressure vessel will contain fission products in event
of accident.
– Thick concrete walls also surround reactor.
• Inside reactor:
– Metal fuel rods containing uranium pellets hit
repeatedly with neutrons.
– Chain reaction releases energy and more neutrons.
– Reactor core contains control rods: control how
quickly fission happens by absorbing neutrons
which prevents them from causing fission
reactions with uranium fuel.
• Released heat used to generate electricity
(heat steam in power plants, etc).
• Breeder reactor: a reactor that generates fuel
as it works.
– Plutonium used as fuel in breeder reactor.
– Produces heat energy too.
Nuclear Power Plant
• Example: Diablo Canyon nuclear power plant.
– Generates enough energy for 2 million Californian
households.
– Equivalent to burning 20 million barrels of oil
Advantages of Nuclear Energy
• Nuclear fuel = concentrated energy source.
• Power plants do not produce greenhouse gases =
no global warming.
• Release less radioactivity than coal-fired power
plants.
• France generates ¾ of its electricity from nuclear
power and produces less than 1/5 the amount of
pollution per person than the U.S.
• Uranium occurs naturally in rock and soil.
• As it decays it gives off radon: radioactive gas
that is odorless and colorless.
– Can seep into buildings from the surrounding rock
and soil.
– Dangerous levels can build up without proper
ventilation.
– Estimated that 5,000 to 20,000 people die each
year from cancer caused by exposure to radon.
Why Aren’t We Using More Nuclear
Energy?
• Building and maintaining a safe reactor is very
expensive
• Storing Waste
– Fission products are dangerously radioactive for
years.
– The used fuel, liquids and equipment from the
reactor core are hazardous wastes.
– Storage sites must be in an area that will remain
geologically stable for a long time.
• Ex: Plutonium-239 waste will be dangerous for 192,000
years.
• Safety Concerns
– Potential for fission process to get out of control.
– Ex: 1986- Chernobyl
• Engineers turn off safety devices to run unauthorized
test.
• Test causes explosions that destroy reactor and release
radioactive materials into the air.
• Areas of Northern Europe and Ukraine are still
contaminated.
• Nuclear reactor had no containment building and
safety guidelines were violated.
• 50 people killed immediately; 116,000 leave their
homes; approx 15,000 got cancer eventually.
• Meltdown: process by which a nuclear chain
reaction goes out of control and melts the
reactor core. Release huge amounts of
radiation into the environment.
• Exposure to radiation can cause:
nausea, vomiting, headache, loss
of some white blood cells, cancer.
• 25 rems = detectable changes in
blood.
• 100 rems = no immediate harmful
effects.
• >100 rems = start to show above
symptoms.
• 300 rems = hairloss, damage to
nerve cells and cells that line the
digestive tract, difficulty clotting,
loss of white blood cells.
• 50% of people exposed to 450 rems die.
• 800 or more rems always fatal (no effective
treatment).
• In time, survivors can develop cancer.
• Ex: X-ray = 0.1 to 1 rem
Radioactive Waste
• Waste is radioactive.
– Approx. 1.4 tons of waste produced in one year
from one fission plant.
• Types of waste:
– High-level wastes: radioactive wastes that emit
large amounts of radiation.
• Uranium fuel rods, control rods, water used to cool and
control chain reactions, vessel that surrounds the fuel
rods.
– Medium-level and low-level wastes: not as
radioactive, although a much larger volume of
these are generated.
• Mine wastes scattered around uranium mine,
contaminated protective clothing from workers, also
produced by hospitals and laboraties.
The Future of Nuclear Power
• Nuclear Fusion: lightweight atomic nuclei
combine to form a heavier nucleus and
release a LOT of energy.
– This is the process that powers all the stars,
including our sun.
– Safer than fission because it creates less
dangerous radioactive biproducts.
• Difficult to achieve.
– Nuclei must be heated to high temperatures.
• 180,000,000 ⁰F
– Nuclei must be maintained at high concentrations
and properly confined.