Chapter 16 – Nuclear Energy Pages 250 – 263 Mrs. Paul Environmental Science.

Chapter 16 – Nuclear Energy

Pages 250 – 263Mrs. 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.