Nuclear Reactors

Nuclear Reactors• Fission has been developed as an energy source to

produce electricity in reactors– Within the reactors, controlled fission occurs– And we harness the heat from fission to create electricity

Diagram of a nuclear power plant.

Schematic of the reactor core.

• Fuel rods – contained enriched uranium

• Moderator – slows the neutrons down so the uranium fuel can capture them more efficiently

• Control rods • Coolant –

So how do we control it?• Control rods:

control the fission process with cadmium rods that absorb neutrons

Enrico Fermisupervised construction of theworld's first nuclearreactor.

Schematic of the reactor core.

• Fuel rods – • Moderator –• Control rods – absorb

neutrons; regulate the power level of the reactor

• Coolant – usually water; extracts the heat produced during fission

Diagram of a nuclear power plant.

The 4 bad parts of fission…1. Reactor components2. Uranium3. Heat production4. Nuclear waste

You notes should include why these 4 things create disadvantages for getting all our energy from fission.

The bad part of Fission: 1. Reactor Components

• The concentration of uranium is not great enough to allow an explosion– A failure in the cooling system can lead to temperatures high

enough to melt the reactor core• This is called a “melt down”

Melt Down• A melt down was narrowly avoided at Three

Mile Island (in Pennsylvania) in 1979• A total melt down occurred at Chernobyl in

the Soviet Union in 1986• Reactor No. 4 at the power plant exploded releasing 30

to 40 more times radiation than the bombs dropped on Hiroshima and Nagasaki

– The Soviet government didn’t own-up to the disaster until scientists in Sweden recorded high levels of nuclear fall-out

– People are still not allowed in the area surrounding the power plant

Chernobyl Melt Down

The bad part of fission:2. Uranium

• Discovered in 1789– Not rare – more abundant than tin– Widely scattered on Earth in the crust

• Most accessible deposits:– United States, Canada, South Africa, Australia

– Used in small amounts as a coloring agent for glass and ceramics• Natural nuclear reactor existed in Gabon millions of years ago

The bad part of fission:2. Uranium

• U-238 – radioactive, but not fissionable• U-235 – fissionable, but only 0.7% of natural

uranium.– 3% U-235 needed for fuel rods.

• Scientists “enrich” the uranium found in nature so that it contains 3% of U-235

• For atomic bombs, the amount of U-235 needed is 90%!

The bad part of fission:2. Uranium

•Breeder reactors: change non-fissionable U-238 and convert it into fissionable Pu-239 while the reactor runs

–Completed by bombarding U-238 with neutrons

•Controversial–very toxic, poisonous, and flames in air

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The bad part of Fission:3. The heat produced is pumped into water

The bad part of fission:4. Nuclear Waste

• Most nuclear waste created over the last 50 years is in temporary storage

• In 1982 the Nuclear Waste Policy Act was passed– Established a timetable for choosing and preparing sites

deep underground for the disposal of radioactive materials– The current plan calls for the nuclear waste to be packaged

in glass blocks that will be packed in corrosion-resistant metal and buried in a deep, stable rock formation

• The hope is that the waste will be isolated until radioactivity decays to safe levels

4. Nuclear Waste

4. Nuclear Waste• In 1998, the Waste

Isolation Pilot Plant in New Mexico was issued a license by the EPA to receive nuclear waste

• Yucca Mountain has been studied as a site for 20 years for the high level waste generated at power plants