Nuclear Energy & the Environment (College Board AP® Environmental Science): Study Guide

Nuclear disasters

• Any kind of disaster can have detrimental impacts on the environment and human health

• As nuclear power plants handle enormous amounts of heat, gasses, and byproducts, its dangers are more pronounced

• Meltdowns, explosions, thermal pollution, and the exposure of radioactive components to the environment or to humans are a few instances of nuclear accidents

• Three Mile Island in the USA in 1979

  • Partial meltdown of the nuclear reactor due to a cooling malfunction in reactor 2

  • A slight increase in cancer rates in the area affected by the release of radioactive contamination

• Chernobyl, Ukraine (at the time part of the USSR), was the site of a reactor explosion in 1986

  • 50 direct deaths from hot pressurized steam and radiation poisoning (UN estimate)

  • An estimated 4,000 people have or will die as a result of exposure to radioactive materials

  • Radioactive fallout entered the atmosphere and fell over 40 different countries, including Scandinavia and the UK, resulting in over 572 million people receiving some exposure

  • 23,000 radiation-induced cancers and 16,000 thyroid cancers due to iodine 131 exposure

• The Fukushima-Daiichi nuclear reactor failed in Japan in 2011

  • The tsunami that resulted from the 2011 earthquake flooded parts of the power station, causing a loss of power, which meant they lost the ability to cool the reactor. This led to explosions, a meltdown of the reactor and the release of radioactive contamination

  • 154,000 people evacuated

  • There has been an increase in thyroid cancers in the area since 2011 but this may be that more are being detected due to the screening program established after the event

Radioactive decay

• Radioactive half-life is the amount of time it takes for 50% of a radioactive substance to decay (breakdown)

  • Uranium 235 has a half-life of 704 million years

  • This means it would take 704 million years for the activity of an uranium 235 sample to decrease to half its original amount

• Half-lives vary from less than a second to billions of years

  • Iodine 131 has a half-life of eight days

  • Plutonium 239 takes 24,000 years for half of the atoms to spontaneously disintegrate

  • Uranium 238's half life is 4.5 billion years

Nuclear Fuel

Uranium 235 (U-235)

• Earth's natural U-235 is less than 1%

• U-235 differs from U-238 because it can be a self-sustaining fission chain reaction

• The critical mass is the minimum amount needed for a chain reaction

• Only small amounts of U-235 is needed for a reaction

• Processing uranium to separate U-235 is called enrichment

• Nuclear power facilities contain 3% U-235, while weapons contain 85%

Uranium-238 (U-238)

• The most common uranium isotope is U-238, with a 4.5 billion-year half-life

• When hit by a neutron, it decays into plutonium-239

• Most-depleted uranium is U-238

Plutonium-239 (Pu-239)

• Breeder reactors produce Pu-239 from U-238 with a half-life of 24,000 years

• A typical commercial nuclear power plant produces one-third of its energy via plutonium fission

• The control rods must be replaced frequently owing to Pu-239 buildup.

• Pu-239 can be used for nuclear weapons and international inspections measures Pu-239 production