September 2012

Radioactive Waste 4 - Spent Nuclear Fuel Disposal 2 - Repository

          A standard human way of dealing with something that you want to get rid of is to dig a hole and bury it. This has been a popular proposal of disposing of spent nuclear fuel and many countries that use nuclear power either have or are working on such repositories. The authorities in these countries claim that such repositories can be safe, economical and protect the environment but a large part of the public remains highly skeptical.

Radioactive Waste 2 - Spent nuclear fuel

          Nuclear reactors burn nuclear fuel to generate electricity. Most reactors burn uranium oxide in the form of ceramic pellets in long tubes. The tubes comprise the core of the reactor where the fission reaction takes place. The zirconium cladding of the fuel rod tends to migrate into the center of the pellets while the lower boiling point fission products move to the edge of the pellet. Small bubbles form in the pellet which fill with cesium-137 from decaying xenon.

Nuclear Batteries

          Nuclear batteries have been developed that utilize radioactive elements to generate electrical energy.  The first such battery was demonstrated in 1913 by Henry Moseley. There has been ongoing research since then in perfecting the technology. There are two basic designs for such batteries.

Thorium 6 - molten salt reactors

           In previous posts we have discussed thorium reactors based on solid fuels. There is another approach to creating a reactor that will burn thorium. Thorium and uranium can be dissolved in liquid composed of molten salts. The liquid is then pumped between a core and a heat exchanger where the heat is transferred generate steam.

Thorium 5 - solid thorium reactors

          Between 1967 and 1989, 27 different experimental thorium reactors were designed and built to research the potential of thorium for nuclear fuel. These test reactors were built in Canada, Germany, India, the Netherlands, Norway, Sweden, Switzerland, the United Kingdoms, the United States. Here are some examples of thorium reactors. 

Thorium 5 - Reactor research

          Between 1967 and 1989, 27 different experimental thorium reactors were designed and built to research the potential of thorium for nuclear fuel. These test reactors were built in Canada, Germany, India, the Netherlands, Norway, Sweden, Switzerland, the United Kingdoms, the United States. Here are some examples of thorium reactors.  

Thorium 4 - fuel cycle

          The thorium fuel cycle is based on the use of the common isotope Th-232 as what is called the fertile material in the reactor. Natural thorium is not fissile meaning that it cannot create self-sustaining reactor. The Th-232 must be transmuted into the fissile material, U-233, via neutron capture. The U-233 is the actual nuclear fuel for the reactor.

Thorium 3 - The Supply

          Thorium is the 36th most abundant element on Earth. It is four times more abundant than uramium. There has been no concerted international effort to exlplore for deposits thorium ores. Accurate estimates of world reserves of thorium are not available.  Known thorium deposits could supply a major part of the Earth’s energy needs for hundreds of years. Some estimates are as high as 1000 years at current world energy use.

Thorium 2 - The Element

           I have already written about thorium under the general subject of nuclear reactors. I have decided to cover thorium in more depth because of its possible use as a nuclear fuel.

          Thorium is a radioactive element with the symbol Th and the atomic number 90. It was discovered in 1828 by the Swedish chemist Jons Jacob Berzelious. The element was named for Thor, the hammer wielding Norse god.

Polonium

          Polonium is a chemical element with the symbol Po and an atomic number of 84. It was discovered in 1898 by Marie and Pierre Curie and named after Poland where Marie was born. They removed uranium and thorium from pitchblende ore and discovered that the ore became more radioactive. Polonium was the first new radioactive element they discovered in the processed ore.

Sources of Energy

          The human race has an insatiable appetite for energy. Since harnessing fire many thousands of years ago, humanity has developed new ways to power civilization. Fortunes have been made, wars have been fought and great harm has been done to the environment in the quest for energy.