Types of Nuclear Waste

Nuclear waste comes in several forms: spent fuel rods, contaminated reactor components, and waste from uranium mining and enrichment.

Spent Fuel Rods

Spent fuel rods contain two types of waste, fission bi-products and transuranics, and constitute 99% of all nuclear waste when measured in terms of radiation, despite the small volume of waste they constitute.

Fission Bi-Products

Fission bi-products are the atoms that result when a uranium-235 atom splits, and many of these atoms are radioactive. One of these bi-products, Strontium-90, is also very dangerous if it gets into the water supply, because it has many of the same properties as calcium and will replace calcium in your bones, if ingested.

Transuranics

Natural uranium is less than 1% uranium-235; the vast majority is uranium-238, which is a neutron-absorber that helps control the fission chain reaction. However, when a uranium-238 atom absorbs a neutron, it becomes radioactive uranium-239. Uranium-239 decays (through beta-decay) into neptunium-239, which is also radioactive and decays into plutonium-239. Plutonium-239 is also radioactive and has a half-life (the time for half of it to decay) of 24,000 years. The sequence of neutron absorption and decay can be expressed by the following equations:

1 neutron +

1 neutron +

1 neutron +

(Recall that beta decay is the loss of an electron as a neutron converts to a proton.)

These elements, as well as any element with a higher atomic number than uranium, are called transuranic.

Contaminated Reactor Components

Reactor components also become radioactive over time because radioactive nuclides become lodged in them. These components must be replaced from time to time. The largest problem is when a nuclear reactor is decommissioned and the extremely radioactive reactor core must be disposed of.

Waste from Uranium Mining and Enrichment

Waste from uranium mining and enrichment is not nearly as radioactive as the other forms of waste. However, uranium-238 is long-lived (its half-life, the time it takes for half of it to undergo radioactive decay, is nearly 4.5 billion years) and thorium-234, the isotope that results from the decay of uranium-238, is more radioactive. The half-life of thorium-234 is only 24 days.

Waste Storage

Currently, low-level waste has been buried underground since it is not very dangerous and will be non-radioactive within a couple hundred years. Spent fuel rods, on the other hand, have not yet found permanent storage. They are stored either in dry cask storage containers close to the reactor itself, or in a storage pool of boric acid, which helps cool the fuel rods while absorbing some of the radiation the fuel rods give off. Unfortunately, these storage pools are becoming crowded as no permanent storage has yet been agreed on, and overcrowding could potentially cause a nuclear chain reaction.

Options for storing spent fuel rods include shooting them into space, burying them under the ocean floor, or storing them underground. A permanent storage site has been chosen at Yucca Mountain, Nevada, where tunnels are being dug into the mountain to bury the casks of fuel rods. Of course, the people in Nevada are opposed to the plan because, although the research indicates that this is the safest place in the US to bury them, no one can give an absolute guarantee that the radioactive waste will never leak.

For more info on the effects of radiation visit Citizens Awareness Network (anti-nuclear) at http://www.nukebusters.org/

and the World Nuclear Association (pro-nuclear) at http://www.world-nuclear.org/education/ral.htm

For more info on managing nuclear waste visit the World Nuclear Association at http://www.world-nuclear.org/education/wast.htm

New Technologies for Minimizing Waste

Reprocessing

When nuclear power was first developed, it was assumed that spent fuel would be reprocessed. Plutonium-239, one of the transuranic wastes, could be extracted from the spent fuel rods and used as fuel in another power plant, thereby lessening the waste and creating more fuel at the same time. Unfortunately, plutonium reprocessing was banned in the US because plutonium-239 is weapons-grade material and, if stolen, could be used to make a nuclear weapon. The ban was lifted a few years ago, but as of yet, there are still no reprocessing plants operating in the US, and with the recent terrorist attacks, the possibility of plutonium theft could be a renewed concern.

High Temperature Breeder Reactors

Part of the solution to nuclear waste may be found in the EBR-II reactor, developed here in the US by Argonne National Laboratory. This reactor uses almost 100% of its transuranic nuclear wastes as fuel, and the products caused by these fission reactions have shorter half-lives and are not as dangerous.

In a normal reactor, the transuranic elements don't fission because the neutrons aren't excited enough to induce fission in these larger atoms. However, if they are placed in a high temperature breeder reactor, such as the EBR-II reactor, the neutrons will be much more exited and will have a better chance of causing a fission reaction.

The EBR-II also has the advantage that its fuel is not weapons-grade. When the transuranic wastes are isolated for fuel, the mix of isotopes cannot be used in a bomb.

For more info on advanced reactors visit the World Nuclear Association at http://www.world-nuclear.org/info/inf08.htm

Written and created by Cami Idzerda. Last updated 11/29/2001. 

Email: CIdzerda@aol.com