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Saturday 6 February 2016

100,000 Years Later

The problem of making future predictions about the destiny of long-lived nuclear waste.

What is nuclear waste?

Depending upon what you put into a nuclear power station and how you operate it, you get different products out. Most reactors use uranium dioxide fuel, UO2, and over 90% of the “spent fuel” is still uranium compounds, with a little plutonium. Although it is called spent fuel, so much uranium still exists that it may be recycled to generate more electricity and remains hot for years. However, “ash” products that absorb neutrons and slow the reactions build up as the fuel operates, the rate that energy is produced drops and stops being efficient. Then the fuel will be replaced, useful uranium extracted and recycled and the rest disposed of.

Some kinds of reactors extract more energy and are more efficient, such as fast breeder reactors. These make products like plutonium-239 (Pu-239) that sustain the chain reaction - nuclei falling apart and giving off energy. When the rate plutonium-239 is produced is faster than it is used up, the reactor can get 60 times as much energy from the original uranium and more plutonium products result. However, there are no fast breeder reactors in the UK because plutonium-239 is one component used to make nuclear weapons - not something you want to be storing in large quantities. Plutonium-239 and other minor actinide products of nuclear power generation remain dangerous for over hundreds of thousands of years. Although the longer a radioactive material remains dangerous, the lower the danger (because they produce radioactivity more slowly), fresh spent fuel is so concentrated that standing unprotected before it would get you a lethal dose in seconds, and you would die of radiation sickness in days.

How can we store nuclear waste?