Read more: “Instant Expert 32: Nuclear energy“
All countries that use nuclear power face the problem of how to dispose of their hazardous waste. In addition to the highly radioactive fission products at its Sellafield nuclear installation, the UK has accumulated 112 tonnes of plutonium, separated from spent power reactor fuel and stored as weapons-ready oxide powder. This, according to calculations by the International Atomic Energy Agency, is enough to make 10,000 nuclear weapons. The British government spends billions guarding this stockpile against theft by terrorists.
Getting rid of it could be as simple as converting that plutonium into reactor fuel and burning it in new light water nuclear reactors. Known as the MOX process – named for the “mixed oxide” plutonium-uranium ceramic fuel that would be burned inside the reactor – this would reduce the volume of plutonium, make the rest too radioactive to steal, and produce electrical energy to boot.
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Two light water reactors – built to burn plutonium instead of uranium – could make short work of 100 tonnes of plutonium in 50 years. The spent fuel could be placed directly into a mined geological repository, without any extra processing.
GE Hitachi has proposed a different solution: build two of its next-generation PRISM reactors to do a similar job, but with metallic plutonium-uranium fuel instead of mixed oxide.
PRISM has some good applications, but not for getting rid of Sellafield’s plutonium.
The main problem is that to safeguard the metallic fuel while it waits to be burned in the PRISM reactors, GE proposes making it “self-protecting”: so radioactive that any potential thief would die trying to abscond with it. To do that, GE Hitachi plans to irradiate each of the fuel elements for 45 to 90 days.
Converting and irradiating the entire Sellafield stockpile in this way will take five years. However, burning the resulting fuel for energy in the small PRISM reactors will take 200 years: far longer than either the lifetime of the protective radiation field or the PRISM reactors, which are designed to operate for 50 years.
During that time, only a small fraction of the plutonium will be burned. What will happen to the spent metal fuel after that? GE Hitachi plans to send it – after a complicated conversion process that will make it safe for long-term storage – into a repository.
Why not simply do that in the first place? A better solution for Sellafield’s plutonium problem would be to skip the involvement of reactors altogether, and simply add the existing plutonium oxide directly to the intensely radioactive glass that already needs to be produced in order to permanently contain these highly radioactive liquids.
The best option for Sellafield’s plutonium is what it always has been – burial, preferably without use as reactor fuel.
This article appeared in print under the headline “The Plutonium Problem”
