Here’s an interesting factoid. The UK and US each possess about 100 MT of separated plutonium. However, the UK stockpile is largely civilian, whereas the US stockpile is almost entirely military.

The UK is currently engaged in a debate about what to do with this plutonium. Last year the Royal Society published a report on the subject and last week the Nuclear Decommissioning Authority (the UK public body charged with cleaning up Britain’s messy nuclear legacy) published draft options for public comment.

The NDA report spells out the options, which broadly fall into three categories: “store indefinitely”, “immobilise and dispose” and “reuse and dispose”. It runs through the pros and cons of each option and, frankly, there’s not much point me recounting the argument here—it would take about as long as the report itself.

One conclusion that is worth highlighting, however, because it is potentially particularly controversial concerns immobilization with high level waste:

To achieve this method of plutonium disposition in the UK would require retaining high level waste liquors at Sellafield for the length of the plutonium immobilization programme, which would be around 20 years once the new plant had been built and commissioned. In practice this would mean delaying the vitrification of some of the High Level Liquid Waste currently stored at Sellafield. Given that this is the highest hazard material at Sellafield, and that this strategy would delay completion of hazard reduction of the High Active Liquid Waste until all the plutonium had been immobilised, in 40-50 years, the NDA is minded to dismiss this as a credible option. However, some commentators believe this option offers potentially very high proliferation resistance. In reality, the activity of the high level waste glass drops off sharply after 200-300 years and the waste form will offer no higher proliferation resistance than any of the above candidate wastes.

What I would say is that the NDA report makes it clear quite how tricky a problem this is. For instance, one “easy” option (if you ignore the political and security problems) might be to sell UK plutonium to another state that wants it for MOX fabrication. However, I didn’t realized that

Thorp [the UK reprocessing plant for LWR fuel] derived plutonium does not currently have the capability to be exported as there are no transport container licenses for Thorp plutonium cans.

Moreover, the nature of the problem is very sensitive to the time taken to implement a solution. LWR fuel has a relatively high proportion of Pu-241 which (with a half life of 14.4 years) decays into Am-241. This may be useful in smoke detectors but it is a pain in MOX fuel fabrication (being a strong gamma emitter). Therefore, the feasibility of certain MOX fuel fabrication schemes depends on how quickly they can be implemented (bear in mind that the recent history of the UK’s nuclear programme is full of delays that are best measured on a geological timescale).

Of course, it’s always possible to design new containers or remove the Am-241 chemically. My point is that these problems make determining the “best” solution a nightmare.

Anyway, the NDA is seeking public comments, if you’re interested.

Finally, it would be remiss of me writing on this subject not to mention the International Panel on Fissile Materials. Their 2007 annual report has an excellent chapter detailing the woes of the US programme to deal with separated plutonium and I notice that Martin Forwood has recently published a paper with them on the UK mess. I haven’t read it yet but look forward to doing so.