Urgent: what to do with 100 tonnes of plutonium

The government’s recent green light for the building of new nuclear power stations re-emphasises the urgent need for a long-term strategy to deal with the UK’s stockpile of separated plutonium.

We have the unenviable distinction of having the world’s largest stockpile of separated plutonium of over 100 tonnes. This has almost doubled over the last ten years. The separation of plutonium from the spent fuel from nuclear reactors began in the 1960s with the intention of recycling it as fuel in a new generation of fast reactors. Although work on these reactors was halted in 1994, plutonium separation continued.

Separated plutonium is highly toxic. It is a powder that, if dispersed into the atmosphere in the event of a major security breach or accident, has the potential to cause considerable health and environmental damage,  for example, causing lung, liver and bone cancers. As it is difficult to clean up, its effects would be felt for a long time. Furthermore, as the primary component in most nuclear weapons, it would be possible for a well-informed and equipped terrorist group to create a crude nuclear bomb if it fell into their hands.

Last year we published a report arguing that the government must urgently develop and implement a strategy for the stockpile’s long-term management and disposal, and that this should be done as an integral part of the energy and radioactive waste policies that are currently being developed.

Our report recommended that the best option would be to convert the powdered plutonium into Mixed Oxide (MOX) fuel pellets to decrease the impact of accidental or deliberate dispersal. These pellets could then be used as fuel in a nuclear reactor to produce spent MOX fuel.

Although it seems counterintuitive, spent MOX fuel is safer than separated plutonium because it is more radioactive. This makes it harder to handle and therefore more difficult to steal and use. Spent MOX fuel would also be more difficult to use in nuclear weapons.

The government’s support, as stated in its recent white paper on nuclear power, for allowing energy companies the option of investing in new nuclear power stations presents the possibility that the stockpile could be burnt as MOX fuel in some of the reactors currently being considered.

We welcome the statement in the white paper that the Nuclear Decommissioning Authority is considering the use of MOX fuel as a way to deal with the plutonium it owns. However, in order to do this the recently publicised problems with MOX fuel production at Sellafield will need to be addressed.

 Without new nuclear build, at least some of the stockpile could be transformed into spent fuel by modifying Sizewell B to burn MOX fuel. However the limited life time of Sizewell B means that it would not be possible to burn the whole stockpile in this way. Because of this we recommended that the remaining separated plutonium that is not burned should be converted and stored as MOX fuel.

Ultimately the best method of disposing of the UK’s separated plutonium stockpile is to bury it deep underground either as spent fuel, or less ideally, as MOX pellets.  However, since disposal sites for highly radioactive waste are not expected to be ready until 2075, the government must act and develop a strategy in the meantime.  The status quo of continuing to stockpile a very dangerous material is not an acceptable long-term option.

Professor Geoffrey Boulton FRS, University of Edinburgh is chair of the Royal Society plutonium working group.