By the time reprocessing ends the UK’s stockpile of plutonium is expected to reach around 140 tonnes, after the Nuclear Decommissioning Authority (NDA) agreed to take title to some of the overeseas plutonium stored at Sellafield. This is the largest civil plutonium stockpile anywhere in the world.

The UK, USA, Soviet Union, France, Germany, Japan and India all established programmes to develop a plutonium fuelled nuclear reactor that could produce more fuel than it consumed (a “breeder reactor”) in the hope of solving the long-term energy supply problem. Spent-fuel reprocessing was launched to separate plutonium for manufacturing start-up fuel for the first breeder reactors.

But the problems in each country make it hard to dispute the observation by Admiral Hyman Rickover in 1956, based on his experience with a sodium-cooled reactor developed to power an early U.S. nuclear submarine, that such reactors are “expensive to build, complex to operate, susceptible to prolonged shutdown as a result of even minor malfunctions, and difficult and time-consuming to repair.” 1

Uranium proved to be much more abundant than originally imagined so the high costs and poor reliability and safety record has meant that no commercial breeder reactors have been deployed. New demonstration reactors are being built in India and Russia and China is considering the possibility of building two Russian‑designed breeder reactors. But in the absence of breeder reactors elsewhere, separated plutonium has become a disposal problem and some countries have decided to recycle it into fuel for the same reactors that produced it.

Germany, France and Switzerland have opted to use their plutonium stockpiles in conventional reactors. However this route for making use of the plutonium stockpile was problematic in the UK because of the type of reactors built here. In the absence of the capability to use plutonium in either conventional or fast reactors, separated plutonium has accumulated. This huge policy mistake has left the UK with a much greater dilemma than anyone else.

In 2008 the Government asked the NDA to identify credible options for the long-term management of the UK’s plutonium stockpile. In response to this request, the NDA published a Credible Options Paper in February 2011. This led to the publication of a consultation document by the Department of Energy and Climate Change (DECC) in February 2011. The Government responded to comments on 1st December 2011.2

The Government consultation document sets out three options for long-term plutonium management:

  1. Re-use. The Government’s preferred option is to re-use the material by using it in Mixed Oxide (MoX) Fuel. This would require the construction of a new MoX fuel fabrication plant.
  2. Immobilise and treat as waste. This is the option favoured by most environment groups. The unwanted plutonium would be immobilised and managed as waste.
  3. Indefinite storage. The current default plan assumes plutonium will be stored at Sellafield until 2120. The NDA’s Credible Options paper notes that the execution of any proposed active strategy would take 30 – 50 years anyway. Indefinite storage is not a suitable long-term option. Plutonium stocks need to be placed beyond any possible future use in nuclear weapons, however, thirty to fifty years gives adequate time to develop an immobilisation strategy.

In January 2014 the NDA published a progress report on its apoproach to the management of seprated plutonium. This confirmed that the NDA still felt that reuse was the preferred option and that there are three credible reuse options: – reuse as MOX in light water reactors, reuse in CANDU EC6 reactors and reuse in PRISM fast reactors.


The UK already has a (MoX) Fuel Fabrication Plant at Sellafield (SMP), but this was only licensed to produce MoX fuel using plutonium owned by overseas customers with reprocessing contracts with Sellafield – principally Japan, Germany and Switzerland. SMP was built between 1994 and 1997 at an original cost of £470m, but has been dogged with problems ever since. There were five public consultation exercises and a number of legal challenges, before the first plutonium was introduced into the plant in April 2002. Built to manufacture 120 tonnes of MOX fuel per year, and with an operating lifespan of 20 years, SMP produced no fuel whatsoever until its third year of operation and a total of just 13 tonnes in its 9 years of operation which saw a number of contracts having to be sub-contracted to SMP’s arch-rivals in Europe. Despite dire warnings in 2006 and 2007 from Government commissioned consultants Arthur D Little (who had originally provided Government glowing reports of the plant’s prospects) that without further investment the plant would never operate as originally planned, the NDA continued to support its operation and in so doing wasted an estimated £1.4bn of taxpayers’ money.3 SMP was “one of the most embarrassing failures in British industrial history,” according to a leaked US embassy cable. 4

In August 2011 the NDA announced that SMP would close. It put the blame squarely on the Japanese earthquake. A complete refurbishment of the plant financed at an estimated cost of £200m by Japanese utility customers had been expected to start soon, but the postponement of any further use of MOX fuel in Japan SMP’s sole contract and lifeline was lost. (See Sellafield MoX Plant nuClear News No.31)

SMP left taxpayers with a £2.2bn bill instead of turning a healthy profit. An internal government report revealing the full extent of the failure of SMP concluded that the facility was “not fit for purpose” and its performance over a decade was “very poor”.


DECC published the conclusions of its consultation on the long term management of UK-owned civil plutonium in December 2011. This confirmed the Government’s preliminary view that a new MoX Plant should probably be built. But the Government said it doesn’t have sufficient information yet to make a specific decision to proceed with procuring a new MOX plant. Only when it is confident that the MoX option can be implemented safely and securely, that it is affordable, deliverable, and offers value for money, will it be in a position to proceed. (See Plutonium – the madness continues nuClear News No.35.)

The Government’s preferred option is based on the assumption that we don’t make the same mistakes with a second MoX fuel fabrication facility, especially if we bring in the French who already have a working MoX plant. But experience in the United States where Areva is building a MoX plant, which is reportedly costing five times as much as anticipated and is hopelessly behind schedule, does not bode well for the future.5

In May 2012 DECC launched a consultation on its proposed process for applications and decisions on the justification of proposals for the reuse of plutonium as a means of long-term management of the civil plutonium stockpile. Applicants seeking a justification decision for the reuse of plutonium will need to satisfy the Justification Authority (the Secretary of State for Energy and Climate Change and Devolved Administrations where relevant) that the health detriments are offset by the benefits associated with the practice.

A Justification exercise based on underestimated costs will not give a reliable result. The Government should examine the reasons for the cost overruns of the American MoX programme. Spent MoX fuel would be a much more hazardous waste form to deal with than conventional spent fuel. Furthermore, the use of MoX fuels rather than as a waste product would involve quite unacceptable safety and security risks and would pose a potential threat to civil liberties with large armed plutonium waste convoys being transported up and down the country between Sellafield and potential new MoX burning reactors. Such transports would also lead to inevitable concerns over emergency planning and malicious attack. (See NFLA Radioactive waste Policy Briefing No.34, July 2012.)

In May 2013 the Government responded to the consultation a year earlier. It said “there is a strong inter-relationship between reuse of plutonium as MOX and new nuclear reactors; nuclear reactors need to be available to irradiate the fuel as the final part of the process … While the Government has set out a preferred policy, there is not yet sufficient information to decide whether to proceed with implementing this policy, including procurement of a new MOX plant.”

On 6th July 2015 AREVA issued a press release about opening a new office near Sellafield. This confirmed its support for the AREVA Convert Project. This is a plan to build a new facility at Sellafield to transform the UK’s plutonium stockpile into MOX fuel for use in Light Water Reactors.

PRISM Reactors

The NDA, which has responsibility for managing the UK’s plutonium stocks, announced on 27th June 2012 that it is looking at the merits of two proposals to build new reactors – the PRISM fast reactor and the Enhanced CANDU 6 reactor – as a means of plutonium disposition – alongside plutonium reuse as MoX in Light Water Reactors. Discussions have taken place with General Electric-Hitachi (GEH) and Candu Energy inc. regarding their proposals.

If it can look again at reactor options as a way of managing plutonium stocks it should also re-examine immobilisation options. Prof. Allison Macfarlane, now confirmed as Chair of the US Nuclear Regulatory Commission, and others including Professor Frank Von Hippel, say the UK’s proposals to covert plutonium stockpiles into MoX fuel are likely to run into technical and political difficulties, as well as escalating costs.

Britain should seriously evaluate the less costly and less risky method of direct plutonium disposal, and take the opportunity to lead the world towards a better solution for reducing stockpiles.” 6

Briefing on PRISM reactors available here: PRISM reactors, N2NP Briefing, September 2012


In June 2015 it was reported the Canmox scheme had emerged as a front-runner among the options under consideration and had taken a step forward with the signing of an agreement between the Canadian Government and the NDA to enhance cooperation in civil nuclear energy. Ontario-based Candu Energy is proposing to turn plutonium into mixed oxide (MOX) pellets at a dedicated fabrication facility at Sellafield. The MOX fuel could then be used in four thermal reactors to produce up to 3GWe of electricity. Canmox claims to be able to deal with the entire stockpile of plutonium, regardless of the grade or contamination. The distinguishing feature of the Candu technology is the use of heavy water as a moderator that provides enhanced neutron efficiency, allowing for fuel flexibility. According to Candu Energy: “The arrangement galvanizes joint research and development, regulatory co-operation, technology transfer and investment into the UK nuclear sector and has the potential to unlock a powerful energy source for UK electricity consumers.


Despite the NDA insisting that re-use is its favoured option for the management of separated plutonium a Sellafield local stakeholder committee meeting on June 9th, 2015 heard that the UK’s Regulators, the Environment Agency and the Office for Nuclear Regulation, had been tasked by the NDA to review the option of immobilizing plutonium. The NDA says research work on the immobilization of plutonium is being carried out to find out if the process can be “industrialised” so that it could be used to treat material that is unsuitable for reuse or for disposition of the entire stockpile if Government decided not to pursue re-use.

See also Slow Progress on Plutonium Stockpiles, NuClear News No.76

CORE Press Release 15th July 2015

Plutonium Separation in Nuclear Power Programs, International Panel on Fissile Materials, 2015


Published: 3 December 2012
Last updated: 17 August 2015