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Will PRISM solve the UK's plutonium problem? (Jim Green)

Nuclear Monitor Issue: 

NM777.4382 The UK Nuclear Decommissioning Authority (NDA) released a position paper in January outlining potential options for future management of separated plutonium stockpiles.[1] All the options are problematic yet the paper is silent as to why plutonium is separated from spent fuel in the first place, and whether it's such a great idea to be planning to build more power reactors producing more plutonium.

The UK already has a stockpile of over 100 tonnes of separated plutonium from its nuclear power program, expected to increase to 140 tonnes by 2018.[1] Business as usual is not an option, especially if that involves continued production and separation of plutonium. The UK Royal Society noted in a 2011 report that the plutonium oxide powder, which is stored in drums, "poses a serious security risk" and "undermines the UK's credibility in non-proliferation debates."[2]

Plutonium separation and stockpiling clearly increases proliferation risks, and it involves spent fuel reprocessing − acknowledged to be "environmentally dirty" by a World Nuclear Association executive, no less.[3] And reprocessing is pointless − precious little of the plutonium or uranium separated during reprocessing is used as reactor fuel. Yet global plutonium stockpiles continue to grow, now amounting to over 260 tonnes globally.[4] The UK is the worst offender − it has the largest stockpile of separated plutonium.

The options being considered for separated plutonium management in the UK are:

  • Incorporating separated plutonium into mixed uranium−plutonium oxide MOX fuel for use in conventional light-water reactors;
  • Reuse in Candu Energy 'Enhanced CANDU 6' reactors;
  • Reuse in 'Power Reactor Innovative Small Module' (PRISM) fast reactors proposed by General Electric Hitachi (GEH);
  • Non-reuse options − long-term storage followed by disposal, or immobilisation followed by disposal.


The NDA report states that reuse in CANDU reactors "remains a credible option", that MOX is a "credible and technically mature option", while PRISM "should also be considered credible, although further investigation may change this view." Non-reuse options are given short shrift although they may be the least-worst of the options, while non-production options are given no shrift at all.

The report states that "all the technologies being considered have pros and cons and that no 'perfect' solution exists" and suggests the possibility of pursuing a "multi-track approach". Given the history of nuclear white elephants at Sellafield − the MOX plant, the THORP reprocessing plant and the Windscale Piles among others − the multi-track approach may result in a multiplicity of white elephants.

The NDA seems in no hurry to progress the matter and plans to undertake further studies over the next 1−2 years in conjunction with technology suppliers: "Currently, we believe there is insufficient understanding of the options to confidently move into implementation and consider that significant further work must be undertaken, focussing on technical and commercial risks and uncertainties ..."

The NDA report further states that "this is a long term programme with bulk reuse of plutonium likely to commence around 2030-2035 and concluding several decades after that." The NDA wants to focus on options which "allow decisions to be made on a timescale that is commensurate with any strategic imperatives", adding that the timescale is around 25 years.


The NDA regards MOX as a "credible and technically mature option for the majority of plutonium and, given the current planned new build reactor types, remains implementable." However the UK's experience with MOX has been disastrous − £1.4 billion wasted on a MOX fabrication plant at Sellafield that produced very little MOX and was shut-down in 2011.[5]

It is far from certain that reactors capable of using MOX fuel will be operating decades into the future in the UK. Overseas demand for MOX is limited − it accounts for just 2% of nuclear fuel worldwide [6] − and uncertain. It is also doubtful whether reactor operators would be willing to use MOX instead of fresh uranium fuel in UK reactors. The NDA report obliquely mentions these problems: "Due to the relative immaturity of the UK new build programme, at this stage, the appetite of developers to ultimately include MOX in their considerations remains uncertain."

Among many other problems with MOX:

  • MOX-fuelled reactors produce more plutonium than they consume;
  • extracting weapons-useable plutonium from MOX is far easier than extracting it from spent fuel;
  • a MOX fuel cycle requires the operation of dangerous, polluting, proliferation-sensitive reprocessing plants to separate plutonium from spent fuel.
  • the NDA estimates that about 85−90% of the plutonium stockpile could be used in MOX fuel, while "plutonium whose condition is such that it could not be converted into MOX would be immobilised and treated as waste for disposal."


MOX amounts to an elaborate method of incorporating plutonium into spent fuel and begs the question: why separate plutonium from spent fuel in the first place?


The CANDU option involves a variation of MOX fuel (CANMOX) in heavy water-moderated, heavy water-cooled reactors.[7]

The NDA report states that spent fuel from CANDU reactors could then be disposed of in "the Geological Disposal Facility".[1] That would be the Geological Disposal Facility that doesn't exist − the Geological Disposal Facility that won't exist for decades, at least. Presumably the non-existence of a Geological Disposal Facility is one issue that might arise in a "full disposability assessment" which, as the NDA notes, "has yet to be undertaken."

The NDA mentions uncertainties around aspects of the CANDU proposal, noting that "some of the fuel fabrication systems have not been delivered at full industrial scale for plutonium fuels", and that there "remains uncertainty over the extent of the fuel performance demonstration programme that would be required". Thus the CANDU proposal "would require some development work, related mostly to fuel performance and industrialisation of fuel fabrication." The timeframe for "disposition" of the plutonium stockpile using CANDUs could range from 2 to 60 years.


PRISMs [8] − the latest manifestation of much-hyped but non-existent 'integral fast reactors' (IFR) − don't exist so represent a bigger technological leap than the evolutionary CANDU−6 proposal. GEH says it offers PRISMs on the world market − but there aren't any takers and none have been built.

GEH proposes two 311 MWe PRISM reactors with the following processes:

  • conversion of separated plutonium to a sodium-bonded U/Pu/Zr metal fuel using Direct Electrolytic Reduction, Pyroprocessing and metal casting techniques;
  • irradiation of this metal fuel in PRISM reactors, in a burn rather than breed mode; and
  • storage of the spent fuel pending disposal (no recycle of spent fuel, in line with current UK new nuclear build assumptions).


The NDA notes that the facilities required by the PRISM approach have not been industrially demonstrated, so further development work to be undertaken with the cost and time to complete this work still to be defined in detail. GEH estimates that licensing these first of a kind PRISM reactors would take around six years. GEH envisages first irradiation (following development, licensing and construction) in 14−18 years but the NDA considers that timeframe "ambitious considering delivery performance norms currently seen in the UK and European nuclear landscape".

Internal 2011 emails, released under Freedom of Information laws, revealed that the NDA said it had carried out a "high-level assessment" of PRISM and "the technology maturity for the fuel, reactor and recycling plant are considered to all be low".[9]

Contrast that with the breezy confidence of IFR/PRISM cheerleaders − Mark Lynas says GEH could get a PRISM reactor "up and running in 5 years – the PRISM is fully proven in engineering terms and basically ready to go."[10]

PRISM cheerleaders argued in 2011 that the first PRISM could be built in the US by 2016.[11] However the US Nuclear Regulatory Commission has yet to receive a licensing submission from GEH [12] and there are no concrete plans for PRISMS in the US let alone any concrete pours.

PRISM waste

The NDA states that it has carried out a 'Generic Disposability Assessment' which found that, "whilst challenging, a disposal safety case can probably be made for disposal of sodium bonded PRISM Spent Fuel derived from the irradiation of the plutonium stocks in the UK." GEH proposes methods to remove the sodium from spent fuel in the event that a disposability safety case cannot be made.

IFRs are promoted on the grounds that they could recycle spent fuel repeatedly, leaving only relatively short-lived fission products (with half lives of 10−30 years) to be disposed of as waste. But the aims of the UK PRISM proposal are far more modest. GEH's Eric Loewen says: "What we're proposing is to disposition it; that means irradiating it in the reactor so that the plutonium is fissioned and the material is at the same radiation standard as spent fuel."[13]

So it is uncertain whether PRISM spent fuel would be suitable for geological disposal, and further processing might be required to achieve disposability in the non-existent Geological Disposal Facility, i.e. sodium removal, generating another waste stream. Compare that with the statements of the IFR cheerleaders, most of them self-proclaimed pro-nuclear environmentalists:

  • George Monbiot: "IFRs, once loaded with nuclear waste, can, in principle, keep recycling it until only a small fraction remains, producing energy as they do so. The remaining waste ... presents much less of a long-term management problem, as its components have half-lives of tens, not millions, of years."[14]
  • Mark Lynas: "The most compelling reason to look seriously at the PRISM is that it can burn all the long-lived actinides in spent nuclear fuel, leaving only fission products with a roughly 300-year radioactive lifetime. This puts a very different spin on the eventual need for a geological repository."[15]
  • Monbiot, Lynas, Fred Pearce, Stephen Tindale and Michael Hanlon: "The PRISM reactor offered by GE-Hitachi [is] a fourth-generation fast reactor design which can generate zero-carbon power by consuming our plutonium and spent fuel stockpiles, thereby tackling both the nuclear waste and climate problems simultaneously ..."[16]

Cheerleaders would argue that IFRs could theoretically recycle spent fuel until nothing is left but short-lived fission products. But that's precisely the problem. Attractive theories have given us a global legacy of 260 tonnes (and counting) of separated plutonium; a legacy of failed fast reactor projects (the super-dud Superphenix in France, to mention just one); and failed white elephants such as the MOX and THORP plants at Sellafield. In the case of IFRs, as nuclear engineer Dave Lochbaum from the Union of Concerned Scientists puts it: "The IFR looks good on paper. So good, in fact, that we should leave it on paper. For it only gets ugly in moving from blueprint to backyard."

Cheerleaders also talk up the 'proliferation resistance' of the IFR fuel cycle. Theoretically, IFRs could consume more plutonium than they produce, and plutonium would never be separated from other actinides in a modified form of reprocessing called pyroprocessing. But in the case of the UK:

  • proliferation risks are heightened by separating plutonium from spent fuel;
  • internal 2011 emails reveal that the NDA is concerned about increased proliferation risks from converting plutonium oxide powder into metal PRISM fuel: "This would introduce more security/proliferation risk."[9]; and
  • PRISMs will incorporate plutonium into spent fuel ... which begs the question: why separate plutonium from spent fuel in the first place?


PRISM economics

The NDA report states that GEH believes that PRISMs could be implemented "under commercial arrangements". But it's unclear what that means. GEH already has its hands out for funding from the US Export-Import Bank.

GE executive Mark Elborne says PRISMs could "provide significant revenue for UK taxpayers".[17] Again, it's not at all clear what that means. PRISMS could theoretically provide a more cost-effective means of partially addressing plutonium problems than other proposals, but it's unclear how they could be a money-spinner for UK tax-payers unless GEH propose donating profits from the sale of electricity to the UK government.

GEH executive Daniel Roderick claims that if given the go-ahead, GEH will form a consortium to build the PRISM plant at no up-front cost to the UK taxpayer, and that GEH "will only charge for each kilogram or tonne of plutonium we dispose of."[18] How long until either or both of those positions are reversed? Not so many years ago, the UK government insisted that new reactors would not be subsidised while EDF claimed that EPR reactors could produce electricity for £28.80 / MWh; last year the UK government agreed to guarantee EDF payment of over three times that amount along with other massive subsidies including a £10 billion loan guarantee.

GEH refuses to release estimates of PRISM capital and operating costs, saying they are "commercially sensitive".[19] Cheerleaders aren't so shy about offering implausible estimates for IFRs − for example Steve Kirsch says the "first one [1 GWe IFR] will probably cost around [US]$1 to $2 billion".[20]

[1] UK Nuclear Decommissioning Authority, January 2014, 'Progress on approaches to the management of separated plutonium – Position Paper',
[2] Royal Society, Oct 2011, 'Fuel Cycle Stewardship in a Nuclear Renaissance',
[3] Steve Kidd, 11 May 2004, "Achilles heel or own goal?", Nuclear Engineering International,
[4] Fissile Materials Working Group, 6 May 2013, 'How do you solve a problem like plutonium?',
[5] Fiona Harvey, 3 August 2011, 'Sellafield Mox nuclear fuel plant to close',
[9] Rob Edwards, 24 Jan 2012, 'Plans for Sellafield plutonium reactor rejected',
[10] Mark Lynas, 1 March 2012, 'UK moves a step closer to nuclear waste solution',
[11] 'Disposal of UK plutonium stocks with a climate change focus',
[13] Stuart Nathan, 13 May 2013, 'Prism project: A proposal for the UK's problem plutonium',
[14] George Monbiot, 2 Feb 2012, 'We cannot wish Britain's nuclear waste away',
[15] GEH, 'Public Comments on PRISM',
[16] A Letter to David Cameron, 15 March 2012,
[17] 20 Jan 2014,
[18] Steve Connor, 2 April 2012, 'Plans to build a nuclear fast reactor at Sellafield come a step closer',

(Written by Nuclear Monitor editor Jim Green.)