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Plutonium disposition in the United Kingdom - Immobilization option re-opened?

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Martin Forwood with Mycle Schneider

The case for re-using the UK's separated plutonium in nuclear reactors looks less secure than previous official pronouncements would suggest. The U.K.'s stockpile is estimated by the Nuclear Decommissioning Authority (NDA) to have reached 140 tons by the time reprocessing operations at Sellafield are completed around 2020. 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. Clarifying some detail of the review in a subsequent email to local group CORE (Cumbrians Opposed to a Radioactive Environment), the NDA responded:

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. (emphasis added).

Until now, research on the immobilization option has been specifically targeted at the treatment of the small proportion of stockpiled plutonium termed as "residues" and considered through chemical contamination to be beyond re-use. The research is funded by the NDA and carried out by the National Nuclear Laboratory (NNL) in Workington, north of Sellafield, in collaboration with the Australian Nuclear Science and Technology Organisation (ANSTO). The residues are estimated by the NDA in tens of kilograms rather than tons. The NNL is quoting about 100 kilograms of residues and that it was looking at purer plutonium and not just waste. The conditioned plutonium waste would be stored until final disposal in a geological repository.

The current revelation that, should the Government change its mind, immobilization might be used to dispose of the entire stockpile is the latest hint that the re-use of plutonium as plutonium-uranium Mixed Oxide (MOX) fuel in the UK is not yet irrevocably cast in stone. Following its public consultation on the management of UK plutonium, the Government concluded on the December 1st, 2011 that of the three high level plutonium management options (re-use, immobilization or indefinite storage) identified earlier through a suite of NDA consultations, plutonium re-use was its "preferred option". That option continues to be officially advocated today.

Yet signs of a wavering commitment to the re-use as MOX option surfaced in February 2012--just eight weeks after the Government had announced its preferred option--when the NDA took the somewhat mystifying step of inviting nuclear third parties to submit "additional alternatives" to the re-use as MOX option. Whether or not the Authority had even at that stage been "spooked" by some aspect of the option's deployment in the UK remains to be seen but the invitation clearly begs the question as to why the NDA needed to cast its net for other ideas so soon after providing the original advice on which the Government based its preference.

The invitation drew responses from GE Hitachi and from CANDU Energy, the former proposing the deployment at Sellafield over a 60-year period of its PRISM reactor as part of an integral fuel fabrication/reactor plant solution for Plutonium disposition, and the latter proposing the deployment of its Enhanced CANDU 6 (EC6) reactor and associated facilities to provide a solution for plutonium disposition. However, both reactor designs so far exist only on paper.

A progress update on both proposals, published by the NDA in January 2014, noted that

currently, we believe there is insufficient understanding of the options to confidently move into implementation and consider that significant further work must be undertaken, focusing on technical and commercial risks and uncertainties, to enable DECC and UK Government to ultimately select and subsequently implement its preferred reuse option.

The time needed for this further work was estimated at between 1-2 years. The same update also revealed further doubt on the commitment to the re-use as MOX option by the NDA who had been keeping an eagle eye on the "significant cost increases and schedule overruns" at the U.S.DOE's MOX Fuel Fabrication Facility project at Savannah River--the development of which "affects NDA confidence in the predictability of implementation and costs of reuse as MOX". The continuing escalation of costs and increasing delays to the Savannah River project is unlikely to bolster NDA confidence levels.

The immobilization option currently being funded by the NDA and researched by the National Nuclear Laboratory (NNL) is the Hot Isostatic Pressing (HIP) process which, under high pressure and temperature, converts the plutonium into a ceramic waste form suitable for long-term storage and ultimate disposal. Though the HIP process for Sellafield's residues has taken preference to other immobilization technologies including immobilization in cement-based grouts, as glass via vitrification or as a ceramic in "low specification" MOX, the NDA's Plutonium Credible Options Analysis (Gate A) published in 2010 concludes that whilst the HIP process is technically immature for large scale bulk plutonium, it requires less development and is economically more favorable than the vitrification option.

A pilot plant for the immobilization of plutonium residues at NNL's central laboratory at Sellafield is expected to start active commissioning in 2017. The process is described by NNL as "a powerful emerging technology that offers a route for the immobilisation of orphan waste streams and also has the potential to meet wasteform requirements for future nuclear fuel cycles".

Flagged up for spring this year, a Government policy announcement on plutonium management never materialized and there is currently no indication as to when such an announcement will now be made. No date has been provided for the completion of the Regulators' review of the immobilization option.

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