Programmes for the recycling of plutonium were developed in the 1970s when it appeared that uranium would be in scarce supply and would become increasingly expensive. It was originally proposed that plutonium would be recycled through fast breeder reactors, that is, reactors with a uranium ‘blanket’ but which would produce slightly more plutonium than they consume. Thus it was envisaged that the world’s ‘low cost’ uranium resources, then estimated to be sufficient for only 50 years’ consumption, could be extended for hundreds of years.
As things transpired, the pressure on uranium resources was very much less than expected and prices remained low in the period up to 2003. This was caused by the discovery of several new extensive and low-cost uranium deposits, the entry onto the world market of large quantities of uranium from the dismantling of nuclear weapons and the slower growth of nuclear power than was expected back in the 1970s. There became little incentive to develop fast breeder reactors, particularly as these present major engineering challenges, which could prove expensive to resolve. Nevertheless, since the late 1970s, around 30% of spent fuel arisings from commercial nuclear reactors outside the former Soviet Union and its satellite states have been covered by reprocessing contracts with plants in France and the UK. Without fast breeder reactors, there has been an accumulation of separated plutonium stockpiles.
Mixed oxide (MOX) fuel was introduced mainly to reduce the stockpiles of plutonium, which were building up as spent fuel reprocessing contracts were fulfilled. MOX was therefore an expedient solution to a perceived problem, which had been created by changed circumstances. The MOX programmes have demonstrated that plutonium has some advantages as a nuclear fuel and so the stockpiles have economic value. The MOX era, however, may pass relatively quickly, even if plutonium stockpiles worldwide are not substantially reduced. Revived interest in nuclear power in the 21st Century, as a clean air solution which contributes to world sustainable development, is encouraging the development of new materials and technologies. In addition, the substantial rise in uranium prices since 2003 and the difficulties with commissioning waste repositories have prompted the beginning of a revaluation of recycling.
Currently 12 of the countries with nuclear energy programmes are committed to a closed nuclear fuel cycle but there are signs that the number will soon increase. In particular, the USA is reassessing its previous policy, set strongly against reprocessing with subsequent recycling of recovered materials. The decision to introduce MOX fuel from ex-weapons plutonium in civil reactors was an important factor in that country’s change of policy and the first assemblies are now in use in reactors operated by Duke Power. In November 2005 the American Nuclear Society released a position statement saying that it “believes that the development and deployment of advanced nuclear reactors based on fast neutron fission technology is important to the sustainability, reliability and security of the world’s long-term energy supply.” This will enable “extending by a hundred-fold the amount of energy extracted from the same amount of mined uranium.” The statement envisages onsite reprocessing of used fuel from fast reactors and says that “virtually all long-lived heavy elements are eliminated during fast reactor operation, leaving a small amount of fission product waste which requires assured isolation from the environment for less than 500 years.”
The Global Nuclear Energy Partnership (GNEP) programme, announced by the US Department of Energy in early 2006, fits in closely with this. A major issue addressed is the efficiency of the current nuclear fuel cycle. The ‘once through’ cycle only uses part of the potential energy in the fuel, while effectively wasting substantial amounts of useable energy that could be tapped through recycling. While European countries and Japan have recycled some of the residual uranium and plutonium recovered from the spent fuel in light water reactors through MOX utilisation, no one has yet employed a comprehensive technology that includes full actinide recycle. In the USA this question is pressing since significant amounts of used nuclear fuel are stored in different locations around the country awaiting shipment to the planned geological repository at Yucca Mountain in Nevada. This project is much-delayed, and in any case will fill very rapidly if it is used simply for used fuel rather than the separated wastes after reprocessing.
An early priority in GNEP is therefore the development of new reprocessing technologies to enable recycling of most of the used fuel. One of the concerns when reprocessing used nuclear fuel is ensuring that elements separated are not used to create a weapon. The Purex process, used in all existing reprocessing plants, has been employed for over half a century and has resulted in the accumulation of 240 tonnes of separated reactor-grade plutonium around the world (though some has been used in MOX). While this is not viable for weapons use, it is no longer seen as appropriate and future reprocessing will result in the plutonium being combined with some uranium and possibly with minor actinides. GNEP creates a framework where states that currently employ reprocessing technologies can collaborate to design and deploy advanced separations and fuel fabrication techniques that do not result in the accumulation of separated pure plutonium.
The once through cycle only uses part of the potential energy in the fuel, while effectively wasting substantial amounts of useable energy
Several developments of Purex which fit the GNEP concept are being trialled in different countries, notably Urex+ in the USA and Coex in France. The latter separates uranium and plutonium (and possibly neptunium) together as well as a pure uranium stream, leaving other minor actinides with the fission products. The central feature of these variants is to keep the plutonium either with some uranium or with other transuranics which can be destroyed by burning in a fast neutron reactor – the plutonium being the main fuel constituent. Trials of some fuels arising from Urex+ reprocessing in the USA are being undertaken in the French Phenix fast reactor.
The second main technological development envisaged under GNEP is the advanced recycling reactor – basically a fast reactor capable of burning minor actinides. Thus used fuel from light water reactors would be reprocessed at a recycling centre and the transuranic product transferred to a fast reactor onsite, which both produces electricity at a capacity of perhaps 1000MWe and incinerates the actinides. A key objective of this programme is to obtain design certification of a standard fast reactor from the US Nuclear Regulatory Commission. Related to this, nearly all the new reactor models being developed under the Generation IV and the International Project on Innovative Nuclear Reactors and Fuel Cycles (Inpro) projects have closed fuel cycles recycling all the actinides. Although part of the motivation remains making savings in the use of the (now more expensive again) natural uranium resource, the key today is saving on used fuel arisings and developing ways to deal with the existing volumes of used fuel created by commercial nuclear power to date.
Looking at the more immediate term, Electricité de France (EdF) will continue to send for reprocessing 850 tonnes of its 1,200 tonnes of used fuel discharged each year. The remainder is preserved for later reprocessing to provide the plutonium required for the startup of Generation IV reactors, the prototype of which is envisaged by 2020. In Japan, the Rokkasho-mura reprocessing plant should be commissioned soon. European reprocessing of Japanese used fuel ended in 2005 and it is envisaged that 16-18 reactors will eventually be loaded with MOX fuel. Aomori prefecture in 2005 also approved construction of a MOX fuel fabrication facility but this is not expected to open until 2012 at the earliest – until then, fabrication of MOX for Japan will take place in Europe.
In the UK, the plant reprocessing Magnox fuel will close in 2012, following the permanent shutdown of all the reactors it serves and there continue to be uncertainties surrounding the future of the Thorp reprocessing plant and the associated MOX fuel fabrication facility. Nevertheless, the UK has a substantial inventory of both separated reactor-grade plutonium (over 100 tonnes) and a substantial amount (about 60,000 tonnes) of depleted uranium. This could form the foundation of an advanced reactor programme but a Royal Society report in September 2007 recommended that the plutonium be used in MOX fuel. This will depend on persuading reactor operators in the UK (including those running any new reactors) to adopt this as a fuelling strategy – it is by no means certain that they will. Russia may eventually achieve its stated aim of closing its fuel cycle, although it has so far achieved very little in this direction. Plans for expanding the Mayak reprocessing facility or building a second plant, as well as a fuel fabrication facility, have so far come to nought, but the revival in the Russian nuclear industry and its interest in playing a similar role to what the USA envisages for itself in GNEP, suggest that there will soon be some new developments.
Finally, the strong upward movement in uranium prices suggests that utilities owning inventories of reprocessed uranium (RepU) will look once again at utilising these. The greater expense at the conversion and enrichment stages may now be outweighed by the substantially increased prices for fresh fuel. EdF is at centre stage here, owning significant quantities of RepU as a strategic asset. A few years ago, these could fairly be viewed on the other side of the balance sheet, as a long-term liability, but such an assessment is now outdated. Certainly many European utilities (and maybe also some in the USA) are looking at RepU in a new light and possibly seeking to add to those who have already gone down this road (albeit in relatively small quantities).
To summarise, it seems clear that recycling remains a very live issue in the nuclear sector, indeed with an apparent push from several quarters to pursue it more vigorously in the future. Used fuel management is a huge and still growing business and options are being sought that hit a variety of requirements, certainly not merely economic but also considering environmental, resource sustainability and non-proliferation objectives.
Steve Kidd is Head of Strategy & Research at the World Nuclear Association, where he has worked since 1995 (when it was the Uranium Institute). Any views expressed are not necessarily those of the World Nuclear Association and/or its membersRelated ArticlesUK government supports nuclear again First step of UK design assessments