Reprocessing used fuel: devil or saint?

25 February 2008

The advantages and disadvantages of used nuclear fuel reprocessing have been debated since the dawn of the nuclear era. There is a range of issues involved, notably the sound management of wastes, the conservation of resources, economics, hazards of radioactive materials and potential proliferation of nuclear weapons. Sifting through these is not easy, with strong counter-claims made by opposing parties, but it is undoubtedly true that in recent years, the reprocessing advocates appear to be winning once again, perhaps most clearly demonstrated by the apparent change in position of the USA under the Global Nuclear Energy Partnership (GNEP) programme.

To begin with, it’s important conceptually to distinguish reprocessing from recycling. Reprocessing is stage one – the separation of uranium and plutonium out of used fuel and conditioning of the remaining material as waste. Fuel assemblies removed from a reactor are very radioactive and produce heat, so are cooled (mostly at the reactor site or otherwise at a central storage facility or at the reprocessing plant) for a number of years as the level of radioactivity decreases considerably. For most types of fuel, reprocessing occurs anything from 5 to 25 years after reactor discharge. Recycling is then stage two – the use of the uranium and plutonium from the reprocessing plant, which can be either as mixed oxide (MOX) fuel or reprocessed uranium (RepU) fuel in current reactors or as fuel for future Generation IV reactors. Reprocessing effectively sets up the possibility of recycling. This doesn’t necessarily have to follow, but in practice, the two stages are bound together as reprocessing will likely only be undertaken with a view to eventual recycling.

Although world uranium resources are extensive, many people do not them see them alone as a lasting solution to world energy needs. If nuclear power expands rapidly, the quantity of uranium mined and processed each year may have to rise from the current 40,000 tonnes per annum, to 100,000 tonnes and beyond. The management of nuclear waste remains one of the main concerns of the public and could also constrain the future expansion of nuclear. For nuclear power to be seen as sustainable, it is important that natural uranium resources are conserved as much as possible and that wastes are managed in a safe and durable way. Reprocessing arguably contributes to sound stewardship of uranium resources by allowing the recycling of reusable materials, which introduced as MOX fuel and RepU can save around one quarter of uranium needs. It also minimises high-level waste toxicity and volume; after treatment, the level of toxicity is only one tenth of what it was and its volume down to one fifth. The wastes can be conditioned into a passive form that will be safely stored pending final disposal. The scientific and technical community generally feels confident that there already exist technical solutions to such used fuel and nuclear waste conditioning and disposal, with a wide consensus on the safety and benefits of geological disposal.

A great deal of reprocessing has been going on since the 1940s, originally for military purposes, to recover plutonium for weapons (from low burnup used fuel, which has been in a reactor for only a very few months). So far, some 80,000 tonnes (of 280,000 tonnes discharged) of used fuel from commercial power reactors has been reprocessed.

In the UK, metal fuel elements from the first generation gas-cooled commercial reactors (Magnox) have been reprocessed at Sellafield for about 50 years. The 1500 tonnes per year (t/y) plant has been successfully developed to keep abreast of evolving safety, hygiene and other regulatory standards. Some 15,000 tonnes of RepU from Magnox reactors has been used for enriched Advanced Gas-cooled Reactor (AGR) fuel. From 1969 to 1973, oxide fuels were also reprocessed, using part of the plant modified for the purpose. A new 900t/y thermal oxide reprocessing plant (Thorp) was commissioned in 1994 and the corresponding MOX fuel plant in 2001, namely the Sellafield MOX Plant.

In France one 400 tonne per year reprocessing plant is operating for metal fuels from gas-cooled reactors at Marcoule. More significantly, however, at La Hague, reprocessing of oxide fuels has been carried out since 1976, and two 800t/y plants are now operating, while there is also the Melox MOX fuel fabrication facility. Currently, the reprocessing of 1150 tonnes of Electricité de France used fuel per year produces 8.5 tonnes of plutonium (immediately recycled as MOX fuel) and 815 tonnes of RepU. EdF has demonstrated the use of RepU in its 900 MWe power plants, but it is has been uneconomic during the years of low uranium prices, due to conversion costing significantly more than for fresh uranium, and enrichment needing to be separate because of U-232 and U-236 impurities in the reprocessed fuel. Provision has been made, however, to store reprocessed RepU for up to 250 years as a strategic reserve.

Elsewhere in the world, India has a 100t/y oxide fuel plant operating at Tarapur, while Japan is currently commissioning a major (800t/y) plant at Rokkasho, having had most of its used fuel previously reprocessed in Europe at La Hague and Sellafield. Russia has a 400t/y oxide fuel reprocessing plant (Mayak) at Ozersk (Chelyabinsk). In the USA, no civil reprocessing plants are now operating, though three were originally built. The final one, at Barnwell in South Carolina, was closed in 1977, owing to a change in government policy, ruling out all civilian reprocessing as a facet of US non-proliferation policy.

Much of the opposition to reprocessing centres on a huge amount of hype about plutonium created by anti-nuclear forces. Talk of dependence on a ‘plutonium economy’, if nuclear power expands much further, is still common in their publications. Yet despite its ionising radiation and being chemically toxic, plutonium is far from being “the most toxic substance on Earth” or so hazardous that “a speck can kill”. On both counts there are substances in daily use that, per unit of mass, have equal or greater chemical toxicity (such as arsenic and cyanide) and also radiotoxicity (the plutonium decay product americium-241 used in smoke detectors).

Plutonium is one among many toxic materials that have to be handled with great care to minimise the associated but well understood risks. Thousands of people have worked with plutonium, with their health protected by the use of remote handling, protective clothing and extensive health monitoring procedures. The main threat to humans comes from inhalation, where it can be trapped and readily transferred, first to the blood or lymph system and later to other parts of the body, notably the liver and bones. It is here that the deposited plutonium's alpha radiation may eventually cause cancer. Nevertheless, the hazard is similar to that from any other alpha-emitting radionuclides that might be inhaled. It is less hazardous than those that are short-lived and hence more radioactive, such as the decay products of radon gas, which (albeit in low concentrations) are naturally common and widespread in the environment.

The other aspect of plutonium which raises the ire of nuclear opponents is its alleged proliferation risk. Opponents of the use of MOX fuels commonly state that such fuels represent a proliferation risk because the plutonium in the fuel is said to be ‘weapons-useable’. But MOX is a mixture of uranium and plutonium oxides, with the plutonium being very much in the minority. For light water reactor fuel, the plutonium content is typically around 5%. MOX cannot possibly be used in nuclear weapons or nuclear explosives. To separate the plutonium content from MOX fuel elements would be a major undertaking, similar to reprocessing.

In addition, there would be serious technical difficulties in attempting to make nuclear weapons from plutonium of the quality currently used for MOX and none of the countries possessing nuclear weapons has ever made weapons using plutonium of this quality. Rigorous International Atomic Energy Agency (IAEA) safeguards also apply to this material in non-nuclear-weapons states party to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). It is misleading to conclude, because this material is subject to safeguards, that it is therefore ‘weapons-useable’. The plutonium isotope most suitable for weapons use is Pu-239 and weapons comprise at least 92% (and usually more) of this. This plutonium is produced in dedicated plutonium production reactors, specially designed and operated to produce plutonium of this quality by removal and reprocessing of fuel after short irradiation times. The plutonium produced in the normal operation of light water reactors, from which MOX fuel is being made, has a substantial proportion of higher plutonium isotopes, so that it typically comprises less than 60% of Pu-239. The remainder contains a large proportion of isotopes which create serious technical difficulties for weapons use, namely Pu-238, Pu-240 and Pu-242.

Another criticism of reprocessing centres around the transportation of materials, notably the shipments of used fuel from Japan and other countries to the reprocessing facilities in France and the UK and the subsequent return of MOX fuel and high-level wastes. This is very much a special case of the difficulties of transporting any fissile materials today but, in reality, involves no greater risk to human health and to weapons proliferation. The sea shipments have been made by purpose-built vessels and involve special casks that have been subject to rigorous impact testing. The only risk to human life has come from the actions of protesters who have regarded the shipments as visible symbols of technologies with which they remain uncomfortable.

Finally, the reprocessing facilities themselves have come under attack through alleged risk to the local population through contamination of the air and of nearby beaches and the possible risk to people much further away by contamination of the sea. Studies have so far failed to show any conclusive risk to either the workforces or the local population – the leukaemia clusters found near Sellafield in UK have been explained by alternative causal factors. Both French and UK plants, however, have stringent targets for reducing the concentrations of radionuclides in the nearby seawater, although it is not accepted that the current or previous levels are in any way harmful to human health.

In summary, the reprocessing of used fuel should not give rise to any particular public concern and offers a number of potential benefits in terms of optimising both the use of natural resources and waste management. Whether it will become the generally accepted way of dealing with used nuclear fuel remains to be seen, as several major countries are still very much attached to a once through fuel cycle, with used fuel sent directly to a repository.

Author Info:

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 members

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