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Non-nuclear energy

EUROPART

Fission and radiation protection
Fusion
   

European Research Programme for the Partitioning of Minor Actinides

To manage their spent nuclear fuels, several European countries have chosen the closed fuel cycle involving fuel reprocessing to recover unused fuel elements. The resulting nuclear wastes, containing fission products and associated minor actinide elements, is vitrified. These vitrified nuclear wastes must be stored in safe, secure locations for extended periods of time. A preferred storage option is in deep geological repositories, but the selection of sites for these repositories must consider the fact that these vitrified wastes contain very long-lived radionuclides. In particular, the contribution of the small proportion of actinide elements in the wastes to its long-term radiotoxicity is significant. The elimination of these long-lived radionuclides from the vitrified wastes (partition) would dramatically decrease the long-term radiotoxicity of the nuclear wastes and could simplify the selection and operation of deep geological repository sites.


Investigating techniques and developing concepts

In Europe, a significant portion of the electricity supply is produced by nuclear reactors. Two strategies have been adopted in European countries to manage spent nuclear fuel. Either the fuel is disposed of directly in a deep underground disposal site – a strategy known as “open cycle”, or reprocessing of spent fuel is undertaken to recycle unused fuel elements, such as uranium and plutonium. In this latter case, known as the “closed cycle”, the resulting nuclear waste is composed of fission products and the minor actinides, principally the elements neptunium (Np), americium (Am) and curium (Cm). These highly active nuclear wastes are conditioned and sealed in a glass matrix and will be disposed of in deep underground disposal sites.

These wastes are highly radiotoxic and require storage for a very long period of time whilst they constitute a risk. However, that time period can be reduced considerably if the minor actinides are eliminated from the waste material during fuel reprocessing. For example, if minor actinides are eliminated from the vitrified wastes, the time required for storage could drop from ~15 000 years to around 250 years. EUROPART will investigate techniques for eliminating minor actinides from the waste material, known as partitioning, that could provide a useful strategy for the management of nuclear wastes. After separation, the minor actinides could be transformed into shorter-lived and/or less-toxic elements by nuclear means (known as transmutation), either in current reactor technologies or in special future reactors specifically designed for the purpose. This overall strategy is called partitioning and transmutation (P&T) and is attracting intense research efforts.

Evolution of the radiotoxicity of an UOX spent fuel (Courtesy: CEA)
(Courtesy: CEA)

Definition of methods and processes

The EUROPART project will define partitioning methods for the elimination of the minor actinides from the nuclear waste flows deriving from the reprocessing of real high-burn-up uranium oxide (UOX) or multi-recycled mixed oxide (MOX) spent fuel. It will also define partitioning methods for the corecycling of all the actinides contained in the spent nuclear fuels that could arise from future nuclear reactor designs such as those described as the so-called hybrid or generation IV reactors that will employ advanced dedicated fuel cycles or ADS (Accelerator Driven System) concepts.

Two principle research techniques have been selected as candidates for development of minor actinide partitioning processes. First, hydrometallurgy will use the high active aqueous effluents that are produced by the reprocessing of spent fuels using the PUREX process. These liquids contain all the nuclear wastes, i.e. fission products and the minor actinides, and will be processed either using the technique of solvent extraction or by extraction by chromatographic methods. This method will also be considered for the processing of wastes from the future designs of nuclear reactors. The second technique is pyrometallurgy where nuclear wastes coming from the reprocessing of actual or future nuclear spent fuels are dissolved in molten salts (either halides or fluorides) at elevated temperature (several hundreds of degrees centigrades), and then the separation of the minor actinides, or all the actinides, is tackled using several pyrometallurgical methods. These methods include electro-deposition as metals; liquid extraction using a molten metallic solvent; or selective precipitation as oxides.

Detailed chemistry and system design

In the hydrometallurgy area, the majority of the research focuses on the study of partitioning methods based on the use of solvent extraction methods with some work dedicated to the development of co-conversion methods for fuel or ADS target preparation. The research in pyrometallurgy will cover a variety of areas. The development of specific partitioning methods will be studied, including the study of the fundamental chemistry of trans-curium elements in molten salts. In addition, the conditioning of nuclear wastes will be looked at as well as studies on total system design.

A strong project management team will be concerned not only with the technical issues arising from EUROPART, but also with information and communication, science and society, gender issues. Training and education of the young researchers will also constitute an important part of the project. In particular, processes for possible industrialization of partitioning strategies will be defined.

Potential to greatly shorten duration of radioactive waste hazard

The management of nuclear waste is a complex but unavoidable issue. Long-term storage in deep geological disposal sites is a technically achievable and proven safe option for secure storage but has yet to gain pan-European approval from the majority of citizens. Partitioning, in concert with transmutation techniques, may help to gain approval by providing a waste material less radioactive that requires storage for dramatically shorter time periods – periods that are understandable and give a definable and relatively close end point.

Project website:
http://www.europart-project.org

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