CORDIS provides links to public deliverables and publications of HORIZON projects.
Links to deliverables and publications from FP7 projects, as well as links to some specific result types such as dataset and software, are dynamically retrieved from OpenAIRE .
Deliverables
The operation of nuclear fission reactors gives rise to long-lived radionuclides, which may be considered a potential risk born by future generations that must be minimized. To achieve this goal, these radionuclides can be transmuted by neutron irradiation in fast burner reactors or in dedicated reactors such as accelerator-driven systems (ADS). The spent fuel and/or targets from these reactors could be processed by pyrochemical methods. An other possibility would be to immobilize the separated radionuclides in specific high durability matrixes before geological disposal.
PYROREP is a R & D program aiming to:
- Determine the practicalities of separating uranium, plutonium and minor actinides from FP using pyrochemistry in a molten chloride or fluoride system.
- Obtain basic data to allow conceptual design and assessment of reprocessing processes suitable for fuels and targets
- Consolidate and revive European expertise in pyroprocessing
Within the scope of the PYROREP contract, substantial progress was made by the project working teams. Many basic data values concerning the behaviour of fission products and actinides (U, Pu and Am) in molten salts and metals were measured for first time or confirmed in both fluoride and chloride media. It would be logical to continue this work notably by acquiring basic data first on curium and subsequently, if technically feasible, on the transcurium nuclides. These elements are not found in substantial quantities in spent fuel today, but the their presence will tend to increase appreciably as the actinides become subject to multiple recycling in MOX fuel or in double-component or doublestrata burner systems.
The main R&D focus of the PYROREP contract was on the separation step, which represents the core of the future pyrochemical separation process(es). In fluoride media, the investigation of reductive salt/metal extraction yielded very promising results for both An recovery and FP decontamination yields. For electrolytic processes in chloride media it has been shown that, from the strict standpoint of actinide/lanthanide separation, an aluminium cathode would provide better results than a cadmium cathode, although the latter could be used if it is not indispensable to recover and separate the actinides from the lanthanides with very high efficiency. Conversely, recovering the separated actinides from an aluminium cathode appears to be more difficult than for a liquid cadmium cathode, which can easily be evaporated. Development work should be carried out on the use of an aluminium cathode to take advantage of these potentially interesting results.
The data acquired to date are sufficient to begin designing and quantifying preliminary schemes for reprocessing processes. From the standpoint of a fuel cycle policy based on Partitioning and Transmutation (P&T), effective implementation will require not only a very high actinide recovery factor (typically 99.9%) but also sufficient FP decontamination to recycle less than 5% of the initial negative reactivity of the FP with the actinides. This criterion should also be confirmed and/or qualified by taking into account not only the neutronic criterion but also the FP content recycled in the burner system and the risk of creating a hold up loop for some FP in the cycle. The system studies clearly show that the required performance cannot be obtained by a single separation stage. In each case at least two and perhaps three separation stages based on different separation principles must be implemented (electro refining plus reductive salt/metal extraction in one case, or volatilisation of some FP in a reducing medium followed by digestion of noble metals by a metal phase and reductive extraction in the second case). It is still necessary to demonstrate experimentally by combining all these process steps that the announced performance can be achieved.
An/FP separation, which constitutes the core of the process, will probably be applied to a variety of different fuels (oxide, metal, nitride, carbide, or molten fluoride) and should therefore logically be the primary focus of attention. However, An/FP separation must be preceded and followed by equally important steps designed to dissolve the elements in the molten salt upstream, and to recover the finished products downstream. These steps depend to a greater extent on the nature and type of the fuel, and must be investigated in greater detail in the future as the fuel specifications are defined.
Pyrochemical processes generate metal and salt waste flows of a substantially different nature than the waste currently produced by aqueous processes. A major effort will be necessary in the future to optimise the management routes for this waste-particularly for chlorinated salt waste, which is incompatible with the glass matrices used today-either by dechlorination or by developing dedicated containment matrices such as sodalites.
Unlike enhanced aqueous reprocessing processes that can be implemented with technology comparable to that used in today's reprocessing plants, the deployment of pyrochemical processes would require considerable technological R&D that must be undertaken as soon as the fuel specification for the future systems is sufficiently defined. Today the effort could focus on developing the continuous salt/metal contactors that will be necessary regardless of the type of fuel and the separation technique finally adopted.
It is also clear that pyrochemistry R&D efforts should be better coordinated in each European country to make the best use of the available human and material resources. The PYROREP contract has made an initial contribution toward this objective by pooling the research teams and creating a community of researchers who-even if their strategic objectives differ-have acquired together and now share a common wealth of knowledge in this area. From this standpoint it will be essential in the future to facilitate and encourage contacts and exchanges between teams of researchers. Independently of the very large quantity of scientific results obtained during the three-year work program, an important additional benefit of this contract has been for different research groups to interact and exchange their experience. The project has been a vehicle for interaction among the persons involved and has led to increased knowledge and skills in handling molten salts and radioactive materials.
In the contract, five partners (BNFL, ITU, CRIEPI, CIEMAT and ENEA) are working on the basis of the process developed in Argone DOE laboratories i.e electrorefining in LiCl-KCl. CRIEPI associated with JRC ITU carry out in Karlsruhe experiments on a small-scale installation for the demonstration of pyrometallurgical reprocessing. This year electrorefining experiments have been carried out using the individual metals (uranium and plutonium) as anode but recently also using uranium, plutonium, zirconium alloy.
Other experiments are focussed on the difficult separation of MA from Ln´s, by means of electrolysis.
Before Am studies, inactive experiments in molten LiCl-KCl eutectic have been conducted. For lanthanum, neodymium and americium elements, a combination of transient electrochemical techniques (cyclic voltammetry, chronopotentiometry and square wave voltammetry) have been applied in order to investigate valency and reduction mechanisms with the aim of optimising the conditions for an efficient separation of Am by electrolysis. These investigations have been followed by, electrodeposition tests of La, Nd and Am on solid and liquid Cd cathodes. BNFL associated with AEA-T is working on the same process and focused on the controlling parameters of the electro-refining; they have already performed U transport and deposit onto solid and liquid cathode. ENEA, which has less experience in this field than the other laboratories, started designing and building an experimental electro-refiner with the final objective to study thorium behaviour in the electrochemical process. At the end of the first year project, some adjustments of the project schedule due to an internal reorganisation of the ENEA pyrochemical team have been necessary. To date, the main parts of the apparatus are being built and they be fitted together. The apparatus will be checked from the outset of 2002. CIEMAT associated with UVA carried out experiments aimed at analysing and predicting the kinetic behaviour of lanthanide elements, which are the most difficult fission products to separate from actinides due to their similar chemical properties in LiCl-KCl.
Studies were carried out to determine La, Ce, Pr, Y and Nd thermodynamic properties and to obtain the electrochemical deposition mechanisms of La, Ce and Nd. In parallel CIEMAT also focused on determining the stability of the compounds formed and the reaction rates when direct chlorination from the oxide form is performed. Fundamental data acquisition in the eutectic LiCl-KCl at 4500C is one of the main aims of this study.
In this way, chemical stability of the rare earth (i.e. La, Ce, Y,) trichlorides, and their oxide compounds in the eutectic LiCl-KCl at 4500C has been determined. Studies on the chemical stability of praseodymium and neodymium chlorides and their oxide compounds are in progress. Preliminary experiments on UO2 chlorination were performed by several chlorinating gaseous mixtures (HCl, Cl2, Cl2+C tube and powder) in order to establish the experimental conditions of SIMFUEL matrix chlorination. ENEA associated with CEA focus on the study of one possible candidate matrix for the contaminated used LiCl/KCl salt. As glass currently used in reprocessing is not adapted to high contain chloride wastes, sodalite (Na8[(Al6Si6O24)] Cl2) in which some Na atoms could be exchanged by other alkaline atoms has been proposed. The aims of this study is for ENEA, to synthesise sodalite, assess exchange capability of Na atoms with other fission products atoms and for CEA carried out some standard leaching tests in order to estimate this matrix performance.
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