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Plasmochemical Production of MOX Fuel

#1416


Mixed Oxide Fuel (MOX) -Born in Plasma

Tech Area / Field

  • FIR-FUE/Reactor Fuels and Fuel Engineering/Fission Reactors

Status
3 Approved without Funding

Registration date
30.11.1998

Leading Institute
VNIIKhT (Chemical Technology), Russia, Moscow

Supporting institutes

  • Siberian Chemical Combine, Russia, Tomsk reg., Seversk

Collaborators

  • Ecoprogress International, Belgium, Brussels\nCOGEMA, France, Velizy\nLockheed Martin Corporation / Bechtel BWXT Idaho / Idaho National Engineering Laboratory, USA, ID, Idaho Falls\nBelgonucléaire, Belgium, Brussels

Project summary

Reprocessing of ex-weapon Pu has an international importance.

Major object: reprocessing of plutonium, originally produced for nuclear weapons, to the mixed UO2/PuO2 - fuel intended for production of fuel elements for the fast and thermal neutron reactors.

The proposed here plasma technique saves uranium and utilize the weapon plutonium. Plutonium concentration in the mixed oxide is in the range from 5 to 30 mass. %, depending on technical requirements.

A principal specialty of the plasma chemical synthesis of metal oxides is very fast and efficient decomposition of the feed solution. High enthalpy of the dispersed stream allows to develop a high-productivity technique for synthesis of pure uranium oxides and mixed oxides. A small-size plasma converter of continuous regime meets principal nuclear safety requirements. Liquid wastes after reprocessing of concentrated feed solutions (condensate) have rather negligible volume and can be easily utilized or recycled to prepare the input feed solution.

Plasma chemical technique allows to depart from an additional reduction stage before pressing of wet pellets; a “solid” U(Pu)O2+x -solution is formed immediately in the reactor. The plasma reprocessing cuts a number of production operations; all solid wastes are easily soluble in nitric acid and then recycled.

The pre-treated feed solution of a determined composition is dispersed by a sprayer into the air plasma stream at 4000-5000 K. The solution drops are heated rapidly (for 0.001-0.01 s) to a solvent evaporation and to decomposition of the solid residue forming finely pided (less than 3 m) powdery oxides. After the plasma reactor a resulted powdery-gaseous mixture (T = 800 K) are separated using centrifugal separators and filters. A gas flow after separation comes to the condenser and then to the absorber, for total absorbing nitrogen oxides.

The plasmachemical powders - due to ultra-fine dispersion and high specific surface of the particles - have very high chemical activity and require relatively low sintering temperature.

This technique has to be demonstrated at the Siberian Chemical Combine (Seversk, RUSSIA). The proposed here approach has no analogue over the world.

The project compiles a system of R&D works: development of a mathematical model, study of plasma de-nitration kinetics, optimization of technical parameters of the process, determination of physical and mechanical properties of powdery oxides, designing of equipment, etc. Major task of the project is a development of technology for synthesis the MOX-fuel (5-30 mass % of Pu) applicable for pellets production with density of 10.7-10.8 g/cm3 and nitric acid solution.

TECHNICAL APPROACH AND METHODOLOGY

Different competitive techniques for production of fine-dispersed powdery materials (e.g., oxides of less-common metals), based upon a decomposition of the appropriate salts (and solutions) were mentioned and briefly discussed earlier: ammoniac or carbonate co-precipitation; oxalate precipitation; sol/gel process; electrochemical precipitation; mechanical mixing, and cryogenic technique.

However, all mentioned here approaches have very principal imperfections:


· Big amount of the waste nitrates;
· Work operations with dusting and high dangerous plutonium materials;
· Periodical regime of the process;
· Non-homogeneity of final mixed oxides.

To approve an integrity and efficiency of the plasma chemical approach for production of homogeneous oxide powder (de-nitration nitric acid U/Pu – solutions), below the general process is analyzed in some details. The general scheme of plasma de-nitration of the mixed U/Pu nitrate was determined taking into account the results of preliminary experiments in the ARRICT and SCC. The basic results are summarized below:

The mixed U-Pu (5-30%) nitrate may be completely converted by to homogeneous UO2-PuO2 powder and nitric acid using an air plasma torch.

The interaction of the injected feed solution with plasma torch has three main stages. At first stage the drops are heated up to the boiling point and partially dried; the second stage is the complete water evaporation; and finally - overheating and decomposition of the salt residual. Detailed analysis of all mentioned above stages has shown that the most important and complicated operation is the solvent evaporation Additionally, this process is very power-consuming - especially for diluted solutions, and affect the quality of the final oxide.

The plasma reprocessing is practically wasteless technique: U and Pu nitrates completely convert to the powdery oxides.

The heart of the nuclear-safe plasma converter is the plasma chemical reactor supplied by a high-frequency inducting (HFI) plasma generator. Real size and other parameters of a bench-scale converter will be determined using mathematical and physical modelling of the process and appropriate software.

Basic technological characteristics of the plasma chemical reactor:


- productivity – MOX, kg per hour Up to 4
- electrical power of HFI plasma torch (PT), kW Up to 50
- mean mass temperature of air plasma, K Up to 4500
- feed solution consumption, kg/s 0,015-0,23
- total concentration in feed solution, g/l Up to 500
- pressure inside reactor, atm 0.8

EXPECTED RESULTS

The main technical task of the Project is the development the MOX-fuel production process using plasma technique. The aim product, containing Pu in the range from 5% to 30%, must be suitable for production the pellets of density 10.40-10.85 g/cm3. The by-product - nitric acid solution – may be easily used in chemical industry.

The work will be completed with a testing of the designed and installed bench plant, and a demonstration of the developed technological process in the SCC. The appropriate recommendations for the commercial application of the obtained results will be provided.

Final results may be shared with another companies on a commercial base.


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