Roger Boen

Test of actinide-lanthanide separation in an aluminum-based pyrochemical system

Abstract The investigation of the actinide and lanthanide distribution between a liquid metal and a molten fluoride salt shows a significant increase of the separation coefficient by using an aluminum-based pyrochemical system instead of a zinc-based system. The obtained values partly depend on the LiF/AlF3 ratio and can reach more than 30 000 when AlF3 is in excess with regard to the formation of the cryolite (Li3 AlF6). Furthermore, in the metal phase, the aluminum interacts with the lanthanides to a lesser extent than in other usual metallic solvents. This opens a new way to explore the feasibility of the separation of actinides and lanthanides in the field of nuclear fuel reprocessing.

Phosphorus : in situ treatment for ZnCl2 formed by incineration of organic waste

Abstract An incineration process has been developed in France for alpha-bearing radioactive organic waste. Such wastes contain polyvinyl chlorides and are rich in chlorine. They also contain zinc from neoprene and latex. Zinc chloride forms during incineration. At the combustion temperature, this gaseous compound is entrained with the smoke and recondenses during off-gas cooling. Depending on the incinerated waste composition, it may account for up to quasi totality of the particle matter recovered on the filters. Zinc chloride is hygroscopic at room temperature and is highly corrosive in contact with metals when hydrated. This implies that the facility must be maintained at a temperature of 200°C at all times. As a secondary waste material, the ZnCl 2 must be stored in dry conditions, and eventually requires a specific containment or decontamination treatment. It is advantageous to inhibit the production of zinc chloride by favoring the formation of a more stable compound: zinc phosphate. A thermodynamic study of the stability of zinc phosphate with respect to zinc chloride showed that any excess P 2 O 5 over the stoichiometric fraction was sufficient to shift the equilibrium completely toward the phosphate side. This suggests that lowering the temperature also favors zinc phosphatation. Incineration tests were carried out with phosphorus in the waste material, either by increasing the quantity of waste containing P, or by using a phosphorus additive. The tests conclusively validated the thermodynamic study and showed that the phosphatation reaction was not limited by the kinetics. Other applications of phosphorus treatment could be envisaged: phosphatation of radionuclides which have highly volatile chlorides such as cesium chloride and phosphatation of heavy elements whose formation of chloride during incineration of domestic waste raises disposal problems.

Modeling and estimating the distribution of trivalent actinides and lanthanides between molten fluorides and liquid metal

Abstract Separation of actinides and lanthanides between a fluorinated phase rich in LiF and a metallic phase showed that the deviation ( E ) between the theoretical and experimental results for the trivalent actinides and lanthanides can be described using a relative ionic potential Δ PI between Li + and the cations An 3+ or Ln 3+ , such that for each of the two groups E = α Δ PI + β , where α is temperature-dependent and β varies with the nature of the system. The results obtained in the MSBR development program were analyzed to determine α at various temperatures for both series of elements, and to propose expressions for Δ G ° f (AnF 3 ) versus temperature in the liquid phase (where An represents Np, Am, Cm or Cf). E was measured for U(III) and La(III) in the LiF–CaF 2 /Zn–Mg system at 720°C, and an empirical model was developed to simulate the distribution of all the trivalent actinides and lanthanides in the same system.