A low-temperature synthesis method for AnO₂ nanocrystals (An = Th, U, Np, and Pu) and associate solid solutions

Abstract

Production of actinide oxide powder via dry thermal decomposition of corresponding oxalates is currently carried out on the industrial scale at temperatures exceeding 500°C. Although it is simple, this method presents some disadvantages such as high decomposition temperature with a direct effect on the surface area, pre-organised morphology of the nanoparticles affecting the sintering behaviour, etc. We have recently proposed the decomposition of An IV -oxalates under hot compressed water conditions as a straightforward way to produce reactive actinide oxide nanocrystals. This method could be easily applied at low temperatures (95-250°C) in order to generate highly crystalline nano-AnO 2 . We present here the formation conditions of AnO 2 (An = Th, U, Np, and Pu) and some associated solid solutions, their stability, and grain growth during thermal treatment. The involvement of water molecules in the mechanism of the oxalate decomposition under the hot compressed water conditions has been demonstrated by an isotopic exchange reaction during the thermal treatment of the hydrated oxalate in H 2 ij 17 O] through MAS-NMR and Raman techniques. CrystEngComm, 2018, 20, 4614-4622 This journal is |

Kinetic study on the grain growth of PuO2 nanocrystals

“…The nanocrystalline PuO 2 powder used in this study has been synthesised using the newly implemented oxalate decomposition method in hot compressed water. [8][9][10] In short, a 0.8 molar (M) Pu IV solution in 4 M HNO 3 has been directly precipitated with oxalic acid (10% excess) as Pu(C 2 O 4 ) 2 $6H 2 O. The precipitate was washed several times with distilled water in order to remove any trace of nitrate and 100 mg Pu-oxalate hexahydrate were placed in a 10 ml Teon reactor together with 5 ml distilled water.…”

“…[1][2][3][4][5][6] More recently the actinide oxalates were used as the starting material for the synthesis of actinide dioxide nanopowders via thermal treatment. [7][8][9][10] The oxalate route offers several advantages: it is oen applied in the nuclear fuel cycle and therefore is state of the art in separation, 11 recycling of the actinide ions, 12 fuel production 13 or the reprocessing of spent fuel. 14,15 The main differences between the wet and the dry oxalate decomposition are the lower temperature and the formation of spherical particles for the wet oxalate decomposition, [8][9][10] whereas the powders resulting from the dry decomposition maintain the platelet shape of the original oxalate.…”

“…[7][8][9][10] The oxalate route offers several advantages: it is oen applied in the nuclear fuel cycle and therefore is state of the art in separation, 11 recycling of the actinide ions, 12 fuel production 13 or the reprocessing of spent fuel. 14,15 The main differences between the wet and the dry oxalate decomposition are the lower temperature and the formation of spherical particles for the wet oxalate decomposition, [8][9][10] whereas the powders resulting from the dry decomposition maintain the platelet shape of the original oxalate. 7 The bulk modulus of spherical UO 2 nano-particles obtained by thermal decomposition of inorganic media 2 was measured to be 50% lower compared to the bulk.…”

Advancing the Production Routes of Nanosized Actinide Oxides Solid Solutions

“…The oxalate decomposition under hot compressed water allows formation of nanosized mixed oxides such as (U,Th)O2 [2] and (Np,Pu)O2 [3]. Moreover, the method is effective for the production of multicomponent actinide solid solutions, as demonstrated for (Th,U,Np)O2 and (Th,Np,Pu)O2 [3].…”

Synthesis of nanostructured ThO2 pellets

“…Advanced methods for the production of nanocrystalline oxide materials were developed during the last years. Very recently, we have reported the decomposition of oxalates under hot compressed water to obtain highly sinterable actinide oxides nanopowders. We have extended this method toward decomposition of other substances.…”