International audienceSintering experiments on soda-lime glass microspheres have been performed using spark plasma sintering in the temperature range 485°C-560°C. Samples with relative densities between 64% and 99.6% have been obtained in about 10 min. For almost fully dense samples, the microstructure exhibits an unusual "interface-like" aspect for a glass. The densification mechanism has been investigated. For temperatures below 522°C, densification proceeds by formation of necks between spheres. For temperatures of and above 522°C, it is proposed that densification proceeds by viscous flow, accommodated by plastic deformation of microspheres, and is controlled by diffusion of oxygen anions in the glass

A freeze-granulated powder made of UO 2 and PuO 2 , containing 15 mol% of Pu/(U+Pu), was sintered under reducing conditions (oxygen potential of-468 kJ/mol at 1700 °C). Constructing trajectory, using the constant rates of heating and the master sintering curves approaches and calculating the diffusion coefficients by exploiting the results of the sintering runs enabled to propose that densification was probably controlled by grain boundary diffusion and grain growth by the grain boundaries. An activation energy around 525 kJ/mol was obtained for densification, which was close to what was reported for grain boundary diffusion of plutonium cations in U 0.55 Pu 0. 45 O 2-x polycrystalline materials. The sintered microstructure appeared homogeneous regarding the plutonium and uranium cations spatial distribution. By combining the master sintering curve approach for anisothermal and isothermal conditions, it was possible to predict the evolution of the relative density over time for any type of thermal path.

Industrial borosilicate glasses containing fission products and minor actinides can be subjected to structural damage caused mainly by a-self-irradiation effects. In this field of glasses under extreme conditions, we present an X-ray Absorption Near-Edge Structure investigation of two six-oxide borosilicate curium-doped glasses (based on the International Simplified Glass (ISG) composition). The first sample is an 8-year ISG damaged glass, which has already accumulated an a-decay dose greater than 6.10 18 a g À1 , a value corresponding to a damaged but stabilized structural state. The second sample results from annealing of the latter ISG damaged glass. Three species, Cm, Pu and Zr were probed at L 3 -edge, L 3 -edge and K-edge, respectively. From the experimental results, Cm and Pu species appear respectively in ?3 and ?4 oxidation states in both glasses. No Cm local environment changes are observed. In contrast, a small variation in Pu local environment appears between the damaged and annealed glasses, reflecting a possible coordination variation or Pu-Zr substitution. A more drastic effect appears for Zr local environment, where a sevenfold coordinated site grows over time under a-self-irradiation effects, at the expense of the initial major sixfold site of symmetry. Moreover, annealing the damaged glass does not permit to retrieve a similar structural state to the one of a just melted curium-doped ISG.