One of the most important compounds that are used in structural ceramics is alumina. During the last years, a variety of synthesis methods have been developed to obtain raw materials with suitable characteristics in terms of particle composition, size and shape. Controlled precipitation method (CP) allows to reach these demands and with this method is possible to control the synthesis to guarantee characteristics of the ceramic powder. One stage of the CPM is the formation of intermediate complexes of cations whose oxide derives to obtain. In this work the results of study of the formation of aluminum intermediate complexes are presented. We used potentiometric and conductimetric titration to follow the advance of the process. We utilized UV-visible and IR spectroscopies to characterize the liquid phase present in the system

Any environmental performance assessment of spent nuclear fuel disposal requires a prediction of the spent fuel matrix alteration rate when contact with groundwater is established. Taking into account the disposal design, the groundwater at the expected depth of the repository are generally reducing. These reducing redox conditions near the spent fuel surface may be changed to oxidising conditions by the radiolysis of water, due to radiation associated with the waste. This study is focussed on determining the influence of the γ radiation on the spent fuel matrix alteration rate under simulated repository conditions. A series of sequential leaching experiments under controlled conditions have been done. The experiments simulate the repository environmental conditions when engineering barriers are degraded and groundwater arrives at the surface of the spent fuel. In these experiments SIMFUEL (SIMulated FUEL) was used as analogue of spent fuel. Two types of leachant (i.e., granitic water and bentonitic-granitic water) were used in the leaching experiments. These experiments were irradiated using γradiation at an industrial irradiation facility with a 60 Co source. The results obtained in this study show different behaviour as a function of both the leachant used in the leaching experiments and the initial atmosphere used in the experiments. As a preliminary conclusion of this experimental work, under γ radiation and a small partial pressure of H 2 (1 bar) in the first steps of the leaching process has a beneficial effect since U in solution is lower than any other conditions and overall alteration rate is minimized. For experimental times longer than one day, a clear increase of the U in solution is revealed in the experimental run products.

No abstract

For improving the accuracy of the performance assessment studies related to the spent fuel safety under storage conditions, it is necessary to develop a new matrix alteration model. These models must be based on laboratory experiences and they should be capable of extrapolating storage environmental conditions. The most recent models developed include the oxidation and dissolution process of the spent fuel matrix, but the influence of a possible process of secondary phase formation over the spent fuel surface was not yet taken into account. This is a key process that could produce a reduction of the matrix dissolution rate/radiation shielding behaviour; however, the surface precipitation of the secondary phase could induce a localized corrosion process, in which case the dissolution rate of the spent fuel would be increased.This paper is focussed on microstructural characterization of secondary phases formed in co-precipitation experiments performed under anoxic conditions in granitic-bentonitic simulated groundwater. In order to simulate the influence of the container material, the co-precipitation experiments were performed in the absence and presence of iron powder. The solid phases formed were characterized using the following techniques: XRD; SEM-EDX, and TEM-EDX.The XRD diffraction pattern showed that under anoxic conditions, a mixture of phases were obtained (sodium and potassium uranate and schoepite), whereas uranate phases were detected when only iron was present. The characterization study indicates that the U secondary phase formed (under reducing conditions and in the presence of iron powder) growth from the iron surface. The crystal size of the secondary phase is independent of the presence of iron powder (and it is always less than 3 µm). Furthermore, the microstructural study showed the growing of U phases over iron powder.Mater. Res. Soc. Symp. Proc. Vol. 985

No abstract