%675$&7New glassy matrices, able to incorporate new highly concentrated radioactive liquid wastes (HLW), are being studied. Investigations were performed on rare earth-rich glasses, known as very durable matrices. The selected basic glass composition was (wt. %) : . To determine both the environment around the rare earth in this glass and its evolution according to its concentration (1.3 -30 wt. % Nd 2 O 3 ), EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the L III -edge of neodymium and optical absorption spectroscopy were used. By coupling these two characterisation methods, several hypotheses are proposed about the nature of the rare earth neighbouring in the glass.,1752'8&7,21New nuclear fuels with high discharge burn-up (60 000 MWj/t) have been studied for some years in France and should allow a use about twice as long as what is currently achieved in power reactors. Reprocessing of this nuclear spent fuel will generate HLW more concentrated in fission products and minor actinides than nowadays. Therefore, new glass compositions have to be developed, able to immobilise these wastes as a whole. These matrices must exhibit excellent chemical durability and higher glass transformation temperature (T g ) than those of the current borosilicate nuclear glasses.As the actinides and lanthanides quantity is expected to be higher in the new spent fuel, our research turned towards rare earth-rich glassy matrices. Indeed, previous investigations on lanthanide aluminoborosilicate glasses (LaBS) or lanthanide aluminosilicate glasses, showed that this type of glasses displayed high glass transformation temperatures and considerably high chemical durability, probably because of the presence of high rare earth amounts [1,2]. Nevertheless these compositions were not chosen in this work because of their high melting temperature (T m & ,QGHHG SURFHVV SUREOHPV FRXOG DULVH IURP WKH YRODWLOLW\ RI VRPH fission products during melting and from the limited resistance of stainless steel containers during melt casting at such high temperature. An alternative glass composition was tested in the simplified seven-component glass system SiO 2 -B 2 O 3 -Na 2 O -Al 2 O 3 -CaO -ZrO 2 -Nd 2 O 3 . In this simplified system, more than 75 wt. % of the new HLW are simulated (the other 25 wt. % did not play a fundamental role in the properties of the glass and were thus eliminated for this Mat. Res. Soc. Symp. Proc. Vol. 807

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