A CS-133 MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE STUDY OF CESIUM ENVIRONMENTS IN BARIUM HOLLANDITES AND SYNROC

Barium aluminum hollandite is a major phase in Synroc, a ceramic desig ned for the immobilization of high-level waste (HLW) from nuclear fuel reprocessing, Radioactive cesium substitutes into the channel sites, and such hollandites give Cs-133 MAS nuclear magnetic resonance (NMR) spectra consisting of a single peak at 211 ppm in the absence of param agnetic ions. However, the peak shifts to 690 +/- 30 ppm and becomes e xtremely broad when Ti3+ replaces Al3+ in the channel walls of the hol landite structure, apparently because of Fermi contact interaction bet ween een the Cs nucleus and the unpaired electron of Ti3+ Cs-133 MAS N MR of Synroc and hollandites is very sensitive to the presence of wate r-soluble CsAlTiO4 which would compromise the aqueous durability of Sy nroc. Cs-133 MAS NMR spectra of Synroc-C, hot-pressed in metal bellows at temperatures as. high as 1325 degrees C, do not indicate significa nt formation of CsAlTiO4. Synroc samples loaded with Cs and Sr only we re shown by MAS NMR as well as electron microscopic techniques to be c apable of incorporating nearly 10 wt. % Cs before CsAlTiO4 is formed.