Description: Lanthanum phosphate is a promising host material for reprocessed light water reactor wastes (e.g., PW-4b). This is demonstrated by the high density of the composite waste form and by the low leach rates of both Cs and Sr. Additionally, crystallographic data on LaPO/sub 4/ pellets loaded with 10 wt % simulated PW-4b indicate the presence of only one phase, i.e., monoclinic monazite. The rare-earth orthophosphates have also been shown to be a viable waste form for Savannah River (SRW) defense wastes. Compaction and sintering studies indicate that the rare-earth phosphate mixture employed here is preferable to pure LaPO/sub 4/ for containing SRW. Higher density and more homogeneous samples were obtained by using the mixed phosphates as compared to pure LaPO/sub 4/ as the host material. It is shown that aluminum removal from the composite SRW is not necessary when incorporating this type of waste into a rare-earth phosphate host. The current results support the view that lanthanide orthophosphate waste forms (i.e., monazite) are potentially superior to borosilicate glasses in the following respects: (1) lower processing temperatures (approx. 1000/sup 0/C versus 1160/sup 0/C for glass); (2) significantly higher waste per volume loadings for a given wt % of waste for monazites relative to glass; and (3) the current leaching data show that monazite-type waste forms are clearly superior to glass in retaining Sr, and, in particular, Cs.
Date: January 1, 1981
Creator: Petek, M.; Abraham, M.M. & Boatner, L.A.
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