PARTITIONING OF URANIUM AND RARE-EARTH ELEMENTS IN SYNROC - EFFECT OFIMPURITIES, METAL ADDITIVE, AND WASTE LOADING

AEM techniques employing digital filtering, least squares profile fitt ing, and experimental k-factor calibrations were used to investigate 1 6 Synroc samples containing simulated Purer (PW-4b-D) HLW at loadings of 10, 15, 19, and 23 wt%. A second group of Synroc samples with 10 wt % HLW also contained additional impurities of F, Na, MgO, P2O5, and Fe 2O3. A third set of samples with 10 wt% HLW contained different metal additions of Al, Ni, and Ti, and a sample with no metal addition for c omparison. In samples with low Na2O content, it was confirmed that ele ment partitioning is mainly controlled by the ionic radius criterion, with smaller Y, Gd, and U ions having a preference for zirconolite and the larger Ce and Nd ions favoring perovskite. Average relative parti tioning coefficients (D-Z/P = wt% metal oxide in zirconolite divided b y wt% metal oxide in perovskite) of 8 samples with 10 wt% HLW and simi lar to 0.5 wt% Na2O are 0.14 +/- 0.01, 0.39 +/- 0.03, 1.7 +/- 0.2, 3.8 +/- 1.0, and 2.2 +/- 0.8 for Ce, Nd, Gd, Y, and U, respectively. Elem ent partitioning is not strongly affected by additional impurities of F, MgO, P2O5, or Fe2O3; metal addition; or waste loading. Additions of up to similar to 3.6 wt% Na2O lead to an increase in the amount of pe rovskite at the expense of zirconolite as well as a systematic shift i n the partitioning of REEs and U from zirconolite into perovskite.