Spectrochemical Analysis of ‘Fissium’ for Cerium and Lanthanum

Abstract

Summary ‘Fissium’ is a synthetic spent Pu-rich reactor fuel which has a nominal weight per cent composition of 2.5 Fe, 0.7 Ce, 1.3 La, 0.7 Mo, 1.3 Ru, and 0.8 Zr. It is used as a stand-in for irradiated fuel in the study of pyrometallurgical methods of treatment for the removal of fission products. To evaluate the Ce and La contents of the fuel alloy as well as the by-products of this treatment, a spectrochemical method was developed which has a coefficient of variation of 6 per cent and comparable accuracy when amounts ranging from 40 to 200 μg are determined. The recommended procedure involves the following steps: dissolution of the solid sample in HCl, HNO3, or HClO4; oxidation of Pu to the hexavalent state with HClO4; separation of Ce and La from Pu and other elements by precipitating them as the fluorides along with Eu which is added as a coprecipitant; conversion to an HCl medium; spectrographic analysis of the sample and a set of standards, utilizing spark excitation with copper electrodes; photometry of suitable spectral lines, including those of the internal standard, Eu, on a calibrated emulsion to evaluate the concentrations by conventional means. After dissolution of the sample, the succeeding steps can be readily completed for six samples in duplicate by the expenditure of 8 man-hours of work. The least practical amount of element to process is 10 μg. A factorial experiment involving Ce, La, Nd, Pu and other fissium element concentrations indicated that bias existed for Ce and La determinations at the 20-μg level of each, but not at the 50-μg and higher levels. No significant difference is observed when the relative proportions of Ce and La are varied tenfold in the absence of Nd. Erratic and incomplete recovery of Ce is noted if the concentration of HClO4 is less than 1N during the F− precipitation; HClO4 in concentrations up to 3N gives satisfactory results. Processing of standards, both with and without the fission elements, by the recommended procedure yields data which are not significantly different spectrographically from those observed for unprocessed aliquants.