Measurement of Trace Uranium-235 and Plutonium-239, 240 in Waste Tank Material at the Savannah River Site

At the Savannah River Site (SRS), large quantities of radioactive liquid waste are evaporated to reduce volume before eventual processing through the In-Tank Precipitation process (ITP). Actinides in the liquid waste are only slightly soluble in the highly alkaline waste solution. Since some of the actinide isotopes are fissionable, the quantities being processed through the evaporator system are of interest. To better quantify the concentration and mass of fissionable material entering the evaporator system and eventually deposited as salt, analysis of the actinide elements were necessary. The predominant fissionable actinide isotopes of interest are U235 and Pu239. To enable the reliable measurement of these radionuclides, the Central Laboratory has developed high speed separation techniques to measure U235 content by Isotope Dilution Mass Spectrometry and Pu239-240 by alpha spectrometry. Due to the high radioactivity levels in the samples all separations are performed in shielded analytical cells. Uranium is purified and concentrated using a high speed extraction chromatography technique that employs applied vacuum and columns containing tri (2-ethylhexyl) phosphate (TEHP) solvent coated on a small particle inert support (SM-7 BIOBEADS ™). The uranium method enables measurement of U235 concentrations to 1 x 10\"4 g/L. Plutonium is purified and concentrated using a high speed anion exchange technique (BIO RAD™ AG MP-1 200-400 mesh resin). The Pu method enables measurements of Pu239'240 to 2 x 1Q-* g/L.