The determination of 235U by the isotope dilution method

Abstract

Summary This paper describes an examination of the precision which might be achieved by using an isotopic dilution method for the determination of 235U in the feed solution of an enriched uranium fuel chemical processing plant such as the Dounreay M.T.R. chemical plant. Four solutions were prepared to simulate diluted samples of feed solution; they contained uranium with an isotopic content ranging from 93% 235U to 50% 235U. Separation of uranium was made by solvent extraction with tri(iso-octyl)amine, and isotopic analyses were then made using two Metropolitan-Vickers M.S.5 mass spectrometers. Both 233U and natural uranium were examined as possible tracers. Using 233U as the tracer the results for the four solutions yield a mean precision (3 σ) of 0.37% for a result based on six replicate analyses, and 0.83% for one based on a single analysis. These values include the random errors involved in the mass spectrometric calibration of the tracer, but not errors associated with the gravimetric preparation of a 235U standard, or those which would be concerned with taking a sample from a plant. The results obtained using a natural uranium tracer are less satisfactory, and possible explanations are suggested.