In-Line X-Ray Fluorescence Analysis of Special Nuclear Materials in Dissolver Solution: Laboratory Development and Simulation Studies

摘要

An automated x-ray fluorescence analysis apparatus and sampling system has been designed for a proof-of-principle test of on-line x-ray fluorescence assay of special nuclear materials in dissolver solutions. A sampling technique is described in which the sample may be a large aliquot or an entire, ''totally sampled'' batch of solutions. The total sample technique used with an internal standard gives total mass assays with no need for a tank volume measurement, thereby eliminating errors of aliquotting and tank volume measurement. The test XRF apparatus has been used for the generation of a data base consisting of the usable concentration ranges and times required for attaining targeted standard deviations for assays of dilute plutonium dissolved in high-density uranium solutions, using the uranium-thorium pair as surrogate for plutonium-uranium. Error propagation equations have been derived for governing the efficient accumulation of high-precision data under the extremely low signal-to-noise conditions encountered with dilute SNM in dense matrices. The data base, used as input to the error propagation equations, is used for specifying the parameters of x-ray fluorescence analysis equipment that will meet any targeted assaying precision and assay time requirements. Assay accuracy at low levels of analyst is critically dependent on the accuracy of the background determination. A data-taking strategy which uses a short dwell time at each spectrometer setting is effective in compensating for long-term instrumental drift. The effects on assay time and precision of the reflecting power and diffraction halfwidth of the analyzing crystal, spectrometer design, signal-to-noise ratios, x-ray detection system, and exciting x-ray power are discussed. 8 refs. (ERA citation 11:023177)