Application of on-line plutonium isotopic concentration monitors at a nuclear fuel reprocessing plant

Gamma-ray spectroscopy is used to assay plutonium solutions flowing through thin sample cells. The direct measurement of gamma-ray intensities are used to determine the plutonium isotopic content and total concentration. The development of spectral analysis algorithms, the use of appropriate instrument internal standards, techniques to minimize spectral acquisition times, and methods to deduce the /sup 242/Pu content are discussed. Results of experiments on plutonium solutions in the 200 to 500 grams/liter concentration range of typical light water reactor isotopic content are given. These solutions typify the purified plutonium product streams in a reprocessing plant. The isotopic and total plutonium assay results as determined by this technique are within 0.5% of the reference values, as determined by mass spectrometry and controlled potential coulometry, respectively. Similar techniquescan also be applied to low concentration plutonium solutions. Plutonium isotopic ratios can be determined by this technique and the alpha specific activities computed. For low concentration (10/sup -0/ to 10/sup -4/ grams/liter) streams, cerium activated Vycor scintillation detectors can then be used for plutonium monitoring. This is compared with other proposed methods of on-line plutonium analyses. Modes of operation of these monitors for real-time inventory and diversion detection are discussed.