Study on the direct measurement method for trace plutonium in samples from spent fuel reprocessing

To directly, rapidly, and accurately measure trace plutonium in reprocessing samples, two α scintillation counters were developed for the direct measurement of liquids and solids after source preparation. An analytical method for directly determining trace plutonium in process samples was established. Both counters used ZnS(Ag) crystals sprayed onto light-guiding plexiglass as detectors for measuring α nuclide activity concentrations in complex samples containing simultaneous α, β, and γ nuclides. Test results indicated a 75.2 % detection efficiency for the first α scintillation counter for ²³⁹Pu surface sources with good linearity over the concentration range 5 × 10⁻⁶ g/L to 1 × 10⁻³ g/L in aqueous plutonium solutions. It could also directly measure the α activity concentration in aqueous Pu solutions without source preparation. The second α scintillation counter, used a baking-dish measurement method. It exhibited excellent linearity for aqueous plutonium concentrations over 1.0 × 10⁻⁵ to 1 × 10⁻³ g/L with ≤1 % precision in the 5 × 10⁻⁵ to 1 × 10⁻² g/L range. Both systems featured rapid and simple operation.