Safeguards Analytical Laboratory
Chemical Analysis Unit - Uranium Laboratory
Materials free of fission products and/or plutonium are initially treated in the uranium laboratory. The main task of this laboratory is the analysis of such samples for the determination of uranium and thorium elemental assays and preparation of sample fractions for the mass-spectrometric or gamma-spectrometric determination of the uranium isotopic composition.
A large variety of sample materials is treated:
- uranium oxide powders and pellets
- "green pellets"
- scrap materials, swipes, contaminated materials and other waste materials from the nuclear fuel cycle
- uranium nitrate solutions or dried salt
- "yellow cake"
- uranium hexa- and tetra-fluorides
- uranium metal and metal alloys with aluminum and/or zirkonium
- uranium graphite
- mixed oxides of uranium and thorium and "BISO" and "TRISO" made thereof (special types of coated particles for high-temperature, gaz-cooled reactors. Particle coatings are made of layers of graphite and silicium carbides)
The major technique applied is the Davies and Gray potentiometric titration, which is applied in its original NBL-modified form or in a robotized automate set-up using a scaled-down version. Both variants deliver routinely results with a precision and accuracy below 0.05% relative (standard deviation). Propagating all uncertainty components, including systematic uncertainties of calibration and certified values of primary reference materials, the total uncertainty for routine sample results (mean of two dissolutions and titrations) is estimated as ±0.07% relative (95% confidence interval).
Robotized Davies and Gray potentiometric titrator
Other tasks and techniques of the uranium laboratory comprise:
- density measurements of uranium solutions and heavy water samples
- preparation of heavy water standards and density standards
- spiking of uranium samples
- preparation and characterisation of control and reference materials and standards
- maintenance and cleaning of sample containers for gazeous uranium hexa-fluoride