Detection of traces of fluorine in micrometer sized uranium bearing particles using SIMS

Abstract

The isotopic analysis of micrometer sized uranium bearing particles, released from nuclear facilities, has been proven to be an efficient tool for safeguarding purposes. However these analyses are not always sufficient for identifying specifically some crucial nuclear operations, like uranium conversion, which are most of the time carried out with natural uranium. A secondary ion mass spectrometry (SIMS) methodology to detect and analyze micrometer sized particles that contain both uranium and fluorine is described. Following the particle detection, which is performed automatically, individual particles are analyzed under microbeam conditions to measure both a precise uranium isotopic composition and the relative amount of fluorine. We first confirm that the sample thermal treatment is prohibited to preserve the fluorine signature of the particles. The methodology was applied to uranium particles coming from the fuel cycle upstream from the enrichment step. This study demonstrates that, contrary to uranium isotopic measurements, the measurement of the relative amount of fluorine allows discrimination between uranium ore concentrate particles and particles coming from a conversion plant. Moreover, the results, obtained for particles which were collected 4 years ago in the surroundings of a conversion plant, show also that the sample storage in a plastic bag at ambient temperature and in the dark is enough to prevent a significant loss of fluorine and the disappearance of the conversion signature. Finally the methodology was applied successfully to an unknown real-life environmental sample.