UNDER-DETERMINATION OF SR-90 IN SOILS CONTAINING PARTICLES OF IRRADIATED URANIUM OXIDE FUEL

A much used method for the determination of Sr-90 in soil depends on extraction of the soil with 6 mol l-1 HCl, followed by beta-counting. For soils containing particles of irradiated uranium oxide, we postulate that this extraction could result in a variable underestimate owing to incomplete chemical recovery of strontium from the uranium oxide matrix. In experiments on two soils, collected from near Windscale (now Sellafield) in 1956 and near Chernobyl in 1990, about 25% of the total Sr-90 present in the soil was recovered in 24 h by HCI extraction at room temperature, and the presence of high-radioactivity particles both before and after extraction was demonstrated by autoradiography. For a further 11 particle-containing Chernobyl soils, Sr-90 determination, based on classical HCl extraction, yielded, on average, 54% (range 33-85%) of the total Sr-90, as determined by oxidative alkaline fusion. While we accept that HCl extraction is well established as a reliable method for the determination of soil Sr-90 derived from weapons fallout, we conclude that more rigorous analytical pre-treatment is essential in instances where the Sr-90 may be associated with fuel particles.