Brit Salbu

Hot particles in accidental releases from Chernobyl and Windscale nuclear installations

Fuel particles released during the accident at the Chernobyl reactor (1986) and during the operation at the Windscale (UK) pile (1952–57) were investigated with respect to structure using scanning electron microscopy and composition using X-ray microanalysis and γ-, β- and α-spectrometry. Particles from Chernobyl released at a relatively high temperature have in general a compact crystalline-like structure with a relatively uniform surface layer of uranium. Aggregates consisting of small-sized (1–2 µm) spherical uranium granulates were also identified. These granulates were similar to particles identified in Norway. About 25% of the particles investigated were covered by lead, which is attributed to a release during the last stage of the accident. Particles from Windscale released under low-temperature conditions have a flake-like layered structure, varying in size (10–250 µm) and activity levels. Thus the travelling distance for these particles may be substantially longer than previously anticipated for spheres. The surfaces of these particles were also composed of uranium. The mobility of radionuclides associated with fuel particles of different structure is believed at least initially to be low when compared with those associated with condensed particles or with ionic tracers. However, mobilization of especially 90Sr due to weathering of hot particles should be expected in the years to come.

Under-determination of strontium-90 in soils containing particles of irradiated uranium oxide fuel

A much used method for the determination of 90Sr in soil depends on extraction of the soil with 6 mol l–1 HCl, followed by β-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 90Sr present in the soil was recovered in 24 h by HCl 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, 90Sr determination, based on classical HCl extraction, yielded, on average, 54%(range 33–85%) of the total 90Sr, as determined by oxidative alkaline fusion. While we accept that HCl extraction is well established as a reliable method for the determination of soil 90Sr derived from weapons fallout, we conclude that more rigorous analytical pre-treatment is essential in instances where the 90Sr may be associated with fuel particles.

Changes in gill reactivity of aluminium species following liming of an acid and aluminium-rich humic water

Changes in gill reactivity of aluminium species following liming of an acid and aluminium-rich humic water