Highly Radioactive Ruthenium Particles Released from the Chernobyl Accident: Particle Characteristics and Radiological Hazard

Abstract

After the Chernobyl accident highly radioactive Ru particles, more than 100 kBq in activity and more than 10 �m in diameter, were found hundreds of kilometres away from the plant. Since particle sampling and analyses have not necessarily been adequate, an approach based on inventory calculations is used for estimating their radiological hazard. Elemental composition of the particles suggests that short-lived nuclides may essentially contribute to the risks, although usually only 103Ru and 106Ru were detected. Because large Ru particles are not of inhalable size, skin doses are calculated for various particle compositions, sizes and decay times. Calculations support the assumption that Ru particles are metallic precipitates. The composition may have a notable impact on skin doses which are not necessary the largest for particles originating from fuel of high burnup. Even an individual particle may be a severe radiological hazard. A dose of 50 mGy.cm-2 for the basal cell layer may be exceeded in one hour provided that an Ru particle larger than 8 �m in diameter is deposited on the skin.