Fission Product Activity Measurements in Air Particulate Filters Collected after Fukushima Accident at Palermo, Italy

In the framework of routine operation of AGN-201 COSTANZA Nuclear research reactor, measurements of radionuclide air concentration are periodically performed by filtering an high volume of air through paper filters and by using HPGe gamma-ray spectrometry. After Fukushima accident, a series of samplings was carried out with a daily frequency so to detect the possible arrival of air radioactive contamination and to follow its evolution. Particulate collection was performed by suction of atmospheric air through 45cm × 45cm Sofiltra-Poelman HYN-75 (Bleu type) cellulose filter paper using a high-volume air sampler located on the roof of our department 20 m above ground-level. The sampling time was generally set to 14 h from 6 p.m. to 8 a.m. the next day; the filtered air volume is typically 10,000-13,000 m3. After particulate sampling, the filters were sprayed with a suitable fixer, cut into strips, folded and pressed into 6 cm side and 0.7 cm thickness packets by a 15-t press. These samples are then measured by HPGe gamma spectrometric systems. The analysis of the spectrometric measurements highlights the presence of 131I, 134Cs, 136Cs , 137Cs and, only for a sample, traces of 132Te-132I. The trend of air concentration values shows a rapid initial increase, related to the most significant release from Fukushima plant, followed by a steady decrease in the values caused by air masses dilution and, only for 131I and 136Cs, radioactive decay. From a dose to population point of view, no significant values are obtained. Compared with the values determined immediately after the Chernobyl accident, the concentration values are from 1,000 to 100,000 times lower while, for only 137Cs, are comparable with the ones highlighted after the Algeciras (Spain) accident.