Analysis of radionuclide concentration in air released through the stack of a radiopharmaceutical production facility

Abstract

The quantities of positron emitting radionuclides used in medical diagnostics and the number of radiopharmaceutical production facilities have been estimated to be growing worldwide. In this field, an amount of these radionuclides might become airborne and escape into the environment during the process of production and/or during administration by hospital personnel. Therefore, the analysis of dose to the operating staff as well as to the public, due to releases through the stack, is a very important issue. To this end, sampling and measurement of radionuclide concentration in air released through the stack of a Nuclear Medicine Center (NMC), provided with a cyclotron for radiopharmaceuticals production, must be routinely carried out with an automatic measurement system. In this work is presented the analysis of the air concentration data recorded in “San Gaetano” NMC at Bagheria (Italy). The contaminated air at stack comes from cyclotron vault during irradiation, from Radiochemistry Laboratories during radiopharmaceuticals synthesis, from diagnostics room during medical scanning and other areas. Sampling of air was carried out continuously and gamma-ray spectrometric measurement are made on-line and for a short time by using a shielded Marinelli beaker filled with sampled air and a gamma detector. The use of this system allows to have 720 values per day from 2002, year of the start of operation with the cyclotron, until 2013. Therefore, the concentration values are very many and an analysis software is needed. The analysis allows either to determine the dose to the population and to evaluate possible improvements in the plant devices to reduce the air concentration at stack. Among engineered safety feature actuation systems, the provision of Air Compressing Stations (ACS), used for both hot cells and cyclotron vault releases, and a change in the position and height of the stack allow to ensure low level discharges from the stack and to reduce the dose to reference group of population. A comparison with the results of a simulation code based on a Gaussian Plume air dispersion modelling allow us to confirm the no-radiological significance of the stack effluent releases in terms of potential dose to population reference group, sited more than 100 m away from the plant.