Sensitivity tests and risk evaluation for steelworks portal systems

Fourteen portal systems installed at the entrance of as many iron scrap recycling plants have been tested. The systems which underwent the test were supplied bythree manufacturers: Bicron, Eberline and Exploranium. For the tests, a truck trailer loaded with iron scrap was equipped with guide tubes for the introduction of radioactive sources. During the whole experimental campaign, the truck trailer was not modified, to assure test reproducibility. Analyzing the collected data, it was determined the lowest exposure intensityin air from a 137Cs source still able to cause an alarm when, centered in the load, passes through anyportal. On the basis of this value it follows a risk evaluation for a steelworks equipped (in agreement with the rules of Lombardia region) with a portal at the entrance, area monitors for critical sites and gamma spectrometer for steel specimen. © 2004 Elsevier Ltd. All rights reserved. Keywords: Orphan sources; Portal system; Smelting accident 1. Introduction Several reports (Lubenau and Yusko, 1998) on accidental smelting of radioactive sources in furnaces confirm the possibilitythat radioactive material might be mixed with scrap. In Italysome accidents took place in the past; the major are here listed (Risica and Neccetelli, 2000): • 1990 137Cs contamination of an aluminium refineryin two facilities and the relevant waste dump; • 1991 137Cs contamination of an unauthorized dump of wastes from aluminium melting; • 1991 241Am contamination of some copper alloymanufacturer and melting firms; • 1993 137Cs contamination of a part of the Brescia and Montirone goods yard; ∗ Corresponding author. Tel.: +39-223996366; fax: +39- 223996309. E-mail address: fabrizio.campi@polimi.it (F. Campi). 1350-4487/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2004.05.007 • 1995 137Cs contamination of dust from settled fumes in a steel mill in the decommissioning phase; • 1997 137Cs and 60Co contamination of the Alfa Acciai steel mill; • 1998 137Cs contamination of the soil in a scrap storage depot. The most severe accident was that happened at Alfa Acciai steel mill, in which 7 GBq of 60Co and 150 GBq of 137Cs were molten in furnace. The consequences of the accident were rather limited. Indeed, part of the final product was contaminated byCo-60, but the dust abatement plant had been effective in avoiding release of 137Cs in the surrounding environment. Nevertheless, the total cost of the accident was more than 25 million Euros, including the decontamination of the plant and the missed profits. After this accident, the Lombardia Regional Council issued an Ordinance (Regione Lombardia, 1997) to impose different radiometric surveys on metal scrap to be recycled. A first monitoring must be performed on the scrap container at the entrance of the steel mill. The Ordinance does not specifywhat