In late October 2005 at the Beltrame plant in Susa Valley (Italy) a radioactive source was accidentally burned in the blast furnace. The source was not discovered by the detectors at the entrance, evidently because of some shielding effect. This caused the contamination of foundry dust, air intake system, and of the filters. There was no dispersion in the environment and risks to workers. All contaminated dust was collected in big bags and placed within containers waiting to know for their destination. The global activity is now estimated at 4 GBq. Five different contamination scenarios, have been analyzed, i.e., possible ways by which such an amount of radioactive material could have been introduced into the foundry. The considered contamination (4 GBq) is compatible with the total activity of some calibration sources. In both cases, Cs-137 is in the form of a quite small radioactive source capsule, sealed and surrounded by a shielding material assembly, such as Pb. The source capsule would have a quite high radioactive concentration, and then a total mass in the order of grams. It has therefore to be classified – for sure – as a High Radioactivity Material, or, once it is inadvertently thrown away, as High Level Waste (HLW), according to the Italian regulation (III Categoria). The lead assembly shielding explains why the assembly passed through the check of the gamma sensor without creating alarm.