There were three incidents at the Outokumpu steel mill in Tornio between July and September where a radioactive americium source ended up in melting with recycled metal.
The latest – and fourth – incident took place on Friday the 12th of October. This time, however, the radiation source was discovered before melting.
The steel mill’s own radiation monitoring system and appropriate protective measures have prevented radioactive materials from spreading outside the factory facilities. Although the factory workers have not been exposed to radiation they have been forced to use respirators.
“The disappearance of radioactive materials is always a serious matter. Potential health risks have been limited to the factory area but thanks to the correct radiation protection measures, personal and environmental exposure have been avoided,” says Tommi Toivonen, head of the Radiation Practices Regulation division of the Radiation and Nuclear Safety Authority STUK.
“We have informed the other authorities and passed information on to the International Atomic Energy Agency, IAEA, in order to find out the origin of the radiation sources. The radiation user is always responsible for the proper disposal of the radiation source,” he continues.
So-called orphan radiation sources, i.e. radiation sources that have not been properly managed, are sometimes found among recycled metal but it is unusual to have several incidents at the same factory within a short period of time. Facilities that treat recycled metal use radioactivity sensors. However, detecting americium sources among scrap metal is extremely difficult.
“These recycled metals have been shipped to Finland from the Netherlands and the Baltic countries, but the batches of metal most likely originate from outside of Europe. The radiation sources have been disposed of with recycled metal either on purpose or due to negligence,” says Toivonen.
The last time the radiation detectors at the Tornio steel mills detected americium sources among recycled metal was last Friday before the batch of metal in question was melted. This time, the alarm was caused by a lightning conductor made in Brazil with three not so active americium sources.
The facility in Tornio has a good radiation protection process in place, which has protected the employees from exposure to radiation. When americium ends up in melting, most of the time it ends up in the slag created during the melting process and, to a lesser degree, in the combustion gases. Based on previous similar cases, it is known that americium does not end up in manufactured steel. The Tornio steel mill takes samples from the slag and sends them to STUK’s laboratory to be measured. Slag containing americium as well as the combustion gas filters are collected at the factory and stored separately from other materials for final disposal later on.
Americium is a radioelement used, for instance, in soil density gauges and industrial measuring devices. The scale of the sources that have ended up in melting has been approximately 1–2 gigabecquerels.
STUK has reported the incident to the IAEA. According to STUK’s estimate, because of the reoccurrence of the incidents, this is a case of an exceptional safety incident, which is to say that it is a category 1 event on the INES (International Nuclear Event Scale) scale.
Source: STUK
