Lost radiation sources cause problems in the steel industry
The Radiation and Nuclear Safety Authority (STUK) received six notifications within a year on radiation sources which had ended up in melting with recycled metal in the Outokumpu Tornio steel mills. The safety functions at the mills are in order, so radiation did not threaten anyone’s safety.
STUK placed the series of incidents in category 1 on the International Nuclear and Radiological Event Scale (INES). Category 1 means on the seven-level scale “an anomaly affecting safety”.
Tommi Toivonen, Director of the Radiation Practices Regulation department at STUK, points out that radiation sources accidentally ending up in melting are always potentially dangerous. The radiation measurement and notification system must be functional and the employees must know what to do in such a situation.
The radioactive substances of the melted radiation sources were mainly bound with the slag of the waste, partly with dust that stuck to the filters of the mills. The processing and dumping of slag cause additional work for the mills.
An international problem
In the Outokumpu Tornio steel mills, americium (Am-241) radiation sources were melted five times and barium (Ba-133) was melted once among scrap metal between December 2019 and December 2020. Since the events were noticed only in melting, it is not known whether there has been one or several radiation sources in each melting.
The exact origin of the radiation sources in loads arriving from abroad is not known. Americium is used as a radiation source in industrial moisture and density gauges, while barium in the calibration sources of health care and industrial equipment, among others.
Steel mills measure radiation from all incoming recycled metal. Even a well-functioning control cannot always detect radiation sources that are covered by radiation shielding inside a large scrap load, as the surrounding recycled metal attenuate radiation efficiently. Especially americium (Am-241) is hard to detect among recycled metal.
“Radiation sources are detected among arriving scrap metal rather often in Finland when compared to other countries”, says director Tommi Toivonen. According to him, this is a sign of Finnish companies’ good supervision and responsibility. Radiation sources are detected and also reported to the authorities.
Radiation source problem is an international problem. “Here in Finland, we treat the effects of the disease, but the disease itself must be cured through international cooperation”, says director Toivonen. The situation in Finland would improve if the radiation source users took care of their radiation sources appropriately and the sources remained under the control of authorities throughout their entire life cycle. The development of measuring techniques could also alleviate the problem so that lost radiation sources would be better detected among the material flow.
IAEA INES-news https://www-news.iaea.org/
Director Tommi Toivonen, puh. (09) 759 88 660
Media contacts, tel. +358 10 850 4761
Director Tommi Toivonen, puh. +358 0 759 88 660
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