Several orphan Am-241 sources, which were inadvertently included in scrap metal, were melted in a Finnish steel factory. One event happened in 2019 and four events in 2020 as follows
- 2019, January 18th, estimated activity 1 100 MBq
- 2020, February 28th, estimated activity 1 400 MBq
- 2020, September 5th, estimated activity 1 500 MBq
- 2020, November 8th, estimated activity 2 300 MBq
- 2020, November 28th, estimated activity 4 200 MBq
Also, in one event Ba-133 (estimated activity 120 MBq) was melted on December 10th, 2020 in the same steel factory.
It is possible that more than one source might have been melted in one or more of the events mentioned above.
The melting of the sources was detected by the radiation pulse rate monitoring within the steelworks smelting process. The activities of the melted sources were estimated from the activity concentrations of slag and dust.
The sources were traced by the operator to stainless steel scrap delivered from Europe (the Netherlands, Poland, Germany and the United Kingdom). Origin of the scrap metal is unknown.
Due to its physical properties most of the Am-241 activity is partitioned into the slag phase (approx 99%) and dust phase (1%). Based on measurements Ba-133 behaves like Am-241.
Radioactive materials in the dust phase were captured in the filtration with other particulates and thus there were no environmental releases. Small percentage of the dust phase were released into the mill environment resulting the surface contamination. In the Am-241 and Ba-133 melts, the steel remained uncontaminated. Nobody was exposed.
The factory has screening detectors of incoming scrap. Due to attenuation by other scrap, the sources could pass through, despite of the modern screening technology used.
Event date: Sat, 28-11-2020