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Contaminated batch of recycled steel results in radiation incident in Outokumpu's Tornio site

24 February 2012 at 4.25 pm EET

Outokumpu's Tornio melting furnace was exposed to a source of radiation during the night between Thursday and Friday which was identified as americium. The mill security system revealed the radiation source and standard security actions were carried out according to the company processes. Four meltshop employees were exposed to radiation as they entered the melting furnace during maintenance work.

Finnish Radiation and Nuclear Safety Authority (STUK) informs about the incident as follows:

"Preliminary measurements made by Finnish Radiation and Nuclear Safety Authority (STUK) indicate that one of the employees was potentially exposed to a dose of approximately ten millisieverts of radiation. The dose was limited and does not pose adverse health effects to the employee. According to the seven-step International Nuclear Event Scale (INES), such a dose is a level 2 incident - meaning that it is a material safety risk event. The first measurements of the three other employees observed no abnormal radioactivity. This incident didn't pose any hazard to employees outside the meltshop furnace area.

The measured radiation dose of this incident can be compared to standard radiation dose guidelines set for workers engaged in radiation fields. According to the guidelines, the average radiation dose limit is 20 millisieverts per annum over a five year period and the annual maximum dose must not exceed 50 millisieverts in any given year.

The radioactive material was identified to be the isotope americium 241. Americium 241 is for example used in industrial measurement devices that require high sensitivity."

Outokumpu's supplier contracts for recycled steel clearly stipulate that the material must not contain any radiating elements. In this case however, americium ended up in the melting process through recycled steel.

Outokumpu conducts radiation measurements at the Tornio site today and over the weekend to ensure that the smelter has no harmful amounts of radioactive materials. Samples at the melt shop will be taken and sent to the STUK Radiation Laboratory for analysis.

As a standard procedure, Outokumpu conducts radiation measurements in various stages of the production process in order to ensure that no radiating materials end up in the process. Measurement devices containing americium may enter the melting process, as the sealed radiation sources cannot be detected even with the most sophisticated radiation detectors until the shield of the radiation source breaks down in the melting process.