New calibration standards for accurate radioactivity measurements in the steel industry
Metal recycling conserves natural ore resources and supports sustainable development, hence benefitting industry, consumers and the environment. However, several accidents in the past decades where inadvertently collected scrap metal contained radioactive material resulted in stricter controls and development of new standards to detect contaminated scrap metal and protect citizens and the environment from its harmful effects.
In close collaboration with European Metrology Institutes, JRC scientists organised an inter-laboratory comparison to determine the reference value of the radioactivity concentrations in newly developed calibration standards made from cast steel. The exercise resulted in two new reference standards of Cobalt-60 (60Co) in cast steel. Cobalt-60 is the most common radionuclide that may be encountered cast steel (the final product). The Cobalt-60 contamination can accidentally occur due to scrap metal melting incidents.
Around 50% of the yearly steel production in the EU comes from recycling scrap metal. However, despite the radiation controls at the entrance of scrap yards or steel foundries, a loaded truck carrying scrap that contains radioactive material/source may, shielded by other metal load, enter the foundry undetected.
This may lead to accidental melting of the radioactive metal, mixing it with uncontaminated metal. Cobalt-60 is one of the main radionuclides involved in such melting incidents, apart from Caesium-137 (137Cs). While 137Cs mainly gets mixed with fume dust, 60Co is captured in the cast steel.
The European metal foundries are aware of the problem and increasingly apply radioactivity monitoring of steel products. It is of utmost importance to perform accurate measurements to prove that the legal limits of radioactivity content are met, and it is challenging to ensure the quality of such measurements. In today's global steel market, it is obvious that harmonisation of the analytical methodologies is critical.
In the European project 'MetroMetal' (Metrology for European Metal industry), scientists from the JRC collaborate with 13 National Metrological Institutes (NMIs) to develop measurement methods and calibration standards to be used in steel mills for measuring radioactive contamination in steel products while ensuring measurement reliability. The JRC with its partners has already produced a reference material for detecting 137Cs and 60Co in fume dust.
Two new calibration standards of 60Co in cast steel matrix were developed in response to the need for specially-designed activity standards to be used in metal works. To certify their radioactivity concentration, the JRC organised an inter-laboratory comparison study amongst all the partners of the project. The new reference standards of 60Co in steel enabled the JRC to plan the conception of a future certified reference material (CRM) of contaminated steel. Thanks to the new reference standards metal works in Europe and beyond now have a reliable tool to help them ensure the quality control of their production and the safe use of their products.