Determination of Natural Radioactivity in Iron and Steel Materials

It has been known since the 1990s that two natural radioisotopes from the uranium-238 (²³⁸U) decay series, polonium-210 (²¹⁰Po) and lead-210 (²¹⁰Pb), originally present in trace amounts in raw materials, are volatilised and concentrate in the form of dusts during iron ore sintering. In the UK, most of the dust generated during this process is collected by means of electrostatic precipitators and recycled back into the production system using conveyor belts. Nevertheless, a small proportion passes into the atmosphere via stack emissions and some fugitive dusts can also escape into the workplace during maintenance operations. Tata Steel UK Ltd, a major European steel making company, has developed and validated in-house radioanalytical methods for the measurement of ²¹⁰Po and ²¹⁰Pb in a wide range of iron-making materials including raw feedstock, waste dusts, occupational and emission filter samples. The data gathered have enabled a better understanding of the fate of ²¹⁰Po and ²¹⁰Pb throughout the integrated steel making route, providing essential information to support environmental permits for discharges to the atmosphere and for confirming that chronic exposure to these two natural radioisotopes does not lead to significant radiological doses to the workforce. Additionally, since the implementation of the BSS Directive 2013/59 Euratom and the Construction Products Regulation (CPR), there is a need for the European steel industry to characterise the levels of radium-226 (²²⁶Ra), thorium-232 (²³²Th) and potassium-40 (⁴⁰K) in slag materials and confirm that those materials do not pose a significant risk of internal and external exposure to radiation when reused or recycled in building materials. This paper highlights the technical challenges encountered when measuring those natural radioisotopes in various iron-making materials, including the difficulty of validating radioanalytical methods in the absence of suitable certified reference materials.