Dear Sir or Madam,
I would like to make some specific comments and provide some detailed information relevant to the steel industry.
i/ Table 2.1: Exposure to 210Po and 210Pb is not related to the recycling of metal scrap
The sources of exposure are linked to the storage and recycling practices of residues or by-products generated from the iron ore sintering and blast furnace processes. In a study conducted by Public Health England (formerly known as National Radiological Protection Board) in 2003, the maximum annual doses to workers at the blast furnace, landfill workers and workers manufacturing and using building materials containing slag were estimated to be below 20µSv [1].
More recently, several monitoring campaigns were undertaken in a UK iron ore sintering plant to assess the potential radiation doses from intakes via ingestion and inhalation of occupational dusts containing elevated concentrations of 210Po and 210Pb. The annual dose figures were calculated based on a highly cautious approach and were found to range from 8 to 1,943 µSv, mainly due to the high variability of the radioactivity concentration of raw materials entering the process, the abatement efficiency of the electrostatic precipitators used to clean the waste gas streams, the effectiveness of ventilation controls in the workplace and the nature of the resulting off-gas dusts [2].
Please note there is a typographical error in the table: the column title Annual effective dose should be in mSv and not mS y-1.
ii/ Table 2.2: The radionuclides with highest activity concentration in the steel industry are not 232Th and 228Ra
Since the nineties, it is recognised worldwide that the two natural radionuclides from the 238U decay series, 210Po and 210Pb, originally present in trace amounts in raw materials, are volatilised and concentrate in the form of dusts during iron ore sintering and in the blast furnaces [3].
Individual doses from atmospheric releases from all currently operating integrated steel plants in the UK have been estimated and found to be less than 10 µSv/y for all age groups. Therefore the annual effective dose figure provided in this table seems reasonable. It is important to note that this type of radiological impact assessment is required by the UK environmental regulators before they can confirm the most appropriate permit conditions for operating a sinter plant (e.g. annual emission limits in Bq, monitoring requirements...).
Please note there is another typographical error in this table: 223Ra (slag) should be replaced by 226Ra (slag) when speaking about use of metal recycling slag for road construction.
[1] Crockett G. M., Smith K. R., Oatway W. B., Mobbs S. F. 2003 Radiological impact on the UK population of industries which use or produce materials containing enhanced levels of naturally occurring radionuclides, Part II: The steel production industry, Report NRPB-W48
[2] Dal Molin F., Anderson D. R., Fisher R., Frost D., Read D. 2017 Dose assessment from chronic exposure to industrial NORM in iron ore processing. J. Radiol. Prot. 37, 402 - 421
[3] Tanzi C. P., Knetsch G. J. 2012 Po-210 and Pb-210 in the Netherlands: releases to air from industrial plants compared to environmental monitoring, Proceedings of the 1st European symposium on naturally occurring radioactive materials (EU-NORM) held in Tallinn, Estonia, 59 – 67