The assessment of exposure to ionizing radiation at spoil banks

Until 1970, Polish hard coal mining was not considered to be a source of radiation exposure arising from the presence of enhanced concentrations of natural radionuclides. After radioactive scales in pipelines for the draining of brines had been found, a need emerged for an assessment of the radiological risk. During the next few years, many different surveys were carried out, resulting in a comprehensive system of occupational radiological protection. In 1982, in accordance with the relevant national regulations, enforcement of the system was extended to the whole of Polish underground mining. The system of protection consists of systematic measurements of particular factors contributing to the miners' radiation risk, such as radioactive aerosols, sediments and waters. Unfortunately, less attention has been given to exposures that can occur as a result of the release of naturally radioactive materials to the environment. The territory around the Upper Silesian Coal Basin is densely populated. Since the phenomenon of enhanced natural radioactivity has become well known to members of the public, many social problems are emerging. The majority of them were, unexpectedly, related to waste rock piles that were deemed to be as hazardous as radioactive scales and sediments. According to the claims of local society, an assessment of the radiation exposure at waste rock piles had to be done. Concentrations of natural radionuclides in samples extracted from underground rocks slightly exceed the natural background on the earth's surface. This results in an enhanced gamma dose rate at places where this kind of waste was dumped. Additionally the structure of spoil banks creates the possibility of an increase in radon exhalation. Taking into consideration the total amount of spoil and gangue and the current international recommendations, the enhanced level of external radiation and radon exhalation seems to be significant from the point of view of radiological science. Due to the fact that the waste rock has not undergone any chemical transformation, the potential for enhanced radiological risk is directly related to the geological origin of the rock that constitutes that waste. Therefore, two different mining regions have been chosen for investigation. The coal seams exploited in those regions lie in different carboniferous systems, so the properties of the rocks occurring with the coal differ from each other. Measurements of radiation risk have been done on three waste rock piles that vary in age and state of land reclamation. For comparison, the same measurements have been done in neighbouring rural areas. The results of investigations show that the major contribution to the slightly enhanced radiation risk at these areas arises from external radiation due to the enhanced concentration of natural radioactivity in the waste material. (author)