Impact of ICRP-60 on the operation of underground mines

Reduction of occupational exposure from: 50 mSv to 20 mSv per annum for uranium miners faces difficulties. For miners this affects the gamma radiation dose and ALI's except radon gas and its short lived daughters of Uranium and Thorium whereas the ICRP planned to review radon daughters exposure limits. New dose limits introduce other mines, e.g. phosphate mines, to be considered as occupational areas. Reclassification of radiation workers has to be done; control, licensing, cost, Gamma dose rate is influenced by the grade and type of ore body and the mining method. The primary mode of radionuclide intake in the mine environment is inhalation, however, ventilation is the principal control of airborne dust. The current average radon daughters dose rate in several underground mines among those are phosphate mines in Egypt is well above 20 mSv/a. Recorded values of Egyptian phosphate mines are more than 1 WL of radon daughters (1WL = 62 uSv/h) considering 2000 h/y, therefore, the annual dose = 124 mSv/a. Mining method dictated by location, size and shape of ore body, hydrology. Priority is given for conventional safety of work place, e.g. rock collapse as well as care of economics of the process and mine development. It is well defined that the control of gamma radiation dose is very much dependent upon the geometry of ore body. Shielding of ore trucks could not be justified (fuel consumption and its pollution). Bulk ore handling method may reduce gamma doses but it generates dust which may increase inhalation doses of long lived alpha emitters. Ventilation is the principal method to control inhalation hazards of dust and radon daughters, but high rates of ventilation has reverse effects of generating more dust and drying wet surfaces of ores. Accordingly, reduction in radon daughters exposure will result in high cost of production. In Egypt radon and thoron (risk/problems) are previously monitored in phosphate mines (upper Egypt). Values greater than 1 WL were measured in many locations of those phosphate mines. Those mines have sufficient radon daughters concentration that workers should be classified as radiation workers. Considerable financial burden on operating mines, regulatory considerations would be required if ICRP-60 is to be adopted. Moreover detailed studies and data are required, on weighing factors of organs considered by ICRP-60 which has to be reviewed to the local conditions. Total radiation work period of 50 y is considerably long compared to miner work period of 20 y. The relevant conventional health hazards are to be considered. (author)