An improved mathematical model for prediction of air quantity to minimise radiation levels in underground uranium mines Durga Charan Panigrahi, Patitapaban Sahu, Devi Prasad Mishra * Department of Mining Engineering, Indian School of Mines, Dhanbad 826 004, India article info Article history: Received 6 July 2014 Received in revised form 31 October 2014 Accepted 7 November 2014 Available online Keywords: Mathematical model Underground uranium mine Air quantity 222 Rn sources Radon daughters Inhalation exposure abstract Ventilation is the primary means of controlling radon and its daughter concentrations in an underground uranium mine environment. Therefore, prediction of air quantity is the vital component for planning and designing of ventilation systems to minimise the radiation exposure of miners in underground uranium mines. This paper comprehensively describes the derivation and verification of an improved mathe- matical model for prediction of air quantity, based on the growth of radon daughters in terms of potential alpha energy concentration (PAEC), to reduce the radiation levels in uranium mines. The model also explains the prediction of air quantity depending upon the quality of intake air to the stopes. This model can be used to evaluate the contribution of different sources to radon concentration in mine atmosphere based on the measurements of radon emanation and exhalation. Moreover, a mathematical relationship has been established for quick prediction of air quantity to achieve the desired radon daughter con- centration in the mines. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Radiation exposure in underground uranium mines Uranium ore is mined either by opencast or underground mining methods depending on the size, depth, strike length, grade and other relevant characteristics of the ore deposit. During the mining and processing of uraniferous ore, the workers are exposed to radiation from uranium. It is a well known fact that the radio- logical hazards in underground uranium mines are more serious and difficult to tackle than in opencast mines due to ventilation problems. In uranium mines, the radiological hazard of the miners is primarily caused due to inhalation of radon ( 222 Rn) and its daughter products, which can contribute more than 50% of the total effective dose (Porstendorfer, 1994; UNSCEAR, 2000). The epide- miological studies revealed that prolonged exposure of under- ground uranium miners to radon and its daughter products leads to lung cancer (Grosche et al., 2006; Gulson et al., 2005; Tomasek, 2012). The concentration of radon in underground uranium mine at- mosphere mainly depends on the emissions of radon from the ore body, broken ore, backfill mill tailings and mine water. The radon exhalation from uranium ore mostly depends on several factors, viz. radium ( 226 Ra) content, porosity and moisture content of the ore and barometric pressure (Martin et al., 2002; Mudd, 2008; Rock and Walker, 1970; Strong and Levins, 1982; Thompkins, 1982). Broken ore piles are the sources of higher radon exhalation due to increased exposed surface area (Franklin et al., 1980; Lawrence et al., 2009; Washington and Regan, 1974). It has also been re- ported that radon exhalation from the backfill tailings is quantita- tively more significant than from the uranium ore itself due to higher bulk porosity and enhanced surface area (Mishra et al., 2014). Mine water oozing out from uranium mineralised zones through the bore holes and fissures releases the dissolved radon into mine atmosphere (Misaqi, 1975). 1.2. Miners' risk of increased radon emanation When a miner inhales the mine air, radon being a gas is exhaled along with the breathed out air. However, its decay products, which are the atoms of heavy metals, deposit in the respiratory system and continue to irradiate the lung tissues even after one leaves the workplace. In mine atmosphere, the short-lived radon daughters interact with the aerosols and occur in two modes such as * Corresponding author. Tel.: þ91 9430191673; fax: þ91 326 2296628, þ91 326 2296563. E-mail address: devi_agl@yahoo.com (D.P. Mishra). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad http://dx.doi.org/10.1016/j.jenvrad.2014.11.008 0265-931X/© 2014 Elsevier Ltd. All rights reserved. Journal of Environmental Radioactivity 140 (2015) 95e104