Long-distance migration law of radon in overburden of abandoned goaf during coal spontaneous combustion

Zhikang Chan; Bin Zhou; Junfeng Wang; Zhifan Lu; Qifan Yang; Zhiyu Dong; Kaili Dong

doi:10.1016/j.jenvrad.2023.107284

Long-distance migration law of radon in overburden of abandoned goaf during coal spontaneous combustion

J Environ Radioact. 2023 Dec:270:107284. doi: 10.1016/j.jenvrad.2023.107284. Epub 2023 Aug 25.

Authors

Zhikang Chan¹, Bin Zhou², Junfeng Wang³, Zhifan Lu¹, Qifan Yang¹, Zhiyu Dong¹, Kaili Dong¹

Affiliations

¹ College of Mining Engineering, Taiyuan University of Technology, Taiyuan, 030024, Shanxi, China.
² College of Safety and Emergency Management Engineering, Taiyuan University of Technology, Jinzhong, 030600, Shanxi, China. Electronic address: zhoubin@tyut.edu.cn.
³ College of Mining Engineering, Taiyuan University of Technology, Taiyuan, 030024, Shanxi, China. Electronic address: wangjunfeng@tyut.edu.cn.

PMID: 37634424
DOI: 10.1016/j.jenvrad.2023.107284

Abstract

The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30-350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m³) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m³, and the radon from the underground space appears on the surface at this temperature. In the range of 70-150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m³. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend.

Keywords: Abandoned goaf; Coal spontaneous combustion; Fire source detection; Long-distance migration; Radon exhalation.

MeSH terms

Coal / analysis
Coal Mining*
Fires* / prevention & control
Radiation Monitoring* / methods
Radon* / analysis
Spontaneous Combustion

Substances

Radon
Coal