An initial ACARP project was completed in October 2003 to demonstrate the use of radon detecting technique for locating an underground heating area from surface. The project reviewed the radon technique including its principles, operation procedures, data processing, and applications. A field demonstration of the radon technique was also undertaken at Dartbrook mine.

The technique was developed by Taiyuan University of Technology and has been used in over 20 underground Chinese coal mines to detect the location of underground spontaneous combustion.

It works like this: radon-222 gas occurs naturally as a decay product of the long-lived uranium-238 that is a common radioactive element in rock/coal/soil strata. If spontaneous combustion of coal occurs underground, the radon emanation ratio from coal, and its migration through the overlying coal/rock strata increases significantly. This results in an elevated concentration of radon above the point of spontaneous combustion occurring underground. Measuring and analysing the radon concentrations at the surface allows an underground area of spontaneous combustion of coal to be detected.

In the field test, radon detecting techniques were able to identify zones of temperature abnormalities over a known heating area in the longwall 7 goaf at Dartbrook mine. The tests demonstrated elevated radon concentration vertically above areas of assumed spontaneous combustion, which was in agreement with the analysis of gas monitoring data.

"The demonstration of locating underground heatings with surface radon detecting technique is quite encouraging, however the scientific reasoning for the process is also quite challenging," said key researcher, Dr Sheng Xue, CSIRO Exploration and Mining.

A second round of research was awarded ACARP funding last year and commenced last month to further the understanding of the technique. The core scientific principle is that radon emanation from coal is temperature dependent, ie. is propelled by sponcom, but little data is available in the public domain to illustrate the dependence. Factors such as coal type, moisture content and particle size are also thought to have an impact.

The main stages of the next phase of the project include a bench-scale investigation of the temperature dependent mechanism of radon emanation from coal and its vertical movement in overburden strata, prototype development of a radon collector/cup and detector, specific for mine use, and a mine trial of the prototype.

It is hoped the success of this project will lead to the commercial application of the surface radon detecting technique in the Australian coal industry with major benefits to the coal industry. These would include improvement in spontaneous combustion management capability leading to a significant reduction in risk for underground coal mines, as well as development of a practical technique to remotely detect the location of spontaneous combustion.

This project will also benefit from an established close collaboration between CSIRO and Taiyuan University of Technology that developed the radon detection technique.

"Detailed studies of the underlying science of the radon technique are of fundamental importance to apply and further develop the technique in the Australian coal industry," Dr Xue said.

Further information can be obtained from ACARP report C12005.