Guidance about radiation safety on mining operations

Radiation is energy that travels through vacuums, air and some material and is part of the natural environment.

• Background radiation
  • Includes cosmic rays from outer space, gamma radiation from uranium, thorium, and potassium in the ground, radon gas in the air, and radioactive elements in our food and water.
• Non-ionising radiation
  • Ranges from extremely low frequency radiation, through the audible, microwave, and visible portions of the spectrum into the ultraviolet range.
• Ionising radiation
  • Most atoms are stable and will never change, but certain atoms ‘decay’ and become stable as completely different elements.
  • The decay process can cause excess energy to be released as alpha, beta and gamma radiation.

Naturally occurring radioactive material (NORM) is a term describing materials containing radionuclides that exist in the natural environment. In mining, these might be minerals associated with:

• uranium ores
  • Uranium ore is mined for the ability to eventually produce energy in nuclear reactors.
• mineral sands
  • Heavy mineral sands are radioactive due to the presence of the radioactive element thorium
  • Thorium is present in monazite (a source of rare earth metals), zircon, and the minor heavy minerals (xenotime and leucoxene).
• rare earth elements (REEs)
  • Rare earth ores contain radioactive thorium and uranium, so active radiation control is needed in these mines and extraction plants.
• other examples
  • Mines, concentrators and smelters where you sometimes find radioactive materials are those handling tin, tantalum and niobium, gold, tungsten or molybdenum.

Exploration

During exploration for naturally occurring radioactive minerals, or where such minerals are incidentally encountered, the main control will always be to limit the generation of dust and potential exposure to it, particularly during soil sampling and splitting, and reverse circulation (RC) drilling, which can all produce substantial levels of dust. Controls need to prevent the dust being breathed in or swallowed.

If work activities are unavoidably dusty, a respirator or dust mask and good housekeeping and personal hygiene practices (e.g. washing before eating, laundering clothing outside of living areas) are required.

Gamma doses will only require active control if people are working continuously on a large outcrop of radioactive mineralisation or close to a large amount of high grade ore.

Devices used in exploration that have a radiation source include downhole or well logging tools, and portable or handheld X-ray fluorescence (XRF) analysers (used to determine chemical composition). Precautions for these devices are described below.

Radiation sources and irradiating apparatus

Many mine site laboratories have equipment such as X-ray diffraction (XRD) and X-ray fluorescence (XRF) units. The operators of such equipment need to be trained and licensed under the Radiation Safety Act 1975.

Significant radiation sources frequently found on mines are the sealed gamma and neutron sources (typically Cobalt-60 or Caesium-137) in bin level gauges and slurry density gauges. These gauges must be subject to formal controls to allows work to be carried out near them safely. Isolations and removals may only be performed under supervision of the radiation safety officer or another licensed person.

Other sealed sources found in mines include inline X-ray fluorescence sources used for analysis of mineral content during the milling and processing of ores. Borehole logging sources are used for analysis of minerals during the drilling of exploration boreholes.

Radiation management plan (RMP)

Control of radioactive material and monitoring of both employee and environmental exposure to radiation are part of the minimum requirements for an approved radiation management plan (RMP). The radiation safety officer is the key person ensuring radiation control and monitoring techniques are adequate and effective.

Radiation controls

The principal methods to minimise radiation exposure are to:

• reduce the time near
• increase the distance from

areas where exposure is possible, as well as reducing dust and shielding against gamma exposure.

Minimising the spread of dust containing radioactive material, and monitoring for gamma hotspots are basic control methods.

Areas such as vehicle or control cabins and crib rooms need to be kept dust free.

At some sites, active control and individual monitoring are required to ensure worker doses are kept below specified annual limits.

All Australian uranium mining and mineral sands operations are required to contain all radioactive wastes, in mined out pits or in engineered tailings dams. Mineral sands operations are usually required to either bury the radioactive monazite tails in the base of worked out pits, or to dilute them with non-radioactive tails and place in the pits, or in dredge ponds, during backfilling.

The main techniques used to determine individual exposure to radiation are personal thermoluminescent dosimeter badges (TLD) badges worn to assess gamma exposure, and personal air samplers used for dust monitoring and estimation of alpha exposure.

In addition, survey meters can be used for area monitoring surveys, while surface alpha contamination surveys check for cleanliness of work areas and crib rooms.

Monitoring equipment must be working correctly and calibrated annually.

Safe work practices

All workplaces should use the hierarchy of controls to progressively reduce the risk of injury or exposure to employees.

The choice of personal protective equipment (PPE) that may be required will depend on the type and amount of potential exposure. PPE that is likely to be used includes overalls, safety glasses, P2 dust mask, safety boots and gloves.

Good housekeeping personal hygiene is important, including washing hands and ensuring clothing is dust free before crib breaks.

The following toolbox presentations give a practical overview on how to manage risks when working with radioactive materials in the field.