Obligation to report exposure to natural radiation

The responsible party must carry out an investigation of practice that causes exposure to natural radiation in which the radiation exposure may be higher than the reference value. Such practices include at least:

• practices for the processing, use, storage or recovery of materials and wastes containing naturally occurring radioactive substances, with an activity concentration of more than one becquerel per gram (1 Bq/g) of uranium-238, thorium-232 or their disintegration products;
• mining and underground excavation;
• the production of rare earths;
• the production of thorium compounds and the manufacture of products containing thorium;
• the processing of niobium/tantalum ore;
• the production and refining of oil and gas;
• the production of geothermal energy;
• the production of titanium dioxide pigment;
• thermal phosphorus production;
• the zircon and zirconium industry;
• the production of phosphate fertilizers;
• the production of cement and the maintenance of the clinker ovens used therein;
• the use of peat and coal-fired power plants and the maintenance, repair and removal from use of the boilers in these plants;
• the production of phosphoric acid;
• the reduction smelting of metallic ores and concentrates;
• the production of household water in ground water processing facilities;
• the mining and processing of ores other than uranium ore;
• primary production of iron.

STUK may also require a report from other practices if they are capable of causing radiation exposure caused by natural radiation exceeding the reference value.

Exploration is not a practice directly subject to the obligation to investigate, but the practice may require clarification if the concentrations of uranium or thorium in the aggregates are higher than one becquerel in a gram (1 Bq/g). The average concentrations of naturally occurring radioactive substances in drilling waste and cores must be known in exploration, so that radiation protection and clearance levels can be taken into account in waste treatment, if necessary.

In accordance with the radiation legislation, which was revised in 2018, the parties responsible for the investigation must carry out the investigation before the commencement of the operations. If the operations are already underway and no investigation has been carried out, it must be carried out without delay.

The content of the report is described in Regulation STUK S/6/2022, section 3, sections 5–7. The report must include the quantity and quality of the materials, waste and emissions containing naturally radioactive substances arising from the practice, as well as a description of their further treatment or disposal. The report may also include an exposure assessment.

For the purpose of the investigation, the responsible party must take samples for radioactivity investigations. Once the results are available, a report will be prepared. STUK reviews the report and ensures that the exposure of workers and the general public has been shown to be below the reference values.

The report must be submitted to STUK using this electronic form (Formbox, in Finnish)

For the analysis, the radioactivity of the materials to be processed must be known. To this end, representative samples of the materials must be taken and radioactivity determined. In addition, the dose rate of external radiation must be measured at different workstations if such materials are handled at the workstation where the dose rate may be higher than the level of background radiation. Dose rate measurements can also be used in sampling to survey accumulations and target sampling.

Radioactivity investigations of materials are commissioned, for example, from ash, sludge, sediments, filters, raw materials, end products, by-products or waste. If there are water discharges, their radioactive substances must be investigated. Particularly in mining or metallic ore enrichment, radioactive materials that occur in nature in discharged water must be investigated.

STUK's regulatory control of natural radiation provides assistance, if necessary, in selecting the materials to be investigated. Radioactivity tests in the laboratory typically last approximately two months.

The party responsible for the practice notifies the measurement results in the report. Dose rate measurements must indicate the measuring instrument used, the distance to the object to be measured, the unit (usually µSv/h) and the background dose rate. The dose rate measurement is based on the ambient dose equivalent rate H*(10).

Radioactivity tests of materials must be carried out by a reliable and appropriate method and the results must be metrologically traceable. It is therefore advisable to use a laboratory with accreditation for radioactivity determinations.

The party responsible for the practice compares the results of material testing with the clearance levels:
Clearance levels for naturally occurring radionuclides in solid materials (STUK SY/1/2018):                             

Nuclides in the uranium-238 series include thorium-234, protactinium-234m, radium-226, lead-210 and polonium-210.

Radionuclides in the thorium-232 series include radium-228 and thorium-228.

In the investigation, the responsible party must assess the exposure of workers and the general public if the activity concentration of one or more radionuclides of the uranium-238 and thorium-232 series in solid materials exceeds 1 Bq/g.

If the activity concentrations of all radionuclides investigated in the uranium-238 and thorium-232 series in solid materials are less than 1 Bq/g, a description of the materials processed in the practice and a description of the practice are sufficient for the report. No further assessment of natural radiation exposure is required.

The clearance levels for solid materials do not apply to water discharges. Their radiation exposure to the population must always be assessed on a case-by-case basis. The limit value for minor discharges is 0.1 millisieverts per year (mSv/year).

Exposure must be assessed when the activity concentration of one or more radionuclides of the uranium-238 or thorium-232 series in solid materials exceeds 1 Bq/g or when water discharges contain naturally occurring radioactive substances.

When assessing exposure, it is advisable to make use of a Radiation Safety Expert.

The assessment of radiation exposure must take into account the external and internal exposure of workers and members of the public, including potential exposure during and after the practice. If waste is generated in operations where the activity concentrations are higher than the clearance levels, STUK's approval for the final disposal of the waste is sought in the report.

Further information about waste (stuk.fi)

Internal exposure is estimated by calculation on the basis of radioactivity determinations made on the materials used in the process. External radiation exposure is calculated using the dose rates of the workstations and the working hours spent at the workstations. Alternatively, external exposure may also be estimated by calculation using the concentration data.

In the exposure assessment, STUK must be notified of:

• information on who performed the investigation;
• details of the radionuclides and exposure pathways relevant to the exposure as well as the key criteria for assessing the exposure;
• an estimate of the radiation doses received by the worker and the number of workers exposed to radiation;
• an estimate of the radiation doses received by members of the public and the number of people exposed to radiation;
• the measures limiting radiation exposure which have been accounted for when assessing the occupational and public exposure.

The investigation must be repeated or updated if there is a change in the practices or conditions which could lead to exposures above the reference values. This can happen, for example, when the raw material or its origin changes. 

STUK recommends that the report be updated every five years.

The report must be submitted to STUK using this electronic form (Formbox, in Finnish)