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What are NORM residues?
- Radionuclides of the naturally occurring decay chains of uranium-238, uranium-235 and thorium-232 are present in traces in all rocks and mineral ores.
- So when using raw materials, natural radionuclides are generally introduced unintentionally into industrial processes. In some branches of industry, natural radionuclides can accumulate in parts of the material flux.
- In specialist literature, these residues are often referred to as “naturally occurring radioactive materials" ("NORM” for short).
- With the introduction of Part 3 of the Radiation Protection Ordinance, the protection of workers and the general public against increased radiation exposure from natural radioactive materials was regulated in Germany for the first time.
General information on natural radioactivity
When the specific activity within a decay chain is the same for all radionuclides, this is known as “radioactive equilibrium”. Chemical processes (for example dissolution processes involving water) and physical processes (for example gas emissions of the radioactive noble gas radon or the transportation of radionuclides by water) can result in the redistribution of radionuclides. This redistribution process can disturb the equilibrium. As a consequence, natural radionuclides are present in all areas of the environment (air, soil, water, plants, animals).
Depending on the mineralogical composition of the rock - in particular ore mineralisations - the radionuclide content varies. An upper limit for the natural background content of uranium and thorium (and its decay products) in soil and rocks is generally 0.2 becquerels per gram (corresponds to 200 becquerels per kilogram); in individual cases (for example granite), a specific activity of up to 0.5 becquerels per gram has been recorded. Special thorium and uranium minerals may have demonstrate specific activity of several becquerels per gram. The radionuclides in the decay chain are – with the exception of the noble gas radon – all heavy metals. Chemically and physically, they behave in the environment and in industrial processes in a comparable way to other, non-radioactive heavy metals.
Residues with enhanced natural radioactivity from industrial processes
When using raw materials (for example ores), natural radionuclides are generally introduced into technological processes. In some branches of industry, employees or the general public can as a consequence of natural radioactivity be subject to increased radiation exposure. Causes are either the use of raw materials with enhanced radionuclide content or radionuclide enrichments in the residues due to certain technological processes.
In specialist literature, these residues are often referred to as “naturally occurring radioactive materials" ("NORM” for short). Examples of this are the precipitates in production tubing of the crude oil and natural gas industries, which - depending on the deposit - can show high levels of the radioactive element radium.
NORM can generally be recycled, as long as no increased radiation exposure is expected to affect individuals among the general public in the intended reuse. If from a technological or economic point of view this is not appropriate, the residues must be disposed of safely in landfills.
Legal regulations for residues
In Part 3 of the Radiation Protection Ordinance dated 20 July 2001, the protection of workers and the general public against increased radiation exposure from natural radioactive materials was regulated in Germany for the first time. The materials taken into consideration are not used because of their radioactive properties or their suitability as nuclear fuel; the enhanced radionuclide content occurs as an (undesirable) side effect of certain conventional industrial processes. Legislators therefore considered it sensible to limit regulations to the processes and materials that can significantly increase radiation exposure because of the application or disposal method that is typical today.
An increased exposure to radiation for individuals within the general public is considered to be present when the reference level for the effective dose of 1 millisievert per year is exceeded. Exceeding this level, arrangements for the protection of the general public must be undertaken. The reference level is based on the fluctuation of natural radiation exposure and is also established in other areas of radiation protection. Workers who deal with NORM within their work are considered here to be part of the general population.
With the help of comprehensive investigations in relevant branches of industry, a number of residues have been identified where further arrangements may be required for the protection of the general public during disposal or recycling. A rating scale for this is indicated by the surveillance limits in Appendix XII of the Radiation Protection Ordinance.
If these surveillance limits are exceeded, the responsible radiation protection authority in the federal state can release the residues from monitoring on application. To do this, evidence must be given to demonstrate
- that the reference level of 1 millisievert per year for the general public will be adhered to in the intended recycling or disposal and
- that the planned recycling or disposal is permitted under waste disposal laws at all.
As when dealing with these types of residues there is no potential for sudden release or accident, the legislator has refrained from requiring a permission usually required under radiation protection law. Generally, the industries affected implement the measures on their own responsibility. They must however report the findings of their investigations to the competent state authorities. On demand, these authorities can then issue further requirements or checks.
Experiences to date following the enforcement of Part 3 of the Radiation Protection Ordinance show that the regulations have increased the awareness of everyone involved of the possible problems and dangers when dealing with materials that contain enhanced natural radioactivity.
As a consequence, radiation exposure levels have fallen in some areas without the affected industry branches being overly burdened.
The Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB) and the Federal Office for Radiation Protection (BfS) support the enforcement of Part 3 of the Radiation Protection Ordinance by the relevant state authorities by means of sub-statutory policies and recommendations. So for example the Commission on Radiological Protection (SSK) has on the instigation of the BMUB published a recommendation for the representative sampling of residues.
The BfS supports implementation by establishing guidelines for assessing the radiation exposure and by developing measurement guidelines. Furthermore, the BfS is currently checking whether the recommendations and guidelines on the subject of mining legacies are transferable to residues under Part 3 of the Radiation Protection Ordinance.
State of 2017.05.09