All building materials that originate from minerals always contain a certain amount of radionuclides. These are mainly potassium, uranium, thorium and the radionuclides that are created as their radioactive decay chains. Of these, the most significant is radium (Ra-226). The Ra-226 presence in building materials causes exposure to persons living in dwellings - either by inhalation of radon daughters that decay from radium and release from the building material to indoor air, or by hard gamma radiation that releases from the building material as a consequence of the radioactive decay of the natural radionuclides to be present.
How to measure radioactivity in building material?
The measurement of the radium concentration and the other natural radionuclides in building materials is carried out in a laboratory. To measure radioactivity, it is necessary to take a sample of material with a weight from 1 to 2 kg; to crush the sample to a grain size of few millimetres; and to dry and send the sample to the laboratory. The sample is measured by gamma spectrometry, that is, gamma radiation that originates in the sample by radioactive decay is measured and analyzed. The measurement of the natural radionuclide concentration in the building material is classified as the significant performance from the standpoint of radiation protection, and hence, this performance requires SUJB permission. There are now 12 companies in the Czech Republic that have received the permission. You can find the list of the companies, which have received the permission (the names and contact addresses) on SUJB web page - www.sujb.cz
The radium content in the building materials that are used in the Czech Republic achieves normally the order of tens of Bq/kg. The higher values are usually found in the materials that are produced from raw waste material (e.g., fly ash, slag and clinker) and some types of stone, for example, granite. In the table, you can find the mean value and the maximum values of the radium concentrations in the building materials that were used in the Czech Republic (produced and imported) from 1998 to 1999. From the standpoint of the exposure to the population in houses, the most significant materials are the materials from which the majority of houses have been built (e.g., concrete, bricks and blocks). The estimate of the exposure mean value of building materials in the Czech Republic (according to the results from 1999) ranges from 0.4 to 0.6 mSv per year, that is ten times less compared to the exposure to radon that enters the houses from soil.
Duties of producers/importers of building materials
The requirements for measurement and evaluation of content of natural radionuclides in building materials are set by Law No. 263/2016 Coll. (the Atomic Law), § 9 a § 101, as amended. More information is here.
Limit and guidance levels
If the radium content is higher than the specified limit value, the building material must not be used. The limit values are specified in the following way: 150 Bq/kg (for the materials that are frequently used for construction, for example, bricks, concrete, etc.); 200 Bq/kg (for the material used in a limited quantity for construction, for example, wall tiles, etc.); and 1,000 Bq/kg for the building material that is exclusively used for the construction of non-residential areas, e.g., roads. In addition, there is a tendency to reduce the nuclide concentrations in building materials as reasonably as possible. Hence, the other indicators were introduced - so-called guidance levels that are lower than the limit values (for example, 80 Bq/kg for the materials that are frequently used in building industry). If the limits are exceeded, it is considered that radioactivity by a reasonable method, for example, by a change in technology, should be reduced. In 1999, the guidance level was exceeded in 4 percent of the measured samples, and the limit value was exceeded in 1 percent of the measured samples.
Self-made building material
Our legislation does not require any measurement of the radium concentration in the building materials that are produced for own need, and no limit has been specified for such materials. This is the interest of a builder to avoid materials in which the radium concentration exceeds the limit values that are specified for production and import. The measurement of the radium concentration would be mainly suitable in the cases of "risk" materials, that is, slag and fly ash in which the limit value may be exceeded several times. The additional remedial measures in houses that are constructed from such material would be a complicated and expensive matter in the future.
Measurement results of the radium content (Ra-226) in building materials in the Czech Republic
|Fly ash and slag||75,5||363|