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Radionuclides in building materials

  • When using rocks and soils for building purposes, radionuclides contained therein or released from them may lead to a radiation exposure of the population.
  • The mean value of the gamma local dose rate (ODL) in buildings caused by the natural radionuclides in building materials is about 80 nanosievert per hour. ODL values above 200 nanosievert per hour are rare.
  • The building materials traditionally used in great quantities in Germany, are generally not the cause for enhanced radiation exposures due to radon in buildings.

When using rocks and soils for building purposes, radionuclides contained therein or released from them may lead to a radiation exposure of the population. Of special importance are the radionuclides of the radioactive decay chains of uranium-238, thorium-232 and potassium-40.

Causes for the radiation exposure of occupants of indoor spaces caused by natural radionuclides in building materials are

  • the gamma radiation emitted by the building materials affecting the body from outside and
  • the inhalation of the gas radon and its decay products released from the building materials in the interior of houses.

Examination and evaluation

For over 40 years, examinations and evaluations of the natural radioactivity contained in building materials and building products have been carried out in Germany.

Therefore, the Federal Office for Radiation Protection (BfS) has data of the specific activities of the relevant radionuclides from over 1,500 samples of natural stones, building materials and mineral residues. In 2007, examinations of 120 samples building materials have been updated and published in a report BfS-SW-14/12 (in German only). For a large number of samples, the radon release was additionally determined.

Specific activities of natural radionuclides in natural stones, building materials and residues
(given are mean value and range (in brackets) in becquerel per kilogram)
MaterialRadium-226Thorium-232Potassium-40
Granite100
(30 - 500)
120
(17 - 311)
1,000
(600 - 4,000)
Gneiss75
(50 - 157)
43
(22 - 50)
900
(830 - 1,500)
Diabase16
(10 - 25)
8
(4 - 12)
170
(100 - 210)
Basalt26
(6 - 36)
29
(9 - 37)
270
(190 - 380)
Granite10
(4 - 16)
6
(2 - 11)
360
(9 - 730)
Gravel, sand, gravel sand15
(1 - 39)
16
(1 - 64)
380
(3 - 1,200)
Natural gypsum, anhydrite10
(2 - 70)
< 5
(2 - 100)
60
(7 - 200)
Tuff, pumice stone100
(< 20 - 200)
100
(30 - 300)
1,000
(500 - 2,000)
Clay< 40
(< 20 - 90)
60
(18 - 200)
1,000
(300 - 2,000)
Brick, clinker brick50
(10 - 200)
52
(12 - 200)
700
(100 - 2,000)
Concrete30
(7 - 92)
23
(4 - 71)
450
(50 - 1,300)
Sand-lime brick, porous concrete15
(6 - 80)
10
(1 - 60)
200
(40 - 800)
Slag from Mansfelder copper-slate1,500
(860 - 2,100)
48
(18 - 78)
520
(300 - 730)
Gypsum from flue gas desulfurisation20
(< 20 - 70)
< 20< 20
Brown coal filter ash82
(4 - 200)
51
(6 - 150)
147
(12 - 610)

The mean value of the gamma local dose rate (ODL) in buildings caused by the natural radionuclides in building materials is about 80 nanosievert per hour. ODL values above 200 nanosievert per hour are rare.

Radon

Radon of special importance

The gaseous radon-222 produced from radium-226 due to radioactive decay is of special interest from the radiation protection point of view. According to the latest findings, a significant portion of the lung cancer cases among the German population is caused by exposure to radon and its decay products in buildings.

The radon release from building products is determined by the specific activity of radium-226 and other material characteristics determining the radon transport (such as porosity). Examinations have shown that the traditional use of building materials such as

  • concrete,
  • brick,
  • porous concrete and
  • sand-lime brick

are generally not the cause for the annual mean value of the indoor radon concentration recommended by the Federal Office for Radiation Protection being exceeded. This is not to exceed 100 becquerel per cubic metre.

The contribution of radon-222 from building products to the indoor radon concentration is maximum 70 becquerel per cubic metre. In building products currently commercially available, values clearly below 20 becquerel per cubic metres were measured.

Higher radon concentrations in some building materials

Radon release rates that may result in higher indoor concentrations were occasionally measured in residues from the incineration of coals with enhanced uranium/radium concentrations (formerly used locally to fill ceilings and referred to as “coal slag”). There were also rare cases where they were measured on natural stones with enhanced specific activities of radium-226. Despite the comparatively high specific activity of radium-226 in Mansfelder copper-slag, no enhanced radon concentrations were measured in buildings made from this material.

In some countries higher radon concentrations were detected in buildings where the so-called chemical gypsums (residues of phosphorite processing) had been used as well as in lightweight concretes made by using alum shale. There are some very few occurrences of above-average radon concentrations in the traditional mining regions, where debris or residues from ore processing with enhanced radium concentration were used as building material, as concrete or mortar additive or as foundation in house building.

Thoron

According to present knowledge, no materials were used in Germany for building purposes which, as a result of enhanced thorium concentrations, could lead to radiation-protection relevant exposures to the gas radon-220 (thoron) and its decay products. The possibility of unbaked clay as building material leading to individual cases of enhanced thoron values in room air, cannot be entirely excluded, however.

You will find more information on the topic clay and thoron in the article "Clay as building material".

Law

Legal limitation of building material

In some residues from industrial processes the natural radioactive materials accumulate. When using these residues, for example as secondary raw material in building, enhanced radiation exposures of the population cannot be excluded.

1. Radiation protection legislation

The restriction of the effective dose resulting from external exposure in common rooms for single persons of the population is defined in the Radiation Protection Act (Strahlenschutzgesetz, StrlSchG) by a reference value of 1 millisievert per year in addition to the effective dose of the background outside. Under Radiation Protection Act, a reference value serves as a standard for testing the suitability of measures. According to Radiation Protection Act, a reference value is not a limit value that must not be exceeded.

An appropriate examination has to be carried out for all industrial residues listed in Annex 1 or all raw materials listed in Annex 9 of the Radiation Protection Act, if these materials are intended to be used for buildings including common rooms.

The proof of compliance with the reference value of the effective dose of 1 millisievert per year has to be done by means of the calculation of an activity index as given in Annex 17 of the Radiation Protection Ordinance (StrlSchV). This index is calculated from the activities of the radionuclides

  • Radium-226,
  • Thorium-232 and
  • Potassium-40

enclosed within the building materials and considers thickness and density of it.

2. Building legislation

According to the Building Product Directive (BauPVO, Directive EU No. 305/2011), a building product may only be placed on the market in the EU Member States if it fulfils the key requirements for hygiene, health and environment protection, among others with respect to the release of hazardous radiation. This EU Directive is directly binding in German law and has been effective for the manufacturers since 1 May 2013.

The European Institution for Standardisation (CEN) received the task from the European Commission to standardize the measurements of Radium-226, Thorium-232 and Potassium-40 and to develop an European standard to calculate the effective dose.

Natural stones

Natural radionuclides in natural stones

Radionuclides in building materials Radionuclides in building materialsMedia values of the specific activity of natural radionuclides in natural stones

Today, natural stones are used more frequently in all areas of building, inside and outside the house. Therefore, the Federal Office for Radiation Protection, with the support of Deutscher Naturwerkstein-Verband e.V., examined in 2006 a number of marketable tiles and other sheet materials of various origin with respect to their content of natural radioactivity and from the radiation protection point of view.

The main focus was on gamma spectrometric measurements of the specific activities of

  • radium-226,
  • potassium-40 and
  • thorium-232.

The results have been shown in the chart. The presented median values (central values) mean that half of the samples examined are above and half are below this value.

The material is classified here according to rock type.

It should be pointed out that, for considerations that are oriented towards special applications, processing and maintenance of the materials, the trade does not always use correct names for the stones. For example, when it says “granite”, it is not necessarily granite stone; this term is also used for gneiss, diorites, granodiorites and other stones.

Specific activities of the examined natural stones

The specific activities of the examined natural stones is

  • for potassium-40 in the range between 10 and 1,600 becquerel per kilogram,
  • for radium-226 between under 10 and 355 becquerel per kilogram and
  • for thorium-232 between under 10 and 330 becquerel per kilogram.

For comparison and complementation cf. the above Table. Apart from the radionuclide concentration and the radon release, the possible radiation exposure and complementation cf. the above Table due to the individual building materials depends on the conditions of use.

As a result of the measurements by BfS, it can be seen that the examined currently available building products and also the examined natural stones can be used in buildings without any restriction, even if they are used on large surfaces. The reference value for the effective dose of 1 millisievert per year for persons of the population due to radionuclides of natural origin (except for radon) has been met in all cases.

Under Radiation Protection Act, a reference value serves as a standard for testing the suitability of measures. According to Radiation Protection Act, a reference value is not a limit value that must not be exceeded.

State of 2023.01.13

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