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Naturally occurring radioactivity in industrial by-products from coal-fired power plants, from municipal waste incineration and from the iron- and steel-industry
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Naturally occurring radioactivity in industrial by-products from coal-fired power plants, from municipal waste incineration and from the iron- and steel-industry K.-H. Puch a , R. Bialucha b , G. Keller c a VGB PowerTech e.V., Klinkestraße 27-31, 45136 Essen, Germany b Forschungsgemeinschaft Eisenhüttenschlacken, Bliersheimer Straße 62, 47229 Duisburg, Germany c Universität des Saarlandes, Institut für Biophysik, Universitätsklinik, Geb. 76, 66421 Hamburg, Germany
The Council Directive 96/29/Euratom on the basic safety standards was to be converted by May 13th, 2000 into national law. The EC Member Countries were asked to identify paths with elevated radioactive exposures. For these exposures, regulations were then to be made in national law. In the 1st draft, the industrial by products from coal-fired power plants, from municipal waste incineration and the iron- and steel-industry were listed in the amendment of the German radiation protection enforcement. For these by products values for nuclide concentrations were already available and these were supplemented by extensive investigations. This proved that the nuclide concentrations for the two important natural decay series are under 200 Bq kg−1 . Through this evidence, it is guaranteed that no regulation is necessary for these materials and the listing in the appendix XII is not justified. In this form, the amendment of the radiation protection enforcement was implemented in August 1st, 2001.
1. Introduction Every year in Germany 17.3 Mt of ash are produced in coal burning in the form of boiler slag, bottom ash and fly ash. 7.3 Mt result from the burning of bituminous coal and 9.6 Mt from lignite (Table 1). 98% of the bituminous coal ash is utilized in the construction and mining industries. The majority of lignite ash is used for the filling and recultivation of open pit mines. It is utilized either unmixed or mixed with FGD gypsum and/or FGD water. The amount of by-products from municipal waste incineration plants is about 3.2 Mt. The main product is bottom slag (2.5 Mt). The allotment of fly ash and different salts is 0.35 Mt. RADIOACTIVITY IN THE ENVIRONMENT VOLUME 7 ISSN 1569-4860/DOI 10.1016/S1569-4860(04)07123-2
© 2005 Elsevier Ltd. All rights reserved.
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Table 1 Production and utilization of by-products from power stations in Germany in 2000 By-product Bituminous coal-fired power stations
Lignite-fired power stations
Boiler slag Bottom ash Fly ash Fluidized bed combustion ash Subtotal Bottom ash Fly ash Fluidized bed combustion ash Subtotal Total
Production (Mt)
Utilization (Mt)
2.35 0.53 4.12 0.42
2.35 0.51 4.12 0.42
7.42 1.83 7.90 0.19
7.40 1.83 7.90 0.19
9.92 17.34
9.92 17.32
Table 2 Production of blast furnace slag in Germany in 2000 Production
Mt
Slag from non-phosphorous steel making Slag from other iron making processes Total production Destocking Total
7.46 0.07 7.53 0.10 7.63
Table 3 Production of steel making slag in Germany in 2000 Production
Mt
Slag from oxygen steel making Slag from electric steel plants Slag from special processes Total
3.50 1.67 0.64 5.81
The bottom slag is a useful material for earth- and road construction. Fly ash and salts are utilized in the mining industry. The production and utilization of the different by-products from the iron- and steel-making industry is shown in Tables 2 and 3. The total amount of 13.44 Mt of slag is utilized as building material, for earthwork and road construction, in the cement industry and as fertilizer. Like any other natural rock, industrial by-products contain radioactive nuclides resulting from the natural decay series. This is why they emit ionizing radiation. In the following, it will be examined whether handling in the plants as well as disposal of by-products and
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K.-H. Puch et al. Table 4 The mean effective radiation dose per year from natural radiation exposure to the public in the Federal Republic of Germany in 1994 according to [1] Source
Mean effective dose in mSv y−1
Cosmic radiation Terrestrial radiation – outdoors (5 h d−1 ) – indoors (19 h d−1 ) Inhalation of radon decay products – outdoors (5 h d−1 ) – indoors (19 h d−1 ) Incorporated natural radioactive materials Total natural radiation exposure
0.3 0.1 0.3 0.2 1.2 0.3 2.4
their utilization as building material lead to an increase in radiation exposure that is healthendangering to the personnel or the public. According to a publication of the German authorities, the natural human radiation exposure in Germany is between 2 and 6 mSv y−1 (effective radiation dose) with a mean value of 2.4 mSv y−1 (Table 4) [1]. Along with the civil radiation exposure of 1.5 mSv y−1 (primarily by the use of ionizing radiation and radioactive materials in medicine), the total exposure is some 3.9 mSv y−1 (mean value).
2. Natural radioactive nuclides in industrial by-products 2.1. Coal fired power plants The natural radioactivity of coal, and thus of the ash produced through its firing, mainly results from radionuclides in the decay series of uranium–radium, thorium and uranium–actinium, as well as from potassium-40. The inert gas radon, which is also produced in the decay series, may partly escape through the solid substances into the air. Radon-220 is less important because of its half life period of 56 s. The uranium–actinium series is not dealt with because its content of nuclides is only small when compared with total radiation. Because of the age of coal, the radionuclides are balanced, i.e. all nuclides in a given decay series have specific activities which, in a balanced position and depending on the ramification, are in a given relation to each other. For this reason, it is general practice to give an account of the activity concentrations of a representative radionuclide for each series, usually radium-226 and thorium-232 for the uranium and the thorium decay series, respectively. In the firing of the coal, most of the radionuclides remain in the ash. The ash content of bituminous coal used in power stations in Germany is in the range of about 7 to 40%, the mean being 15%. Examination of the radioactivity of solid material passing through power stations has shown that more than 90% of the radioactivity in coal is retained in the ash. Only a small percentage of the radioactivity can be found in flue gas desulphurization products like FGD gypsum (Fig. 1) [2]. Due to the ash content, the natural radioactive nuclide concentration in fly ash exceeds that in coal by a factor of 2 to 15.
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Fig. 1. Mass balance and activity flow in a coal fired power plant according to [2]. Upper value: thorium series with the following nuclides: Th-232, Ra-228, Ac-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Po-212 (64%), Tl-208 (36%); lower value: uranium series with the following nuclides: U-238, Th-234, Pa-234, U-234, Th-230, Ra-226, Rn-222, Po-218, Pb-214, Bi-214, Po-214. Table 5 Activity concentration of bituminous coal fly ash (in Bq kg−1 ) Origin
D D PL D GB AUS diverse D D D D Overall
Source
[3] [4] [5] [2] [6] [7] [8] [9] [10] [11] [12]
No. of samples
CRadium-226 MV
min
max
CThorium-232 MV
min
max
CPotassium-40 MV
min
max
28 26 10 3 4 9 50 5 3 20 6 164
210 264 237 126 89 90 127 172 122 90 224 170∗
80 85 70 93 72 7 75 148 87 51 192 7
390 370 611 137 105 160 235 204 177 165 281 611
130 120 200 121 68 150 96 118 88 83 106 114∗
60 44 89 96 53 7 42 100 73 59 93 7
260 190 514 155 94 290 131 140 115 120 122 514
700 n.i.a. 833 700 900 220 437 955 n.i.a. 1039 827 652∗
330 n.i.a. 385 459 800 20 205 881 n.i.a. 760 740 20
1110 n.i.a. 1776 877 1250 570 765 1018 n.i.a. 1480 1000 1776
MV: mean value; n.i.a.: no information available. ∗ Weighted mean value.
The radionuclide concentration in an ash is determined by the radionuclide concentration in the coal, the ash content of the coal and the conditions in the power station. Owing to the low activity concentration in German lignite, the lignite coal ash has a very low value too. Its activity concentration is similar to that in natural soil and thus it causes no increase in radiation. Therefore it is not dealt with further in this report.
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Table 6 Activity concentration of coal fly ash from German power stations (in Bq kg−1 ) Source
[3] [12] [4] G1 [2] [9] [11] [10] [13] G2 Overall
No. of samples 28 6 26 60 3 5 20 3 8 39 99
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
210 224 264 235 126 172 90 122 113 111 186
80 192 85 80 93 148 51 87 59 51 51
390 281 370 390 137 204 165 177 182 204 390
130 106 120 123 121 118 83 88 79 90 110
60 93 44 44 96 100 59 73 69 59 44
260 122 190 260 155 140 120 115 105 155 260
700 827 n.i.a. 722 700 955 1039 n.i.a. 836 881 785
330 740 n.i.a. 330 459 881 760 n.i.a. 380 380 330
1110 1000 n.i.a. 1110 877 1018 1480 n.i.a. 1240 1480 1480
MV: mean value; n.i.a.: no information available; G1: total evaluation of measurements before 1980; G2: total evaluation of measurements after 1980.
A summary of international measurements of activity concentrations in bituminous coal fly ash can be found in Table 5. The mean values for radium-226, thorium-232 and potassium-40 are 170, 114 and 652 Bq kg−1 , respectively. An evaluation of the values for bituminous coal ash from German power stations (Table 6) shows that the mean values for radium-226 and thorium-232 are similar to those in Table 5 (186 and 110 Bq kg−1 , respectively), whereas the mean value for potassium-40 is 785 Bq kg−1 which is slightly higher than the mean in Table 5. An interesting point to note is that the results in the later analyses [2,9–11,13] differ from those in the earlier ones [3,4,12]. The earlier investigations [3,4,12] focused on the emission of radioactivity from coal-fired power stations through the chimney. To determine the emission, either so-called “clean gas ash” discharged with the flue gas, or fly ash in the last stage of the electrostatic precipitator was examined. In this stage, the ash is extremely fine and comparable to clean gas ash. It is well known that the radioactivity of coarser ash, like that in the first stages of the electrostatic precipitator, is lower than that of the fine ash in the last stage [4,14]. The later measurements, however, concentrated on the evaluation of the total ash collected in the electrostatic precipitator, just as it is utilized. These measurements then resulted in clearly lower values for radium-226 and thorium-232 whereas the value for potassium-40 was slightly higher. The mean values in Table 5, evaluated from all of the values measured, therefore include a conservative approximation. The overall mean values and their band-widths have been proven reliable through several independent studies. The results shown in Table 7 for boiler slag display slightly lower mean values. In Table 8, the analyses of bottom ash are presented. In the tested cases, the activity concentration was lower than that of the respective fly ash. Besides the direct radiation of the radionuclides, the radioactive gases radon-222 and radon220 (also called thoron), as well as their short-lived daughters, contribute to the radiation. In
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Table 7 Activity concentration of boiler slag (in Bq kg−1 ) Source
[10] [12] [15] [13] Overall
No. of samples 24 3 4 2 33
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
138 195 166 130 146
68 181 144 121 68
245 211 207 140 245
93 93 136 119 100
59 85 107 76 76
162 104 170 162 170
835 765 512 910 794
441 666 337 660 337
1240 851 677 1160 1240
MV: mean value. Table 8 Activity concentration of bottom ash (in Bq kg−1 ) Source
[13] [16]
No. of samples
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
2 n.i.a.
70 108
70 46
70 166
40 79
40 25
40 120
355 514
340 196
370 742
n.i.a.: no information available; MV: mean value.
order to assess the radioactivity of a material, not only must the activity concentration be considered, but also the exhalation of the radon and thoron stemming from the material itself. As a result of their production at high temperatures ranging between 1200 and 1700 ◦ C, the ashes from furnaces burning pulverized coal have a glassy structure. This causes the ash to have a relatively low emanation rate in comparison with other materials [17]. The quantity of emanated radon atoms which actually are released into the air depends on the structure of the pore system in the building material. Therefore, in order to know the radiation contribution of a building material, the content of radionuclides as well as the exhalation rate must be known. The exhalation rates of particular materials with and without bituminous coal ash will be dealt with later. 2.2. Iron- and steel-marketing industry The activity concentration measurements for air cooled blast furnace slag and granulated blast furnace slag underline the same magnitude for the mean values of both materials (Tables 9–11). The range between the min- and max-values is large for both types of slag. This effect is influenced by the different raw materials in the different plants. But the mean values are below 200 Bq kg−1 . 2.3. Municipal waste incineration plants The examination of different by-products from municipal waste incineration plants shows the expected low activity concentrations (Tables 12–14). The values for all materials are at the same level. Compared with the other products, there is no further need to mention these.
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K.-H. Puch et al. Table 9 Activity concentration in iron and steel making slags in the year 1991 (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Steel making slag Granulated blast furnace slag Air cooled blast furnace slag
5 116 64
0 43 70
1 180 200
Table 10 Activity concentrations in air cooled blast furnace slags (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Min Max Mean value
66 145 99.3
28 129 58.6
60 405 205.0
Table 11 Activity concentrations of granulated blast furnace slags (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Min Max Mean value
81 360 150.2
30 125 64.8
70 320 141.9
Table 12 Activity concentrations of fly ash from municipal waste incineration plants (MWIP) Nr.
25 33 35 39 26 32
Sample
Fly ash MWIP A Fly ash MWIP B Fly ash MWIP C Fly ash MWIP D Fly ash MWIP E Fly ash MWIP F Mean value
Concentration in Bq kg−1 CThorium-232
CRadium-226
CPotassium-40
15 8 9 14 16 21 14
19 16 14 20 25 25 20
2019 2410 890 756 423 393 1148
The question arises, where do the above listed activity concentrations range compared to the limits of the Council Directive 96/26 Euratom [18] setting the basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation, dated May 13, 1996. This will be set up as an example for fly ash.
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Table 13 Activity concentrations of bottom slag from municipal waste incineration plants (MWIP) Nr.
34 31 27 36 37 38 40 43
Concentration in Bq kg−1
Sample
Bottom slag MWIP A Bottom slag MWIP B Bottom slag MWIP C Bottom slag MWIP D Bottom slag MWIP E Bottom slag MWIP F Bottom slag MWIP G Bottom slag MWIP H Mean value
CThorium-232
CRadium-226
CPotassium-40
11 9 10 15 15 13 16 14 13
14 15 11 18 19 17 21 17 17
208 193 206 215 179 213 186 159 195
Table 14 Activity concentrations of salts from municipal waste incineration plants (MWIP) Nr.
29 30 41 42
Sample
Salt MWIP B Salt MWIP C Salt MWIP D Salt MWIP e Mean value
Concentration in Bq kg−1 CThorium-232
CRadium-226
CPotassium-40
2 2 2 2 2
6 5 2 5 4
218 10 21 22 49
3. Exposure of personnel 3.1. In the power station Inhalation and ingestion of dust particles as well as direct radiation are the potential ways in which exposure may occur while handling ash. Dust-forming fly ash is most often forwarded pneumatically from the electrostatic precipitator through a closed system into a storage silo. Thus, in general, there is no direct contact between the personnel and the ash in the transport-, storage- and loading-facilities. Silos are emptied either through a mixing screw, with a 10 to 15% addition of water, onto a truck or a conveyor belt, or through flushing pipes in suspension with water, or transferred in dried form through a closed system into a silo-truck. Exhaust- or filtering-systems prevent the release of dust into the open. A considerable buildup of dust is possible only during system disruption. Radiation exposure is almost totally eliminated through the shielding effect of the walls of the forwarding mechanisms and silos. Direct contact of personnel with power station ash is restricted to repair works, i.e. to short intervals of time. For reasons of general health protection (exposure to dust), filtering masks and safety clothing must be worn when the occasionally
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necessary repair and inspection work is conducted in the precipitator or in the silos. Thus, ingestion and inhalation are almost eliminated. Handling of ash from coal combustion in power stations does not lead to any significant increase in radiation exposure. 3.2. At the disposal site Compared to some other industrial nations, very little of the ash from bituminous coal power stations is disposed of in Germany. Only 75 000 tonnes, i.e. 1%, of the bituminous coal ash produced in 1996 were disposed of including 37 000 tonnes of fly ash. On account of its dusty, unfavorable form, the primary focus of the following examination will be on the fly ash mono-disposal site model. The fly ash is either transported to the disposal site by truck or by conveyor belt, after having been conditioned with 10 to 15% water in a mixing screw, or it is pumped by pipeline in suspension with water into a lagoon. In the former case, the conditioned fly ash is unloaded and compacted by a bulldozer or other suitable appliance. If drying occurs at the surface, a dust build-up can be avoided through dampening or application of blanketing layers. Larger developments of dust can thus be excluded. The continuous presence of personnel at the unloading of dampened fly ash is not necessary. If the fly ash is being pumped as a suspension into a lagoon, personnel are needed in the disposal area merely for conversion work. Therefore, the radiation exposure of those working at the disposal site is negligible. The mean effective dose equivalent in Germany caused by terrestrial radiation has been measured to be on average 0.4 mSv y−1 [1]. Measurements at German disposal sites [10] displayed a local radiation of 0.14 µG h−1 , whereby a 2000 h y−1 stay outdoors would produce an effective dose of 0.28 mSv y−1 . This effective dose at a fly ash disposal site is within the scattering range of the natural terrestrial radiation too. The measured radon concentrations at an open fly ash disposal site in UK and those in its direct vicinity, windward as well as leeward, did not show significant differences [6]. Given a measured radon concentration of 4 Bq m−3 and a stay of 2000 h, a disposal site worker would be exposed to an effective dose of 0.06 mSv y−1 .
4. Radiation exposure of the public through building materials containing power plant residues 4.1. General In Germany, 98% of the residues resulting from the firing of bituminous coal are utilized in civil engineering and in mining. With respect to radiation exposure of the public, the cases of special consideration are those in which the ash is utilized in the manufacturing of building materials used for the building of dwellings. The most important cases in Germany are: – the use of fly ash as a concrete addition or cement additive, – the manufacturing of masonry blocks using fly ash, bottom ash and/or boiler slag as components.
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4.2. Radiation exposure to the public through living in dwellings The mean effective dose equivalent in Germany caused by living in dwellings has been measured to be 1.5 mSv y−1 [1]. This exposure level is a result of radon, thoron, their shortlived daughter nuclides and direct radiation from building materials. An average duration of stay of 19 h d−1 was used in the calculation of these radiation doses. With more than 80% (1.2 mSv y−1 ) of the radiation exposure in dwellings being caused by radon-222 (radon) and radon-220 (thoron) and their short-lived daughters, only 0.3 mSv y−1 comes from direct radiation. It is known from systematic research that the mean value of the radon concentration in the air in Germany, in dwellings and in the open air, is 50 and 14 Bq m−3 , respectively. In an extensive examination of more than 6000 dwellings, the radon concentration varied between 0 and more than 10 000 Bq m−3 [1]. According to a statement from the German Commission for Radiation Protection, no measures are necessary for radon concentrations less than 250 Bq m−3 (normal range) [19]. If the concentrations are higher, the situation should be examined to determine if restoration measures with affordable expenditure are possible. The ICRP (International Commission for Radiation Protection) recommends that for values higher than 200 to 400 Bq m−3 proper measures ought to be taken to reduce the radon concentration. Radiation sources are radon from the soil as well as the natural radiation of the building materials. The entire building material in a house contributes an approximate 30 Bq m−3 to the radon concentration [17], with higher concentrations originating in the soil [19,20]. Therefore, according to Keller [17], an examination of building materials is not necessary, since the building materials produce a relatively low radioactive exposure when compared to other sources. On the other hand, it is necessary to examine the radioactive properties of new building materials in order to prevent an increase in radioactive exposure. In the past, various equations have been suggested for an approximation of the contribution of building material to the radioactive exposure in dwellings, starting from varying assumptions and maximum acceptable doses. Examples of these are: the Krisiuk equation [21] (often referred to as the Leningrad Equation) where only direct radiation is considered, the Austrian standard S 5200 equation [22] and the recommendations of Keller et al. [23,24] in which radon is considered in various ways. In all of these assessments, the actual concentration of radon in the air is approximated in a lump sum manner. This leads to false estimations when the actual physical characteristics differ greatly from the accepted parameters. Besides radon-producing radionuclides in the building material, the emanation and the exhalation rates are of considerable importance with respect to the release of radon into the air. While the radionuclide concentration in composite building materials can be calculated from the radionuclide concentration of their components, such a calculation cannot be used to determine the exhalation rate, since this is determined by the structure of the building material. As the radiation contribution of radon and its short-lived daughters from building materials is high compared to the quantity coming from direct radiation, knowledge of the exhalation rate is of special importance for the assessment of radiation emanating from building materials.
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4.3. Radioactivity from concrete For reasons of concrete technology, the portion of fly ash used as a concrete additive normally ranges between 40 and 120 kg m−3 of concrete. The measurements made on concrete in Germany and abroad [25–27] have uniformly shown that the exhalation rates of concrete with fly ash addition, despite its higher activity concentration, increased negligibly or not at all. This is regarded to be due to the glassy structure of bituminous coal fly ash as well as to the alteration in the system of pores in the concrete (decrease of mean pore diameter). Keller [25] examined standard concrete using, among others, Ordinary Portland Cement and Blast Furnace Slag Cement as binders, replacing about 25% of the Portland Cement by fly ash. The portion of fly ash used was 84 kg m−3 . Table 10 shows that, despite higher activity concentrations, the radon222 exhalation rate was lower in concrete with fly ash addition when compared to concrete containing ordinary Portland cement. The radon-220 exhalation rate was slightly increased. Van der Lugt and Scholten [26] have determined the radon emanation values for the basic components in concrete, as well as the comparatively low emanation rates for fly ash. Owing to these low rates of emanation and the effect of the pozzolanic reaction of fly ash on the pore system of the concrete, the contribution of fly ash to the exhalation of radioactivity is only small. The investigations showed that a replacement of up to 35% of the cement with a radium226 activity of 45 Bq kg−1 by fly ash A with the highest radium-226 activity of 290 Bq kg−1 , did not increase concrete radon exhalation. On replacement of 25% of the cement by fly ash B with a radium-226 activity concentration of 87 Bq kg−1 the exhalation rate was even reduced by approximately 50%. The radiation dose from building material can be calculated if the radionuclide concentrations and exhalation rates are known. It can be seen that all concretes deliver small amounts of radiation. With values between 0.17 and 0.29 mSv y−1 all concretes ranged far below the mean radiation dose measured in dwellings. The concrete with fly ash displayed an increase in the radiation dose of only 1.6% over the reference concrete, although the radium concentration in the concrete including fly ash was approximately twice that of the reference concrete. In conclusion, it can be said that concrete made of the common basic components makes only a small contribution of radiation when compared with other building materials (see [20]). In the aforementioned reflections it has not yet been taken into account that concrete in buildings is usually coated with floor pavement, plaster, wallpaper, paint or other coverings additionally reducing material exhalation [28].
4.4. Radioactivity from masonry blocks Only a few analytical results are available for radionuclide content and exhalation rate from masonry blocks containing ash from coal-fired power stations. Calculations by Green [6] lead to the conclusion that the increase of activity concentration due to ash is at least partly compensated by the small exhalation rate of the ash. Therefore masonry blocks with coal ash do not significantly increase the radiation exposure compared to conventional masonry blocks.
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5. Summary Each year in Germany 24 Mt of industrial by-products are produced by coal firing in power stations, municipal waste incineration plants and in the iron and steel making industry. The by-products are utilized to a large extent in the building and mining industries. On firing, the radionuclides mostly remain in the ash. In Germany, radionuclide concentration in lignite ash is in the range of natural soils due to the very low radionuclide concentration of the coal. Ash from bituminous coal contains radionuclides in the same amount as natural rocks. The exposure of workers handling coal ash within the power station and at the disposal site is only insignificantly increased compared to the natural radiation background. There is also no significant additional exposure of the public from ash disposal sites. The use of by-products in building materials contributes a negligible share to the radiation dose received in living in dwellings.
References [1] Bericht der Bundesregierung an den Deutschen Bundestag über Umweltradioaktivität im Jahr 1994, Deutscher Bundestag – 13, Wahlperiode, Drucksache 13/2287. [2] O. Mugrauer, D.E. Becker, P. Guglhör, Strahlenexposition durch den Umgang mit Reststoffen aus der Kohleverbrennung und den daraus hergestellten Verbrauchsgütern, in: Proceedings VGB Conference “Forschung in der Kraftwerkstechnik 1993”, in: VGB-TB 231, VGB Kraftwerkstechnik GmbH, Essen, 1993. [3] Bericht der Bundesregierung über Umweltradioaktivität im Jahr 1985, Deutscher Bundestag – 10, Wahlperiode, Drucksache 12/2677. [4] W. Kolb, Radioaktive Stoffe in Flugaschen aus Kohle, PTB Mitteilungen 89 (1979) 77–82. [5] S.A. Marcinkowski, J. Pensko, Radioaktivitätsmessungen an in Polen zur Herstellung von Bauprodukten genutzten Randprodukten in der Kraftwerksindustrie, TIZ-Fachberichte 103 (1979) 272–277. [6] B.M.R. Green, Radiological significance of the utilization and disposal of coal ash from power stations, Contract 7910–1462, National Radiological Protection Board, 1986. [7] J. Beretka, P.J. Mathew, Natural radioactivity of Australian fly ashes, in: Conference Proceedings, Ash Tech, London, 1984. [8] G. van der Lught, Radioactiviteits meetingen aan vliegasmonsters en consequenties voor beton met Lytag, Research Report, KEMA, Arnhem, The Netherlands, 1989. [9] Test results of the University of Saarland, Germany, unpublished. [10] D.E. Becker, O. Mugrauer, K.-H. Lehmann, Strahlenexposition durch den Umgang mit Reststoffen aus der Kohleverbrennung, Report on the research project St.Sch 1132, TÜV Bayern-Sachsen, München, 1992. [11] J. Dörich, private communication. [12] B. Chatterjee, et al., Untersuchungen über die Emission von Radionukliden aus Kohlekraftwerken. Gesellschaft für Strahlen- und Umweltforschung mbH München, CSF Bericht-S-617, Neuherberg, 1980. [13] K.-H. Puch, W. vom Berg, Radioaktivität von Nebenprodukten aus Kohlekraftwerken. 3, in: Internationales Symposium für Strahlenschutz, TÜV Bayern–Sachsen, 1995. [14] G. Keller, Die Konzentration natürlicher radioaktiver Stoffe in Saarkohle und Saarkohlenasche, in: Fachverband für Strahlenschutz e.V., Tagungsbericht “Radioaktivität und Umwelt”, 12. Jahrestagung, 1978. [15] J. Bretschneider, Vergleich der Strahlenexposition durch radioaktive Emissionen aus konventionellen Kraftwerken und aus Kernkraftwerken, Institut für Strahlenhygiene des Bundesgesundheitsamtes ISH-Bericht 9, Neuherberg, 1981. [16] B. Zeller, Radioaktivitätsbilanzen in Steinkohlekraftwerken, Diplomarbeit im FB Technisches Gesundheitswesen, FIZ Gießen–Friedberg, 1995. [17] G. Keller, Die Strahlenexposition der Bevölkerung durch Baustoffe unter besonderer Berücksichtung von Sekundärrohstoffen, VGB Kraftwerkstechnik 74 (1994) 717–720.
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[18] Richtlinie 96/29/Euratom des Rates vom 13. Mai 1996 zur Festlegung der grundlegenden Sicherheitsnormen für den Schutz der Arbeitskräfte und der Bevölkerung gegen die Gefahren durch ionisierende Strahlungen, Amtsblatt Eur. Gemeinsch. Ser. L 159 (29.6.1996) 1–28. [19] Empfehlung der Strahlenschutzkommission: Strahlenschutzgrundsätze zur Begrenzung der Strahlenexposition durch Radon und seine Zerfallsprodukte in Gebäuden, Bundesanzeiger vom 16.08.1994, S. 8766. [20] J. Brandt, W. Rechenberg, Natürliche Radioaktivität von Beton, Beton 43 (1993) 582–586. [21] E.M. Krisiuk, A Study on Radioactivity in Building Materials, Research Institute for Radiation Hygiene, Leningrad, 1971. [22] ÖNORM S5200: Radioaktivität in Baustoffen, prestandard, Dec. 1988. [23] G. Keller, H. Muth, Radiation exposure in German dwellings; some results and a proposed formulae for dose limits, Sci. Total Environ. 45 (1985) 299–306. [24] G. Keller, K.H. Folkerts, H. Muth, Discussing possible standards of natural radioactivity in building materials, Radiat. Environ. Biophys. 26 (1987) 143–150. [25] G. Keller, Einfluß der natürlichen Radioaktivität, Arcus (1984) 249–256. [26] G. van der Lught, L.C. Scholten, Radon emanation from concrete and the influence of using fly ash in cement, Sci. Total Environ. 45 (1985) 143–150. [27] K. Ulbak, N. Jonassen, K. Baekmark, Radon exhalation from samples of concrete with different porosities and fly ash additives, Radiat. Prot. Dosim. 7 (1–4) (1984) 45–48. [28] G. Keller, Die Strahleneinwirkung durch Radon in Wohnhäusern, Bauphysik 15 (1993) 141–145.
Naturally occurring radioactivity in industrial by-products from coal-fired power plants, from municipal waste incineration and from the iron- and steel-industry K.-H. Puch a , R. Bialucha b , G. Keller c a VGB PowerTech e.V., Klinkestraße 27-31, 45136 Essen, Germany b Forschungsgemeinschaft Eisenhüttenschlacken, Bliersheimer Straße 62, 47229 Duisburg, Germany c Universität des Saarlandes, Institut für Biophysik, Universitätsklinik, Geb. 76, 66421 Hamburg, Germany
The Council Directive 96/29/Euratom on the basic safety standards was to be converted by May 13th, 2000 into national law. The EC Member Countries were asked to identify paths with elevated radioactive exposures. For these exposures, regulations were then to be made in national law. In the 1st draft, the industrial by products from coal-fired power plants, from municipal waste incineration and the iron- and steel-industry were listed in the amendment of the German radiation protection enforcement. For these by products values for nuclide concentrations were already available and these were supplemented by extensive investigations. This proved that the nuclide concentrations for the two important natural decay series are under 200 Bq kg−1 . Through this evidence, it is guaranteed that no regulation is necessary for these materials and the listing in the appendix XII is not justified. In this form, the amendment of the radiation protection enforcement was implemented in August 1st, 2001.
1. Introduction Every year in Germany 17.3 Mt of ash are produced in coal burning in the form of boiler slag, bottom ash and fly ash. 7.3 Mt result from the burning of bituminous coal and 9.6 Mt from lignite (Table 1). 98% of the bituminous coal ash is utilized in the construction and mining industries. The majority of lignite ash is used for the filling and recultivation of open pit mines. It is utilized either unmixed or mixed with FGD gypsum and/or FGD water. The amount of by-products from municipal waste incineration plants is about 3.2 Mt. The main product is bottom slag (2.5 Mt). The allotment of fly ash and different salts is 0.35 Mt. RADIOACTIVITY IN THE ENVIRONMENT VOLUME 7 ISSN 1569-4860/DOI 10.1016/S1569-4860(04)07123-2
© 2005 Elsevier Ltd. All rights reserved.
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Table 1 Production and utilization of by-products from power stations in Germany in 2000 By-product Bituminous coal-fired power stations
Lignite-fired power stations
Boiler slag Bottom ash Fly ash Fluidized bed combustion ash Subtotal Bottom ash Fly ash Fluidized bed combustion ash Subtotal Total
Production (Mt)
Utilization (Mt)
2.35 0.53 4.12 0.42
2.35 0.51 4.12 0.42
7.42 1.83 7.90 0.19
7.40 1.83 7.90 0.19
9.92 17.34
9.92 17.32
Table 2 Production of blast furnace slag in Germany in 2000 Production
Mt
Slag from non-phosphorous steel making Slag from other iron making processes Total production Destocking Total
7.46 0.07 7.53 0.10 7.63
Table 3 Production of steel making slag in Germany in 2000 Production
Mt
Slag from oxygen steel making Slag from electric steel plants Slag from special processes Total
3.50 1.67 0.64 5.81
The bottom slag is a useful material for earth- and road construction. Fly ash and salts are utilized in the mining industry. The production and utilization of the different by-products from the iron- and steel-making industry is shown in Tables 2 and 3. The total amount of 13.44 Mt of slag is utilized as building material, for earthwork and road construction, in the cement industry and as fertilizer. Like any other natural rock, industrial by-products contain radioactive nuclides resulting from the natural decay series. This is why they emit ionizing radiation. In the following, it will be examined whether handling in the plants as well as disposal of by-products and
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K.-H. Puch et al. Table 4 The mean effective radiation dose per year from natural radiation exposure to the public in the Federal Republic of Germany in 1994 according to [1] Source
Mean effective dose in mSv y−1
Cosmic radiation Terrestrial radiation – outdoors (5 h d−1 ) – indoors (19 h d−1 ) Inhalation of radon decay products – outdoors (5 h d−1 ) – indoors (19 h d−1 ) Incorporated natural radioactive materials Total natural radiation exposure
0.3 0.1 0.3 0.2 1.2 0.3 2.4
their utilization as building material lead to an increase in radiation exposure that is healthendangering to the personnel or the public. According to a publication of the German authorities, the natural human radiation exposure in Germany is between 2 and 6 mSv y−1 (effective radiation dose) with a mean value of 2.4 mSv y−1 (Table 4) [1]. Along with the civil radiation exposure of 1.5 mSv y−1 (primarily by the use of ionizing radiation and radioactive materials in medicine), the total exposure is some 3.9 mSv y−1 (mean value).
2. Natural radioactive nuclides in industrial by-products 2.1. Coal fired power plants The natural radioactivity of coal, and thus of the ash produced through its firing, mainly results from radionuclides in the decay series of uranium–radium, thorium and uranium–actinium, as well as from potassium-40. The inert gas radon, which is also produced in the decay series, may partly escape through the solid substances into the air. Radon-220 is less important because of its half life period of 56 s. The uranium–actinium series is not dealt with because its content of nuclides is only small when compared with total radiation. Because of the age of coal, the radionuclides are balanced, i.e. all nuclides in a given decay series have specific activities which, in a balanced position and depending on the ramification, are in a given relation to each other. For this reason, it is general practice to give an account of the activity concentrations of a representative radionuclide for each series, usually radium-226 and thorium-232 for the uranium and the thorium decay series, respectively. In the firing of the coal, most of the radionuclides remain in the ash. The ash content of bituminous coal used in power stations in Germany is in the range of about 7 to 40%, the mean being 15%. Examination of the radioactivity of solid material passing through power stations has shown that more than 90% of the radioactivity in coal is retained in the ash. Only a small percentage of the radioactivity can be found in flue gas desulphurization products like FGD gypsum (Fig. 1) [2]. Due to the ash content, the natural radioactive nuclide concentration in fly ash exceeds that in coal by a factor of 2 to 15.
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Fig. 1. Mass balance and activity flow in a coal fired power plant according to [2]. Upper value: thorium series with the following nuclides: Th-232, Ra-228, Ac-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Po-212 (64%), Tl-208 (36%); lower value: uranium series with the following nuclides: U-238, Th-234, Pa-234, U-234, Th-230, Ra-226, Rn-222, Po-218, Pb-214, Bi-214, Po-214. Table 5 Activity concentration of bituminous coal fly ash (in Bq kg−1 ) Origin
D D PL D GB AUS diverse D D D D Overall
Source
[3] [4] [5] [2] [6] [7] [8] [9] [10] [11] [12]
No. of samples
CRadium-226 MV
min
max
CThorium-232 MV
min
max
CPotassium-40 MV
min
max
28 26 10 3 4 9 50 5 3 20 6 164
210 264 237 126 89 90 127 172 122 90 224 170∗
80 85 70 93 72 7 75 148 87 51 192 7
390 370 611 137 105 160 235 204 177 165 281 611
130 120 200 121 68 150 96 118 88 83 106 114∗
60 44 89 96 53 7 42 100 73 59 93 7
260 190 514 155 94 290 131 140 115 120 122 514
700 n.i.a. 833 700 900 220 437 955 n.i.a. 1039 827 652∗
330 n.i.a. 385 459 800 20 205 881 n.i.a. 760 740 20
1110 n.i.a. 1776 877 1250 570 765 1018 n.i.a. 1480 1000 1776
MV: mean value; n.i.a.: no information available. ∗ Weighted mean value.
The radionuclide concentration in an ash is determined by the radionuclide concentration in the coal, the ash content of the coal and the conditions in the power station. Owing to the low activity concentration in German lignite, the lignite coal ash has a very low value too. Its activity concentration is similar to that in natural soil and thus it causes no increase in radiation. Therefore it is not dealt with further in this report.
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Table 6 Activity concentration of coal fly ash from German power stations (in Bq kg−1 ) Source
[3] [12] [4] G1 [2] [9] [11] [10] [13] G2 Overall
No. of samples 28 6 26 60 3 5 20 3 8 39 99
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
210 224 264 235 126 172 90 122 113 111 186
80 192 85 80 93 148 51 87 59 51 51
390 281 370 390 137 204 165 177 182 204 390
130 106 120 123 121 118 83 88 79 90 110
60 93 44 44 96 100 59 73 69 59 44
260 122 190 260 155 140 120 115 105 155 260
700 827 n.i.a. 722 700 955 1039 n.i.a. 836 881 785
330 740 n.i.a. 330 459 881 760 n.i.a. 380 380 330
1110 1000 n.i.a. 1110 877 1018 1480 n.i.a. 1240 1480 1480
MV: mean value; n.i.a.: no information available; G1: total evaluation of measurements before 1980; G2: total evaluation of measurements after 1980.
A summary of international measurements of activity concentrations in bituminous coal fly ash can be found in Table 5. The mean values for radium-226, thorium-232 and potassium-40 are 170, 114 and 652 Bq kg−1 , respectively. An evaluation of the values for bituminous coal ash from German power stations (Table 6) shows that the mean values for radium-226 and thorium-232 are similar to those in Table 5 (186 and 110 Bq kg−1 , respectively), whereas the mean value for potassium-40 is 785 Bq kg−1 which is slightly higher than the mean in Table 5. An interesting point to note is that the results in the later analyses [2,9–11,13] differ from those in the earlier ones [3,4,12]. The earlier investigations [3,4,12] focused on the emission of radioactivity from coal-fired power stations through the chimney. To determine the emission, either so-called “clean gas ash” discharged with the flue gas, or fly ash in the last stage of the electrostatic precipitator was examined. In this stage, the ash is extremely fine and comparable to clean gas ash. It is well known that the radioactivity of coarser ash, like that in the first stages of the electrostatic precipitator, is lower than that of the fine ash in the last stage [4,14]. The later measurements, however, concentrated on the evaluation of the total ash collected in the electrostatic precipitator, just as it is utilized. These measurements then resulted in clearly lower values for radium-226 and thorium-232 whereas the value for potassium-40 was slightly higher. The mean values in Table 5, evaluated from all of the values measured, therefore include a conservative approximation. The overall mean values and their band-widths have been proven reliable through several independent studies. The results shown in Table 7 for boiler slag display slightly lower mean values. In Table 8, the analyses of bottom ash are presented. In the tested cases, the activity concentration was lower than that of the respective fly ash. Besides the direct radiation of the radionuclides, the radioactive gases radon-222 and radon220 (also called thoron), as well as their short-lived daughters, contribute to the radiation. In
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Table 7 Activity concentration of boiler slag (in Bq kg−1 ) Source
[10] [12] [15] [13] Overall
No. of samples 24 3 4 2 33
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
138 195 166 130 146
68 181 144 121 68
245 211 207 140 245
93 93 136 119 100
59 85 107 76 76
162 104 170 162 170
835 765 512 910 794
441 666 337 660 337
1240 851 677 1160 1240
MV: mean value. Table 8 Activity concentration of bottom ash (in Bq kg−1 ) Source
[13] [16]
No. of samples
CRadium-226
CThorium-232
CPotassium-40
MV
min
max
MV
min
max
MV
min
max
2 n.i.a.
70 108
70 46
70 166
40 79
40 25
40 120
355 514
340 196
370 742
n.i.a.: no information available; MV: mean value.
order to assess the radioactivity of a material, not only must the activity concentration be considered, but also the exhalation of the radon and thoron stemming from the material itself. As a result of their production at high temperatures ranging between 1200 and 1700 ◦ C, the ashes from furnaces burning pulverized coal have a glassy structure. This causes the ash to have a relatively low emanation rate in comparison with other materials [17]. The quantity of emanated radon atoms which actually are released into the air depends on the structure of the pore system in the building material. Therefore, in order to know the radiation contribution of a building material, the content of radionuclides as well as the exhalation rate must be known. The exhalation rates of particular materials with and without bituminous coal ash will be dealt with later. 2.2. Iron- and steel-marketing industry The activity concentration measurements for air cooled blast furnace slag and granulated blast furnace slag underline the same magnitude for the mean values of both materials (Tables 9–11). The range between the min- and max-values is large for both types of slag. This effect is influenced by the different raw materials in the different plants. But the mean values are below 200 Bq kg−1 . 2.3. Municipal waste incineration plants The examination of different by-products from municipal waste incineration plants shows the expected low activity concentrations (Tables 12–14). The values for all materials are at the same level. Compared with the other products, there is no further need to mention these.
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K.-H. Puch et al. Table 9 Activity concentration in iron and steel making slags in the year 1991 (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Steel making slag Granulated blast furnace slag Air cooled blast furnace slag
5 116 64
0 43 70
1 180 200
Table 10 Activity concentrations in air cooled blast furnace slags (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Min Max Mean value
66 145 99.3
28 129 58.6
60 405 205.0
Table 11 Activity concentrations of granulated blast furnace slags (in Bq kg−1 ) Slag
CRadium-226
CThorium-232
CPotassium-40
Min Max Mean value
81 360 150.2
30 125 64.8
70 320 141.9
Table 12 Activity concentrations of fly ash from municipal waste incineration plants (MWIP) Nr.
25 33 35 39 26 32
Sample
Fly ash MWIP A Fly ash MWIP B Fly ash MWIP C Fly ash MWIP D Fly ash MWIP E Fly ash MWIP F Mean value
Concentration in Bq kg−1 CThorium-232
CRadium-226
CPotassium-40
15 8 9 14 16 21 14
19 16 14 20 25 25 20
2019 2410 890 756 423 393 1148
The question arises, where do the above listed activity concentrations range compared to the limits of the Council Directive 96/26 Euratom [18] setting the basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation, dated May 13, 1996. This will be set up as an example for fly ash.
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Table 13 Activity concentrations of bottom slag from municipal waste incineration plants (MWIP) Nr.
34 31 27 36 37 38 40 43
Concentration in Bq kg−1
Sample
Bottom slag MWIP A Bottom slag MWIP B Bottom slag MWIP C Bottom slag MWIP D Bottom slag MWIP E Bottom slag MWIP F Bottom slag MWIP G Bottom slag MWIP H Mean value
CThorium-232
CRadium-226
CPotassium-40
11 9 10 15 15 13 16 14 13
14 15 11 18 19 17 21 17 17
208 193 206 215 179 213 186 159 195
Table 14 Activity concentrations of salts from municipal waste incineration plants (MWIP) Nr.
29 30 41 42
Sample
Salt MWIP B Salt MWIP C Salt MWIP D Salt MWIP e Mean value
Concentration in Bq kg−1 CThorium-232
CRadium-226
CPotassium-40
2 2 2 2 2
6 5 2 5 4
218 10 21 22 49
3. Exposure of personnel 3.1. In the power station Inhalation and ingestion of dust particles as well as direct radiation are the potential ways in which exposure may occur while handling ash. Dust-forming fly ash is most often forwarded pneumatically from the electrostatic precipitator through a closed system into a storage silo. Thus, in general, there is no direct contact between the personnel and the ash in the transport-, storage- and loading-facilities. Silos are emptied either through a mixing screw, with a 10 to 15% addition of water, onto a truck or a conveyor belt, or through flushing pipes in suspension with water, or transferred in dried form through a closed system into a silo-truck. Exhaust- or filtering-systems prevent the release of dust into the open. A considerable buildup of dust is possible only during system disruption. Radiation exposure is almost totally eliminated through the shielding effect of the walls of the forwarding mechanisms and silos. Direct contact of personnel with power station ash is restricted to repair works, i.e. to short intervals of time. For reasons of general health protection (exposure to dust), filtering masks and safety clothing must be worn when the occasionally
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necessary repair and inspection work is conducted in the precipitator or in the silos. Thus, ingestion and inhalation are almost eliminated. Handling of ash from coal combustion in power stations does not lead to any significant increase in radiation exposure. 3.2. At the disposal site Compared to some other industrial nations, very little of the ash from bituminous coal power stations is disposed of in Germany. Only 75 000 tonnes, i.e. 1%, of the bituminous coal ash produced in 1996 were disposed of including 37 000 tonnes of fly ash. On account of its dusty, unfavorable form, the primary focus of the following examination will be on the fly ash mono-disposal site model. The fly ash is either transported to the disposal site by truck or by conveyor belt, after having been conditioned with 10 to 15% water in a mixing screw, or it is pumped by pipeline in suspension with water into a lagoon. In the former case, the conditioned fly ash is unloaded and compacted by a bulldozer or other suitable appliance. If drying occurs at the surface, a dust build-up can be avoided through dampening or application of blanketing layers. Larger developments of dust can thus be excluded. The continuous presence of personnel at the unloading of dampened fly ash is not necessary. If the fly ash is being pumped as a suspension into a lagoon, personnel are needed in the disposal area merely for conversion work. Therefore, the radiation exposure of those working at the disposal site is negligible. The mean effective dose equivalent in Germany caused by terrestrial radiation has been measured to be on average 0.4 mSv y−1 [1]. Measurements at German disposal sites [10] displayed a local radiation of 0.14 µG h−1 , whereby a 2000 h y−1 stay outdoors would produce an effective dose of 0.28 mSv y−1 . This effective dose at a fly ash disposal site is within the scattering range of the natural terrestrial radiation too. The measured radon concentrations at an open fly ash disposal site in UK and those in its direct vicinity, windward as well as leeward, did not show significant differences [6]. Given a measured radon concentration of 4 Bq m−3 and a stay of 2000 h, a disposal site worker would be exposed to an effective dose of 0.06 mSv y−1 .
4. Radiation exposure of the public through building materials containing power plant residues 4.1. General In Germany, 98% of the residues resulting from the firing of bituminous coal are utilized in civil engineering and in mining. With respect to radiation exposure of the public, the cases of special consideration are those in which the ash is utilized in the manufacturing of building materials used for the building of dwellings. The most important cases in Germany are: – the use of fly ash as a concrete addition or cement additive, – the manufacturing of masonry blocks using fly ash, bottom ash and/or boiler slag as components.
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4.2. Radiation exposure to the public through living in dwellings The mean effective dose equivalent in Germany caused by living in dwellings has been measured to be 1.5 mSv y−1 [1]. This exposure level is a result of radon, thoron, their shortlived daughter nuclides and direct radiation from building materials. An average duration of stay of 19 h d−1 was used in the calculation of these radiation doses. With more than 80% (1.2 mSv y−1 ) of the radiation exposure in dwellings being caused by radon-222 (radon) and radon-220 (thoron) and their short-lived daughters, only 0.3 mSv y−1 comes from direct radiation. It is known from systematic research that the mean value of the radon concentration in the air in Germany, in dwellings and in the open air, is 50 and 14 Bq m−3 , respectively. In an extensive examination of more than 6000 dwellings, the radon concentration varied between 0 and more than 10 000 Bq m−3 [1]. According to a statement from the German Commission for Radiation Protection, no measures are necessary for radon concentrations less than 250 Bq m−3 (normal range) [19]. If the concentrations are higher, the situation should be examined to determine if restoration measures with affordable expenditure are possible. The ICRP (International Commission for Radiation Protection) recommends that for values higher than 200 to 400 Bq m−3 proper measures ought to be taken to reduce the radon concentration. Radiation sources are radon from the soil as well as the natural radiation of the building materials. The entire building material in a house contributes an approximate 30 Bq m−3 to the radon concentration [17], with higher concentrations originating in the soil [19,20]. Therefore, according to Keller [17], an examination of building materials is not necessary, since the building materials produce a relatively low radioactive exposure when compared to other sources. On the other hand, it is necessary to examine the radioactive properties of new building materials in order to prevent an increase in radioactive exposure. In the past, various equations have been suggested for an approximation of the contribution of building material to the radioactive exposure in dwellings, starting from varying assumptions and maximum acceptable doses. Examples of these are: the Krisiuk equation [21] (often referred to as the Leningrad Equation) where only direct radiation is considered, the Austrian standard S 5200 equation [22] and the recommendations of Keller et al. [23,24] in which radon is considered in various ways. In all of these assessments, the actual concentration of radon in the air is approximated in a lump sum manner. This leads to false estimations when the actual physical characteristics differ greatly from the accepted parameters. Besides radon-producing radionuclides in the building material, the emanation and the exhalation rates are of considerable importance with respect to the release of radon into the air. While the radionuclide concentration in composite building materials can be calculated from the radionuclide concentration of their components, such a calculation cannot be used to determine the exhalation rate, since this is determined by the structure of the building material. As the radiation contribution of radon and its short-lived daughters from building materials is high compared to the quantity coming from direct radiation, knowledge of the exhalation rate is of special importance for the assessment of radiation emanating from building materials.
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4.3. Radioactivity from concrete For reasons of concrete technology, the portion of fly ash used as a concrete additive normally ranges between 40 and 120 kg m−3 of concrete. The measurements made on concrete in Germany and abroad [25–27] have uniformly shown that the exhalation rates of concrete with fly ash addition, despite its higher activity concentration, increased negligibly or not at all. This is regarded to be due to the glassy structure of bituminous coal fly ash as well as to the alteration in the system of pores in the concrete (decrease of mean pore diameter). Keller [25] examined standard concrete using, among others, Ordinary Portland Cement and Blast Furnace Slag Cement as binders, replacing about 25% of the Portland Cement by fly ash. The portion of fly ash used was 84 kg m−3 . Table 10 shows that, despite higher activity concentrations, the radon222 exhalation rate was lower in concrete with fly ash addition when compared to concrete containing ordinary Portland cement. The radon-220 exhalation rate was slightly increased. Van der Lugt and Scholten [26] have determined the radon emanation values for the basic components in concrete, as well as the comparatively low emanation rates for fly ash. Owing to these low rates of emanation and the effect of the pozzolanic reaction of fly ash on the pore system of the concrete, the contribution of fly ash to the exhalation of radioactivity is only small. The investigations showed that a replacement of up to 35% of the cement with a radium226 activity of 45 Bq kg−1 by fly ash A with the highest radium-226 activity of 290 Bq kg−1 , did not increase concrete radon exhalation. On replacement of 25% of the cement by fly ash B with a radium-226 activity concentration of 87 Bq kg−1 the exhalation rate was even reduced by approximately 50%. The radiation dose from building material can be calculated if the radionuclide concentrations and exhalation rates are known. It can be seen that all concretes deliver small amounts of radiation. With values between 0.17 and 0.29 mSv y−1 all concretes ranged far below the mean radiation dose measured in dwellings. The concrete with fly ash displayed an increase in the radiation dose of only 1.6% over the reference concrete, although the radium concentration in the concrete including fly ash was approximately twice that of the reference concrete. In conclusion, it can be said that concrete made of the common basic components makes only a small contribution of radiation when compared with other building materials (see [20]). In the aforementioned reflections it has not yet been taken into account that concrete in buildings is usually coated with floor pavement, plaster, wallpaper, paint or other coverings additionally reducing material exhalation [28].
4.4. Radioactivity from masonry blocks Only a few analytical results are available for radionuclide content and exhalation rate from masonry blocks containing ash from coal-fired power stations. Calculations by Green [6] lead to the conclusion that the increase of activity concentration due to ash is at least partly compensated by the small exhalation rate of the ash. Therefore masonry blocks with coal ash do not significantly increase the radiation exposure compared to conventional masonry blocks.
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5. Summary Each year in Germany 24 Mt of industrial by-products are produced by coal firing in power stations, municipal waste incineration plants and in the iron and steel making industry. The by-products are utilized to a large extent in the building and mining industries. On firing, the radionuclides mostly remain in the ash. In Germany, radionuclide concentration in lignite ash is in the range of natural soils due to the very low radionuclide concentration of the coal. Ash from bituminous coal contains radionuclides in the same amount as natural rocks. The exposure of workers handling coal ash within the power station and at the disposal site is only insignificantly increased compared to the natural radiation background. There is also no significant additional exposure of the public from ash disposal sites. The use of by-products in building materials contributes a negligible share to the radiation dose received in living in dwellings.
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