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Natural radionuclide emission from a coal power plant and the population exposure to external radiation in its vicinity
Pergamon
Environment
International, Vol. 22, Suppl. 1, pp. S227-S235, 1996 Copyright 01996 Elseviex Science Ltd Printed in the USA. All rights reserved 0160-4120/96 S15.00+.00
PI1SO160-4120(96)00112-Z
NATURAL RADIONUCLIDE EMISSION FROM A COAL POWER PLANT AND THE POPULATION EXPOSURE TO EXTERNAL RADIATION IN ITS VICINITY Ranko KljajiC and Zoran MaSiC Scientific Institute for Veterinary Medicine, 21000 Novi Sad, Yugoslavia
Zora hnid,
Sneiana
PavloviC, Mom6ilo ToSiC, and Miodrag MandiC
The VinCa Institute of Nuclear Sciences, 11001 Belgrade, Yugoslavia
Vojin GordaniC The Geoinstitute,
11000 Belgrade, Yugoslavia
Predrag PoliC Faculty of Chemistry, University of Belgrade, 11001 Belgrade, Yugoslavia
El 9512-408 M (Received 6 December 1995; accepted 4 July 1996)
Investigations carried out in the vicinity of four coal-tired power plants showed that the average annual emission of natural radionuclides for each MWe of produced electric power is an average of 0.200 MBq for each component of 238U chain, and of 0.130 MBq for each component of 232Th chain, respectively, and of 1.027 MBq for 4%. The average annual absorbed dose of about 1 mGy was found on five locations studied. The results of specific activity measurements on the samples taken from several locations studied showed that there is a concentration of natural radionuclides in ash and slag of up to about five times. The absorbed dose levels found on depots of ash and slag were close to the values recommended by the International Commission on Radiological Protection. Copyright 01996
l3wier Scic~crLid
INTRODUCTION The modern world is facing two basic problems -to provide sufficient amounts of energy and to produce enough food. In the effort to solve these problems, new
technologies using various processes have been introduced. As a result of some processes, such as coal combustion, artificial fertilizer production, and others, a redistribution of natural radioactivity occurs and considerably more population is being exposed to natural radioactivity. The concept of technologically enhanced natural radioactivity was introduced in the mid-seventies. It
S227
represents the exposure to natural sources of radiation which would not exist without the technological activity unintentionally undertaken to produce radiation (UNSCEAR 1982). Earlier studies have shown that the main sources of technologically enhanced natural radioactivity are coal-fired power plants and artificial fertilizers applied in agriculture. Coal-fired power plants have been neglected as radiation sources for a long time. They became important for investigations as a result of the advancement of the scientific knowledge of biological effects of
S228
radiation action on humans and after dose limits reduction in international recommendations and standards. Coal combustion in power plants leads to redistribution of natural radionuclides originating from coal, and to their concentration in ash and slag. The basic problem of technologically enhanced natural radioactivity caused by coal-fired power plants is the increase of the background gamma radiation level. Therefore, the local population is exposed to higher gamma radiation doses than in their absence. Increased concentrations of uranium in different layers of coal occur mainly due to the elution of uranium from rich volcano rocks into layers of coal. It is known that the average concentrations of radionuclides in coal amount to about 500 Bq kg-’ for 40K, and about 20 Bq kg“ for each component of 238U and 232Th chains (UNSCEAR 1982). It was found (Bauman and Kovac 1984; Marovic and Bauman 1986) that decay products of 238U and232 Th in coal are not in equilibrium, which is particularly important for the case of “‘Pb and “‘PO. An increase in the concentration of 2’0Pb compared with the preceding elements of uranium chain in coal can occur if high levels of 222Rn diffuse from the highly active rocks nearby into less active layers of coal. It was found that a!! types of coal used in the coalfired power plants studied contain 12.2-24.4 Bq kg-’ of 238Uand 12.2 l- 16.8 Bq kg-’ of 23Th as we!! as their radioactive decay products (Kljajid et a!. 1995). These values are somewhat lower than their respective concentrations in the earth’s crust. However, some types of coal can have higher contents of natural radionuclides (hard coal). Coal combustion eliminates organic components causing an increase of ash radioactivity compared with coal radioactivity for a factor of five to ten, Concentrations of natural radionuclides in ash and slag are 5-10 times higher than the corresponding concentrations in the earth’s crust (Mihalj 1988; Mihalj et a!. 1989, 1991; KljajiC et a!. 1989). In addition, coal combustion in coal-tired power plants leads to the concentration of natural radionuclides. The enrichment factor for ash and slag can amount from five to ten. Therefore, the goal of this study was to estimate the influence of the coal-fired power plants on the environment and their contribution to the total population exposure to the external radiation in their vicinities (Jacobi 198 1; Mihalj 1988; Mihalj et a!. 1988, 1989; Nakaoka et a!. 1984). Under normal conditions, when electrofilters in coalfired power plants operate with high efficiency, a minor portion of ash produced is released through the chimney into the atmosphere. Depending on the chimney height,
R. Kljajik et al.
the ash is deposited from the plum at a closer or further distance from the coal-fired power plant. The deposited ash and slag at depots may contain natural radionuclides with activities several times higher than respective average activities in the soil (Antic et a!. 1987; UNSCEAR 1982, 1988). Because the ash is insoluble in water, the elution of natural radionuclides into the surface and underground water is not a particular problem except in the case of 226Ra. However, the release of 222Rnfrom ash and slag depots can present a significant problem (Jacobi 1981). It is important to take into account that hundreds of thousands of tons of ash are accumulated on depots as a result of the normal production cycle of a coal-fired power plant, as we!! as the fact that ash and slag containing increased levels of radionuclides can be used as building material and, in some cases, for “improving” soil for agriculture. As the need for coal supply is high, there is an increased potential for discovery and application of coal with higher natural radioactivity. Therefore, it is necessary to pay attention to environmental pollution from coal-fired power plants and to regulate ionizing radiation exposure caused by technologically enhanced natural radioactivity.
EXPERIMENTAL
DETAILS
Four full-year operating coal-fired power plants were selected for the study. All of them are located close to urban areas, while ash and slag depots are located in the vicinities of the coal-fired power plants at distances of about l-3 km. The annual production of natural radionuclides by coal-fired power plants was calculated using data on annual coal consumption, coal activities, ash contents, efficiencies of electrofilters used, as we!! as the average content of radionuclides in coal, ash, and slag. The contents of radionuclides were measured in samples of coal, ash, and slag. Samples were chosen to represent specific points of various technological steps used, as are coal and ash, and different emission levels with respect to wind direction and distances (IAEA 1989). They were prepared from related materials taken from investigated coal-fired power plants according to standard procedures used for natural radionuclides activity measurements: homogenized, dried to constant weight, and sealed in Marinelli beakers to achieve radioactive equilibrium. For specific activity measurements, a standard gamma spectrometric system based on an analyzer with 4000 channels and pure germanium detector with resolution of 1.95 keV at 1.33 MeV,
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Population exposure to radionuclides from a coal power plant
having a relative efficiency of 25% at 1.33 MeV, was used. Energy and efficiency calibration was done by certified 252E~standard in Marinelli geometry according to a standardized procedure (ANSI 1986). The same geometry was used for sample measurements. The 226Ra concentration was determined from gamma lines of 295 keV, 352 keV, 609 keV, and 1765 keV, originating from 214Pb and 2’4Bi as the mean value of the results of these gamma lines. The concentration of 232Th was determined from gamma lines of 583 keV and 911 keV from *‘*Tl and ***AC,respectively. The 40K concentration was calculated from its 1460.8 keV gamma line. The activity of 238U was calculated from the 185 keV gamma line of 235U (Man et al. 1989; Malanca et al. 1993; LaBrecque and Resales 1994; Debertin and Helmer 1988), although it is not the reference method for quantitative determination of uranium content. All necessary radionuclide data needed for the calculations were taken from the work of Lederer and Shirley (1978). Three instruments were used for the measurement of the exposure levels of gamma radiation: 1) The highly sensitive, pressurized ionization chamber (0.35 MPa argon + 1.4 MPa nitrogen) with a low detection limit of 0.072 pC kg-’ s-’ (manufactured by Silena) was used for exposure dose rate measurements. Gamma radiation exposure dose rates were measured at 1 m above the plain surface of uncultivated ground (DeCampo et al. 1972). 2) A field kit for gamma spectrometry (manufactured by Ortec) was used for in situ spectrum analysis. It consisted of a field analyzer with 4000 channels and a high-purity germanium (HPGe) detector with a resolution of 1.8 keV at 1.33 MeV, and a relative efficiency of 18% at 1.33 MeV. According to the spectra obtained, the contributions of selected gamma lines to the total exposure levels were calculated. 3) The thermoluminescent dosimeters in boxes containing three pills each (Prokic and Bolter-Jensen 1993) were used for the absorbed dose measurements. Thermoluminescent dosimeters were exposed for 3 months, 1 m above the plain surface of ground. All measurements in the vicinity of each coal-fired power plant were made at four locations: 3-5 km in front of the coal-fired power plants along the most frequent wind direction, 3-5 km behind the coal-fired power plants along the same direction, and at two locations on the ground of the coal-fired power plants, at the depots of ash and slag. The fifth location was added just for thermoluminescent dosimeter measurements, and it was placed near the electrofilters.
RESULTS AND DISCUSSION
The basic characteristics of coal-fired power plants studied are presented in Table 1. The calculated values of annual amounts of natural radionuclides produced by coal-fired power plants are presented in Table 2. Data indicate that radionuclides of 238U and 232Th chains were not always in equilibrium. The natural radionuclides levels measured in samples of coal, ash, slag, and ash and slag depots are presented in Table 3. The f values represent the estimated total measurement errors, including counting, preparation, and calibration. The results for the 238Ucontents should be considered as informative, keeping in mind that 238U is not an important source of external exposure which is the main subject of this study. A comparison of gamma radiation exposure dose rates at four locations for all the coal-fired power plants examined is given in Table 4. It can be seen that the highest value for coal-fired power plant 1 of 1.14 pC kg-’ s’ was found in the ash and slag depot. For the other three locations, nearly the same values were found. Gamma radiation exposure dose rates for coal-fired power plant 2 had nearly the same values for all locations. The highest exposure dose rate of 0.86 pC kg-’ s’ was found 3-5 km behind the coalfired power plant along the most frequent wind direction. Nearly the same values were found in all locations measured for coal-fired power plant 3. The exposure dose rates for coal-fired power plant 4 were between 0.72 in the depot and 0.91 pC kg-’ s’ at 3-5 km behind the coal-fired power plant along the most frequent wind direction. Data on the participation of selected gamma lines from the stated radionuclides in the total exposure doses were calculated on the basis of in situ gamma spectra obtained by the field HPGe detector in the same locations. Table 5 shows the calculated contributions to the exposure dose rates of gamma radiation originating from the most important natural and fall-out radionuclides at locations 3-5 km in front of and behind the coal-fired power plant along the most frequent wind direction, on the grounds of the coal-fired power plant, and on the depots of ash and slag, for each coal-fired power plant examined. The results of the gamma radiation absorbed dose in the air measured on selected locations in the vicinities of the coal-fired power plants are shown in Table 6. Declared reproducibility of measurements in this dose region is 2%, and the uniformity of thermoluminescent dosimeters is 1.5%.
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R. Kljajid et al.
Table 1. Basic characteristics of coal-fired power plants studied. Coal-fired power plant Basic characteristics
#I
I#2
#3
#4
(MWe)
300
578
779
300
Working capacity (MWc)
220
578
779
280
L
BC
L+BC
BC
Calory value of coal (J kg-‘) *
7500
11860
9560 (L) 13 176 (BC)
10 500
Total coal consumption (Tg)
1850
3200
3474 (L) 1645 (BC)
1888
Combustion temperature
1498
1773
1173
1473
% Ash *
17
25
25 (BC)
22
% Slag *
1
18
2.5 (L) 3.5 (BC)
2.7
Projected efficiency of electrofilters (%)
99.8
99.8
99.3
99.7
Chimney height(m)
164
100
loo-167
310
Projected capacity
Type of coal used *
(“K)
18CL)
* L - lignite; BC - brown coal Table 2. Calculated annual production of natural radionuclides by CPPs studied. Origin
Radionuclide
Activity
(Bq We-’ y-‘)
CPP #I
CPP #2
CPP #3
CPP #4
Chain
226Ra 214Pb 214Bi
0.23 f 0.05 0.23 + 0.05 0.17 f 0.03
0.24 f 0.05 0.26 f 0.06 0.22 f 0.05
0.28 zt 0.07 0.30 f 0.09 0.25 f 0.05
0.12 z!z0.01 0.08 ??0.01 0.08 f 0.01
232Th Chain
228A~ 2OsT1
0.14 f 0.02 0.13 f 0.02
0.08 f 0.01 0.09 + 0.01
0.05 f 0.01 0.05 f 0.01
0.09 f 0.01 0.09 f 0.01
4OK
1.03 f 0.21
0.57 f 0.12
1.15 * 0.25
0.69 f 0.15
238~
Natural Potassium CPP - coal-fired
power plant
The results demonstrate that the highest doses for all coal-fired power plants were measured from January to March, while the lowest ones, from March to June. The doses found on depots of ash and slag and on the grounds behind the coal-fired power plants along the most frequent wind directions were higher than on other locations. The annual doses were the highest on
locations placed 3-5 km behind the coal-fired power plants along the most frequent wind directions. The exception was found on coal-fired power plant 3, where the highest annual dose was found on the ground of the coal-fired power plant. The lower doses found close to the electrofilters were due to the shield effect of metal constructions located between the dosimeters and the
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Population exposure to radionuclides from a coal power plant
Table 3. Specific activity levels in samples from CPPs studied. CPP #
Activity (Bq kg-‘)
Radionuclide
1
238”
226Ra 232Th 4OK 2
3
Depot
19.0 f 51.0* 15.0 f 120.0 f
4.4 4.4 4.6 19.4
95.0 142.0 44.0 406.0
f f f f
9.8 7.4 6.5 24.0
92.0 140.0 46.0 309.0
f f f f
9.6 13.4 6.2 23.0
88.0 116.0 53.0 343.0
f f f f
9.4 3.9 6.3 21.7
18.0 12.0 16.0 95.0
6.4 6.1 6.0 18.6
42.0 40.0 48.0 294.0
f f f f
8.1 5.2 14.3 32.2
15.0 20.0 26.0 144.0
f f f f
3.9 8.3 8.1 26.4
12.0 38.0 49.0 358.0
f f f f
3.4 6.0 9.0 34.2
157.0 f 272.0 f 66.0 f 468.0 f
12.5 10.6 8.1 30.1
230.0 260.0 60.0 430.0
f f f f
15.2 9.0 9.2 33.7
189.0 263.1 63.0 445.0
f f f *
22.6 15.8 11.1 28.6
106.0 * 143.0 f 23.0 f 68.0 f
10.37 15.0 10.0 16.2
75.0 97.0 15.2 47.0
f f f f
3.8 10.1 6.0 19.3
83.0 49.0 23.0 40.0
f f f f
9.1 5.0 6.5 16.9
f f f *
69.0 f 8.3 44.0 f 4.3 15.0 f 5.9 117.0*21.0
4
Slag
Ash
Coal
22.0 21.0 15.0 30.0
f f f f
9.6 3.6 5.6 15.3
CPP - Coal-fired power plant Table 4. Gamma radiation exposure dose rates in vicinities of CPPs studied.
Exposure dose rate (PC kg-’ s-‘)
Location CPP #l
CPP #2
CPP #3
CPP #4
3-5 km in front of CPP *
0.955 f 0.096
0.717 f 0.072
0.762 f 0.016
0.770 f 0.070
On the grounds of CPP
0.914 f 0.090
0.717 f 0.072
0.771 f 0.072
0.910 f 0.090
3-5 km behind CPP **
0.913 f 0.091
0.860 f 0.085
0.754 f 0.075
0.913 f 0.090
Depot of ash and slag
1.144 f 0.150
0.75 1 f 0.075
0.765 f 0.077
0.717 f 0.070
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind CPP along the most frequent wind direction electrofilter filling. It was not technically possible to set the dosimeters into the electrofilters to avoid this undesirable effect. Differences in measured dose values between the spring-summer and autumn-winter seasons were due to different seasonal production intensities of the coal-fired power plants and their annual repair and maintenance service carried out during a period of about one month in the spring-summer season.
Comparing the data for slag and ash given in Table 3, it can be seen that concentrations of certain elements are unequally distributed. This can be explained by different mechanisms of aerosol formation in coal-fired power plants (Mihalj 1988; MaroviC and Bauman 1986; Nokaoka et al. 1984; Antid and SokrZiC-Kostid 1993). During the process of cooling along the way from the boiler to the chimney, smaller ash particles as carriers
R. Kljajid et al.
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Table 5. Calculated contributions
of specific radionuclides
to the exposure dose rate.
Exposure dose rate (PC kg-’ se’) 3-5 km in front of CPP *
3-5 km behind CPP **
0.021 0.016 0.031 0.096
0.294 0.285 0.197 0.226
f f f k
0.056 0.055 0.040 0.045
0.440 0.367 0.067 0.041
0.088 0.075 0.013 0.008
0.646 0.091 0.297 0.737
f f f f
0.128 0.017 0.060 0.147
f f * *
0.018 0.010 0.013 0.048
0.138 0.035 0.045 0.075
f f f f
0.028 0.007 0.010 0.015
0.142 f 0.028 0.110*0.022 0.059 rt 0.01 I 0.128 f 0.025
0.286 0.057 0.072 0.193
+ f f f
0.057 0.01 I 0.014 0.038
0.153 0.147 0.162 0. I58
f f f f
0.030 0.029 0.032 0.03 I
0.187 0.091 0. I I6 0.138
ZL0.037 z+0.018 f 0.023 f 0.027
0.091 0.085 0. I36 0.200
f f f f
0.018 0.017 0.027 0.040
0.098 f 0.085 f 0. I IO f 0.080 f
0.020 0.017 0.022 0.016
I 2 3 4
0.111 0.101 0. I35 0.127
*0.021 % 0.020 f 0.027 f 0.025
0. I20 0.054 0.092 0.101
f f f *
0.024 0.01 I 0.018 0.020
0.097 0.142 0.120 0.080
* f f f
0.019 0.028 0.024 0.015
0.202 0.113 0.094 0.012
0.040 0.021 0.018 0.002
661.6
I 2 3 4
0.042 0.019 0.004 0.054
f f f f
0.008 0.005 0.001 0.01 I
0.033 0.022 0.006 0.053
f f f f
0.006 0.004 0.001 0.01 I
0.045 0.038 0.004 0.128
f f * f
0.009 0.008 0.001 0.025
0.000 0.000 0.000 0.000
Ws
795.8
I 2 3 4
0.005 f 0.001 0.002 f 0.001 0.000 0.005 f 0.001
0.004 0.003 0.002 0.005
f f f f
0.001 0.001 0.001 0.001
Q.004 f 0.001 0.006 f 0.001 0.000 0.012 f 0.004
0.000 0.000 0.000 0.000
228A~
911.1
I 2 3 4
0.076 0.079 0.089 0.083
f * f f
0.015 0.016 0.017 0.016
0. I I6 0.094 0.096 0.057
f f f f
0.023 0.018 0.020 0.012
0.136 0. I03 0.102 0.107
0. I 14 f 0.022 0.093 f 0.018 0.021 0.111 ?? 0.037 * 0.007
228A~
968.9
I 2 3 4
0.124 0.071 0.051 0.094
f f f f
0.024 0.014 0.010 0.017
0.137~0.027 0.062 f 0.012 0.040 f 0.008 0.026 f 0.006
0.131 ho.026 O.ll6*0.023 0.089 f 0.018 0.072 f 0.014
0.154 0.059 0.073 0.033
f f f f
0.030 0.01 I 0.014 0.006
4OK
1460.7
I 2 3 4
0.090 0.053 0.085 0.033
f f f f
0.018 0.010 0.017 0.006
0.102 0.048 0.061 0.067
f f f f
0.020 0.009 0.012 0.013
0.073 0.061 0.087 0.065
f f f f
0.014 0.012 0.017 0.013
0.084 0.044 0.085 0.007
f f f f
0.016 0.008 0.017 0.001
2’4Bi
1764.5
I 2 3 4
0. I3 I 0.065 0.052 0.044
f f f f
0.026 0.013 0.010 0.008
0.108 0.032 0.078 0.058
f * f f
0.021 0.006 0.015 0.012
0.133 0.063 0.100 0.051
f f f f
0.026 0.012 0.020 0.010
0.285 0.051 0.107 0. I45
f f f f
0.057 0.010 0.021 0.029
2O8TI
2614.5
I 2 3 4
0.014 0.007 0.010 0.012
f f f f
0.002 0.001 0.002 0.002
0.001 0.008 0.008 0.009
f f f f
0.001 0.001 0.001 0.002
0.001 0.012 0.011 0.006
f f f f
0.001 0.002 0.002 0.001
0.015 0.007 0.007 0.002
f f f f
0.003 0.001 0.001 0.001
CPP #
Grounds of CPP
Radionuclide
E (keV1
226Ra
186.2
I 2 3 4
0.109 0.082 0.158 0.483
* * + f
2’4Pb
295.2
I 2 3 4
0.091 0.051 0.066 0.244
228A~
338.4
I 2 3 4
2O8Tl
583.1
‘3’cs
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind the CPP along themost frequent wind direction
f f f f
f f f f
0.027 0.020 0.020 0.021
Depot
f f f f
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Population exposure to radionuclides from a coal power plant
Table 6. Gamma radiation absorbed dose in the air.
Absorbed dose (mGy) Location
3-5 km in front of CPP *
Measuring period Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: On the grounds of CPP
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: Close to electrofilter
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: On the depot
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: 3-5 km behind CPP **
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose:
CPP #1
CPP #2
not measured 0.16 f 0.05 0.46 f 0.09 0.23 f 0.06
0.31 0.16 0.22 0.20
not measured
0.89 + 0.19
0.30 0.17 0.22 0.21
f f f f
+ f f f
0.08 0.03 0.04 0.04
CPP #3 0.31 0.17 0.24 0.24
f f f f
0.07 0.04 0.06 0.06
CPP #4 0.33 0.19 0.23 0.17
f f f f
0.09 0.05 0.05 0.04
0.96 f 0.23
0.94 f 0.23 0.29 0.16 0.27 0.25
0.06 0.04 0.05 0.05
0.33 f 0.07 0.25 f 0.05 not measured 0.19 f 0.04
0.42 0.19 0.32 0.22
f f f f
0.09 0.05 0.07 0.05
0.90 f 0.20
not measured
1.15 f 0.26
f f f *
0.06 0.04 0.05 0.05
0.97 f 0.20
0.07 0.04 0.04 0.05
0.20 f 0.05 0.18 f 0.04 not measured 0.27 f 0.05
0.85 f 0.20
0.81 f 0.20
not measured
0.30 f 0.07 not measured not measured 0.18 f 0.05
0.29 0.22 0.20 0.19
0.27 f 0.19+ 0.19* 0.20 *
not measured
0.90 f 0.22
0.85 f 0.21
1.03 f 0.23
0.32 f 0.19 f 0.24 f 0.21+
0.30 0.19 0.23 0.24
0.32 0.16 0.25 0.24
0.29 0.17 0.21 0.21
f f f f
0.07 0.04 0.05 0.05
0.27 f 0.17 f 0.19* 0.22 f
0.88 f 0.21
0.29 0.16 0.24 0.24
f f f f
0.07 0.04 0.05 0.05
0.93 f 0.2 1
f + * f
0.06 0.04 0.05 0.05
0.07 0.05 0.05 0.05
0.08 0.05 0.05 0.05
0.96 f 0.23
0.25 0.17 0.18 0.21
f f f f
f f f f
0.06 0.05 0.05 0.05
0.07 0.05 0.06 0.05
0.96 f 0.023
0.34 0.18 0.29 0.22
f f f f
f f f f
0.08 0.04 0.06 0.05
0.07 0.04 0.05 0.05
0.97 f 0.21
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind the CPP along the most frequent wind direction
accumulate different elements on their surface. The majority of particles are collected by the electrofilters and cleaning devices preventing them to spread out from the coal-fired power plant. Due to the high efficiency of electrostatic filters amounting up to 99.5%, the majority of fly ash is removed in this way. However, it should be pointed out that, in the case of coal having a high ash content, electrofilters can frequently be blocked, and, therefore, temporarily turned off. During such episodes, enormous amounts of fly ash are released into the atmosphere. This is the
frequent case with coal-fired power plants that use low caloric coal, lignite, and several types of brown coal (Mihalj et al. 1989; 1991). Similar results were found in several previous studies, too (MaroviC and Bauman 1986; Nokaoka et al. 1984; AntiC and SokeiC-KostiC 1993). Comparing the results found and the results of environmental monitoring on locations distant from coalfired power plant impact (SFRY 1991) with known worldwide published average background level values (UNSCEAR 1993), an increment of up to 100% can be
S234
found. The average annual gamma radiation absorbed dose in the air of 1 mGy was found in five locations in the vicinities of four investigated coal-fired power plants. The measured values of absorbed doses on ash and slag depots are close to the 1990 ICRP recommended annual dose limit for public exposure (ICRP 1991). As the latest ICRP recommendations and IAEA Basic Safety Standards (IAEA 1994) have significantly reduced the dose limit for public exposure per year from 5 mSv to 1 mSv, the results obtained imply the need to verify the compliance with regulations through further investigations. As this study was limited to external exposure assessment only, further research should cover investigations in urban areas in all parts of the food chain, such as plants and animals, to obtain relevant information for internal exposure assessment and local population effective dose estimation. Requirements for limiting certain conditions of exposure to natural sources are about to be implemented into national regulations. CONCLUSIONS
The results of specific activity measurements in the samples taken from several locations in the vicinities of coal-fired power plants studied show that there is an increase in concentration of natural radionuclides in ash and slag of up to about five times. An increment of up to 100% was found in the average background level values in the vicinities of coal-fired power plants compared to those on locations distant from coal-fired power plant impact. The measured values of absorbed doses on ash and slag depots are close to the 1990 ICRP recommended annual dose limit for public exposure and imply the need for verifying the compliance with regulations through further investigations. REFERENCES ANSI/IEEE (American National Standards Institute and The Institute of Electrical and Electronic Engineers). IEEE standard test procedures for germanium gamma-ray detectors. New York, NY: ANSI/IEEE; 1986. Antic, D.; Riznid, J.; Marsidanin, B. Comparative analysis of environmental pollution caused by nuclear and coal-fired power plants. In: Proc. XIV symposium of Yugoslav Radiation Protection Association. Belgrade, YU: Yugoslav Radiation Protection Association; 1987: 201-204. (In Serbocroatian) Antic, D.; SokciC-Kostid, M. Radiochemical influence of coal-fired power plants on the environment. In: Proc. II symposium on chemistry and environmental protection. Belgrade, YU: Serbian Chemical Association; 1993: 547-548. (In Serbocroatian)
R. Kljajid et al.
Bauman, A.; Kovac, J. Technologically enhanced natural radioactivity in coal-fired power plants. Man Environ. 9(6): 49-51; 1984. (In Serbocroatian) Debertin, K.; Helmer, R.G. Gamma- and X-ray spectrometry with semiconductor detectors. Amsterdam, NL: North Holland; 1988. DeCampo, J.A.; Beck, H.L.; Raft, P.D. High pressure argon ionization chamber systems for the measurement of environmental radiation exposure rates. Report HASL-260. New York, NY: Health and Safety Laboratory, U.S. Atomic Energy Commission; 1972. IAEA (International Atomic Energy Agency). Measurements of radionuclides in food and the environment: A guidebook. IAEA Technical Reports Series No. 295. Vienna: IAEA; 1989. IAEA (International Atomic Energy Agency). International basic safety standards for protection against ionizing radiation and for the safety of radiation sources. Safety series No. 115-I Vienna: IAEA; 1994. ICRP (International Commission on Radiological Protection). 1990 recommendation of the International Commission on Radiological Protection. ICRP Publication No. 60. Annals of the IRCP 21(13); 1991. Jacobi, W. The population exposure to the radionuclides emission in the vicinity of coal-fired power plant. Report of Gesellschaft fur Strahlungs forschung S-760. Neuherberg, GE: Gesellschaft fur Strahlungsforschung; 1981. (In German) Kljajid, R.; Samek, D.; Mihalj, A.; Hors?, E.; Milosevid, Z. Population radiation exposure levels in the vicinity of coal-fired power plants. In: Proc. conference on energy and the environment. Belgrade, YU: Yugoslav Association of Engineers and Technicians; 1989: 229-232. (In Serbocroatian) Kljajic, R.; Sipka, V.; Radenkovid, M.; Mitrovid, R. Coal and fertilizers as a source of technologically enhanced natural radioactivity. In: Kovacevid, M., ed. Natural ionizing radiation, Belgrade, YU: The Vinca Institute of Nuclear Sciences; 1995: 95-l 11. (In Serbocroatian) LaBrecque, J.J.; Rosales, P.A. External natural radiation exposure rates from the primordial radionuclides in northern Venezuela. Radiat. Prot. Dosim. 55(4): 305-308; 1994. Lederer, C.M.; Shirley, V.S. Tables of isotopes. Washington, D.C.: U.S. Department of Energy; 1978. Malanca, A.; Pessina, V.; Dallara, G. Radionuclide content of building materials and gamma ray dose rates in dwellings of Rio Grande do Norte, Brasil. Radiat. Prot. Dosim. 48(2): 199-203; 1993. Man, C.-K.; Lau, S.-Y.; Au, S.-C.; Ng, W.-K. Radionuclide content of building materials used in Hong Kong. Health Phys. 57(3): 397-401; 1989. Marovif, G.; Bauman, A. Radioactivity of coal-fired power plants. Chemistry in industry 35(8): 427-434; 1986. (In Serbocroatian) Mihalj, A. Radioactivity in the vicinity of coal-tired power plants in Bosna and Hercegovina. M. Sci. Thesis. Faculty of Veterinary Medicine at the University of Sarajevo. Sarajevo, YU; 1988. (In Serbocroatian) Mihalj, A.; Kljajid, R.; Samek, D. Natural radioactivity in coal and its solid combustion products in the Kakanj thermoelectric power plant. In: Proc. Italian-Yugoslav symposium on radiation protection. Roma, IT: Comitato Nazionale per la Ricerca e per 10 Sviluppo dell’ Energia Nucleare e delle Energie Alternative (ENEA); 1988: 353-357. Mihalj, A.; Kljajic, R.; Samek, D.; Saracevic, L.; Horsid, E. The annual emission of natural radionuclides of coal-tired power plants. In: Proc. conference on energy and the environment.
Population exposure to radionuclides from a coal power plant
Belgrade, YU: Yugoslav Association of Engineers and Technicians; 1989: 127- 133. (In Serbocroatian) Mihalj, A.; Samek, D.; Kljajic, R. Estimation ofthe external radiation population exposure in the vicinity of coal-fired power plants. Occup. Rev. 21(237-238): 55-58; 1991. (In Serbocroatian) Nokaoka, A.; Fukushimi, M.; Takagi, Sh. Environmental effects of natural radionuclides from coal-tired power plants. Health Phys. 47: 407-416; 1984. Prokic, M.; Boner-Jensen, L. Comparison of main thermoluminescence properties of some TL dosimeters. Radiat. Prot. Dosim. 47(1/4): 195-199; 1993.
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SFRY (Federal Ministry of Health of SFR Yu). Annual environmental monitoring. Belgrade, YU; 1991. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1982. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1988. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1993.
report on Effects of radiation. Effects of radiation. Effects of radiation.
Environment
International, Vol. 22, Suppl. 1, pp. S227-S235, 1996 Copyright 01996 Elseviex Science Ltd Printed in the USA. All rights reserved 0160-4120/96 S15.00+.00
PI1SO160-4120(96)00112-Z
NATURAL RADIONUCLIDE EMISSION FROM A COAL POWER PLANT AND THE POPULATION EXPOSURE TO EXTERNAL RADIATION IN ITS VICINITY Ranko KljajiC and Zoran MaSiC Scientific Institute for Veterinary Medicine, 21000 Novi Sad, Yugoslavia
Zora hnid,
Sneiana
PavloviC, Mom6ilo ToSiC, and Miodrag MandiC
The VinCa Institute of Nuclear Sciences, 11001 Belgrade, Yugoslavia
Vojin GordaniC The Geoinstitute,
11000 Belgrade, Yugoslavia
Predrag PoliC Faculty of Chemistry, University of Belgrade, 11001 Belgrade, Yugoslavia
El 9512-408 M (Received 6 December 1995; accepted 4 July 1996)
Investigations carried out in the vicinity of four coal-tired power plants showed that the average annual emission of natural radionuclides for each MWe of produced electric power is an average of 0.200 MBq for each component of 238U chain, and of 0.130 MBq for each component of 232Th chain, respectively, and of 1.027 MBq for 4%. The average annual absorbed dose of about 1 mGy was found on five locations studied. The results of specific activity measurements on the samples taken from several locations studied showed that there is a concentration of natural radionuclides in ash and slag of up to about five times. The absorbed dose levels found on depots of ash and slag were close to the values recommended by the International Commission on Radiological Protection. Copyright 01996
l3wier Scic~crLid
INTRODUCTION The modern world is facing two basic problems -to provide sufficient amounts of energy and to produce enough food. In the effort to solve these problems, new
technologies using various processes have been introduced. As a result of some processes, such as coal combustion, artificial fertilizer production, and others, a redistribution of natural radioactivity occurs and considerably more population is being exposed to natural radioactivity. The concept of technologically enhanced natural radioactivity was introduced in the mid-seventies. It
S227
represents the exposure to natural sources of radiation which would not exist without the technological activity unintentionally undertaken to produce radiation (UNSCEAR 1982). Earlier studies have shown that the main sources of technologically enhanced natural radioactivity are coal-fired power plants and artificial fertilizers applied in agriculture. Coal-fired power plants have been neglected as radiation sources for a long time. They became important for investigations as a result of the advancement of the scientific knowledge of biological effects of
S228
radiation action on humans and after dose limits reduction in international recommendations and standards. Coal combustion in power plants leads to redistribution of natural radionuclides originating from coal, and to their concentration in ash and slag. The basic problem of technologically enhanced natural radioactivity caused by coal-fired power plants is the increase of the background gamma radiation level. Therefore, the local population is exposed to higher gamma radiation doses than in their absence. Increased concentrations of uranium in different layers of coal occur mainly due to the elution of uranium from rich volcano rocks into layers of coal. It is known that the average concentrations of radionuclides in coal amount to about 500 Bq kg-’ for 40K, and about 20 Bq kg“ for each component of 238U and 232Th chains (UNSCEAR 1982). It was found (Bauman and Kovac 1984; Marovic and Bauman 1986) that decay products of 238U and232 Th in coal are not in equilibrium, which is particularly important for the case of “‘Pb and “‘PO. An increase in the concentration of 2’0Pb compared with the preceding elements of uranium chain in coal can occur if high levels of 222Rn diffuse from the highly active rocks nearby into less active layers of coal. It was found that a!! types of coal used in the coalfired power plants studied contain 12.2-24.4 Bq kg-’ of 238Uand 12.2 l- 16.8 Bq kg-’ of 23Th as we!! as their radioactive decay products (Kljajid et a!. 1995). These values are somewhat lower than their respective concentrations in the earth’s crust. However, some types of coal can have higher contents of natural radionuclides (hard coal). Coal combustion eliminates organic components causing an increase of ash radioactivity compared with coal radioactivity for a factor of five to ten, Concentrations of natural radionuclides in ash and slag are 5-10 times higher than the corresponding concentrations in the earth’s crust (Mihalj 1988; Mihalj et a!. 1989, 1991; KljajiC et a!. 1989). In addition, coal combustion in coal-tired power plants leads to the concentration of natural radionuclides. The enrichment factor for ash and slag can amount from five to ten. Therefore, the goal of this study was to estimate the influence of the coal-fired power plants on the environment and their contribution to the total population exposure to the external radiation in their vicinities (Jacobi 198 1; Mihalj 1988; Mihalj et a!. 1988, 1989; Nakaoka et a!. 1984). Under normal conditions, when electrofilters in coalfired power plants operate with high efficiency, a minor portion of ash produced is released through the chimney into the atmosphere. Depending on the chimney height,
R. Kljajik et al.
the ash is deposited from the plum at a closer or further distance from the coal-fired power plant. The deposited ash and slag at depots may contain natural radionuclides with activities several times higher than respective average activities in the soil (Antic et a!. 1987; UNSCEAR 1982, 1988). Because the ash is insoluble in water, the elution of natural radionuclides into the surface and underground water is not a particular problem except in the case of 226Ra. However, the release of 222Rnfrom ash and slag depots can present a significant problem (Jacobi 1981). It is important to take into account that hundreds of thousands of tons of ash are accumulated on depots as a result of the normal production cycle of a coal-fired power plant, as we!! as the fact that ash and slag containing increased levels of radionuclides can be used as building material and, in some cases, for “improving” soil for agriculture. As the need for coal supply is high, there is an increased potential for discovery and application of coal with higher natural radioactivity. Therefore, it is necessary to pay attention to environmental pollution from coal-fired power plants and to regulate ionizing radiation exposure caused by technologically enhanced natural radioactivity.
EXPERIMENTAL
DETAILS
Four full-year operating coal-fired power plants were selected for the study. All of them are located close to urban areas, while ash and slag depots are located in the vicinities of the coal-fired power plants at distances of about l-3 km. The annual production of natural radionuclides by coal-fired power plants was calculated using data on annual coal consumption, coal activities, ash contents, efficiencies of electrofilters used, as we!! as the average content of radionuclides in coal, ash, and slag. The contents of radionuclides were measured in samples of coal, ash, and slag. Samples were chosen to represent specific points of various technological steps used, as are coal and ash, and different emission levels with respect to wind direction and distances (IAEA 1989). They were prepared from related materials taken from investigated coal-fired power plants according to standard procedures used for natural radionuclides activity measurements: homogenized, dried to constant weight, and sealed in Marinelli beakers to achieve radioactive equilibrium. For specific activity measurements, a standard gamma spectrometric system based on an analyzer with 4000 channels and pure germanium detector with resolution of 1.95 keV at 1.33 MeV,
S229
Population exposure to radionuclides from a coal power plant
having a relative efficiency of 25% at 1.33 MeV, was used. Energy and efficiency calibration was done by certified 252E~standard in Marinelli geometry according to a standardized procedure (ANSI 1986). The same geometry was used for sample measurements. The 226Ra concentration was determined from gamma lines of 295 keV, 352 keV, 609 keV, and 1765 keV, originating from 214Pb and 2’4Bi as the mean value of the results of these gamma lines. The concentration of 232Th was determined from gamma lines of 583 keV and 911 keV from *‘*Tl and ***AC,respectively. The 40K concentration was calculated from its 1460.8 keV gamma line. The activity of 238U was calculated from the 185 keV gamma line of 235U (Man et al. 1989; Malanca et al. 1993; LaBrecque and Resales 1994; Debertin and Helmer 1988), although it is not the reference method for quantitative determination of uranium content. All necessary radionuclide data needed for the calculations were taken from the work of Lederer and Shirley (1978). Three instruments were used for the measurement of the exposure levels of gamma radiation: 1) The highly sensitive, pressurized ionization chamber (0.35 MPa argon + 1.4 MPa nitrogen) with a low detection limit of 0.072 pC kg-’ s-’ (manufactured by Silena) was used for exposure dose rate measurements. Gamma radiation exposure dose rates were measured at 1 m above the plain surface of uncultivated ground (DeCampo et al. 1972). 2) A field kit for gamma spectrometry (manufactured by Ortec) was used for in situ spectrum analysis. It consisted of a field analyzer with 4000 channels and a high-purity germanium (HPGe) detector with a resolution of 1.8 keV at 1.33 MeV, and a relative efficiency of 18% at 1.33 MeV. According to the spectra obtained, the contributions of selected gamma lines to the total exposure levels were calculated. 3) The thermoluminescent dosimeters in boxes containing three pills each (Prokic and Bolter-Jensen 1993) were used for the absorbed dose measurements. Thermoluminescent dosimeters were exposed for 3 months, 1 m above the plain surface of ground. All measurements in the vicinity of each coal-fired power plant were made at four locations: 3-5 km in front of the coal-fired power plants along the most frequent wind direction, 3-5 km behind the coal-fired power plants along the same direction, and at two locations on the ground of the coal-fired power plants, at the depots of ash and slag. The fifth location was added just for thermoluminescent dosimeter measurements, and it was placed near the electrofilters.
RESULTS AND DISCUSSION
The basic characteristics of coal-fired power plants studied are presented in Table 1. The calculated values of annual amounts of natural radionuclides produced by coal-fired power plants are presented in Table 2. Data indicate that radionuclides of 238U and 232Th chains were not always in equilibrium. The natural radionuclides levels measured in samples of coal, ash, slag, and ash and slag depots are presented in Table 3. The f values represent the estimated total measurement errors, including counting, preparation, and calibration. The results for the 238Ucontents should be considered as informative, keeping in mind that 238U is not an important source of external exposure which is the main subject of this study. A comparison of gamma radiation exposure dose rates at four locations for all the coal-fired power plants examined is given in Table 4. It can be seen that the highest value for coal-fired power plant 1 of 1.14 pC kg-’ s’ was found in the ash and slag depot. For the other three locations, nearly the same values were found. Gamma radiation exposure dose rates for coal-fired power plant 2 had nearly the same values for all locations. The highest exposure dose rate of 0.86 pC kg-’ s’ was found 3-5 km behind the coalfired power plant along the most frequent wind direction. Nearly the same values were found in all locations measured for coal-fired power plant 3. The exposure dose rates for coal-fired power plant 4 were between 0.72 in the depot and 0.91 pC kg-’ s’ at 3-5 km behind the coal-fired power plant along the most frequent wind direction. Data on the participation of selected gamma lines from the stated radionuclides in the total exposure doses were calculated on the basis of in situ gamma spectra obtained by the field HPGe detector in the same locations. Table 5 shows the calculated contributions to the exposure dose rates of gamma radiation originating from the most important natural and fall-out radionuclides at locations 3-5 km in front of and behind the coal-fired power plant along the most frequent wind direction, on the grounds of the coal-fired power plant, and on the depots of ash and slag, for each coal-fired power plant examined. The results of the gamma radiation absorbed dose in the air measured on selected locations in the vicinities of the coal-fired power plants are shown in Table 6. Declared reproducibility of measurements in this dose region is 2%, and the uniformity of thermoluminescent dosimeters is 1.5%.
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R. Kljajid et al.
Table 1. Basic characteristics of coal-fired power plants studied. Coal-fired power plant Basic characteristics
#I
I#2
#3
#4
(MWe)
300
578
779
300
Working capacity (MWc)
220
578
779
280
L
BC
L+BC
BC
Calory value of coal (J kg-‘) *
7500
11860
9560 (L) 13 176 (BC)
10 500
Total coal consumption (Tg)
1850
3200
3474 (L) 1645 (BC)
1888
Combustion temperature
1498
1773
1173
1473
% Ash *
17
25
25 (BC)
22
% Slag *
1
18
2.5 (L) 3.5 (BC)
2.7
Projected efficiency of electrofilters (%)
99.8
99.8
99.3
99.7
Chimney height(m)
164
100
loo-167
310
Projected capacity
Type of coal used *
(“K)
18CL)
* L - lignite; BC - brown coal Table 2. Calculated annual production of natural radionuclides by CPPs studied. Origin
Radionuclide
Activity
(Bq We-’ y-‘)
CPP #I
CPP #2
CPP #3
CPP #4
Chain
226Ra 214Pb 214Bi
0.23 f 0.05 0.23 + 0.05 0.17 f 0.03
0.24 f 0.05 0.26 f 0.06 0.22 f 0.05
0.28 zt 0.07 0.30 f 0.09 0.25 f 0.05
0.12 z!z0.01 0.08 ??0.01 0.08 f 0.01
232Th Chain
228A~ 2OsT1
0.14 f 0.02 0.13 f 0.02
0.08 f 0.01 0.09 + 0.01
0.05 f 0.01 0.05 f 0.01
0.09 f 0.01 0.09 f 0.01
4OK
1.03 f 0.21
0.57 f 0.12
1.15 * 0.25
0.69 f 0.15
238~
Natural Potassium CPP - coal-fired
power plant
The results demonstrate that the highest doses for all coal-fired power plants were measured from January to March, while the lowest ones, from March to June. The doses found on depots of ash and slag and on the grounds behind the coal-fired power plants along the most frequent wind directions were higher than on other locations. The annual doses were the highest on
locations placed 3-5 km behind the coal-fired power plants along the most frequent wind directions. The exception was found on coal-fired power plant 3, where the highest annual dose was found on the ground of the coal-fired power plant. The lower doses found close to the electrofilters were due to the shield effect of metal constructions located between the dosimeters and the
S231
Population exposure to radionuclides from a coal power plant
Table 3. Specific activity levels in samples from CPPs studied. CPP #
Activity (Bq kg-‘)
Radionuclide
1
238”
226Ra 232Th 4OK 2
3
Depot
19.0 f 51.0* 15.0 f 120.0 f
4.4 4.4 4.6 19.4
95.0 142.0 44.0 406.0
f f f f
9.8 7.4 6.5 24.0
92.0 140.0 46.0 309.0
f f f f
9.6 13.4 6.2 23.0
88.0 116.0 53.0 343.0
f f f f
9.4 3.9 6.3 21.7
18.0 12.0 16.0 95.0
6.4 6.1 6.0 18.6
42.0 40.0 48.0 294.0
f f f f
8.1 5.2 14.3 32.2
15.0 20.0 26.0 144.0
f f f f
3.9 8.3 8.1 26.4
12.0 38.0 49.0 358.0
f f f f
3.4 6.0 9.0 34.2
157.0 f 272.0 f 66.0 f 468.0 f
12.5 10.6 8.1 30.1
230.0 260.0 60.0 430.0
f f f f
15.2 9.0 9.2 33.7
189.0 263.1 63.0 445.0
f f f *
22.6 15.8 11.1 28.6
106.0 * 143.0 f 23.0 f 68.0 f
10.37 15.0 10.0 16.2
75.0 97.0 15.2 47.0
f f f f
3.8 10.1 6.0 19.3
83.0 49.0 23.0 40.0
f f f f
9.1 5.0 6.5 16.9
f f f *
69.0 f 8.3 44.0 f 4.3 15.0 f 5.9 117.0*21.0
4
Slag
Ash
Coal
22.0 21.0 15.0 30.0
f f f f
9.6 3.6 5.6 15.3
CPP - Coal-fired power plant Table 4. Gamma radiation exposure dose rates in vicinities of CPPs studied.
Exposure dose rate (PC kg-’ s-‘)
Location CPP #l
CPP #2
CPP #3
CPP #4
3-5 km in front of CPP *
0.955 f 0.096
0.717 f 0.072
0.762 f 0.016
0.770 f 0.070
On the grounds of CPP
0.914 f 0.090
0.717 f 0.072
0.771 f 0.072
0.910 f 0.090
3-5 km behind CPP **
0.913 f 0.091
0.860 f 0.085
0.754 f 0.075
0.913 f 0.090
Depot of ash and slag
1.144 f 0.150
0.75 1 f 0.075
0.765 f 0.077
0.717 f 0.070
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind CPP along the most frequent wind direction electrofilter filling. It was not technically possible to set the dosimeters into the electrofilters to avoid this undesirable effect. Differences in measured dose values between the spring-summer and autumn-winter seasons were due to different seasonal production intensities of the coal-fired power plants and their annual repair and maintenance service carried out during a period of about one month in the spring-summer season.
Comparing the data for slag and ash given in Table 3, it can be seen that concentrations of certain elements are unequally distributed. This can be explained by different mechanisms of aerosol formation in coal-fired power plants (Mihalj 1988; MaroviC and Bauman 1986; Nokaoka et al. 1984; Antid and SokrZiC-Kostid 1993). During the process of cooling along the way from the boiler to the chimney, smaller ash particles as carriers
R. Kljajid et al.
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Table 5. Calculated contributions
of specific radionuclides
to the exposure dose rate.
Exposure dose rate (PC kg-’ se’) 3-5 km in front of CPP *
3-5 km behind CPP **
0.021 0.016 0.031 0.096
0.294 0.285 0.197 0.226
f f f k
0.056 0.055 0.040 0.045
0.440 0.367 0.067 0.041
0.088 0.075 0.013 0.008
0.646 0.091 0.297 0.737
f f f f
0.128 0.017 0.060 0.147
f f * *
0.018 0.010 0.013 0.048
0.138 0.035 0.045 0.075
f f f f
0.028 0.007 0.010 0.015
0.142 f 0.028 0.110*0.022 0.059 rt 0.01 I 0.128 f 0.025
0.286 0.057 0.072 0.193
+ f f f
0.057 0.01 I 0.014 0.038
0.153 0.147 0.162 0. I58
f f f f
0.030 0.029 0.032 0.03 I
0.187 0.091 0. I I6 0.138
ZL0.037 z+0.018 f 0.023 f 0.027
0.091 0.085 0. I36 0.200
f f f f
0.018 0.017 0.027 0.040
0.098 f 0.085 f 0. I IO f 0.080 f
0.020 0.017 0.022 0.016
I 2 3 4
0.111 0.101 0. I35 0.127
*0.021 % 0.020 f 0.027 f 0.025
0. I20 0.054 0.092 0.101
f f f *
0.024 0.01 I 0.018 0.020
0.097 0.142 0.120 0.080
* f f f
0.019 0.028 0.024 0.015
0.202 0.113 0.094 0.012
0.040 0.021 0.018 0.002
661.6
I 2 3 4
0.042 0.019 0.004 0.054
f f f f
0.008 0.005 0.001 0.01 I
0.033 0.022 0.006 0.053
f f f f
0.006 0.004 0.001 0.01 I
0.045 0.038 0.004 0.128
f f * f
0.009 0.008 0.001 0.025
0.000 0.000 0.000 0.000
Ws
795.8
I 2 3 4
0.005 f 0.001 0.002 f 0.001 0.000 0.005 f 0.001
0.004 0.003 0.002 0.005
f f f f
0.001 0.001 0.001 0.001
Q.004 f 0.001 0.006 f 0.001 0.000 0.012 f 0.004
0.000 0.000 0.000 0.000
228A~
911.1
I 2 3 4
0.076 0.079 0.089 0.083
f * f f
0.015 0.016 0.017 0.016
0. I I6 0.094 0.096 0.057
f f f f
0.023 0.018 0.020 0.012
0.136 0. I03 0.102 0.107
0. I 14 f 0.022 0.093 f 0.018 0.021 0.111 ?? 0.037 * 0.007
228A~
968.9
I 2 3 4
0.124 0.071 0.051 0.094
f f f f
0.024 0.014 0.010 0.017
0.137~0.027 0.062 f 0.012 0.040 f 0.008 0.026 f 0.006
0.131 ho.026 O.ll6*0.023 0.089 f 0.018 0.072 f 0.014
0.154 0.059 0.073 0.033
f f f f
0.030 0.01 I 0.014 0.006
4OK
1460.7
I 2 3 4
0.090 0.053 0.085 0.033
f f f f
0.018 0.010 0.017 0.006
0.102 0.048 0.061 0.067
f f f f
0.020 0.009 0.012 0.013
0.073 0.061 0.087 0.065
f f f f
0.014 0.012 0.017 0.013
0.084 0.044 0.085 0.007
f f f f
0.016 0.008 0.017 0.001
2’4Bi
1764.5
I 2 3 4
0. I3 I 0.065 0.052 0.044
f f f f
0.026 0.013 0.010 0.008
0.108 0.032 0.078 0.058
f * f f
0.021 0.006 0.015 0.012
0.133 0.063 0.100 0.051
f f f f
0.026 0.012 0.020 0.010
0.285 0.051 0.107 0. I45
f f f f
0.057 0.010 0.021 0.029
2O8TI
2614.5
I 2 3 4
0.014 0.007 0.010 0.012
f f f f
0.002 0.001 0.002 0.002
0.001 0.008 0.008 0.009
f f f f
0.001 0.001 0.001 0.002
0.001 0.012 0.011 0.006
f f f f
0.001 0.002 0.002 0.001
0.015 0.007 0.007 0.002
f f f f
0.003 0.001 0.001 0.001
CPP #
Grounds of CPP
Radionuclide
E (keV1
226Ra
186.2
I 2 3 4
0.109 0.082 0.158 0.483
* * + f
2’4Pb
295.2
I 2 3 4
0.091 0.051 0.066 0.244
228A~
338.4
I 2 3 4
2O8Tl
583.1
‘3’cs
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind the CPP along themost frequent wind direction
f f f f
f f f f
0.027 0.020 0.020 0.021
Depot
f f f f
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Population exposure to radionuclides from a coal power plant
Table 6. Gamma radiation absorbed dose in the air.
Absorbed dose (mGy) Location
3-5 km in front of CPP *
Measuring period Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: On the grounds of CPP
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: Close to electrofilter
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: On the depot
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose: 3-5 km behind CPP **
Jan Apr July Ott
- Mar - June - Sept - Dee
Annual dose:
CPP #1
CPP #2
not measured 0.16 f 0.05 0.46 f 0.09 0.23 f 0.06
0.31 0.16 0.22 0.20
not measured
0.89 + 0.19
0.30 0.17 0.22 0.21
f f f f
+ f f f
0.08 0.03 0.04 0.04
CPP #3 0.31 0.17 0.24 0.24
f f f f
0.07 0.04 0.06 0.06
CPP #4 0.33 0.19 0.23 0.17
f f f f
0.09 0.05 0.05 0.04
0.96 f 0.23
0.94 f 0.23 0.29 0.16 0.27 0.25
0.06 0.04 0.05 0.05
0.33 f 0.07 0.25 f 0.05 not measured 0.19 f 0.04
0.42 0.19 0.32 0.22
f f f f
0.09 0.05 0.07 0.05
0.90 f 0.20
not measured
1.15 f 0.26
f f f *
0.06 0.04 0.05 0.05
0.97 f 0.20
0.07 0.04 0.04 0.05
0.20 f 0.05 0.18 f 0.04 not measured 0.27 f 0.05
0.85 f 0.20
0.81 f 0.20
not measured
0.30 f 0.07 not measured not measured 0.18 f 0.05
0.29 0.22 0.20 0.19
0.27 f 0.19+ 0.19* 0.20 *
not measured
0.90 f 0.22
0.85 f 0.21
1.03 f 0.23
0.32 f 0.19 f 0.24 f 0.21+
0.30 0.19 0.23 0.24
0.32 0.16 0.25 0.24
0.29 0.17 0.21 0.21
f f f f
0.07 0.04 0.05 0.05
0.27 f 0.17 f 0.19* 0.22 f
0.88 f 0.21
0.29 0.16 0.24 0.24
f f f f
0.07 0.04 0.05 0.05
0.93 f 0.2 1
f + * f
0.06 0.04 0.05 0.05
0.07 0.05 0.05 0.05
0.08 0.05 0.05 0.05
0.96 f 0.23
0.25 0.17 0.18 0.21
f f f f
f f f f
0.06 0.05 0.05 0.05
0.07 0.05 0.06 0.05
0.96 f 0.023
0.34 0.18 0.29 0.22
f f f f
f f f f
0.08 0.04 0.06 0.05
0.07 0.04 0.05 0.05
0.97 f 0.21
CPP - Coal-fired power plant * in front of CPP along the most frequent wind direction ** behind the CPP along the most frequent wind direction
accumulate different elements on their surface. The majority of particles are collected by the electrofilters and cleaning devices preventing them to spread out from the coal-fired power plant. Due to the high efficiency of electrostatic filters amounting up to 99.5%, the majority of fly ash is removed in this way. However, it should be pointed out that, in the case of coal having a high ash content, electrofilters can frequently be blocked, and, therefore, temporarily turned off. During such episodes, enormous amounts of fly ash are released into the atmosphere. This is the
frequent case with coal-fired power plants that use low caloric coal, lignite, and several types of brown coal (Mihalj et al. 1989; 1991). Similar results were found in several previous studies, too (MaroviC and Bauman 1986; Nokaoka et al. 1984; AntiC and SokeiC-KostiC 1993). Comparing the results found and the results of environmental monitoring on locations distant from coalfired power plant impact (SFRY 1991) with known worldwide published average background level values (UNSCEAR 1993), an increment of up to 100% can be
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found. The average annual gamma radiation absorbed dose in the air of 1 mGy was found in five locations in the vicinities of four investigated coal-fired power plants. The measured values of absorbed doses on ash and slag depots are close to the 1990 ICRP recommended annual dose limit for public exposure (ICRP 1991). As the latest ICRP recommendations and IAEA Basic Safety Standards (IAEA 1994) have significantly reduced the dose limit for public exposure per year from 5 mSv to 1 mSv, the results obtained imply the need to verify the compliance with regulations through further investigations. As this study was limited to external exposure assessment only, further research should cover investigations in urban areas in all parts of the food chain, such as plants and animals, to obtain relevant information for internal exposure assessment and local population effective dose estimation. Requirements for limiting certain conditions of exposure to natural sources are about to be implemented into national regulations. CONCLUSIONS
The results of specific activity measurements in the samples taken from several locations in the vicinities of coal-fired power plants studied show that there is an increase in concentration of natural radionuclides in ash and slag of up to about five times. An increment of up to 100% was found in the average background level values in the vicinities of coal-fired power plants compared to those on locations distant from coal-fired power plant impact. The measured values of absorbed doses on ash and slag depots are close to the 1990 ICRP recommended annual dose limit for public exposure and imply the need for verifying the compliance with regulations through further investigations. REFERENCES ANSI/IEEE (American National Standards Institute and The Institute of Electrical and Electronic Engineers). IEEE standard test procedures for germanium gamma-ray detectors. New York, NY: ANSI/IEEE; 1986. Antic, D.; Riznid, J.; Marsidanin, B. Comparative analysis of environmental pollution caused by nuclear and coal-fired power plants. In: Proc. XIV symposium of Yugoslav Radiation Protection Association. Belgrade, YU: Yugoslav Radiation Protection Association; 1987: 201-204. (In Serbocroatian) Antic, D.; SokciC-Kostid, M. Radiochemical influence of coal-fired power plants on the environment. In: Proc. II symposium on chemistry and environmental protection. Belgrade, YU: Serbian Chemical Association; 1993: 547-548. (In Serbocroatian)
R. Kljajid et al.
Bauman, A.; Kovac, J. Technologically enhanced natural radioactivity in coal-fired power plants. Man Environ. 9(6): 49-51; 1984. (In Serbocroatian) Debertin, K.; Helmer, R.G. Gamma- and X-ray spectrometry with semiconductor detectors. Amsterdam, NL: North Holland; 1988. DeCampo, J.A.; Beck, H.L.; Raft, P.D. High pressure argon ionization chamber systems for the measurement of environmental radiation exposure rates. Report HASL-260. New York, NY: Health and Safety Laboratory, U.S. Atomic Energy Commission; 1972. IAEA (International Atomic Energy Agency). Measurements of radionuclides in food and the environment: A guidebook. IAEA Technical Reports Series No. 295. Vienna: IAEA; 1989. IAEA (International Atomic Energy Agency). International basic safety standards for protection against ionizing radiation and for the safety of radiation sources. Safety series No. 115-I Vienna: IAEA; 1994. ICRP (International Commission on Radiological Protection). 1990 recommendation of the International Commission on Radiological Protection. ICRP Publication No. 60. Annals of the IRCP 21(13); 1991. Jacobi, W. The population exposure to the radionuclides emission in the vicinity of coal-fired power plant. Report of Gesellschaft fur Strahlungs forschung S-760. Neuherberg, GE: Gesellschaft fur Strahlungsforschung; 1981. (In German) Kljajid, R.; Samek, D.; Mihalj, A.; Hors?, E.; Milosevid, Z. Population radiation exposure levels in the vicinity of coal-fired power plants. In: Proc. conference on energy and the environment. Belgrade, YU: Yugoslav Association of Engineers and Technicians; 1989: 229-232. (In Serbocroatian) Kljajic, R.; Sipka, V.; Radenkovid, M.; Mitrovid, R. Coal and fertilizers as a source of technologically enhanced natural radioactivity. In: Kovacevid, M., ed. Natural ionizing radiation, Belgrade, YU: The Vinca Institute of Nuclear Sciences; 1995: 95-l 11. (In Serbocroatian) LaBrecque, J.J.; Rosales, P.A. External natural radiation exposure rates from the primordial radionuclides in northern Venezuela. Radiat. Prot. Dosim. 55(4): 305-308; 1994. Lederer, C.M.; Shirley, V.S. Tables of isotopes. Washington, D.C.: U.S. Department of Energy; 1978. Malanca, A.; Pessina, V.; Dallara, G. Radionuclide content of building materials and gamma ray dose rates in dwellings of Rio Grande do Norte, Brasil. Radiat. Prot. Dosim. 48(2): 199-203; 1993. Man, C.-K.; Lau, S.-Y.; Au, S.-C.; Ng, W.-K. Radionuclide content of building materials used in Hong Kong. Health Phys. 57(3): 397-401; 1989. Marovif, G.; Bauman, A. Radioactivity of coal-fired power plants. Chemistry in industry 35(8): 427-434; 1986. (In Serbocroatian) Mihalj, A. Radioactivity in the vicinity of coal-tired power plants in Bosna and Hercegovina. M. Sci. Thesis. Faculty of Veterinary Medicine at the University of Sarajevo. Sarajevo, YU; 1988. (In Serbocroatian) Mihalj, A.; Kljajid, R.; Samek, D. Natural radioactivity in coal and its solid combustion products in the Kakanj thermoelectric power plant. In: Proc. Italian-Yugoslav symposium on radiation protection. Roma, IT: Comitato Nazionale per la Ricerca e per 10 Sviluppo dell’ Energia Nucleare e delle Energie Alternative (ENEA); 1988: 353-357. Mihalj, A.; Kljajic, R.; Samek, D.; Saracevic, L.; Horsid, E. The annual emission of natural radionuclides of coal-tired power plants. In: Proc. conference on energy and the environment.
Population exposure to radionuclides from a coal power plant
Belgrade, YU: Yugoslav Association of Engineers and Technicians; 1989: 127- 133. (In Serbocroatian) Mihalj, A.; Samek, D.; Kljajic, R. Estimation ofthe external radiation population exposure in the vicinity of coal-fired power plants. Occup. Rev. 21(237-238): 55-58; 1991. (In Serbocroatian) Nokaoka, A.; Fukushimi, M.; Takagi, Sh. Environmental effects of natural radionuclides from coal-tired power plants. Health Phys. 47: 407-416; 1984. Prokic, M.; Boner-Jensen, L. Comparison of main thermoluminescence properties of some TL dosimeters. Radiat. Prot. Dosim. 47(1/4): 195-199; 1993.
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SFRY (Federal Ministry of Health of SFR Yu). Annual environmental monitoring. Belgrade, YU; 1991. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1982. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1988. UNSCEAR (United Nations Scientific Committee on the Atomic Radiation). Sources and effects of ionizing New York: United Nations; 1993.
report on Effects of radiation. Effects of radiation. Effects of radiation.