Atomic Energy, Vol. 99, No. 3, 2005
RADIATION CONDITIONS IN OBNINSK
S. M. Vakulovskii and I. I. Kryshev
UDC 551.510.72+550.378+556.531.4+551.464
Monitoring data are used as a basis to examine the radiation conditions in Obninsk, including an analysis of the radioactive emissions from the Physics and Power-Engineering Institute and the Scientific-Research and Physicochemical Institute, the content of technogenic radionuclides in atmospheric air, soil, surface waters, and the components of agricultural natural ecosystems, and an estimate of the dose and radiation risk to the public. The monitoring results show relatively low levels of technogenic radionuclides in the environment, much lower than the admissable values. It is recommended that regular radiation monitoring of the content of tritium in surface and underground waters and also iodine isotopes in air near the ground at Obninsk be continued. The total estimated dose, taking account of numerous pathways of technogenic irradiation of the public in Obninsk, is on the average about 10–5 Sv/yr, which corresponds to a negligibly low radiation risk, less than 10–6 under standard operating conditions of nuclear objects.
An important safety tool when using atomic energy is radioecological monitoring. This is understood to mean a system of regular observations of indicators of radioactive contamination of the environment in order to discover and predict quickly the consequences which are undesirable for man and ecosystems. In general, radioecological monitoring is oriented toward safety (radiation risk) at a publicly acceptable level [1], presuming that the risk of a nuclear technology should not be a substantial addition to the total risk to which man and his environment are subjected in the course of his daily activities. In the radiation safety standards NRB-99, the maximum individual radiation risk under normal operating conditions for technogenic irradiation of the public in the course of one year is 5·10–5. For operating nuclear power plants, in accordance with the sanitation rules SP AS-99 the norm for irradiation the public is established as 250 µSv/yr, which corresponds to the admissable radiation risk 10–5. The negligible risk, separating the region of optimization and definitely acceptable risk, is 10–6. The purpose of the present article is to the analyze the radiation conditions in Obninsk and to estimate the irradiation dose and radiation risk to the public on the basis of the monitoring data. Sources of Irradiation. Obninsk is located in Kaluga oblast’, 100 km from Moscow. About 100 thousand people live on its territory, whose area is 43 km2. The history of Obninsk is inseparably linked with a large nuclear center – the Physics and Power-Engineering Institute, created more than 50 years ago. The first nuclear power plant in the world was starated up in 1954 on the basis of this center. Subsequently, Obninsk became a city of science, the first such high-tech city in the country. The scientific groups in the city performed research and scientific-technical analysis in the fields of nuclear power, radiation technology, medical agricultural radiology, meteorology, ecology, and environmental protection. The main sources of radioactive emissions are the Physics and Power-Engineering Institute and an affiliate of the L. Ya. Karpov Scientific-Research Physicochemical Institute. Significantly smaller quantities of radionuclides appear in the environment as a result of the work performed at the All-Russia Scientific-Research Institute of Agricultural Radiology and Agroecology and the Medical Radiological Scientific Center of the Russian Academy of Medical Sciences, where radioisotopes are used [2, 3]. Taifun Scientific and Industrial Association. Translated from Atomnaya Énergiya, Vol. 99, No. 3, pp. 214–221, September, 2005. Original article submitted December 30, 2004. 1063-4258/05/9903-0651 ©2005 Springer Science+Business Media, Inc.
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TABLE 1. Emissions of Radionuclides into the Atmosphere at the Physics and PowerEngineering Institute, Bq/yr Radionuclide 54
Mn
2000
2001
2002
1.1·105 (0.14)
1.8·104 (0.02)
9.8·104 (0.12)
58
6
4.5·10 (0.7)
6
5.8·10 (0.9)
1.4·106 (0.2)
60
3.5·107 (7.8)
1.6·107 (3.6)
2.8·106 (0.6)
65
6
6.7·10 (8.7)
6
2.1·10 (2.7)
1.1·106 (1.4)
1.2·107 (4.1)
2.3·106 (0.79)
2.2·106 (0.76)
Co Co Zn
90
Sr
9
2.0·10 (14.3)
3.5·10 (25)
9.7·108 (6.8)
Cs
1.6·106 (2.9)
1.5·106 (2.7)
2.7·105 (0.5)
Cs
7
2.6·10 (1.5)
7
4.7·10 (2.8)
1.6·107 (0.9)
I (total) 134 137 144
9
Ce
6.8·105 (0.8)
–
7.0·104 (0.08 )
152
Eu
7
1.9·10 (12.7)
5
8.6·10 (0.6)
1.0·105 (0.07)
154
Eu
1.2·106 (1.3)
4.6·105 (0.5)
1.8·104 (0.02)
14
14
7.1·1013 (3.1)
Inert radioactive gases
5.1·10
(22.2)
6.5·10
(28.3)
Note. The figures enclosed in parentheses in Tables 1–3 indicate the emission as a percent of the admissable value.
TABLE 2. Emissions of Radionuclides from the Physics and Power-Engineering Institute into the Protva River, Bq/yr Radionuclide
2000
2001
2002
Total α-emitting
3.2·108 (23)
4.0·108 (28)
3.2·108 (23)
Total β-emitting
3.1·108 (17)
4.0·108 (22)
4.0·108 (22)
Works on the substantiation and development of the objects of nuclear power, the main objects being research nuclear reactors, charged-particle accelerators, critical stands, objects for fabricating radioisotopes, storage for nuclear fuel, and solid and liquid radioactive wastes, are in progress at the Physics and Power-Engineering Institute. The perimeter of the territory of the Physics and Power-Engineering Institute adjoins city housing. The main radioactive emissions from the Physics and Power-Engineering Institute into the atmosphere occur through three pipes, each about 100 m high. There are other organized sources of emissions ranging in height from 5 to 60 m. The composition of the technological emissions depends on the character of the work and is determined primarily by inert radioactive gases and fission products and activation (Table 1). The emissions of inert radioactive gases at the Physics and Power-Engineering Institute in 2000–2002 were equal to 13 7.1·10 –6.5·1014 Bq/yr, or 3.1–28.3% of admissable levels, iodine isotopes – 9.7·108 – 3.5·109 Bq/yr, or 6.8–25% of admissable levels. For all other radionuclides, the emissions are also below admissable levels. The radioactive emissions from the Physics and Power-Engineering Institute occur via three releases into the Protva River and do not exceed allowed levels (Table 2). The main radioactive emissions from the Scientific-Research and Physicochemical Institute, which contains a research reactor, γ radiation facilities, sites for storing irradiated fuel and radioactive wastes, radiation-chemical facilities, and objects for producing radioactive pharmacological preparations in hot chambers, occur through an 82-m high pipe [2, 3]. In 2000–2002, the 131I emissions were (6–8.5)·1010 Bq/yr, or 9.2–13% of admissable values (Table 3). The emissions of inert 652
TABLE 3. Atmospheric Emissions of Radionuclides by an Affiliate of the ScientificResearch and Physicochemical Institute, Bq/yr Radionuclide
2000
2001
2002
125
I
4.7·107 (2.3)
1.7·107 (0.9)
6.1·108 (30.5)
131
I
6.0·10
10
10
(11.5)
8.5·1010 (13)
132
(9.2)
7.5·10
I
2.6·1010 (5.2)
2.6·1010 (5.2)
3.4·1010 (6.8)
133
I
9
10
1.3·10
(4.3)
9.4·109 (3.1)
135
I
–
1.0·109 (0.5)
1.8·108 (0.09)
Ar
13
13
3.1·1013 (20.7)
41
133 135
4.6·10 (1.5) 2.6·10
(17.3)
Xe
4.4·1013 (11)
Xe
13
3.2·10
2.6·10
(17.3)
4.4·1013 (11)
(10.7)
3.6·10
13
7.8·1013 (19.5) 9.2·1013 (30.7)
(12)
TABLE 4. Content of Radionuclides in Air at the Ground in Obninsk, 10–6 Bq/m3 [2] Year
90
Sr
137
Cs
1993
–
1.2
1994
0.20
1995
0.12
1996 1997
239,240
Pu
131
I
–
1340
1.6
0.11
1890
1.8
0.0067
120
0.24
1.7
0.0092
130
0.22
1.6
0.0143
–
1998
0.18
1.4
0.0093
–
1999
0.22
1.5
0.01
–
2000
0.12
1.4
0.0087
–
2001
0.14
1.5
0.0058
6.4
2002
0.15
2.5
0.0079
10.5
Average
0.18 (7·10–6%)
1.6 (6·10–6%)
0.0092 (4·10–4%)
350 (5·10–3%)
Admissable specific acti-
2.7·106
2.7·106
2.5·103
7.3·106
vity of air for the public according to NRB-99
radioactive gases also did not exceed admissable values. It should be noted that emissions of iodine isotopes are much higher than at the Physics and Power-Engineering Institute. Radioactivity of Environmental Objects. Radiation monitoring of environmental contamination is performed by the Taifun Scientific and Industrial Association – in an observation zone with a radius of 10 km around Obninsk and subdivisions and by the Physics and Power-Engineering Institute and the Scientific-Research and Physicochemical Institute – in sanitary-protective zones surrounding enterprises. The radiometric network of Rosgidromet conducts monitoring in a 100-km zone around Obninsk. The yearly average exposure dose rate from γ radiation in Obninsk and monitoring points around the city fall within the global γ background and is 9–13 µR/h. The yearly average specific activity of radionuclides in air at the ground in Obninsk in 1993–2002 is presented in Table 4. According to the monitoring data obtained by Taifun, the 90Sr content in air in Obninsk is, on the average, 0.18·10–6 Bq/m3, 137Cs – 1.6·10–6 Bq/m3, and 239,240Pu –·0.0092·10–6 Bq/m3. This is 105–107 times lower than the admiss-
653
TABLE 5. Contamination Density of the Soil in Obninsk and Adjacent Territories, kBq/m2 Radionuclide 137 90
Average
Variation range
Cs
3.4
1.8–5.6
Sr
0.96
0.44–1.8
0.063
0.026–0.1
239,240
Pu
TABLE 6. Radionuclide Concentration in Protva River Water Radionuclide
Average
Variation range
NRB-99 intervention level
0.8
0.1 – 9.1
11000
Sr, mBq/liter
5.1
1.4 – 12.3
5000
3
2.3
0.9 – 730
7700
137 90
Cs, mBq/liter H, Bq/liter
TABLE 7. Radionuclide Content in the Components of Agricultural and Natural Ecosystems in the Obninsk Region, Bq/kg Moist Mass 90
137
Sr
Component
Milk
Average
Range
Average
Range
Average
Range
<0.01
0.09
0.05–0.17
42
13–50
Meat
0.024
<0.1
Potatoes
<0.01
0.26
Beets
0.046
Radishes Cucumbers
Natural 40K
Cs
0.08
Tomatoes Squashes
159
0.38
99
0.30
122
<0.04
45
0.08
68
<0.02
28
1.0
26
Berries
1.0
Mushrooms
<0.01
0.6
0.16–1.5
92
Fish
0.056
<0.01–0.1
0.36
0.1–0.8
60
7
4–10
835
570–1110
15
6–44
120
56–210
180
135–210
Algae* Moss*
75–108
*
Bq/kg dry mass.
able concentration. A relatively higher concentration of 131I is observed, but even in this case it is 103–105 times lower than the admissable level. In 1995–1997, the content of radionuclides was measured in soil samples, obtained at 70 points in Obninsk and the adjacent territory at distances up to 30 km from the city. Three samples at a depth of 30 cm were obtained at each point. In all samples, 137Cs was the only technogenic γ-emitting radionuclide which was observed. The soil contamination density fluc654
TABLE 8. Estimates of the Internal Irradiation Dose to the Public in Obninsk Due to Radioactive Contamination of Atmospheric Air, 10–9 Sv/yr Radionuclide 90
Sr
131 137
Average
Variation range
0.05
0.03–0.07
I
21
0.4–113
Cs
0.06
0.04–0.09
3.7
2.3–5.8
27
3–120
239,240
Pu
Total
tuated from 1.8 to 5.6 kBq/m2 (Table 5). Analysis showed that it is described by a normal distribution with maximum value of 3.4 ± 0.8 kBq/m2. The soil contamination in the Obninsk region before the Chernobyl accident in 1986 corresponded to the global level and was also described by a normal distribution with maximum value 1.8 ± 0.4 kBq/m2. The 90Sr content in the upper 30-cm layer of soil varied from 0.44 to 1.8 kBq/m2 with average value 0.96 kBq/m2, which is close to the global level. The 239,240Pu content in the same samples was 0.026–0.1 kBq/m2 with average value 0.063 kBq/m2, corresponding to global contamination. Water objects were examined during the same period of time (Table 6). The average radionuclide concentration in river water is much lower than the NRB-99 intervention level (by a factor of 104 for 137Cs and 103 for 90Sr). Measurements of the tritium content in water objects are of special interest. The tritium concentration in the Protva River upstream from the discharges from the Physics and Power-Engineering Institute does not exceed the background levels, and the tritium content was observed to increase downstream from the discharges and in individual springs. It can be concluded from the data in Table 7 that the 90Sr and 137Cs content is low in most components of the environment compared with naturally-occurring 40K. The results of the monitoring show that, on the whole, the content of technogenic radionuclides in environmental objects is low: atmospheric air, soil, natural waters, and components of agricultural and natural ecosystems. At the same time, constant radiation monitoring of the tritium content in surface and underground waters and iodine isotopes in the air at the ground in Obninsk is required. Dose and Radiation Risk Estimates. Estimates of the irradiation dose to the public are an integral part of the radiation monitoring system. The estimation models take account of the following factors: • external irradiation from soil, clouds or stream of radioactive gas and irradiation due to the volume activity of atmospheric air; • internal irradiation, due to radioactive contamination of atmospheric air and consumption of local food products and water. The database on the content of radionuclides in environmental objects in the region investigated and the results of model calculations of radionuclide transport in the atmosphere, soil, water and food chains, and estimates of dosimetric parameters are used as input information in models of dose estimates [5, 6]. In addition to estimates of the irradiation dose to the public [5, 6], when necessary the radiation dose to biota is also estimated [1]. Data on the spatial arrangement and the passage time of a radioactive cloud or stream of radioactive gas, their geometric dimensions, the radionuclide concentration in the atmospheric air at the ground, and the density of radioactive contamination of the soil are needed as initial data to estimate the external irradiation and the internal irradiation due to contamination of atmospheric air. The initial information is prepared on the basis of monitoring data and models of radionuclide transport in the atmosphere. Generalized standard models are used in cases where the irradiation dose to the public is low compared to the admissable dose limits. Specifically, it is desirable to use the generalized models to estimate the irradiation dose from a radiation hazardous object under normal operation, when radionuclide flows into the environment are small. 655
TABLE 9. Estimate of the Tritium Irradiation Dose for Various Age Groups of the Population as a Result of Water Use, µSv/yr Population age group Populated point
Obninsk
1 yr
10 yr
Adults
0.68
0.52
0.85
Balabanovo
0.007
0.005
0.009
Belousovo
0.018
0.014
0.023
Maloyaroslavets
0.014
0.011
0.018
15
24
Hypothetical use of water from springs near the Physics and Power-Engineering Institute
More complicated dynamical models, which take account of the dynamics of the passage of a radioactive cloud, the nonuniformity of the spatial distribution of the contamination, and the special features of the secondary transport of radionuclides with contaminated soil long after an accident are used to make assessments of the consequences of accidents. The estimates of the internal irradiation dose are presented in Table 8. On the average, the dose is 27·10–9 Sv/yr, which is more than 3·105 times lower than the admissable limit. According to conservative estimates [4], the irradiation dose to the public as a result of emissions of inert radioactive gases is 4–70 µSv/yr, which is much lower than the admissable NRB-99 dose limit of 1 mSv/yr. 41Ar makes the main contribution to the irradiation dose; short-lived krypton and xenon make a smaller contribution. The large uncertainty in the dose estimates is due to the large differences in the computational estimates of the concentration of inert radioactive gases within the region being monitored. An important component of dose formation is external irradiation from soil. For the region investigated, the yearly dose of external irradiation on an open location is 600–940 µSv/yr according to observational data, i.e., it is identical to the natural radiation background. The contribution of 137Cs, contained in the soil as a result of global fallout and the Chernobyl accident, is 20 µSv/yr. The radionuclides entering the environment can accumulate in food chains and become a source of internal irradiation of the public. Water and ground pathways of radionuclide migration are distinguished. The main pathways for entry of radionuclides along water and food chains are the consumption of fish, crustaceans, waterbirds, and drinking water and the use of water from reservoirs for irrigation and watering animals. Radionuclides can enter the human body along ground food chains from agrosystems and natural ecosystems. The main agricultural products which give rise to additional irradiation of the public are milk, meat, potatoes, vegetables, fruits, and grain products. An important source of additional irradiation of the public under certain conditions could be the consumption of mushrooms, berries, and the meat of birds and wild animals. The Scientific and Industrial Taifun Association estimates the irradiation dose from the contamination of the food to the public in Obninsk to be about 2.2·10–6 Sv/yr on the average or about 0.2% of the yearly dose limit for the public 1 mSv [4]. This is about 100 times less than the internal irradiation dose from natural 40K taken up with food (2.5·10–4 Sv/yr). The maximum levels of irradiation of the public, which are due to 90Sr and 137Cs contamination of food, are 4.5·10–6 Sv/yr, which is much less than the operative norms. The consumption of potatoes, milk, fruits, and vegetables makes the main contribution to the dose from contamination of food (about 60%). The 137Cs contribution is, on the whole, greater than that of 90Sr. Estimates of the dose due to tritium irradiation as a result of water use were of special interest. According to computational estimates, a higher dose is characteristic for the adult population, which can be regarded in this respect to be a critical group (Table 9). The tritium irradiation dose resulting from drinking water to the public in Obninsk is low and is 0.9 µSv/yr on the average, which is 103 times less than the admissable limit. The irradiation dose in surrounding populated points is even lower. The hypothetical dose due to the use of water from sources with the highest tritium concentration (springs near the Physics and Power-Engineering Institute) reaches 24 µSv/yr or 2.4% of the admissable dose limit 1 mSv/yr 656
(with unlimited water use from contaminated springs during the feeding season). These estimates show, even though they are hypothetical, that radioecological monitoring of tritium around the Physics and Power-Engineering Institute must be continued. The total estimated dose taking account of the numerous pathways for technogenic irradiation of the public in Obninsk is on the average about 10–5 Sv/yr. This corresponds to a negligibly low radiation risk, less than 10–6, for standard operating conditions of nuclear objects. Risk analysis for various scenarios of hypothetical radiation accidents falls outside the scope of the present work and requires a special analysis. Conclusions. In summary, many years of experience in operating nuclear objects in Obninsk shows that the technogenic radioactivity is low and has no significant influence on the irradiation dose to the public and natural biota.
REFERENCES 1. 2. 3. 4. 5. 6.
I. I. Kryshev and E. P. Ryazantsev, Ecological Safety in the Nuclear-Power Complex, IzdAT, Moscow (2000). Radiation Conditions on the Territory of Russia and Adjacent Countries in 1993–2002. Yearbooks, NPO Taifun, Obninsk, Gidrometeoizdat, St. Petersburg. I. I. Silin, Ecology and Economics of Natural Resources of the Protva River Basin (Kaluga and Moscow oblasts), Kaluga (2003). Procedure for Estimating and Predicting Irradiation Doses and Radiation Risk, NPO Taifun, Obninsk (1996). Radiation Safety Standards (NRB-99), Minzdrav Rossii, Moscow (1999). International Basic Safety Standards for Protection Against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115-1, IAEA, Vienna (1996).
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