products plus radioactivity of 235U also multiplied by the number of its daughter products. 234U can be omitted because 234U is a member of 238U decay family. In reality, different migration ability of decay products (especially, gaseous radionuclides) in geological environment can tear the decay chains and decrease significantly specific radioactivity of uranium ore. With proper accounting for migration ability of some radionuclides, specific radioactivity of uranium ore containing 0.1% U is equal to about 4 µCi/kg, i.e. twenty times higher than acceptable level. Natural uranium, recovered from uranium ore and chemically separated from its decay products, contains three uranium isotopes - 235U, 238U and 234U. Specific radioactivity of natural uranium is evaluated to be 700 µCi/kg, i.e. 3500 times higher than acceptable level. This means that already at initial stages of nuclear fuel cycle its enterprises have to deal with materials whose specific radioactivity exceeds significantly the sanitary norms.
Nuclear enterprises are able to produce the following negative effects on the environment and human organisms:
1.Radiation injuries since nuclear technologies deal with materials – emitters of ionizing radiation.
2.Thermal impact caused by hot-water effluents from NPP steam turbines into the air atmosphere and other objects of hydrosphere.
3.Chemical impact of toxic materials contained in tails from hydrometallurgical processing of uranium ore at initial NFC stage, in wastes from radiochemical SNF reprocessing at final NFC stage and in common domestic wastes from routine activity of nuclear enterprises.
4.Alienation of large territories that takes place mainly at initial NFC stage related with mining and primary processing of uranium ores.
Although each of these negative effects deserves an individual analysis, radiation impact calls the most public concerns. That is why main attention will be given below to radiation effects produced by routine operation of nuclear enterprises on the environment and human organisms.
2.1. Natural radiation background
In order to evaluate the radiation threats from nuclear enterprises, the following question should be answered: in what radiation field created by natural sources of ionizing emissions do the environment and
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the Earth population reside in the present time? The Earth’s biosphere had existed for many billions of years. During such a lengthy time period all representatives of the Earth’s biosphere had cultivated some adaptive mechanisms which allowed them to accommodate and survive under all natural negative conditions including natural radiation background. The negative effects produced by natural radiation background can be used to estimate ecological threats from various nuclear technologies. The problem of the humankind is to form the situation when nuclear technologies do not produce so severe radiation impact on the environment that exceeds substantially the radiation impact produced by natural background.
The following main contributors into natural radiation background can be noted:
-cosmic rays;
-radioactivity of rocky minerals (uranium, thorium, their decay products, isotopes from middle part of Mendeleev’s table – 40K, 48Ca, 87Rb);
-radioactivity of soil, atmosphere, hydrosphere and biosphere. Statistical information about natural radiation background in various
world regions, including Russia, can be presented as average annual individual effective doses from natural sources of ionizing radiation.
1. Cosmic rays.
Range over the world regions – from 300 to 1000 µSv/year. Average over the world – 390 µSv/year.
Average over Russia – 460 µSv/year.
2. External irradiation by terrestrial radionuclides.
Range over the world regions – from 300 to 600 µSv/year. Average over the world – 480 µSv/year.
Average over Russia – 440 µSv/year.
3. Internal irradiation by terrestrial radionuclides.
Range over the world regions – from 400 to 10000 µSv/year. Average over the world – 1570 µSv/year.
Average over Russia – 1470 µSv/year.
Total radiation impact from natural background:
Average over the world – 2440 µSv/year.
Average over Russia – 2370 µSv/year.
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Thus, it may be concluded that radiation impact from natural sources of ionizing radiation on human organism can be evaluated at an approximate level of 2,4 mSv/year. This value corresponds to the collective effective dose received by full the Earth’s population at the level of 1,5·107 person·Sv/year.
Theses two values, namely 2,4 mSv/year per a person and 1,5·107 person·Sv/year, will be used further .to compare radiation threats at various NFC stages with natural background of ionizing radiation.
According to the RF regulations, additional radiation burden from nuclear enterprises must be well below 1 mSv/year for population and 20 mSv/year for staff.
2.2. Ecological effects of various NFC stages
2.2.1. Mining and hydrometallurgical treatment of uranium ore
At this NFC stages the staff members of uranium mines, HM-plants and population of adjacent regions can suffer from both external and internal irradiation since large amounts of radioactive materials are brought onto the Earth surface and can migrate into the environment. The main striking effects are caused by radioactive dust, aerosols and
some gaseous radionuclides from U and Th decay families, namely 226Rn (radon) from 238U decay family and 220Rn (thoron) from 232Th de-
cay family.
The following values can be taken from statistical information about radiation doses at the stages of uranium ore mining and its HMtreatment:
1.Average annual effective dose from external irradiation is evaluated as 10 mSv/year for the staff members involved into uranium ore mining.
2.Roughly the same radiation dose (about 10 mSv/year) is received in the form of internal irradiation. Thus, collective effective dose received by the staff members involved into uranium ore mining is evaluated as 1,7 person·Sv/GWe·year.
3.Average-world individual effective dose received by the staff members involved into operation of HM-plants is evaluated as 12 mSv/year for external irradiation and 5 mSv/year for internal irradiation. Thus,
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collective effective dose received by the staff members of HM-plants is evaluated as 0,4 person·Sv/GWe·year.
4. Collective effective dose received by population of adjacent regions is evaluated as 0,2 person·Sv/GWe·year, i.e. by one order of magnitude lower that that for the staff members involved into uranium ore mining.
It is noteworthy that these NFC stages are maximally related with alienation of large territories for disposition of HM-plants and their wastes (tails). According to the RF regulations, two alienation forms may be applied< namely temporary alienation (with possibility for future re-cultivation) and permanent alienation (for disposition of radioactive tails): 60 ha/GWe·year for temporary alienation and 2 ha/GWe·year for permanent alienation.
2.2.2. Affinage of uranium concentrate, isotopic uranium enrichment and fabrication of fuel rods
At these NFC stages collective effective doses received by the staff members are evaluated as 0,1 person·Sv/GWe·year at the stages of uranium concentrate affinage and uranium isotope enrichment, and as 0,6 person·Sv/GWe·year at the fabrication stage of fresh fuel assemblies.
Collective effective doses received by population of adjacent regions are evaluated as 2·10-4 person·Sv/GWe·year from liquid effluents, and as 19·10-4 person·Sv/GWe·year from gaseous effluents.
Thus, initial (front-end) part of nuclear fuel cycle (mining and HMtreatment of uranium ores, affinage of uranium concentrate, uranium isotope enrichment and fabrication of fresh fuel assemblies) can be characterized by the following radiation impacts:
1.Collective effective dose received by the staff members is evaluated as 4 person·Sv/GWe·year.
2.Collective effective dose received by population of adjacent regions is evaluated as 0,25 person·Sv/GWe·year.
Total capacity of the world nuclear power system is about 375 GWe in 2014. So, collective effective dose can be calculated as 1,6·103 per-
son·Sv/year, i.e. about 0.01% from radiation impact of natural background (1.5·107 person·Sv/year).
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2.2.3. Use of nuclear fuel at NPP
Even normal NPP operation mode is accompanied by accumulation of radiowastes in nuclear fuel and in some other NPP components. Main radiation sources in the wastes are fission products and minor actinides in nuclear fuel, corrosion and activation products in structural materials of fuel and in other metal in-pile structures of nuclear reactors. Penetration of radiowastes into the environment and biosphere encounters a series of protective barriers including fuel pellets and their metal claddings, the reactor vessel, circuits for coolant circulation and NPP containment. Nevertheless, some small fraction of radiowastes is able to come into the environment with coolant leakages, at the repair and maintenance works, at replacement of defected equipment units. Besides, some radionuclides can escape the spent fuel storage pool as liquid effluents from the washing-out process of contaminated filters and ion-exchange purification systems.
NPP with RBMK-type reactors is usually characterized by relatively higher radiation impact than NPP with VVER-type reactors. The closed primary circuit of VVER-type reactors promotes the longer retention of radionuclides in comparison with the open primary circuit of RBMKtype reactors where boiling light-water coolant can circulate. Gaseous and volatile radiowastes can rapidly escape the boiling coolant with vapor and release into the environment through the condenser’s ejector.
Collective effective doses received by NPP staff are evaluated as 3,9 person·Sv/GWe·year for VVER-type reactors and 20,3 person·Sv/GWe·year for RBMK-type reactors.
Under nominal operation conditions of Russian NPP, collective effective doses received by population of adjacent regions are evaluated as 0,13 person·Sv/GWe·year for VVER-type reactors and 0,6 person·Sv/GWe·year for RBMK-type reactors. As total capacity of Russian nuclear power system is equal to about 23 GWe in 2014 with approximately the same contributions from VVER and RBMK-type reactors, collective effective doses 8 person·Sv/year for population of adjacent regions and 450 person·Sv/year for NPP staff members. These values are negligibly small as compared with natural radiation background (1.5·107 person·Sv/year).
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