Thermal pollution of the environment
As is known, cooling of the condensers at NPP with electrical output of 1 GWe requires water flow rate at the level of 50 m3/s and warms up water on 100С. Following from these NPP operation data, minimal area of water-table in NPP heat-sink pool is evaluated as 6 km2/GWe. If the heat-sink pool is also used for some other purposes (fish breeding, tourism, rest of people), then the minimal area must be roughly doubled, up to 13 km2/GWe.
The water warming-up effect can change water density, viscosity and gas solubility. The warmed water evaporates quicker and, thus, promotes forming the damper climate.
Thermal pollution of hydrosphere caused by hot-water effluents into NPP heat-sink pool can lead to appearance of vertical water stratification with relatively hotter superficial layers. Consequently, oxygen concentrations in cold, near to the bottom, layers can remarkably decrease. General water warming-up effect intensifies decomposition of organic residuals and water-plants, upgrades demands of fishes for oxygen. All these effects can provoke creating the areas of mass fish starvation.
Mechanical traumatism of fishes by the water-intaking tools in combination with toxicity of chlorine that is applied to prevent overgrowing of these tools with water-plants can result in even more negative effect as compared with that of hot-water effluents only.
2.2.4. Radiochemical SNF reprocessing
Radiochemical reprocessing of spent fuel assemblies differs two possible organizational options of nuclear fuel cycle, namely the closed NFC and open (once-through) NFC. SNF reprocessing extracts valuable and relatively low-active nuclear materials (uranium and plutonium) and returns (recycles) them to the fabrication stage of fresh fuel rods and fuel assemblies for their further usage in nuclear power reactors. Unfortunately, radiochemical SNF reprocessing is inevitably accompanied by accumulation of liquid, solid and gaseous radiowastes in very large quantities. These radiowastes have to be treated and ultimately disposed of in stable geological formations.
According to the IAEA information, collective effective doses received by the staff members of the SNF reprocessing plants differ each
116
other depending on the country where these plants are put into operation:
France – 0,6 person ·Sv/GWe·year;
Great Britain – 11,0 person ·Sv/GWe·year; Russia – 1,8 person ·Sv/GWe·year.
Analogous values for population of adjacent regions (within radius of 50 km) cover the range from 20 to 30 person·Sv/GWe·year. If a mean value of collective effective dose received by the staff members, 10 person·Sv/GWe·year , for instance, as in Great Britain, is adopted as a reference point, then total collective effective dose (global nuclear power capacity is ~375 GWe in 2014) can be determined as 3.75·103 person·Sv/year, i.e. two orders of magnitude higher than that for population of adjacent regions. However, even this high value equals about 0.025% from collective effective dose produced by natural sources of ionizing radiation (1.5·107 person·Sv/year).
2.2.5. Treatment and disposal of radiowastes
The currently world-wide adopted strategy of radiowastes management includes the following main stages:
1.Long-term controlled storage of radiowastes at nuclear enterprises.
2.Conditioning of radiowastes, i.e. the radiowastes treatment in order to reduce their volume and transform them into any forms suitable for containerization, transportation and ultimate disposal in stable geological formations which are able to decrease drastically any probability for radionuclides to penetrate into the environment.
3.Ultimate disposal of steel containers filled up with solidified radiowastes in stable geological formations (salt mines, sedimentary clayey and rocky formations).
Full absence of real geological repositories and, as a consequence, full absence of experiences on their long-term operation and maintenance leads to a necessity to use only theoretical evaluations of the radiation effects produced by radiowastes on the environment and human organism. These evaluations presume that steel containers filled up with radiowastes could fail after 1000 years of their disposal, and the solidified radiowastes could escape their inert matrices and penetrate into the environment after 10000 years of their disposal.
117
The following conclusions can be derived from these theoretical evaluations:
1.Ultimate disposal of spent fuel assemblies discharged from power light-water reactors (no reprocessing option) leads to collective effective dose at the level of 270 person·Sv/GWe for 10000 years.
2.Ultimate disposal of radiowastes produced by radiochemical reprocessing of spent fuel assemblies from power LWR (reprocessing option) can reduce collective effective dose down to the level of 50 person·Sv/GWe for 10000 years.
It seems very improbable that direct disposal of spent fuel assemblies without their reprocessing will be practiced for a sufficiently long time period. General trend in nuclear power development consists in implementing the closed NFC option, i.e. radiochemical reprocessing of spent fuel assemblies, recycle of fertile and fissile materials, ultimate disposal of radiowastes from SNF reprocessing. Consequently, average annual collective effective dose from geological repositories of radio-
wastes can be evaluated as 0,2 person·Sv/year.
2.2.6. Total ecological effects of NFC
By summing up the results obtained in analysis of various NFC stages from standpoint of their radiation impact on the environment and human organism, the following collective effective doses can be presented:
1. At initial (front-end) part of NFC (mining and primary treatment of uranium ore, affinage of uranium concentrate, uranium isotope enrichment, fabrication of fresh fuel assemblies) collective effective dose is evaluated as 1,6·103 person·Sv/year, i.e. 0,01% from radiation impact of natural background (1,5·107 person·Sv/year).
2. At main NFC stage (use of nuclear fuel at Russian NPP) collective effective dose received by NPP staff is evaluated as 450 person·Sv/year while collective effective dose received by population of adjacent regions is evaluated as 8 person·Sv/year. Both values are negligibly small as compared with natural radiation background.
3. Radiochemical SNF reprocessing (back-end part of NFC) can produce collective effective dose received by the staff members at the level
118
of 3,7·103 person·Sv/year, i.e. 0,025% from radiation impact of natural background.
4. Ultimate disposal of radiowastes (back-end part of NFC) in stable geological formations can produce, according to some theoretical evaluations, collective effective dose at the level of 0,2 person·Sv/year.
So, by summing up the collective effective doses received by staff members and population of adjacent regions, it can be concluded that total radiation impact of nuclear enterprises on the environment and human organism does not exceed 0,04% from radiation impact of natural radiation background. Of course, all these evaluations are correct only under normal operation conditions of nuclear enterprises. Under some accidental conditions, radiation impact of nuclear enterprises can be substantially higher as we have seen on the examples of well-known catastrophic events at Chernobyl and Fukushima NPP, at Kyshtym repository of radiowastes.
2.3. Some ecological problems in the USA
According to publications of American environmentalists, natural radiation background on the USA territory slightly differs from that on the RF territory and from the world-averaged values. The following statistical data can characterize contributions from main components into average natural radiation background in the USA:
1.Radon in structural materials – 2 mSv/year.
2.Radioactivity of the Earth’s crust (soils and rocks) – 0,28 mSv/year.
3.Cosmic rays – 0,27 mSv/year.
4.Radioactivity of human body (human blood contains radionuclide 40K with half-life of 1,25·109 years) – 0,40 mSv/year.
Subtotal – 2,95 mSv/year.
As for artificial (anthropogenic, or man-made) irradiation, American environmentalists presented the following statistical information:
Artificial irradiation
1.Medical procedures – 0,53 mSv/year.
2.Consumer products – 0,10 mSv/year.
3.Weapon-test fallout – 0,01 mSv/year.
4.Nuclear power industry – 0,01 mSv/year.
119
Subtotal – 0,65 mSv/year.
Elective irradiation
1.Use of natural gas – 0,06 mSv/year.
2.Airline flights – 0,02 mSv/year.
3.Watching color TV – 0,01 mSv/year.
4.Sleeping with another person – 0,01 mSv/year.
Subtotal – 0,10 mSv/year.
By summing up all the subtotals, total average annual radiation effect produced by natural, artificial and elective exposures of American citizens can be evaluated as:
2,95 mSv/year + 0,65 mSv/year + 0,1 mSv/year = 3.7 mSv/year. This dose is remarkably higher than the world-averaged value (2,4
mSv/year).
One else very interesting approach has been developed by the US scientists to evaluation of the average time period by which a human life could be shortened through encountering a particular risk. This average time period is defined as the “Loss-of-Life-E xpectancy” and obtained from analysis of broad statistical information. Under the approach, many harmful factors which are able to shorten a human life have been investigated, including radiation impact produced by natural background and routine operations of nuclear enterprises. The American specialists wished to answer the following question: how long could the Loss-of-Life-Expectancy be depending on personal life choices, occupations, type of diseases, circumstances and, at last, on electricity generation technologies?
The following unexpected results have been obtained. Loss-of-Life-Expectancy for life choices
1.Unmarried males – 3000 days.
2.Smoking males – 2590 days.
3.Unmarried females – 1600 days.
4.Smoking females – 1530 days.
5.Alcohol abuse – 365 days.
6.Vehicular accidents – 207 days.
Loss-of-Life-Expectancy for various occupations
1.Living in poverty – 3500 days.
2.Low social-economic status – 1670 days.
120