Disposal methods for radioactive waste from nuclear power plants and environmental radiation monitoring methods

Absrtact. Air pollution has a serious impact on human health. Deterioration of the air environment causes 7 million premature deaths annually. Despite the active implementation of various environmental programmes and technical resources aimed at preserving and protecting the environment from anthropogenic factors, over 90% of the world's population live in cities that do not meet the air quality recommendations of the World Health Organisation (WHO). Intense and constant technogenic load necessitates continuous monitoring of atmospheric air quality. Sufficient, systematic and representative information is needed to study the spatial and temporal distribution of substances in the air basin, to predict pollution levels and to make correct environmental decisions. Environmental monitoring is a tool for obtaining such information. In this work the analysis of influence of radioactive waste of nuclear power plants on a radiation level of environment is executed and the tasks of its ecological monitoring in areas of location of the enterprises of nuclear power industry are considered.


Introduction
Nowadays, nuclear power plants are an indispensable source of electricity generation worldwide.Many scientists consider them safe because they do not emit "greenhouse gases", but whether this is actually the case is examined in this paper.The relevance of the study is that radioactive emissions from nuclear power plants can cause irreparable damage to the environment, so it is important to monitor and control the amount of radionuclides in the atmosphere in time.In addition, it is necessary to understand how the emission readings change over time, as well as what methods are used in research.
The aim of the study is to analyse methods and techniques for monitoring the environment near nuclear power plants.
In order to achieve the objective the following objectives have been identified: 1.To analyse the types of radioactive waste of nuclear power plants.2. To consider the methods of environmental and radiation monitoring in the areas of nuclear power plants.3. To carry out quantitative assessment of radionuclide releases after the Chernobyl nuclear power plant (ChNPP) accident.
The object of the study is environmental monitoring, and the subject of the study is methods of environmental quality control in the areas of nuclear power plants location.

Analysis of available research on the topic
CO2 -is one of the most stable molecules and therefore requires a significant amount of energy to convert it.This is usually achieved by means of high-temperature processes.Unfortunately, the required heat, and temperature, is often provided by the energy released from the combustion of fossil fuels (e.g.coal and natural gas), which results not only in significant greenhouse gas emissions, but also in the fact that energy intensity compromises economic viability.More energy-efficient and cost-effective processes that consume CO2 en masse using low-carbon energy sources are needed [1,2].

CO2 emissions from nuclear power plants
Energy-related CO2 emissions account for 60% of total global emissions.Nuclear power contributed to 63 G-tons of CO2 emissions from 1971 to 2022, providing 40% (76,000 TWh) of all low-carbon generation, which also includes hydropower, solar, wind and biomass.Nuclear power thus represents the largest low-carbon source of electricity, generating about 10% of the world's electricity.The global power generating capacity is around 400 GW, supplied by 452 nuclear reactors installed in 31 countries.Globally, nuclear power accounts for 50% of electricity production in France (66 GW) and about 20% in the US (105 GW).
Nuclear power has long been promoted as a carbon-neutral alternative to fossil energy sources to meet basic electricity demand.However, as nuclear technology has developed, its economic competitiveness has been threatened, leading to reduced investment and expansion.A potential solution to this economic problem is the integrated use of all forms of energy generated by a nuclear reactor.These additional forms of energy include inherent multi-component radiation fields (e.g.neutrons, fast electrons and gamma/x-rays) and excess heat loads [3].Thus, nuclear energy, as a low-carbon energy source, can provide an ideal combination of energy (i.e.heat, electrons and radiation) to meet activation and/or CO2 conversion requirements [4].

Analysis of the impact of radioactive waste from nuclear power plants on environmental radiation levels
As mentioned above, nuclear power plants are more environmentally friendly than fossil fuel plants because they do not directly emit CO2 during operation, but the activities involved in building and operating the plant do emit large amounts of CO2.Nuclear power plants use diesel generators for emergency power.These diesel engines or turbines usually serve as a backup power source during a power outage or accident.The operation of these diesel engines or turbines is a source of greenhouse gases at the nuclear power plant.In addition, nuclear power plants produce 'spent fuel' and 'nuclear waste'.
The operation of nuclear power plants and the disposal of radioactive waste contribute to an increase in the level of radiation in the environment.Radioactive waste is classified as high level, intermediate level or low level, depending on the amount and type of radioactivity it emits and how long its harmful radiation persists [5,6].
Low level waste includes various materials that are generated during normal operation of a nuclear reactor, such as: contaminated clothing and equipment (solid waste); cooling water (liquid waste); and ventilation exhausts (gaseous waste).Low-level liquid and gaseous wastes are usually discharged directly to a nearby water body or to the atmosphere via a chimney.The radioactivity of such materials needs to be below strictly regulated levels before release.A problem associated with the release of low level gases is thermal inversion, in which topographical or climatic factors lead to a concentration of releases near the release site [7].
The release of low level liquid waste, especially water used as coolant in a reactor, may also cause thermal contamination (excessive heating) in the receiving water body.Low level solid waste is usually placed in metal containers and buried in shallow pits for disposal either at the site of generation or at a licensed disposal facility.Figure 1 shows a scheme for the disposal of low-level waste [8].Intermediate level radioactive waste is radioactive waste that is too high in radioactivity to be allowed to be released directly to the environment, so it is either chemically recycled into high and low level components or it is left in place until its radioactivity has dissipated sufficiently for it to be disposed of as low level waste [9,39,41].
High level radioactive waste is generated from spent fuel.The fuel in nuclear reactors is in the form of bundles of metal alloy fuel rods containing granulated uranium.The fission process in a reactor is initiated by bombarding the fissile uranium with a neutron.The bombardment causes the uranium nuclide to fission and release more neutrons (as well as alpha, beta and gamma radiation).There will still be some fissile material (i.e.uranium fuel) in the spent fuel package.In principle, this material could be recycled for use in new fuel rods.The remaining material is high-level radioactive waste, a highly radioactive, chemically diverse mixture of fission products.Among the waste products causing adverse effects are 239 Pu (plutonium-239), which has a half-life of 24,000 years and is highly toxic, and 90 Sr (strontium-90), a beta emitter that acts much like calcium (Ca) and can replace it in bone structures, making it extremely hazardous to human health.High-level waste is currently stored in underground or surface storage tanks, large concrete compartments or water basins.For permanent disposal, radioactive waste must be isolated from any contact with the biosphere or hydrosphere for at least 10 half-lives.This means that many common fission products must be isolated for centuries or even hundreds of thousands of years.It is extremely difficult to find disposal sites that can keep this waste isolated for so long [10,43].
High-level waste is not only radioactive, but it is also continuously simmering because it constantly generates heat.This places special demands on the containers, which must be highly resistant to corrosion, and on the choice of materials from which the waste is made.The storage facility must be located in a remote location, away from the population and relatively easy to protect, in a stable geological environment with low volcanic and seismic activity, must be large enough to contain sufficient waste, be economically feasible, etc. [11].
Some proposals have considered repositories in outer space, subduction zones and ice caps, but geological containment has been the scientifically accepted way of disposing of nuclear waste since the 1950s.Disposing of waste in outer space is theoretically possible, but not currently technologically feasible.Under the best of circumstances, it would be an expensive and risky undertaking.For example, there is the possibility that a waste repository could collapse on Earth with potentially devastating consequences, or that a spacecraft could collide with waste in orbit.Also, the amount of nuclear waste to be disposed of, which is in the hundreds of thousands of tonnes, would require thousands of flights through the atmosphere, virtually ensuring that an accident is inevitable.Low-cost laser-launch systems can provide access to space and solve the emerging nuclear waste problem."Laser thrust" is a form of radiation thrust in which the energy source is a remote laser system (usually located on the ground) that is separated from the reaction mass [12].
Another method of storing radioactive waste is the subduction zone (Figure 2).Subduction zones occur along plate boundaries where the oceanic lithosphere collides with either continental or oceanic lithosphere.Proposals for disposal in subduction zones are based on the fact that deep-sea depressions, where subduction actively occurs, have very high deposition rates.Any waste canisters placed in such a trench would theoretically be backfilled within a relatively short time period.We also know that some ocean floor sediments sink into the mantle along with the sinking lithospheric plate, it is possible that waste canisters could also be submerged in the mantle [14,43].
The problem with this proposal is that there is no detailed understanding of the processes taking place in the deep ocean troughs.In order for the waste to be disposed of quickly, the sediment in the trenches would have to liquefy, allowing the containers to sink to the bottom.It is assumed that the sediments in the trenches do liquefy occasionally, but it is not at all clear at what time intervals this occurs.The technical problems involved in transporting waste containers to the bottom of the deepest parts of the ocean, and the political problems involved in obtaining international agreements to do so, are also serious.
Another method of disposal is through ice caps.It has been calculated that a canister of highly radioactive waste would melt to the bottom of a Greenland or Antarctic ice cap within a few years.The ice would have closed behind the sinking canister and the waste would have ended up several kilometres deep at the bottom of the ice cap.The ice would be very effective in dissipating the heat generated by the waste, and the site would be removed from any current or likely future human activity.However, this option would require the waste to be transported long distances -a risky and dangerous process.After all, international agreements would also be needed to dispose of waste in these remote areas.And scientists do not have a deep understanding of what might happen to the waste once it reaches the bottom of the ice sheet [15,16,42].
Proposals calling for above-ground geological disposal have received the most serious attention.Geologists agree that an ideal underground repository for radioactive waste should have the following characteristics [10].
1.The host rock should have few cracks and low permeability.
2. The intervening rock should effectively reject heat and chemically absorb any potential leakages.
3. The intervening rock should not contain minerals of present or future economic potential.
4. Local groundwater runoff should be minimal and in a direction away from the biosphere.
5. Only very long groundwater flow paths should be directed in a direction that is accessible to humans.
6.There should be little rainfall in the area.7. The aeration zone must be dense.8.The erosion rate should be very low.9.The probability of earthquakes or volcanic activity should be very low.
10.The likelihood of future climate change in the region should not have a significant impact on groundwater.
Let us consider what types of reservoir rocks for geological containment exist.The first type is shale.Disposal of highly radioactive waste in shale is likely to require the use of deep wells, similar to those used to dispose of toxic waste.A natural deposit of radioactive material in oil shale is located in the African country of Gabon.The site has served as a natural laboratory where scientists have been able to observe, simulate and test the migration of radioactive materials through the oil shale.Their findings show that migration rates are very low and that shale can serve as an effective barrier in a high-level waste repository [17,40].
The next type is salt repositories.Salt is found in layered sediments in marine sedimentary strata and in inverted drop-shaped sediments called domes.When salt domes are mined, a cavity called a vault is often left in the middle of the dome.Salt vaults are well suited to the disposal of radioactive waste for several reasons.Firstly, the presence of a salt body implies that it has not encountered groundwater since its original formation, otherwise the salt would have been dissolved and carried away with the solution.Secondly, salt is plastically deformable, that is, it tends to bend or flow rather than break.This means that it is unlikely that any cracks would form that would allow the seeping waste to enter the environment [18].
As salt is a good conductor, the heat from the waste will be effectively dissipated.Salt has been considered as a potential host rock for high-level waste in both Canada and the United States, and an existing radioactive waste disposal facility in Germany is located in an old salt storage facility.
Another type of repository is volcanic tuffs.The burial site currently favoured by many scientists in the US is Yucca Mountain, Nevada.It is located in a thick ridge of volcanic tuffs.The site was chosen because of the thickness and lateral continuity of the rock massif, as well as its highly permeable weldment and its location in an unsaturated zone, some 300 metres above the water table.The rock contains some minerals called zeolites, which may prove to be effective chemical absorbers in the event of a leakage [19,20].
The final method of storing radioactive waste is through cavities in crystalline rocks.The preferred disposal option in Canada is to excavate a large repository in very deep stable plutonic rocks, such as the granitic rocks of the Canadian Precambrian Shield.These older crystalline rocks have been tectonically stable for a very long time.However, crystalline rocks tend to break down, especially when exposed to high temperatures [21,22].
The nuclear and radioactive waste industry operates according to recognized safety standards.International and regional organizations such as: International Atomic Energy Agency (IAEA), Nuclear Energy Agency (NEA), Organisation for Economic Co-operation and Development (OECD), European Commission (EC) and International Commission on Radiological Protection (ICRP) are developing procedures, standards and guidelines to help countries outline and implement an internationally approved set of standards [22].

Theoretical study of the problem of radiation safety in nuclear power plants
As the nuclear industry develops, there is a growing interest in human radiation exposure to the environment, so systematic radiation monitoring is needed.
The radiation safety of nuclear power plants is one of the key issues in developing energy systems.The main task is to control radioactive emissions and study the impact of harmful substances entering the atmosphere, on people, wildlife in aquatic, terrestrial and natural agricultural ecosystems.In the production processes of nuclear power plants, from construction to decommissioning, there is a wide range of technical impacts on nature, such as: deterioration of tectonic structure, topography, soil composition; land acquisition; contamination of water bodies; formation of life-threatening waste [23,38,40].
Nuclear power plants are the main component in the nuclear power process.At the moment, there are 11 operating NPPs in the Russian Federation with 38 power units [24].Reliability of nuclear power plants is established in the process of site selection and development of technical documentation.At the stage of design and construction of new power plants or units, technical and environmental studies are carried out to determine the location of new construction sites, and documents are developed to carry out environmental radiation quality control measures, selection and investigation of control points are carried out; surveillance items, list of evaluated criteria, and test methods and regulatory and technical documentation are approved.The results obtained contain a quantitative assessment of radionuclide parameters that are analysed to determine the impact of nuclear power plants on the environment.Radioecological monitoring should be checked and carried out in a timely manner [25,26].
Environmental monitoring is an information system for observing, assessing and predicting changes in the state of the environment, designed to highlight the anthropogenic component of these changes against the background of natural processes.The environmental monitoring system should accumulate, systematise and analyse information on: the state of the environment; the causes of observed and probable changes in the state (i.e.sources and factors of impact); and the acceptability of changes and pressures on the environment in general.Three main activities can be distinguished which include environmental monitoring: -monitoring of influencing factors and the state of the environment; -assessment of the actual state of the environment; -predicting the state of the environment and assessing the predicted state.It should also be noted that the monitoring system itself does not include environmental quality management, but it is a source of information necessary for making environmentally relevant decisions [26,39].
The system method of environmental monitoring is based on the study of the impact of harmful emissions on the environment and provides a comprehensive accounting of measurement results and analysis of the results of their comparison with standard indicators, expressed through qualitative and quantitative characteristics of environmental safety [27].
The method of environmental impact assessment in the development of a monitoring system contains a set of measures including the identification, analysis, tracking and monitoring of environmental risks compared to their planned values [28,29].
In the process of ecological monitoring a large number of tasks are carried out, for example: fixing the current state of chemical and radiation pollution, detecting the fundamental stages of contamination of different natural systems, finding the main sources causing pollution, assessing the current ecological and radiation situation, studying radionuclide behaviour and also a number of tasks caused by the operation of nuclear power plants [30].The main task in planning, construction and operation of nuclear power plants is to control the permissible level of radiation hazard for workers, residents of nearby areas and the surrounding nature.Taking into account the impact of normalized releases from nuclear power plants during their standard operation in relation to the existing background contamination is a difficult task, which is realized by environmental and radiation monitoring as well as by consecutive calculations applying quantitative values for a particular location and region [31,42].
In order to obtain correct and correct results of assessing the impact of power plant emissions on people and the environment, it is mandatory and one of the main criteria is the formation of baseline materials on the amount of radionuclides and chemical elements in the atmosphere, based on which the analysis of the environmental situation of the region in which the plant is located is made [32].
In the process of control, observation areas are selected and investigated; a list of parameters under consideration, monitoring procedures (time interval, frequency and duration), also control methods and normative and technical documents are formulated [33].
The principle and general algorithm of engineering and environmental studies and radiation and environmental monitoring is presented in Figure 3.

Analysis of the impact of radionuclides on the environment and humans
Using the Chernobyl nuclear power plant (ChNPP) accident as an example, let us analyse the impact of radionuclides on the environment and humans.The Chernobyl accident was the worst industrial accident of the last century involving radiation.The unprecedented release of many different radioisotopes led to radioactive contamination of vast areas surrounding the accident site.The impact on the inhabitants of these areas varied and therefore the health and radioecological consequences could not be quickly and reliably assessed.More than 37 years of ongoing studies have provided a better understanding of the situation, but are still neither complete nor comprehensive enough to determine the long-term risk.A reliable estimate can only be made after observation of the natural life expectancy of the observed population [34].
A number of different groups of people were exposed to radiation: workers involved in the initial emergency response to the accident and members of the general population, who were either evacuated from settlements in the vicinity of the Chernobyl nuclear power plant shortly after the accident or who continued to live in the affected areas of Belarus, Russia and other countries.Through domestic efforts and extensive international cooperation, important information on the radiation dose and health status of these populations has been obtained [34].
Three main groups of people are distinguished for whom assessment of the health consequences of radiation after Chernobyl is particularly important.These are workers who were involved in actions during the accident or in mitigation, those people who lived near the Chernobyl site and were evacuated after the accident, and those who continued to live in contaminated areas further away from the Chernobyl nuclear power plant.They were all exposed to radiation at different times after the accident, under different circumstances and with different spectra and amounts of radioactive elements.Thus, the accumulated effective doses vary greatly between the groups.
The first group was the liquidators.There were about 600 Chernobyl emergency workers on site before 26 May and about 600 000 liquidators, including both civilians and military personnel, before 1990.The estimated external doses to 134 emergency workers with symptoms of acute radiation sickness ranged from 0.8 to 16 Gy, significantly higher than the estimated internal doses of 0.021 to 4.1 Gy to the thyroid of 23 firefighters who died of bone marrow failure.It has been suggested that the lower thyroid doses may have been caused by stable iodine tablets taken by emergency workers.Among liquidators, average effective doses ranged from 15 to 170 mSv, with individual variations from 10 to 500 mSv in 1986-1987.
Internal thyroid exposure could range from 0.15-3 Gy, averaging 0.21 Gy for those who were involved in work at and around the Chernobyl nuclear power plant during the first few months after the accident, after which the short-lived radioiodine isotopes decayed rapidly [30].
The next group of victims was the evacuated residents.Mass evacuations were carried out for residents of settlements closest to the Chernobyl NPP, depending on the radiological situation and their distance from the power plant.On 27 April, about 50,000 people were evacuated from the town of Pripyat, located 3 km from the Chernobyl nuclear power plant.This is where most of the Chernobyl personnel and their families lived before the accident.During the 10 days after the accident, until 7 May 1986, a similar number of people who lived in the 30-km zone surrounding the Chernobyl nuclear power plant were evacuated from parts of Ukraine and Belarus.Active evacuation continued until September 1986, with a total of about 116 000 persons, mostly from areas of Ukraine and Belarus.Estimates of external effective doses, reconstructed for about 30 000 residents within a 30 km zone, indicate that the dose range was from 0.1 to 380 mSv, with an average of 17 mSv [35].
The mean 131I thyroid doses, determined from about 5000 direct measurements and about 10 000 questionnaires collected from evacuees from Ukraine, were 0.11-3.9Gy for children, 0.066-0.39Gy for adolescents and 0.066-0.40Gy for adults.For the evacuated Belarusians, the Gy estimates were 1-4.3, 1 and 0.68 Gy, respectively.These studies showed an important inverse correlation between 131I dose to the thyroid and age at exposure [36].
However, although the main health consequences of the Chernobyl accident have become more evident in recent years, scientists are still far from understanding the full implications of environmental damage.Atmospheric research and monitoring are still needed to find out what effects the accident has caused.

Conclusion
There is no doubt that clean energy sources are crucial for protecting the environment, especially in light of the era of climate change.The controversy lies in the form of clean energy.Supporters of nuclear power argue that it is an efficient and easy-to-implement energy source.Opponents of nuclear power propose a combination of technologies that would enable solar, wind and geothermal energy.Solar, wind and geothermal energy still pose environmental problems, but are not considered as serious as those generated by nuclear or coal-fired power plants.As far as nuclear power is concerned, the safety of nuclear installations is an important issue.This has led to numerous new reactor designs focusing on passive safety.But the risk of accidents due to extreme natural phenomena and/or human error still remains.According to some theoretical perspectives on safety, the probability of a catastrophic event cannot be reliably assessed and consequently societies must decide on the level of risk they are willing to accept when using and subsequently disposing of nuclear material.Other perspectives have highlighted the many individual organizational and practical steps that can reduce the risk of accidents due to the actions of operators and personnel at nuclear power plants.
Thus, theoretical views on safety and incidents suggest that ensuring a proper safety culture around the world is a major challenge.Nuclear waste management also continues to face widespread social and political issues.The following conclusions can be drawn from this study.
-The potentially serious environmental impacts of nuclear power plants indicate that fundamental problems include the potential for catastrophic failure of the power plants themselves, as well as the extremely high cost and potential failure of nuclear waste storage sites, especially given the 1000-year safety requirement.Both involve safety and security measures and costs that extend far into the future.
-There can never be an absolute guarantee for the safety of nuclear power plants or nuclear waste storage sites, the use of nuclear energy comes down to deciding what level of risk is acceptable for a given society.
-Environmental monitoring must be carried out in a timely manner, since the radiation safety of nuclear power plants is one of the key issues when developing energy systems.The main task is to control radioactive releases and the effects of harmful substances released into the atmosphere, on people, wildlife in aquatic, terrestrial and natural agricultural ecosystems.
The Chernobyl accident was a prime example of how important it is to maintain safety at a nuclear power plant.An appropriate level of safety is ensured by a system of physical barriers erected in the way of radioactive substances, as well as measures aimed at maintaining their safety.

Fig. 3 .
Fig.3.Scheme for assessing the radiation situation in the NPP region and conducting radiation and environmental monitoring[33]