The exclusion zone occupies the territory where the Chernobyl accident has happened. So, it’s no secret that experts from all over the world consider the Chernobyl disaster to be one of the largest in the history of nuclear power. The exploded 4th power unit hasn’t left any obstacles in the way of the detrimental effect of high doses of radiation on humans. Furthermore, all physical barriers between the radioactive materials inside the reactor and the environment have disappeared.
The radiation impact on the environment and humans from the escaping transuranic elements has reached its maximum hazardous level. Territories within a radius of 30 km from the explosion turned out to be critically dangerous for living. Moreover, scientists recorded a fatal excess of isotope indicators in10 kilometers from the destroyed reactor. On this basis, a large-scale evacuation (for peace time) of the local population took place. In addition, all economic activities just stopped.
In April 2016, the Chernobyl Radiation and Environmental Biosphere Reserve was created by the Decree of the President of Ukraine. It stretches across almost the entire territory of the Exclusion Zone and the Zone of Unconditional Resettlement. Radiation pollution is one of the main factors that the management of the Reserve takes into account. The plan of radiobiological and radioecological research also takes place with this consideration.
Contaminated areas
All radiation accidents have their peculiarities, including specific composition and form of fallout. Any such accident cuts across the distribution of fission products and radioactive isotopes in the so-called contaminated areas. Radioactive contamination of Chernobyl origin is characterized by the spatial heterogeneity of the density of radionuclides and physicochemical forms of fallout.
A significant part of the radionuclides was in the composition of “hot particles”, that is, particles of fuel and structural materials of the reactor. They, possessing extremely high specific activity, got into the environment in the initial phase of the accident. The largest “hot particles” fell directly on the territory of the Chernobyl NPP. As a result, finely dispersed fractions of “hot particles” formed most of the contamination. The radioactive pollution outside the Exclusion Zone is dominated by the condensation components of radionuclides.
The dynamics of the radiation situation as a whole is determined by two groups of factors. The first is the rather definite processes of physical decay of radionuclides. The second is complex chains of migration of radionuclides in the natural and man-made environment. The latter contain horizontal washout of surface contaminated soil layers, vertical deepening along the soil profile, technical decontamination, and biological migration.
Radiation monitoring
Nowadays, the following elements influence on the radiation situation in the Chernobyl Zone.
Cs-137 is the most biologically hazardous isotope, which accounts for 90% of the external radiation dose to the personnel of the Exclusion Zone. The half-life of cesium-137 is about 30 years. Moreover, it’s quite a fusible and volatile element, which determines the global picture of pollution.
Sr-90 is an isotope that has significant mobility in ecosystems. Strontium-90 is effectively incorporated into the “soil – plant – animals – precipitation – soil” chain. This isotope is water-soluble. In addition, it’s the main component of the flow of radioactive substances that fall outside the zone by water. It’s a refractory element. Therefore, there is its overwhelming majority in the exclusion zone. The half-life is approximately 29 years.
Pu – isotopes 238, 239, 240 are refractory elements in terms of physical properties. So, the overwhelming majority of it fell out within the Exclusion Zone. Plutonium has a significant alpha radiation hazard and is chemically extremely toxic. However, plutonium doesn’t have significant ecological and biological mobility. Its half-life is 24 thousand years. Accordingly, the isotopes of this element will determine the radiation situation in the Zone in the very distant future.
Am-241 is a decay product of Pu-241, the only radionuclide from the accidental release. Its activity is increasing now. Consequently, its maximum can be reached in the middle of this century. In terms of its characteristics, americium is similar to plutonium, with a half-life of 433 years.
Migration of radionuclides
Radioactive contamination of the area around the ChNPP creates high environmental risks even 34 years after the accident. They have connections with the migration of radionuclides and the danger of their spread outside the Exclusion Zone. This, in turn, necessitates constant monitoring of the radiation situation.
The EAF “Ecocenter” carries out radiation and ecological monitoring of the environment on the territory of the Zone. It includes the determination of the content of radionuclides in the air, surface, underground and waste process waters. It also includes radiation monitoring of soil, components of terrestrial and aquatic ecosystems. Radiation and environmental monitoring concerns food products in the unauthorized placement of “self-settlers” and many other processes.
The monitoring chain includes 146 observation points. The automated radiation monitoring system continuously controls the dose rate of gamma radiation at 39 observation points. These points are located directly on the territory of the Zone, and on the industrial site of the SSE ChNPP in the city of Slavutich.
The dose rate of gamma radiation varies in a wide range: from 15 μR / h to 3.1 mR / h. The highest levels occur in the area of the western trace of radioactive fallout (the village of Buryakovka) and the northern trace (the villages of Usov and Mashevo). As for concentration of radionuclides in the surface water bodies, it depends on the type of water body and the density of radioactive contamination of the catchment areas. So, the highest pollution indicators occur in closed water bodies located on the northern trail of emergency fallouts. First of all, these are the Glubokoe and Dalekoe lakes, as well as the Krasnenskaya oxbow.
Radionuclides in the air
The concentration of radionuclides in the air has the highest values in Mashevo, and the lowest – in Dityatki. The Chernobyl Zone and the Reserve itself are an effective solution for the spread of radionuclides to the adjacent territories. However, the territory of the Chernobyl Biosphere Reserve isn’t only natural landscapes with relatively low levels of radioactive contamination. There are objects that appered during the acute phase of the accident. So, their distinguishing feature is an increased level of radioactive contamination.
Such facilities were created and used in 1986-1989 for radiation monitoring of people, cargo and vehicles. They took part in the organization of radioactive waste management. These facilities include temporary storage sites for radioactively contaminated equipment.
Radiation hazardous objects: “Hot spots” for scientific research
In general, there are 50 objects on the territory of the modern Zone containing radioactive materials or sources of ionizing radiation. They all have direct or potential radiation impact on the environment. Scientists call such locations “radiation hazardous objects”. Most of them are located in the 10 km zone and at the ChNPP industrial site.
The rest lies on the territories included in the infrastructure for radioactive waste management. The activity of some Chernobyl facilities involves the release of radioactive substances into the environment. These are wood burning enterprises and analytical laboratories of the Ecocentre. Their occupation can lead to additional exposure of the reserve personnel and visitors.
There are 3 decommissioned points for sanitizing vehicles and cargo on the territories of the Chernobyl Radiation Biosphere Reserve. The functioning of the Special Processing Points “Parishiv”, “Rudnya-Veresnya” and “Dubrava” has been completed. Moreover, the areas used to accommodate radioactively contaminated equipment near the villages of Rassokha and Zapolye have been decommissioned.
Open-air laboratory
Nowadays, there is one more way how to present the Exclusion Zone: an “open-air laboratory”. Its landscapes are a huge space for scientific research. There is the same division of labor in the world of science as in other branches of the economy. So, national research institutes have their own priority areas of scientific research.
For our country, such a priority is a radioecological and radiobiological research on the territory of the Exclusion Zone. Ukraine has a high scientific evidence base, reflecting the value of the research carried out here. The exclusion zone is a testing ground for a wide range of natural, semi-natural ecosystems and man-made objects. So, this allows carrying out a wide range of research at its locations.
Mainly “hot spots” are of the greatest scientific value. They are the so-called areas with extremely high levels of radioactive contamination. These include the “Red Forest” (a section of mainly pine trees to the west of the ChNPP, with an area of about 10 km2). The western trail of radioactive fallout passed through it. As a result, the forest received a lethal dose of radiation and lost its ability to live.
There are still objects with some radiation peculiarities on the territory of the Chernobyl Reserve. But they require increased attention and appropriate behavior from the point of view of radiation safety.