About some problems of liquidation of the consequences of the Chernobyl accident
About some problems of liquidation of the consequences of the Chernobyl accident

1987… The State Security Committee of Ukraine continues to assist the authorities, ministries and departments in eliminating the consequences of the Chernobyl accident, and to reveal the causes and conditions that reduce the effectiveness of the measures taken.

Leading scientists and experts of the country continue to discuss options for converting the Shelter object into an environmentally friendly system. The solution to this problem boils down to the main question: to leave nuclear fuel in a destroyed reactor or to remove it with burial in accordance with international norms and rules.

As the most acceptable option is proposed by specialists, it provides for concrete screeding of the technological premises of the facility, postponing the question of the complete removal of fuel from the former reactor for 100 years or more.

The conclusion of the Kurchatov IAE Integrated Expedition that the Shelter is currently safe is used as the scientific justification for the implementation of such a project.

At the same time, a number of scientists express concern over the fact that there is currently no scientific forecast for the long-term behavior of concrete under the influence of radiation from nuclear fuel and the temperatures that occur in fuel-containing masses during their additional thermal insulation with a concrete “fur coat”. It is important to remember that modern science has not encountered a solution to such a problem.

In addition, according to the same scientists, the amount of experimental research performed does not allow substantiating the nuclear safety of all accumulations of fuel containing masses for a long period. Therefore, the adoption of the concept of ways to render harmless Shelter until the above questions are fully clarified is premature.

Concreting the reactor shaft: there are some concerns

Despite these unsolved problems, the specialists of the Ministry of Atomic Energy Industry persistently propose to implement at the initial stage the option of concreting the reactor shaft and subreactor rooms of the destroyed power unit, motivating the need to fix the top cover of the reactor, due to the possibility of its collapse.

In turn, scientists at the Institute for Nuclear Research of the Academy of Sciences of the Ukrainian SSR consider it necessary to develop an alternative option for reliable isolation of the Shelter, which would include a sample of fuel-containing masses with their subsequent burial. It is proposed to carry out additional research work for its implementation, aimed at justifying the safety of all accumulations of fuel containing masses.

Particular attention is required to study the accumulations of graphite, fuel, and other elements of the former active zone in the southwestern and northeastern parts of the central hall of the destroyed block. An important area of research by scientists is the determination of the radiation resistance of concrete, taking into account changes in its properties and condition.

In this regard, a number of experts consider it appropriate to hold an additional international discussion on the likely consequences of concreting the reactor shaft and sub-reactor rooms. There is also a need to concentrate efforts on organizing measures for the processing, building up, containerization and disposal of high-level waste. According to experts, the effectiveness of the work carried out in this direction by the NGO “Pripyat” and the “Specatom” software remains insignificant.

Water pollution is an imminent danger

In addition to the above, still one of the main problems in eliminating the consequences of the accident is the protection from contamination of water sources with radionuclides. As a result of the large-scale organizational and engineering measures, according to experts, it was possible to reduce to a certain extent the likelihood of flushing of radioactive substances into the water arteries, the migration of nuclides in groundwater, as well as their wind dust transfer to the water surface.

However, the conditions for the implementation of measures and their complexity did not allow to predict all possible negative consequences. Experts note serious violations of the hydrological regime among them in the 30-kilometer zone and in the adjacent territories as a result of the destruction of reclamation systems, the construction of dams, which led to the rise of groundwater. The conversion of filtering dams into secondary sources of pollution is also noted due to the concentration of a significant amount of radioactive substances in the dam body and bottom sediments in adjacent river sections.

At present, according to experts, the greatest danger may be the flushing of radioactive substances from the surface of the floodplains of the Pripyat and Dnieper rivers, especially during the high flood period with their subsequent removal to the Dnieper cascade of reservoirs. In this regard, the solution of the task of constructing a protective dam on the left bank of the Pripyat River in the Chernobyl region is of paramount importance.

Some experts express concerns that its construction without sufficient scientific study may lead to negative consequences. As the main argument, they cite calculations indicating that a reduction of the collective dose of the population, primarily the city of Kiev, drinking Dnieper waters as potable water, by 80–160 man-rem per year will require costs of 2500–3000 man-rem for personnel working on the construction of the dam. Furthermore, the construction can lead to serious changes in the hydrological conditions of the adjacent territories, and therefore additional scientific study of this project is required.

Radionuclides in the soil mean an urgent “rapid analysis”

Along with the stated problems, experts note that the task of preventing the migration of nuclides from groundwater is becoming increasingly important due to the deepening of radioactive substances in the soil, the deterioration of the temporary localization sites of radioactive waste equipped with deviations from the sanitary rules for their treatment.

Of particular concern are the data obtained that indicate the possible removal of groundwater from radioactive substances concentrated in the Shelter. Under these conditions, the organization of reliable and effective monitoring of the state of groundwater is required by increasing the number of observation wells, the lack of which is felt in the areas where the Chernobyl nuclear power plant is located.

It is also necessary to accelerate the development of technical tools for conducting rapid analyzes for the content of strontium-90, plutonium-239 and other radionuclides. Likewise, it is proposed to conduct a survey and, if necessary, restore the reclamation system, which will improve the hydrological regime, reduce the level of groundwater in the burial areas of “red forest”, as well as floodplains.

In general, the task of preventing the further spread of radionuclides is planned to be solved during the implementation of the Vector program, which provides for the reburial of radioactive waste into stationary equipped repositories that meet sanitary requirements. Its implementation will require significant capital investments, estimated at 120–160 million rubles.

Among the main ones to be urgently worked out by specialists, there is the problem of collecting and disposing of bottom sediments of the Chernobyl cooling pond and other water bodies, which can conditionally be classified as solid and liquid waste repositories. The severity of the problem lies in the fact that the number of bottom sediments to be collected and disposed of is estimated at several million cubic meters, and over time, volumes can be formed that can become physically impossible to process.

The solution to this problem is constrained by the lack of appropriate equipment and technologies. In this regard, experts suggest, along with the scientific and technical study of the possibility of decontamination of water bodies, to predict the contribution of bottom sediments to the pollution of the Dnieper cascade of reservoirs and to provide reliable control over the development of the situation.