Chernobyl flood: to anticipate to prevent

There are KGB agents’ thoughts on assessing the possible negative effects of the spring flood in the Chernobyl zone.

In connection with the upcoming spring flood of 1988 in the zone of the Chernobyl nuclear power plant, its possible negative consequences for water sources due to the flushing of radioactive substances were studied by the Office of the KGB of the Ukrainian SSR in Kiev and the Kiev region using operational and official sources from among agents – specialists of hydrologists and meteorologists; the reliability of the measures taken was evaluated.

The state of the hydrological situation within the 5-kilometer zone, which is the most contaminated with radionuclides, is characterized by the following data.

The area of all water sources, including part of the cooling pond, is 14.9 square kilometers. The main rivers flowing in the zone – Pripyat, Uzh, Ilya, Sakhan, Rodvino, Borshchi, Glynitsa, Benevka – have mixed rain and snow nutrition. The spring flood period accounts for 43 to 64 percent of the annual runoff. The average annual rainfall is 35 mm in March and 30 mm in April.

According to experts of the Leningrad Hydrological Institute, the development of the flood of the current year will be determined by the following hydrometeorological conditions. The thickness of the snow cover in the zone and in the adjacent territory, as well as the water reserve is 150 mm and 27 mm in the field and 120 mm and 24 mm in the forest respectively.

Humidification of the upper meter layer of soil is estimated as average. Thaws and precipitation have caused an insignificant surface runoff in small water intakes, however, this practically does not affect the mean river runoffs that are in the deep winter phase. Water consumption on the Pripyat River is close to the absolute minimum value for a hundred-year period.

Due to the fact that a reliable weather forecast for the long term is not possible, the assessment of the hydrological situation was carried out in two versions: spring without rain and spring with rainfall above normal. However, the maximum water discharge in the Pripyat River, even in the second case, will not exceed last year’s levels. The forecast is currently being updated.

Dam construction: good or stupid waste?

Given the increased contamination of the soil and bottom sediments of water sources with radioactive substances, dams of overflow and filtering types were constructed in 1986 in the zone 131 to prevent their erosion and subsequent entry into the Kiev reservoir with migration on the Dnieper River.

A porous mineral, zeolite, was placed in the body of the filtering dams to ensure partial absorption of radionuclides dissolved in water. In total, 26 thousand tons of zeolite were used. However, the studies showed that the efficiency of using this material in this way was low, primarily due to the loss of its filtering properties due to rapid contamination, including biological substances.

As a result, the filter became a source of secondary pollution. The construction of a significant number of dams in the zone with a complex hydrological regime led to a disruption of the water balance, mainly due to the fact that a significant part of the irrigation and drainage structures was disabled.

All this led to a rise in the groundwater level in the station area, and radioactive waste disposal facilities collected during the aftermath of the accident. According to some experts, this has become one of the reasons for the 6 mm turbine foundation drawdown.

The negative effects of this phenomenon require further study. This circumstance led to the fact that it was decided to lower the level of most dams and gutter equipment.

13 dams are сurrently operating in the zone. Units of the Ministry of Defense of the USSR, the Ministry of Water Economy of the Ukrainian SSR are working on their reconstruction and strengthening. An emergency stockpile of gravel and other building materials has been delivered for 8 dams; it is completed for the remaining 5 dams.

Considering the experience of skipping the flood of last year, it was decided to install containers with zeolite on the spillway parts of the dams this year, which will allow them to be replaced as they become contaminated. The necessary amount of mineral has been brought in, work is underway to load containers. These and other measures are aimed at minimizing the removal of radioactive materials from the surface of the earth to the Kiev reservoir as a result of flushing.

Will Pripyat break through?

According to experts, the largest part of the radioactive substances in the zone is concentrated on the surface soil layer in the form of microparticles. The background is formed mainly due to the so-called “hot particles” and due to aerosols and microparticles in the rest within the most dirty zone (5 km).

Based on the prevailing hydrometeorological conditions and forecasts of the expected water content, the state of the radiation situation, and also according to experts of the Leningrad Hydrological Institute, the removal of cesium-137 from the zone with the waters of the Pripyat River will not exceed the levels of 1987 and will be about 100 curies in dissolved form.

The flushing coefficient, which amounted to 1% in the past year, is expected to be lower this year, therefore, it can be assumed that, given the condition of the dams, the threat of a breakthrough of the waters of the main channel of the Pripyat River is unlikely.

At the same time, the state of the water surface of the river and the presence of tice holes indicate the filtration of water from the cooling pond into the river bed. According to some experts, it is possible that water will flow through the underground channel under the bottom due to the fact that the pond was created on the site of the old river bed. Although the level of water activity in the pond does not exceed 10–11 curie per liter, the removal of radioactivity can occur due to microparticles of bottom sediments. According to fairly rough estimates, it is from 2 to 3 curies per year.

The problem of the Glinnitsa River, which carries water into the Pripyat River from the most polluted sections, has not been completely resolved. The question of building a dam has not been fully studied since it leads to additional waterlogging of the territory of the station, which, according to ecologists, is clearly undesirable.

Considering the above, as well as the actual condition of the cooling pond and the existing stocks of radionuclides, the question of the possibility of contamination of the Pripyat and Dnieper rivers, and as a result of the Kiev reservoir, requires serious research and engineering in the future.

It is necessary to conduct an in-depth study of the erosion of the coast, the movement of bottom sediments as a result of unrest, currents, the possibility of migration of nuclides through the water surface, with groundwater.

Separate consideration is required to prevent the biological mass from entering the station’s underwater channel in the event of mass death of fish in a pond.

We have taken additional measures to strengthen control over the development of the situation through existing opportunities and communication channels”.