Chernobyl: Part. CONTROL OF RADIOACTIVE POLLUTION OF THE ENVIRONMENT AND HEALTH OF THE POPULATION.

Information on the Chernobyl accident and its consequences prepared for the IAEA Report No. 1 (INSAG-1)


C O R E R A N E E
Flash drive
0. Introduction
1. Description of the Chernobyl NPP with RBMK-1000 reactors.
2. Chronology of the development of the accident.
3. Analysis of the process of development of the accident on a mathematical model.
4. Causes of the accident.
5. Preventing the development of an accident and reducing its consequences.
6. Control over radioactive contamination of the environment and public health.
7. Recommendations for improving the safety of nuclear power.





6. CONTROL OF RADIOACTIVE POLLUTION OF THE ENVIRONMENT AND HEALTH OF THE POPULATION

6.1. Estimation of the amount, composition and dynamics of the release of fission products from a damaged reactor.
6.2. Control system
6.3. Main characteristics of radioactive contamination of the atmosphere and terrain, possible environmental consequences
6.4. Doses of exposure of the population in the 30-km zone around the Chernobyl NPP
6.5. Data on irradiation of NPP personnel and emergency services. Experience of treatment.


6.1. Estimation of the amount, composition and dynamics of the release of fission products from a damaged reactor.
The release of radionuclides beyond the emergency block of the Chernobyl nuclear power plant was a time-stretched process consisting of several stages.
At the first stage, the dispersed fuel was ejected from the destroyed reactor. The composition of radionuclides at this stage of emission roughly corresponds to their composition in irradiated fuel, but is enriched with volatile isotopes of iodine, tellurium, cesium, noble gases.
In the second stage, from April 26 to May 2, 1986, the emission power outside the emergency block was reduced due to the measures taken to stop the burning of graphite and to filter the release. During this period, the composition of radionuclides in the release is also close to their composition in fuel. At this stage, the finely dispersed fuel was discharged from the reactor by a stream of hot air and products of graphite combustion.

The third stage of the release is characterized by a rapid increase in the output power of the PD beyond the reactor block. In the initial part of this stage, the primary removal of volatile components, in particular iodine, is noted, and then the composition of radionuclides again approaches the composition in irradiated fuel (on May 6, 1986).

This is due to fuel heating in the core to a temperature> 1700 ° C due to residual heat release. At the same time, as a result of the temperature-dependent migration of PD and the chemical transformations of uranium oxide, a leakage of PD from the fuel matrix and their removal in aerosol form on the products of graphite combustion occurred.

The last, the fourth, the stage that has come after May 6, is characterized by a rapid decrease in the release (Table 2). This was the result of special measures taken, the formation of more refractory compounds PD as a result of their interaction with the introduced materials, stabilization and subsequent lowering of the temperature of the fuel. The nuclide composition of the emission is presented in Table. 3.


Table 2. Daily release of q radioactive substances into the atmosphere from the emergency block (without radioactive noble gases).






Table 3. Assessment of the radionuclide composition of the Chernobyl accident block release.






In air samples and fallout PDs were in the form of separate radionuclides (mainly volatile) and in the composition of fuel particles. In this case, particles (associates) with an increased content of individual radionuclides (cesium, ruthenium, etc.), which were formed as a result of migration of DP in fuel, in materials of backfilling and structures, sorption on surfaces were detected.

The total emission of PD (without radioactive noble gases) was ~ 50 MW, which corresponds to approximately 3.5% of the total amount of radionuclides in the reactor at the time of the accident. These data are calculated on May 6, 1986, taking into account radioactive decay. By this time, the release of radioactive substances was largely completed.

The composition of radionuclides in the accidental release roughly corresponds to their composition in the fuel of the damaged reactor, differing from it by the increased content of volatile PD (iodine, tellurium, cesium, inert gases).


6.2. Control system
At the time of the accident, a regular system of meteorological, radiation and sanitary-hygienic control started working according to the emergency plan. In the first days after the accident, the main attention was paid to urgent tasks of radiation, sanitary-hygienic and medical-biological control.

At the same time, expansion of the control system began taking into account long-term tasks. The organization of the State Committee for Hydrometeorology of the USSR, the Ministry of Health of the USSR and the Union Republics, the Academy of Sciences of the USSR, the Academy of Sciences of the Ukrainian SSR, the Academy of Sciences of the BSSR, the USSR GKaE, the USSR State Agroindustrial Committee, and others participated in its formation.
For the treatment of irradiated people, specialized medical facilities in Moscow and Kiev were involved.

Along with the formation of the control system, a program of radio-ecological, medical-biological and other scientific research on the problems of assessment and prediction of the effects of ionizing radiation on humans, flora and fauna was prepared and started. The primary objectives of the control were:
- Assessment of the possible level of external and internal exposure of the personnel of the Chernobyl NPP, the population of Pripyat and the 30-kilometer zone;
- an assessment of the possible level of exposure of the population of a number of areas outside the 30-kilometer zone, the level of radioactive contamination of which could exceed the permissible limits;
- development of recommendations on measures to protect the public and personnel from exposure beyond specified limits. These recommendations include the evacuation of the population; Restriction or prohibition on the use of food products with a high content of radioactive substances; Recommendations on the behavior of the population in homes and in open areas.

To address these priorities, systematic monitoring of:
- level of y-radiation in contaminated areas;
- the concentration of biologically significant radionuclides in the air and water of reservoirs, in particular ensuring the supply of drinking water;
- density of radioactive contamination of soil and vegetation and its radionuclide composition;
- the content of radioactive substances in food, in particular 131I in milk;
- radioactive contamination of overalls, personal clothes and footwear, vehicles, etc .;
- accumulation of radionuclides in the internal organs of people, etc.


6.3. Main characteristics of radioactive contamination of the atmosphere and terrain, possible environmental consequences
Radioactive pollution of the natural environment as a result of the Chernobyl accident was determined by the dynamics of radioactive releases and meteorological conditions.
The main areas of pollution after the accident formed in the western, north-western and northeast directions from the nuclear power plant, and then on a smaller scale - in the south.

Integration of data on contaminated areas made it possible to determine the total activity of the released radioactive substances (outside the industrial site). In the zone of short-range and long-range deposition in the European territory of the USSR, it was ~ 3.5% (see Section 6.1) of the total activity of the fission and activation products accumulated in the reactor (1.5-2% on the near trail). Summation of activity of radionuclides that fell on the near track and determined by sampling the soil gives a close value of 0.8-1.9%.

The pollution levels of plutonium isotopes in these zones are not decisive from the point of view of carrying out work on decontamination and making economic decisions.
From the first days of the accident, control over the content of radionuclides in the bottom sediments of water bodies was organized both inside and outside the 30-kilometer zone.

According to experts, irradiation levels of up to 10-2 rad / day have no significant effect on terrestrial ecological systems. Within the 30-kilometer zone around the Chernobyl nuclear power plant, higher levels of irradiation were observed in some areas contaminated by radioactive fallout.
The levels of irradiation beyond the 30-kilometer zone around the Chernobyl NPP can not have a significant effect on the species composition of plant and animal communities.

The results obtained are preliminary. The study of the consequences of the impact of the Chernobyl accident on living organisms and ecological systems continues.


6.4. Doses of exposure of the population in the 30-km zone around the Chernobyl NPP
An analysis of radioactive contamination of the environment in this zone has made it possible to estimate the real and projected radiation doses of the population of cities, towns, villages and other settlements.
Based on these assessments, a decision was made to evacuate the population. The measures taken prevented exposing the population above the established limits.
Radiological consequences for the population in the next few decades were estimated. These consequences will be insignificant against the backdrop of natural cancer and genetic diseases.


6.5. Data on irradiation of NPP personnel and emergency services. Experience of treatment.
As a result of participation in emergency response in the first hours after the accident, a portion of the staff received large doses (> 100 rem), as well as burns with the participation in fighting the fire. All victims were provided with immediate medical assistance. By 6 am on April 26, 1986, 108 people had been hospitalized, and during the day - 24 more of the surveyed. One victim at 6 am on April 26, 1986 died of severe burns and one person from the number working on the emergency block was not found. The possible place of his work was in the zone of a blockage and high activity.

On the basis of the criteria for early diagnosis adopted in the USSR, by the end of the first 36 hours, persons with acute respiratory illness (ARS) were most likely to be selected for urgent hospitalization. Clinical institutions in Kiev and a specialized hospital in Moscow were chosen to be hospitalized for hospitalization in order to provide the maximum assistance and competent analysis of the results of the observation.
Among the population, there are no individuals who received large doses leading to ARS.