Scientific results

 RADIOECOLOGICAL INVESTIGATIONS

 

History of Semipalatinsk nuclear test site.

On 21 August 1947 The Soviet government decided to establish a nuclear test site. It’s ajointed with territories of Pavlodar, the former Semipalatinsk and Karaganda regions of Kazakhstan on the left bank of the Irtysh River.

On 29August 1949 there was the first nuclear test in the USSR, which were both the first test at the Semipalatinsk test site and the first above-ground nuclear test.

The last nuclear test conducted in 19.10.1989, when 3 nuclear charges were blown up underground, in a well.

Over the entire period of the Semipalatinsk nuclear test site activity (SNTS) therewere conducted 465 nuclear tests. During the period from 1949 to 1962 were conducted 118 atmospheric (88) and ground (30) tests. The other 347 tests were underground.

 

Radiation impact on the environment and populationwithin atmospheric tests could cause 25 ground and 86 air nuclear explosions. Some impact on the population of the territories adjacent to the poligon, might have an underground nuclear test, accompanied by non-nominal radiological situations. The main dose-related bombings, carried out at SNTS: 29August 1949, 24September 1951, 12August 1953, 24 August 1956, 22 August 1957.

On 18December 1992 was adopted the Law of Republic of Kazakhstan № 1788-XII "On social protection of citizens affected by tests at the Semipalatinsk nuclear test site", which establishes a classification of areas affected by the impact of long-term nuclear explosions.

 

The history of radio-ecological studies conducted by SRI RMandE in the zone of influence of SNTS

 

Studying of radioecological situationof the areas adjacent to SNTS,was carried outsince the first explosion. In the first ten years of testing (1949 - 1959) only thedose powerof gamma-radiation in the path of the radioactive cloud in 15 districts of 75 settlements have measured.

In SRI RMaE (Dispensary № 4 of the USSR MoH) in the period 1953 - 1996 carried out investigations on radiological situation ofsettlements of Semipalatinsk region adjacent to the poligon.

Since 1959 one has begun to identify specific total beta-activity of environment objects in some settlements.

By 1962 according to the archives, there begun a systematic study of radio-ecological situation. Since that time were regarded both objects of the environment, and food on a fairly broad areas.

SRI of radiation medicine and ecology has the abovementioned archival data partially preserved after the collapse of the Soviet Union and the poligon closure. The presence of archival documentation can significantly help in solving the modern radio-ecological issues.

 

Soil study from 1953 to 1996 showed that the contamination of the surface layer of soil is complex because of repeated contamination by local radioactive fallouts from nuclear fusion and nuclear explosions at the Semipalatinsk test site.

In 1962, after the ban of ground and atmospheric testings, reducing both local and global fallouts, processes of natural soil decontamination and radioactive decay, the total supply of beta - radioactive fission products in the soils of studied settlementsis systematically reducing.

From 1953 to 1967 the total specific soil activity on throughout the controlled area has decreased an average by 1774 times, from 1965 to 1978 - by 787 times.

From 1963 to 1994 the activity of Sr- 90 has decreased by 2,3 times, Cs-137 by 1,2 times.

 

The accumulation of radioactive substances in the vegetation caused by factors of different local fallouts, as well as byradionuclides received in different ways: through the root system and as a result of surface contamination.

The sharp decline of activity in the first years after the explosion is explained by the collapse of the short-lived fission products, anddecline distinction – by the nature of fallouts, depending on the distance from the blast site.

For eighty years the decline of total activity does not have such a sharp distinction, since by this time the predominant way is root way of radionuclides receivingto vegetation.

From 1953 to 1968 there was a decline in the total activity of the vegetation by 300 times. By 1966 activity has the natural value.

From 1959 to 1994 there was a decrease in activity of Sr- 90 by 63 times, Cs- 137 by 177 times.

 

The concentration of radioactivity in food depends on the contamination of vegetation by the fission products, and repeats the complex nature of the radiation situation in the studied areas.

During 1958-1994 observations the content of Sr- 90 and Cs- 137 in meat has decreased by 133 and 54 times, respectively. There is a clear tendency to reduce the specific activity (by 5 times).

In milk samples during 1958-1994 the total activity have decreased on average by 15 times, the content of Sr- 90 - by 4 times, Cs- 137 - by 206 times.

 

One way of radionuclidereceipt in human organism is the use of water in food allowance. Residents of the studied area are using the groundwater for household purposes and drinking.

The content of cesium-137 in the water is a highly episodic.

From 1958 to 1968 total specific activity in water has decreased on average by 3 times.

From 1963 to 1994Sr- 90 activity has decreased by 4 times, Cs- 137 - 9 times.

The data obtained is lower than established standards.

 

Over the entire period of nuclear weapons testing from the legal point of view, about 50 000 people undergone to irradiation at less than 7 c Sv dose, from 7 to 100 c Sv - about 80,000 people. The highest dose at more than 100 c Sv have receive approximately 27 000 people.

 

SRI RMaE researches in 1953-1996 allow to make conclusions:

- after the ban of ground and atmospheric tests (1962), reducing of local and global fallouts, the natural processes of soil decontamination and radioactive decay, the total supply of radionuclides in the environmentand food objects of studiedsettlementsis systematically reduced;

- a decade after the end of the testing of nuclear weapons the short-lived andmiddle-lived technogenic radioactive elements in the atmosphere were decayed, relatively long-lived Sr- 90 and Cs- 137 partially decayed, and transferred from the surface to the deeper soil horizons.

- continual reducing of the fission products of nuclear explosions in foods leads to decreasingof the yearly dose ofinfernal irradiationof population;

- exposure rate reflects the content of natural radioactive elements (U, Th, K);

- there is need to further the dynamic monitoring of local radioactive traces in the territory areas, since its results have great social-health and national-economic significance.

 

Modern radio-ecological studies conducted by SRI RMandE in the zone of influence of SNTS

 

Joint research works carried out by SRI ofradiation medicine and ecology (Semey, Kazakhstan) and RI for radiation biology and medicine (Hiroshima University, Japan) specialists since 1995 to study the effects of radioactive fallouts from nuclear weapons tests, both on the environment and on the population of the Semipalatinsk region.

During the period of the studies were sampled the followings:

- soil samples from the territories of 18 settlements of the East Kazakhstan region, and on 9 routes connecting the various villages. It has been studied more than 200 territorysites.

- more than 200 teeth of residents of 20 settlements ofEKR to determine the individual absorbed doses from external irradiation by EPR spectroscopy. Among the studied areasthere are has both highly irradiated and slightly irradiated ones, according to the level of radioactive contamination at the time of the nuclear tests.

Conducted modern researches led to the following conclusions:

1) the levels of Cs-137 in soil samples outside the SNTS area arecomparable to the global level,

When comparing these data with data from other studies (estimated level of global fallouts in the Semipalatinsk region, data of Russian studies ofterritories outside SNTS, the content of global fallouts for the Japan Seacoast and the Pacific ocean) it can be seen, that although there are individual areas in which the levels of Cs -137 are exceeds these values, in most samples the content of Cs-137 is the same or lower.

2) the levels of Pu-239, 240 in many areas byseveral hundred times higher than the global level,

The nature of Pu- 239, 240 distributionsin the soils of the studied area are coincides with the character of Cs- 137distribution. But the content of Pu- 239, 240 at a major areasbyseveral tenand hundred times higher than the content observed in Japan (40-120Bq/m2), and the average predicted level of global fallouts in Semipalatinsk region (50 Bq/m2). These results indicate that the nuclear tests conducted by SNTS cause the local fallouts of plutonium far outside the polygon.

3) the isotopic ratios of Pu-240/Pu239 in soils ofstudied areas arelower than the values of global falloutratios.

Atomic ratios of Pu-240/Pu-239 for most samples showed relatively low values (range 0,025-0,100) compared with the value of global fallouts (0,18), which also confirms the pollution of the areas adjacent to SNTS by plutonium that was used in nuclear weaponsproduction. The exceptions are some points that showed relatively high values in the range 0,125-0,22 (Semey and Ust -Kamenogorsk).

The atomic ratio values of Pu-240/Pu-239 considerably changed among the sampling sites, but in general, they increase with increasing distance from the SNTS. The obtained values are comparable to the isotopic ratios of weapons-grade plutonium (0,054-0,063) at the Nevada nuclear test site (Hardy, 1976) andweapons-grade plutonium (0,051) made at Rocky Flat Plant (Cray, Hardy, 1970).

Modern research shows that these territories have large concentrations of Pu.

Radioecological situation in the areas adjacent to SNTS is currently being defined and will be defined in the future by the level of accumulation of long-lived alpha-emitting radionuclides, especially byPu Am.

The actual status of environmental pollution by these components has not yet been studied.

4) The majority of dose valuesdetermined by EPR spectrometry is in the range of 20 cGy .

The highest dose received for the residents of Dolon and Boden settlements in ranges to 450 mGy and 356 mGy, respectively.

 

The main directions of future radioecological researches

1. Conducting of radio-ecological researches of areas adjacent to SNTS, their zoning on radiation risk degree and the development of proposals for the revision of the boundaries of zones of radiation risk.

2. A comprehensive study of the radiation situation of the settlements located in the zone of influence of SNTS, preparing for them radiation-hygienic certificates.

3. Experimental defining of individual and evaluation of collective effective doses of residents of settlements with unfavorable radioecological situation, located in the zone of influence of SNTS.

4. Creation of monitoring system of groundwater and surface water, are genetically related to contaminated sites of SNTS.

5. Creation of monitoring system of radiation situation in the major settlements located in the zone of influence of the STS, and providing its functioning.