First Draft, not for citing!
Radioactive contamination of the Techa River: A Review of Studies.
Dmitriy Burmistrov, Marina Degteva and Richard Wilson
Historical preface
Soviet nuclear science and technology have made great achievements before the Second World War. The bright examples of these achievements are the discovery of nuclear isomers (1935), construction of the most powerful accelerator of charged particles in Europe (1937), and discovery of spontaneous fission of uranium (1940). But the War had completely stopped all Soviet studies in this field (1941 – 1945). During this period scientist of USA and England made revolutionary progress in nuclear power investigation. Unfortunately this progress was used for political pressure. The end of Second World War was marked by use of nuclear weapons against Japan. This fact forced the USSR government to establish a state project for the production of nuclear weapons:the "Uranium Project" [1].
The implementation of the Uranium Project in the USSR took place under great economic depression, with deficit of skilled scientific and technical specialists and material resources. A Special State Committee for Defense was given unprecedented authority to take decisions on the Uranium Project. The results came true in a short time: two experimental design facilities were established in Kirov’s Factory in Leningrad and their developments were immediately implementing in construction of two plants in the Urals. One of them was the first plant for weapon-grade plutonium production in Southern Urals. Ural mountains were the best place for such facility due to convenient and safe position in the middle of the country far from boundaries and close to necessary resources and communications. In the summer of 1945 the site selection survey was made, and in autumn of 1945 the government commission decided to construct the first military reactor on the southern shore of Lake Kyzyltash (Fig.1a,1b). Houses for the enterprise employees were built nearby. Soon a number of auxiliary enterprises were set up, and they were connected by network of roads, power and water supply communications. It was the industrial complex, which is known now as the "Mayak" production association (MPA) [2]. The city was given the name of Ozyorsk in 1994. Before the 1990's the complex was classified, and was called only by its postal code (Chelyabinsk-40, Chelyabinsk-65).
a) b)
Fig 1. First Soviet plutonium production plant: “Mayak” production association (MPA): a) Location of MPA; b) painting of Ozersk town (former Chelyabinsk-40 and later Chelyabinsk-65) with the MPA in the background.
The main purpose of the “Uranium Project” was creation of Soviet nuclear weapons as fast as possible. In addition nuclear technologies were not developed yet and there were not enough knowledge about the fate of radionuclide wastes in natural ecosystems and radiation action on man. Therefore the efforts to prevent technological discharges into the environment were not sufficient, and territories in the vicinity of MPA were severe contaminated by radionuclides, including long lived cesium-137 and strontiom-90.
There were three accidents accomplished by large releases of radioactivity in the environment: 1) Techa River contamination (1949-1956); 2) Kyshtym accident (1957) and 3) Incident with transfer of radioactive dust (1967).
During the period 1949 – 1956 liquid radioactive wastes of radiochemical plant with not very high radioactivity were released directly to the Techa River on a regular way. High active wastes were stored in special tanks. These tanks had to be cooled constantly to prevent self-overheating of highly chemically active and radioactive products. Sometimes eventual leakage occurred through imperfections in cooling system. Since the water from the Techa River was used as cooling agent in this system, very large amount of radioactivity eventually discharged into the river. As the result water and bottom sediments of the river accumulated sufficient amount of radioactivity especially in the Upper reaches. In 1951 the discharge of radioactive materials into the Techa was minimized. Since that the wastes were collected in closed artificial reservoir known now as the Karachay Lake. Later some arrangements were made to close the Upper Techa and prevent future dissipation of radionuclides deposited there. It was the most serious and dangerous accident. Unfortunately it was not the last one. In 1957 cooling system of one of tank storage with high-radioactive liquid wastes failed to operate properly, and the storage overheated and exploded. The plume was carried by wind to the north - east direction forming new radioactive contaminated territory known as East-Ural Radioactive Trace (EURT). And finally in 1967 there was a little snow and the spring and summer were very hot and dry. The level of water in the Karachay Lake decreased dramatically, and the radioactive dust from the bare banks was spread by wind over sorounding territories.
Since 1990's, when related scientific researches were declassified, the number of scientific publication about radioactive contamination in Southern Urals, and particularly about the Techa River contamination, is rapidly growing (see notes). But these papers are very specialized. The purpose of this review is to make the information about the Techa River accident more accessible to wider range of readers.
Techa River.
The Techa River is the right tributary of the Iset River. It belongs to the basin of the Kara Sea (Fig.1a). The river takes beginning from the Irtyash and Kyzyl-Tash Lakes and falls into the Iset River, which in turn falls into the Tobol River. The length of the river is about 240 km, its average depth is about 2m. At the beginning of radioactive pollution there were 40 villages with population about 28 thousand residents (Fig. 2). They were preferably small agricultural villages. Only Brodokalmak village was the center of the administrative region.
The stretches of the river from Kyzyl-Tash Likes to the village of Muslyumovo were for the most part swampy with a poorly marked winding bed overgrown with water plants. The width of the riverbed varied from 3 to 15 m and its depth ranged from 0.5 to 2 m. River bed
Fig. 2. Scheme of the Techa River and of the villages located on its banks before contamination occurred. The number of residents, ethnicity and current status (evacuated or not) are also shown.
a) b)
c)d)
Fig. 3. Scheme of the Upper Techa reaches:
a) At the beginning of the "Mayak" PA operation; b) After creation of the Koksharov Pond; c) After creation of reservoir No 10; d) The upper reaches is made "closed system". The main sources of contamination were reactor cooling water dumped into the Kyzyl-Tash Lake and the liquid radioactive wastes from radiochemical plant. Two other radiation accidents gave minor impact to the Techa River contamination also (Kyshtym accident and Dust Transfer from the banks of Karachay Lake).
Fig. 4. The Metlino village situated 7km downstream the site of releases of liquid radioactive wastes by the "Mayak" plant. The evacuation of residents began in 1951. Later almost all buildings were destroyed. The buildings seen at this picture (the church and the mill) still stay there. They are used now for collection of brick samples for thermoluminescent dosimetry measurements[19-21]. The water reservoir at the first plane is the resevoir N10 created in 1956. Now the buildings are still destroying by natural processes. Metlinsky pond is situated behind the mill buildings.
includes layers of turf, silt and clay. There were flood swamps measured 300 m to 2 km in width along the river shoreline; the most swampy areas were located between the villages of Nadyrov Most and Muslyumovo. The flood soils were composed of turf-bog soils that give way to meadow-turf ones along the boundaries of the swamps. The thickness of the turf layer ranges from 10 cm to 3 m, the turf contains a considerable amount of mineral inclusions and increased percentage of ash. Clay and sandy loam, less frequently sand, compose the underlying layer of turf.
Downstream of the village of Muslyumovo the river has well formed bed, its bottom consists of layers of sand and slime, in some places of sand and gravel. The mean width and depth of the river during the summer time are 22 and 0.5–1 m, respectively.
The Techa River receives its supply of water from melting snow and intensive spring floods. The main source of water supply to the Techa during the summer months is groundwater discharge from water-bearing horizons formed by atmospheric precipitation. The flow rate ranged from 2 to 10 cubic meters per second in the 1950's. The Techa was rather small and shallow river that was one of the reasons of its sufficient contamination by radioactive wastes of the MPA.
In the upper reaches of the Techa a cascade of hydraulic-engineering constructions is located (Fig. 3) [5]. Only the Metlinsky pond existed by the moment of MPA foundation. Later in 1951 the Koksharov Pond was created to prevent direct flow of radionuclides to the Metlino village. It was the first village downstream the Techa River close to MPA (7km from the point of the releases, Fig.4), and the residents accumulated the highest radiation doses there. In 1956 the arrangements were started to restrict the influence and spread of radioactive contamination: residents of upper reaches of the river were evacuated and a series of additional dams were built (Fig.3).
MPA as a source of Techa contamination
The technology of weapon-grade plutonium production at the MPA required a number of stages. At the first stage the natural uranium was irradiated in the uranium-graphite reactors with thermal neutrons to generate plutonium-239 in the fuel. It was so called "Complex A". After irradiation the fuel was treated at the "Complex B": the radiochemical plant for separation of the plutonium-239 from natural uranium. Then the product enriched by plutonium-239 was directed to metallurgical plant to produce high-purity metallic plutonium: "V" plant [2,5].
There ware a number of sources of the Techa River contamination in this technology chain. The reactors in the complex A contained only one cooling circle: the water from Kyzyltash Lake circulated directly through the reactor core and released back to the lake. As a result cooling water contained radionuclides with short half-decay times generated by irradiation of material in active zone of reactor. The water from the contaminated lake solved as one but not the main source of Techa River pollution. There were various kinds of waste products after extraction of uranium and plutonium from the irradiated fuel at the radiochemical plant B. Liquid radioactive wastes with intermediate and low-level radioactivity were dumped directly to the Techa River. In 1949 high-level wastes were routed to the tank farms in special facility: "Complex C". However in order to reduce the volume of material going to the tanks in 1950 a process for “decontamination” of high-level wastes was introduced with a portion of the radioactivity directed to the tanks and a portion released to the river. In July 1951 it was discovered that this process did not work as intended, and that during this period high concentrations of radionuclides had been released into the river. It was also noted that cooling water from the tanks of Complex C was discharged sometimes into the Techa at the same location as the technological wastes. Leaks in the tank-cooling lines caused some of these discharges to be highly contaminated. These “wild releases” were unmonitored and unnoticed until 1951. Over this period, about half of the total release to the Techa River resulted from the technological releases and about half from the wild releases [5].
The amount of released radionuclides and radionuclide composition of the wastes in 1950-1952 were estimated by Dr. Ilyin in his Doctoral Thesis [6,5]. He was the head of the Mayak Central Laboratory, and he could make these estimations on the basis of all available measurements and the knowledge of technological processes at the MPA. Later (1953-1956) the analogous estimations were made by Dr. Marey [7,5] using the results of measurements by special expeditions under supervision of Moscow Institute of Biophysics. The historical methods of radiochemical separation and analysis were sufficient to permit the separation of the groups of radionuclides with long and intermediate half-decay times and with similar chemical properties. Concentrations of short-lived radionuclides could be reconstructed from theoretical ratios for fission products of uranium-235 irradiated by thermal neutrons. These estimations and measurements of radionuclide compositions were then used to estimate contributions of separate radionuclides in so-called "total beta-activity","total alpha-activity" or "gamma-equivalent" the quantities which were relatively easy to measure by counting of beta-particles, alpha-particles or gamma-quanta, emitted from the contaminated samples of water and sediments [5].
According to these estimations about 2.7 millions Ci of radioactive materials were released into the Techa river, and about 95% of this total activity was dumped in the period March,1950-November,1951. Approximately 30% of total radioactivity was carried by long-lived strontium-90 (half decay time is 29 years, Sr-89 also presented, half decay time is 50 days) and csesium-137 (30 years). The rest of radioactivity was carried by ruthenium-103 (39 days) and ruthenium-106 (368 days): about 30%; zirconium-95 (64 days) and niobium-95 (35 days): about 10%; mixture of rare-earth elements: cerium-144 (284 days), yttrium-90 (64 hours) and yttrium-91 (58.5 days), lantan-140 (40 hours), prosiodim-144 (17 min) etc, about 30% in total. The releases were soluble and particulate as well. Almost all cesium, 75% of strontium, and about 50% of zirconium and niobium were in soluble form, but about 98% of rare earth elements entered the river absorbed on suspended particles [5]. In 1952–1955, an additional source of contamination became significant against the background of the decreasing releases of the radiochemical plant. This source was reactor cooling water flowed into the Techa River from Kyzyl-Tash Lake. For example, during seven months in 1953, the activity released from the reactor plant was five times the release from the radiochemical plant. The water of Kyzyl-Tash Lake entering the Techa was also contaminated by such activation radionuclides as phosphor-32 (14 days), sulphur-35 (87.4 days) and calcium-45 (163 days)[5]. The fate of radionuclides in the river system was governed by the following transport processes: radioactive decay, transport and dilution by water flow, sedimentation of particulate fraction of the releases, and sorption and desorption processes in solvable fraction of releases with participation of particles of natural admixtures in the water with consequent sedimentation of these particles [8,9].
The nature of releases, the rehabilitation arrangements in the Upper Reaches, the specific of described transport processes and the transport features of separate radionuclides had determined the following pattern of the contamination [5,8,9]. It was fast decreasing with calendar year since 1951, and with distance from the MPA. The short-lived radionuclides and radionuclides in particulate fraction decayed or settled in the Koksharov and Metlinsky ponds almost totally. In the rest of the river the main contaminants were cesium-137 and strontium-90. The main transport processes here were the dilution by water flow, sorption and desorption of solvable fraction of radionuclides and the sedimentation of contaminated particles of natural admixtures in the water. It is expected also, that zirconium and niobium can give sufficient contribution in the contamination of the whole river in 1950-1952. The distribution of the main contaminants along the river was different. Cesium has stronger sorption ability then strontium. Therefore it was efficiently fixed in the Upper Reaches, but strontium concentrations demonstrated relatively steeper decrease with the distance along the river and in the Middle and Lower reaches of the river its role was predominant. Since 1964 the river can be considered being in the regime of self-cleaning, accompanied by slow decay of cesium and strontium. The radioactivity was accumulated predominantly in river bottom sediments: the ratio of concentrations in bottom sediments to water concentration varies in the range 100-1000 times depending on the nature of sediments. Flood plane soils were contaminated during spring floods, especially during outstanding flooding of the spring 1951. Settlement territories and houses were contaminated due to activity of peoples and agricultural animals.
Environment Monitoring at the MPA in the 1950's.
Regular environmental measurements were started in summer of 1951 when the mistakes in technology of radioactive waste treatment became evident [5]. The most representative measurements (almost each day at representative set of locations) were made for total beta activity of river water. Eventually there was arranged the collection of samples of river sediments and flood plain soils at different locations of the river. And a number of measurements of radiation dose rate in air near the river edge, in the streets of the villages and in houses were made. One of main purpose of these measurements was determination of critical groups of population accumulated large doses to make decisions about their evacuation from contaminated territories. This goal did not require systematic and very precise monitoring. The main attention was paid to maximal measured values. This approach makes now an additional difficulty in reconstruction of more precise individual radiation doses of peoples.