**2. Radionuclides (natural and artificial) in the streams of the Yenisei River**

As a result of long-term activity of MCC, the Yenisei's ecosystem contains considerable amounts of industry-related radionuclides [2]. In particular, an increased level of radioisotope contents in bed deposits and alluvial soils was found [2–6] and distribution and migration of radionuclides both in near-field influence of MCC [7, 8] and in significant distance away from effluent zone, including estuary of Yenisei, were indicated. As early as in the beginning 1970, the pollution zone of Yenisei's bottom land by 137Cs was found by airborne gamma survey. In district of Yeniseysk city (island Gorodskoi around 300 km downstream of MCC), the specific activity of 137Cs reaches 16,300 Bk/kg in some places, power of exposure (PE)—270 µR/h. According to present standards, bottom sediments and alluvial soils at this region are related to solid radioactive wastes. 137Cs is the main radionuclide polluting soils and bottom sediments are 152+154Eu and 60Co [9].

In this chapter, the results of research conducted mainly in the middle course of Yenisei in the 15 km region (from fall place of Ploskiy river (0 km) to Bolshoy Balchug (15 km), **Figure 1**) are described. In this region, at a water flow rate *Q* = 4085 m3 /s the depth and current velocity were defined as *H* ≈ 7 m, *v* = 1.25−1.8 m/s, respectively. Jet with industrial wastes spends along the right bank not more than 0.1 of river's width, i.e. along bottom land, where current velocity and depth are several times lower.

**Figure 1.** Sketch-map of the some region of the Krasnoyarsk Territory near the Mining—Chemical Combine of the Rosatom—surface water of the Yenisei River basin. 1: Shumikha River; 2: Stream No. 2; 3: the Ploskii Stream; − − − − : the boundary of the MCC sanitary-protective zone. ⭐point of collection. Sampling points: '0 km'—56°27′05″N, 93°36′31″E; '2 km'—56°23′18″N, 93°37′13″E, '5 km'—56°23′40″, '15 km'—56°27′05″, 93°42′22″E.

### **2.1. Uranium: natural and artificial**

north direction for nearly 3000 km, crosses various latitudinal geographical zones, falls into the Arctic Ocean, forming estuary zone up to 30 km wide. Length of Yenisei exceeds the same of Danube River (2857 km), Mississippi (3770 km) and Indus (3180 km). Yenisei River is the most

the world. The nominal border between Western and Eastern Siberia lies along Yenisei. There are three hydroelectric power plants (HPP) on the Yenisei River and on the rivers falling into it. River's waters are characterized by high transparency (up to 3 m) and low mineralization (mean value is 54 mg/l) and also by high oxygen concentration. Flow velocity and river width can change considerably: from 1.5 to 12–15 km/h and from 0.2–0.5 to 3–5 km, respectively. Solids of the channel in the uppers are faceted soils that are changed into gravelly sand in the middle course and into sandy-clay in the lower course near the fall into the Arctic Ocean.

There is a constant mixing of water layers because of hydroelectric power plant's activity, thus not affecting water temperature from the depth of water flow even on higher distances after HPP stanch. At the beginning of July, water temperature in Krasnoyarsk district and after 100–150 km further down the course is ~10°C, at the end of July–August it is 15–17°C. River's ecosystem is related to oligotrophy with fauna-rich river, there are more than 500 spe-

There is Mining and Chemical Combine (MCC) in Rosatom, located at Krasnoyarsk, on the bank of the River Yenisei in 50 km downstream of the city of Krasnoyarsk. There are atomic reactors and radiochemical production in the MCC. Since 1958 MCC used water for cooling industrial nuclear reactors for the production of weapon plutonium −238Pu. River water, while passing through the cooling system of reactors, returned to Yenisei. Effluent waters contained a great amount of radionuclides that were formed during neutron activation of traces (solid slurry and dissolved compounds), which are present in river water. Two direct flow reactors were withdrawn in 1992, because the activity level of the effluent waters of MCC was

As a result of long-term activity of MCC, the Yenisei's ecosystem contains considerable amounts of industry-related radionuclides [2]. In particular, an increased level of radioisotope contents in bed deposits and alluvial soils was found [2–6] and distribution and migration of radionuclides both in near-field influence of MCC [7, 8] and in significant distance away from effluent zone, including estuary of Yenisei, were indicated. As early as in the beginning 1970, the pollution zone of Yenisei's bottom land by 137Cs was found by airborne gamma survey. In district of Yeniseysk city (island Gorodskoi around 300 km downstream of MCC), the specific activity of 137Cs reaches 16,300 Bk/kg in some places, power of exposure (PE)—270 µR/h. According to present standards, bottom sediments and alluvial soils at this region are related to solid radioactive wastes. 137Cs is the main radionuclide polluting soils and bottom sedi-

**2. Radionuclides (natural and artificial) in the streams of the** 

) Yenisei holds second place (after the Ob) and the seventh place among all rivers of

/year. Mean water consumption in the estu-

/s. With respect to basin area (2580 thou-

affluent river of Russia with a runoff rate of 624 km<sup>3</sup>

/s and the maximal value is 190,000 m3

ary is 19,800 m3

cies of algae and diatoms [1].

remarkably decreased.

ments are 152+154Eu and 60Co [9].

**Yenisei River**

sand km2

362 Water Quality

Besides the pollution caused by industry-related radionuclides, pollution by natural radionuclide—uranium and its isotopes are also investigated.

The total uranium content is the main factor to determine the radiation level of water sources, its value is standardized and controlled by ecological services. Uranium in water is truly dissolved and found in the form of uranyl carbonate complex anions. In general, river waters contain 600 ng/l of dissolved uranium. Despite that main natural transport agents—water carries uranium in small amounts, one should not exclude that there can be local transfers of uranium in significant amounts [10].

The main feeders, contributing to the radioactive pollution of the Yenisei, are majorly the right bank feeders, situated near MCC outlet: river Kan, on the bank of which the electrochemical plant (ECP, Zelenogorsk city) is situated, and river Bolshaya Tel', flowing along the border of testing area 'Sverniy' MCC (Zheleznogorsk city).

According to data, presented in the monograph [9], the most of the region's waters, related to the bottomland of Kan, contain from 0.04 to 3 µg/l of uranium that is considered as highly pure with respect to natural radionuclide content. In addition, there was no trend in uranium content from the location of selection. Only in one place at the turn of Kan's course to the north vs. course of Bogunay river, it was revealed that all of the waters contain uranium from 1 to 3.3 µg/l. Industrial waters discharged by ECP into Kan near the plant administration were similar to natural uranium content and contained 0.05–0.08 µg/l of uranium.

Natural stream feeding Syrgyl river contained from 0.03–0.07 to 1.0–7.3 µg/l of uranium. The contents in the range 0.3–5.0 µg/l were shown to be natural geochemical background of uranium in the studied region, in particular, in the bottomland of Kan. All of the excesses are considered as abnormal.

The analysis data [1–12] shows that the geochemical background level of uranium in the Yenisei River is in agreement with the mean statistical level for the basins with major contribution of natural uranium resources, e.g. Baikal Lake and rivers of Altai region: from 0.15 to less than 2.0 µg/l.

Uranium content in waters which were collected from Bol'shaya Tel' in the September 2007 at the 1000 m place from the estuary is 3–60 times higher than values obtained for uranium (mean value 0.33 ± 0.08 µg/l) in background samples (Yenisei, tideway). Moreover, this period was indicated by significantly higher uranium concentrations as compared with other studied months. This increase becomes remarkable for the 1000 m place, where uranium concentration is 16 µg/l that is very close to the accepted in Canada and Australia standards for the minimal allowed uranium concentration—20 µg/l and by 8 times exceeds accepted by WHO standard—2 µg/l. Despite that obtained values are lower than the level of exposure (LE = 75 µg/l) accepted by in NRS of Russian Federation [9, 10], uranium concentration in some places of Bol'shaya Tel' in September is, in general, can be considered as abnormal. It is known that natural uranium is a mixture of three isotopes: 238U—99.2739% (T1/2 = 4.468 × 109 years), 235U—0.7024% (T1/2 = 7.038 × 108 years) and 234U—0.0057% (T1/2 = 2.455 × 105 years). In contrast to other isotope pairs, last two isotopes are in constant proportion, regardless of high migration activity of uranium and geography: 238U/235U = 137.88 [13, 14]. The presence of uranium was truly established in the waters of Bol'shaya Tel', it can only be originated artificially: in the sample from 1000 m (October 2006) ~0.05 ng/l and in the sample from Bol'shaya Tel' (March 2007) ~0.03 ng/l. In addition, the ratio of 236U/234U at these places is 1:0.8, respectively.

Besides, water samples obtained in September provided information about anion content of NO3 − (~2 mg/l, while the maximum permissible concentration (MPC) is 45 mg/l), CH3 COO<sup>−</sup> (~7 mg/l) in the waters of Bol'shaya Tel' (1000 m from estuary). It is considered that the presence of such anions can indicate the non-equilibrium conditions in basin solution. Such situation is considered rather usual for liquid radioactive wastes, where acetate and nitrate, due to kinetic limitations of the acetate oxidation by nitrate, can coexist even at high (about 100°C) temperatures [10].

Generalized information about the total uranium content in water samples of the Yenisei River is given in **Figure 2**.

**Figure 2.** Results of determination of total uranium content in Yenisei water at distances from water discharge of MCC '0 km' and '5 km', taken 2006–2009, 'distance from water discharge MCC'.

Presented data indicate uranium content in the estuary of Ploskiy river '0 km' to exceed by 6–9 times background values of uranium typical for Yenisei. Further investigation of isotope composition of indicated water samples revealed that a ratio of uranium isotopes differ from natural isotopes and also the presence of 236U can also evidence the industrial origin of high uranium concentrations as compared with background values. Isotope analysis of some samples has been carried out.

In water samples of Yenisei (pick point '0 km') the ratio of 238U/235U is 119:120. Besides, artificial uranium isotope 236U (T1/2 = 2.39 × 107 years) was found, the ratio of which to 234U equals 236U/234U ~0.1–0.2. Thus, one can state that high uranium concentration in Yenisei waters is caused by MCC activity.
