At the head-end of the nuclear fuel cycle the environment is inevitably contaminated by solid, liquid and gaseous wastes produced in mining, enrichment and processing of uranium ores. Radionuclides of three radioactive families: ²³⁸U, ²³⁵U and ²³²Th are released into the atmosphere in the exploitation of uranium deposits. However, the total radioactivity of the released radionuclides results mainly from the ²³⁸U family where ²³⁰Th, ²²⁶Ra and ²²²Rn are most active. When compared with the other steps of the nuclear fuel cycle, the exploitation of uranium deposits generates lower-level radwaste, but it may induce a local growth of the natural background for a long period of time (hundreds and thousands of years).

Solid waste from uranium mines and open pits includes barren rocks (with background or near-background radioactivity), unamenable uranium ores, tailings from radiometric classification of ores, incidentally mined minerals, tailings from heap leaching, etc.

In the case of underground mining, works on capital construction, mine development and cutting of entries yield 0.2 - 0.3 and more tons of barren rocks and unamenable ores per ton of extracted ore. Open pits produce up to 8 - 10 and more tons of overburden per ton of ore.

Hydrometallurgical processes (HMP) turn the mass being processed almost entirely into waste as tailings. Thus, mining and processing of uranium ores produce from 1.3 - 1.6 (mines) to 10 - 15 (open pits) tons of solid waste per ton of ore.

Liquid waste from uranium mines includes mainly drainable underground waters (at the rate of up to 2000 m³/d and more) whose composition may vary over wide limits (Table 1.1).

Table 1.1

The chemical composition of liquid waste from uranium mines [1.4]

1 - in equalibrium with ²²⁶Ra

Radionuclides (such as uranium, ²²⁶Ra, ²²²Rn, ²³⁰Th, ²¹⁰Po, ²¹⁰Pb) accumulated on the ground and in bottom sludge sediments of local water systems as a result of discharge of mine waters are an essential hazard. Their total activity amounts up to 10 - 15 Bq/l, while maximum permissible concentrations are 0.111 Bq/l.

Tailing dumps are an integral part of uranium mining industry. The tailings include solid and liquid process wastes. The quantity of the solid waste is roughly equal to the quantity of processed ore, while the liquid waste is 2 - 3 times more. The chemical composition of the liquid fraction in the ore pulp sent to the tailing dumps is dependent on the technology of ore processing and various over wide limits (Table 1.2).

Table 1.2

The chemical composition of the liquid phase of ore pulp from hydrometallurgical plants [1.4]

As a source of radioactive contamination, the tailings dump has characteristic features distinguishing it from other industrial sources of contamination. First of all, the tailings dump is a surface source of uncontrolled release of radioactive aerosols which has a rather great open surface formed from finely divided dusty materials (sands, sludges). For this reason, the rules for operating the tailings dumps involve measures on reducing the area of dusty surfaces (slopes of embankments, dried surfaces, etc.). Data on the environmental radiation impact of different wastes discharged by the uranium mining industry are given for comparison in Table 1.3.

For the most part the solid radwaste represents unamenable ores and mainly HMP tailings. Tailings from acid leaching contain more ²³⁰Th than carbonate leaching tailings. The acid and carbonate leaching tailings have almost the same total radioactivities. The specific radioactivity of the HMP tailings is low. Approximately 15% of total radioactivity is removed from the processed ore with the end uranium product. About 70% of initial radioactivity remains in the tailings after the decay of short-lived radionuclides.

Aerosols are dominant in the radioactive contamination of the environment by HMPs. The aerosols falling out on both the plant sites and the surrounding areas contaminate them with long-lived radioactive elements. Concentrated aerosols fallouts of up to 40 Bq/(m²d) may occur at some spots in the plant site.

Table 1.3 [1.11]

Typical parameters of isolation of rehabilitated objects from the environment

A method of underground leaching (UL) of uranium has been introduced since 1965 in addition to traditional mining methods. The UL allows exploitation of poor uranium ore deposits at depths of up to 600 m under adverse geological conditions where the use of traditional mining methods would be economically inefficient. The UL method has been used to mine 9% of prospected uranium resources. When mining by this method uranium passes into solution at the site of uranium deposit. The solution is delivered through wells up to a sorption plant placed on the surface. The balance of process solutions is maintained throughout the uranium UL cycle. At the end of the UL process 0.15 - 0.18 m³ of solutions containing radionuclides remains per ton of rock mass in the ore stratum (Table 1.4). The bulk of the residual solutions is considered as a site for temporary underground disposal of low-level liquid radwaste. When the residual solutions move through rocks, the processes of neutralization, precipitation, sorption, ion exchange and dilution restore the initial composition of stratal waters. The time required to restore the initial composition of the waters is dependent on the velocity of natural motion of underground waters (15 - 20m/y) and can be determined by calculations and modelling. Soils within the UL site are contaminated with sulfates, nitrates and natural radionuclides of the uranium series.

Table 1.4

The chemical composition of residual solutions after underground sulfuric-acid leaching [1.6]

When the exploitation of a uranium deposit by the UL method is completed, the radiation monitoring of the mining site is carried out. Data for elaborating a site rehabilitation project are provided on the basis of the results of the monitoring. The contamination of the productive and adjacent horizons is regularly controlled by taking water samples through observation holes. At the final stage of the UL process the progress in the restoration of the chemical composition of stratal waters is observed through observation holes arranged along the flow direction at intervals of 50, 100 and 200 m and so on within the expected area of propagation of the residual solutions.

Thus, tailings dumps of uranium enterprises make the greatest contribution to the environmental contamination at the head-end stages of the nuclear fuel cycle. In this case ²²²Rn is the most intensive contaminant. Within the nuclear fuel cycle as a whole the contaminating impact of the tailings dumps on the environment is comparable with the impact of NPPs and exceeds tens and hundreds times the environmental impact of mining works per se. Unlike other mining industries, the basic part of costs for the exploitation of radioactive ore deposits must be directed to reduce as much as possible the quantity of radioactively hazardous solid waste from mining works as well as mine waters, ore dust, and ore enrichment and processing tailings.

A production complex of mining and processing enterprises is located in the territories of six CIS countries (the Russian Federation, the Republic of Ukraine, the Republic of Uzbekistan, the Republic of Kazakhstan, the Republic of Tajikistan and the Republic of Kyrgyzstan). The complex consists of the following enterprises:

• Argun (Priargunskii) Industrial Mining and Chemical Association (AMCA),
• Lermontov Industrial Association "Almaz" (IA "Almaz"),
• Navoi Mining and Metallurgical Combine,
• KASKOR Joint Stock Company (until 1992 the Caspian Mining and Metallurgical Combine),
• Industrial Association "Tselinnyi Mining and Chemical Combine" (IA "Tselinnyi MCC"),
• Industrial Association "Eastern Combine for Rare-Earth Metals" (IA "Vostokredmet") (until 1992 the Leninabad Mining and Chemical Combine),
• Scientific and Industrial Association "Eastern Mining and Enrichment Combine" (based on the Eastern Mining and Enrichment Combine),
• Industrial Association "Southern Combine for Polymetals" (based on the Kirgiz Mining Combine),
• Industrial Association "Dnieper (Pridneprovskii) Chemical Plant".

Over the period of activities of these enterprises a great volume of waste has been generated in mining and processing of uranium ores. These are rock spoil heaps (188 million t), HMP tailings dumps and basins of mine waters (543 million m³).

In the territory of Russia the volume of prospected resources whose mining could be profitable amounts to 25% of resources in all of the CIS countries. These natural uranium resources profitable for mining are concentrated in the Strel'tsovsk District, Baikal. In this region the AMCA accomplishes uranium mining and processing.

The Argun Industrial Mining and Chemical Association (AMCA) is sited in the Krasnokamensk District, the Chita Region, 18 km north-east of the town of Krasnokamensk. The Association was established in 1968 to mine, enrich and process uranium-molybdenum ores. Uranium is mined in the Strel'tsovskii ore region in three underground mines and the Tulukui open pit.

Dusty dumps of amenable and unamenable ores, a uranium open pit, a tailings dump, the Urtui coal pit, a hydrometallurgical plant (HMP) for enrichment of uranium and molybdenum, and the Krasnokamensk Heating and Power Plant (HPP) are sources of radioactive contamination for the surrounding territory. The HPP uses the Urtui coals with a high content of natural radionuclides (NRNs). In burning the coals, the NRNs are released in the atmosphere or discharged in an ash-disposal site. That is why the coals’ burning is under control: only coals with uranium content not exceeding 0.006% are allowed to be used as a fuel. In such a way observation of permissible level of the NRN releases set by the NRB-76/87 Rules is ensured.

Mine waters of the AMCA, industrial sewage from the HPP and residential sewage are discharged through a collector in surface storage ponds and the local surface hydrologic system. The sewage from the HMP is discharged in the tailings dump. The total area of the storage ponds and the tailings dump is 4.264 km².

In 1994 the release of uranium radionuclides into Lake Umykei increased by 5.779x10¹⁰ Bq as compared with 1993, but their total release was reduced by about 81.4x10¹⁰ Bq. No excesses over the current standards for releases of radionuclides and their permissible concentrations in the sewage and the collector were recorded.

By using a multistage flow sheet developed at the association for radiometric enrichment of uranium ores the waste from a radiometric enrichment plant is divided into two classes:

• waste with sufficiently high uranium to be used for heap leaching and.
• waste with low uranium comparable to the uranium content of rock.

The actual releases of radionuclides with sewage from the AMCA for 1994, Bq/y

Barren rocks produced in mining and processing of uranium ores are kept in special dumps. The dumps occupy a considerable area and require unprofitable expenses on their maintenance. The dumps of unamenable ores are used, as a rule, for heap leaching to extract an additional product. Waste from heap leaching is used, in turn, in the site to fill worked-out areas. The dumps of unamenable ores and barren rocks take a total area of 2.73 km². Before forming a dump, the grading of an appropriate site is made, including topsoil excavation and filling of a 1-m-thick cushion course from barren rock.

Table 1.5

Radioactive waste produced at the AMCA as of January 1, 1993

The total quantity of radioactive waste including that in the HPP ash-disposal site, the coal dump and a blending stockpile is 284.3 million t at a total activity of 46.6x10¹⁴ Bq.

The tailings dump has been placed in a natural valley with an embankment and the excavated topsoil. The bed of the valley is paved with polyethylene film and a 0.5-m thick layer of inert soil. The tailings dump is half full.

In the association there are 18 sources contaminating the atmosphere with radon-222 and 10 sources releasing natural uranium. In 1994 these sources discharged 2.966x10¹⁴ Bq of radon-222 and 4.718x10¹⁰ Bq of uranium into the atmosphere, whereas the permissible releases are 4.718x10¹⁰ and 8.130x10¹⁰ Bq, respectively. Therefore, no excess of releases above the standards was recorded.

Monitoring and rehabilitation of the areas within the AMCA site, protective sanitary zone (SPZ) and surveillance zone (SZ) are regularly performed. The total area of contaminated territories in 1994 amounted to 8.4826 km², including:

In 1994 the radiation monitoring in the region of the AMCA activities was carried out by expedition surveys of a 20-km-radius area around the enterprise as well as with the help of a stationary radiometric network disposed in a 100-km-radius area around the AMCA (Fig. 1.1) and by episodical radioactive fallout monitoring in the vicinity of the Oktyabr'skii settlement. The expedition surveys included measurements of exposure dose rates (EDRs) and the sampling of vegetation with subsequent gamma-spectrometric analysis. The measured EDR values did not exceed 22 mR/h at a height of 1 m above the surface. Only cosmogenic beryllium-7 with a specific activity of 110 - 445 Bq/kg and terragenic potassium-40 with a specific activity of 3850 - 10210 Bq/kg were detected in the vegetation samples. Therefore, the specific activity of vegetation resulted almost fully from potassium-40 to be 10210 Bq/kg in the neighborhood of the tailings dump near the settlement of Oktyabr'skii. The cesium-137 concentrations were below the threshold of detectability.

According to the results of observations made in the stations of the stationary radiometric network, the average annual EDR ranged from 14 mR/h to 17 mR/h (Krasnokamensk).

The average annual total activity of fallout varied from 2.1 Bq/(m²d) (the village of Dono) to 2,5 Bq/(m²d) (the settlement of Zabaikal'sk). The highest average value, 3.3 Bq/(m²d), was observed in Krasnokamensk in July and the highest average daily value, 25.4 Bq/(m²d) was recorded in the same settlement in March.

In 1994 the radioactivity of atmospheric fallout in the vicinity of the AMCA was practically similar to that averaged over the Transbaikal region. As a whole, the AMCA region, like the entire Transbaikal region, is characterized by a stable increased radioactive contamination of the atmosphere and atmospheric fallouts because of the presence of airborn dust rich in radionuclides of the uranium and thorium series.

A special network of hydrogeological observation holes was developed in the site and beyond it to control a possible penetration of mine waters, seepage waters from the surface of the dumps as well as possible leakages through the waterproofing of the tailing dumps into surface and underground waters. These holes are used for regular observations. The results obtained to date are satisfactory.

Ä - AMCA; - gamma-background monitoring station; - fallout monitoring station

Fig. 1.1. The disposition of radiological monitoring stations in a 100-km-radius zone around the AMCA

Thus, a present-day uranium mining enterprise is a source of radiation impact on the environment (atmosphere, soil, surface and underground waters, vegetation and, as a result, humans and animals).

In this connection, not only various antiradiation measures, but also radioecological monitoring are growing in importance. The system must be capable not only to fix any disturbances found through monitoring but also through a radioecological model describing the impact of an enterprise on the environment and human health. For this purpose measures are taken to equip the enterprise's radioecological service with apparatus and systems for ecological control.

Moreover, a reference network has been developed for complex observations of the soil composition, vegetation, atmosphere, surface and underground waters. This will ensure prompt detection and elimination of the sources of environmental radiation impact and thereby minimization of the radiation risk to the population of the region.

Lermontov Industrial Association (IA) "Almaz "

is in the town of Lermontov, the Stavropol Territory. The association was established in 1950 as an industrial uranium mining enterprise on the basis of the Beshtau and Byk deposits. The association was leading in the field of geotechnological methods of mining and hydrometallurgy. It was the first in the country where the process of underground uranium leaching was introduced.

The IA "Almaz" is located in an unique natural zone within the Caucasian Mineral Waters region. This required search for new directions in the development of the enterprise. Work on complex processing of uranium-bearing phosphorites was initiated in the 70s. A technology for scandium extraction was developed and the corresponding pilot production was organized. A shop for ammophos production was built. A shop manufacturing mining equipment was set up as a subdivision of the enterprise and launched production of electrical immersion pumping plants for borehole underground leaching.

Sources of radioactive contamination of the environment have been left on the site of the enterprise after the completion of works on uranium ore mining and processing. These are dumps of unamenable ores and barren rocks as well as a pumped tailings dump. Their total area is 1366.7 thousand m². The actual volume of unamenable ores and barren rocks in three dumps is 3960.9 thousand m³; the volume of the HMP tailings dump is 12031.6 thousand m³ (Table 1.6).

Table 1.6

Radioactive waste accumulated in the IA "Almaz" as of January 1, 1990

A dump of unamenable ores and barren rocks (53.3 thousand m³ in volume) 4.5 km distant from the Narta settlement was formed during pilot production and isolated from the environment in trenches about 4 m in depth. In mine No.1 and mine No.2 the surfaces of dumps (2107.2 m³ and 1800.4 m³ in volume, respectively) were rehabilitated: covered with a clay and chernozem layer and afforestated. The pumped tailings dump within the HMP site has been operated since 1954 and is now 71% full. Some measures have been taken to diminish the environmental impact of the tailings dump. In particular, the beach of the embankment is isolated by non-radioactive waste phosphogypsum produced in the processing of apatite concentrate.

The construction of the Navoi Mining and Metallurgical Combine (Navoi MMC) was initiated on the basis of uranium deposits in the Kyzylkum province in 1958. In addition, the construction of the first gold mining enterprises was also initiated in 1964 on the basis of deposits of auriferous ores. At present the Navoi MMC incorporates mines, open pits, HMPs, a sulfuric acid production plant, underground leaching shops, etc.

There are three mining departments (MDs) in the structure of the enterprise: the Northern MD, the Southern MD and the Central MD that extract uranium by the UL method.

In the Northern MD the UL grounds disposed over an area of 1283 m² at a distance of 1.0 - 1.5 km from the town of Uchkuduk were decommissioned in 1975 - 89. After the implementation of environmental protection measures the surface exposure dose rate (EDR) within the sanitary & protective zone (SPZ) (3520 thousand m²) has not exceeded 2x10^-2 mR/h. The volume of residual solutions in the depths is no more than 2392 thousand m³.

In the Southern MD five UL grounds, 1.0 - 60 km distant from the settlement of Nurabad, with a total area of 2548 m² were decommissioned in 1982 - 90. Since the sites were rehabilitated, the EDR within the SPZ (3539 thousand m²) has not exceeded (1.9 - 2.5)x10-² mR/h. The volume of residual solutions in the depths is 4389.8 thousand m³.

On-site dumps of unamenable ores were built up for the operation period of a mine 1.5 km distant from the Nurabad settlement. The mine was in operation from 1965 to 1982. The volume of rock and ore mass amounted to 166.7 thousand t. The EDR within the SPZ around the dumps is 1.7x10^-2 mR/h.

In the site of the Central MD 15 km distant from the town of Zarafshan uranium was mined in 1979 - 90. After the site was rehabilitated, the EDR within the SPZ has not exceeded 2.0x10^-2mR/h. The volume of residual process solutions in the productive underground horizon has amounted to 2344.6 thousand m³ at an activity of 1.0x10¹² Bq.

An HMP flooding tailings dump located at a distance of 1 km from the settlement of Durmyan over an area of 6022 thousand m² has been in operation since 1964. This tailings dump is provided with a recycling water supply system and hydraulic feed of the HMP tailings when the fluid fraction of the pulp returns into the HMP. The tailings dump has accumulated to date 52800 thousand t of waste containing uranium, radium and polonium. The EDR in the site has not exceed 3.0x10^-2 mR/h. The SPZ area is 8360 thousand m².

Table 1.7

Radioactive waste accumulated in the Navoi MMC as of January 1, 1990

The KASKOR Joint Stock Company

created in 1992 on the basis of the Caspian Mining and Metallurgical Combine is a large-scale ore mining and processing enterprise that incorporates 28 divisions. The Caspian MMC was established in 1959 on the basis of uranium-phosphorus deposits in the inhabited territory of the Mangyshlak Peninsula in the Republic of Kazakhstan.

One of the KASKOR divisions, a major chemico-hydrometallurgical plant (CHMP) is a big enterprise on complex processing of local uranium-phosphorus ores and graphite concentrate delivered from the Kola Peninsula. Its basic products are uranium concentrate, scandium oxide and fluoride, crystalline scandium, alumino-cadmium hardeners as well as rare-earth concentrates of the light and medium-weight groups. From large-tonnage process waste the plant produces fodder dicalcium phosphate (precipitate), food dicalcium phosphate (dentaphos) and ammonium sulfate.

During the activities of the enterprise 210904 thousand m³ of radioactive waste was accumulated in a CHMP tailings dump, a burial ground and a gypsum and rare-earth concentrate (GREC) storage facility (Table 1.8).

Table 1.8

Radioactive waste accumulated in the KASKOR Joint Stock Company as of January 1, 1990

Note. Each of the storage sites is surrounded by a 0.5-km-radius SPZ.

The CHMP tailings is located 5 km north from the plant site in a natural hollow. During the 27-year operation of the tailings dump the total volume of waste in it had attained 210 thousand m³, that is 70% of the design capacity of the dump. The CHMP pulp directed to the tailings dump contains radionuclides ²²⁶Ra and ²¹⁰Bi. The radiometric survey of soils and ground and the upper aeration layer 0.3 m beneath the surface revealed no contamination with the radionuclides in the territory surrounding the tailings dump. An excess above the natural background is observed at the shore line of the tailings dump where the EDR ranges from 14 to 60 mR/h with the maximum value corresponding to the uncovered tailings sediments.

The burial ground is at a distance of 12 km from the town of Shevchenko and 6 km from the CHMP. The burial ground was in service for 25 years before filled. It accommodates 6000 t of radioactive waste containing radionuclides ²¹⁰Po, ²³⁰Th, ²³⁸U and others. The surface and bottom of the burial ground are isolated from the environment by a compacted clay layer. The EDR at the surface of the burial ground and within its SPZ does not exceed 40 - 60 mR/h.

The GREC storage facility, 10 km away from the town, is waterproofed by isobutylene and concrete. It has a design capacity of 29626 m³ and holds 904 m³ of solid radioactive waste containing ²¹⁰Pb, ²²⁷Ac and ²²⁸Ac. The EDR in the vicinity of the storage facility is 250 mR/h.

The Industrial Association "Tselinnyi Mining and Chemical Combine" was established on the basis of large uranium, uranium-molybdenum and uranium-phosphorus ore deposits in North Kazakhstan. Its construction was started in 1956. The basic production facilities are located at a distance of 20 km from the town of Stepnogorsk. The uranium mining enterprises are located at distances of 120 to 500 km from the basic production facilities.

The association integrates a HMP, a chemical plant, a heap leaching ground, a mining equipment maintenance and repair shop, a geologic group, and power & heating plants.

In the period of its activities the facilities of the association produced 66592 thousand m³ of radwaste accumulated in a flooding HMP tailings dump and on-site dumps of unamenable ores in the mining enterprises (Table 1.9).

Table 1.9

Radioactive waste accumulated in the IA "Tselinnyi MCC" as of January 1, 1990

The flooding tailings dump occupies a space of 7220 m² and is located in the SPZ of the HMP. It was used in 1969 - 90 and filled to 90% of its design capacity. The bottom of the tailings dump is paved with polyethylene film. The tailings dump consists of two ponds. The surface of the one pond is isolated from the environment by polyethylene film. The second, evaporating pond has the unisolated surface. The basic radioactive contaminants in the HMP pulp are the natural radionuclides of the ²³⁸U and ²³²Th series.

Solid radioactive waste from radiometric enrichment and heap leaching is stored in piles within the SPZ at a distance of 0.5 - 7.0 km from the enterprise. The piles are placed on a surface preliminarily compacted by rolling without implementation of special water-proofing measures. The EDR on the surface of the piles does not exceed 0.1 mR/h. The bottom under a 628000-m³ heap leaching dump is covered by asphalt and film to facilitate the collection of productive solutions in sprinkling ore mass and to prevent contamination of the soil.

The Scientific and Industrial Association "Eastern Mining and Enrichment Combine" (SIA "Eastern MEC") succeeded the Eastern Mining and Enrichment Combine founded in 1951 on the basis of the Pervomaiskii and Zheltorechenskii uranium-containing iron ore deposits in the Kirovograd ore region in the Ukraine. The mines simultaneously extracted uranium and iron. As of 1990, the enterprise stored 3770 thousand tons of unamenable ores and barren rocks in dumps with an area of 181.4 thousand m² (Table 1.10).

The bottom of the dumps is formed from loams. Unamenable ores with a volume of 1960 thousand m³ were buried in the cavities of the "Novaya" iron ore mine. This amounts to 8% of the design volume.

Since 1976 a tailings dump with a useful volume of 29200 thousand m³ has been in service at a distance of 7 km from the HMP. As of 1990, it was 87% full, corresponding to 25404 thousand m³ of waste in the form of pulp. The bottom of the tailings dump is water-proofed with compacted natural loam. The EDR in a 950-m-radius supervised zone varies in the range of (1.7 - 2.5)x10^-2 mR/h. Another tailings dump 400 m distant from the HMP had been in service since 1966. At present it has been taken out of service because it was completely filled (8400 thousand m³). The tailings dump was constructed with no waterproofing course. The EDR within the supervised zone is no more than 2.5x10^-2 mR/h.

Table 1.10

Radioactive waste accumulated in the SIA "Eastern MEC" as of January 1, 1990

Since 1976 a tailings dump with a useful volume of 29200 thousand m³ has been in service at a distance of 7 km from the HMP. As of 1990, it was 87% full, corresponding to 25404 thousand m³ of waste in the form of pulp. The bottom of the tailings dump is water-proofed with compacted natural loam. The EDR in a 950-m-radius supervised zone varies in the range of (1.7 - 2.5)x10^-2 mR/h. Another tailings dump 400 m distant from the HMP had been in service since 1966. At present it has been taken out of service because it was completely filled (8400 thousand m³). The tailings dump was constructed with no waterproofing course. The EDR within the supervised zone is no more than 2.5x10^-2 mR/h.

The Association mined uranium by the UL method in the Devladovo and Bratskoe deposits from sedimentary rocks of the Buchak productive horizon enclosed between confining clay horizons.

An underground leaching ground on the Devladovo deposit is at a distance of 5 km from the station of Devladovo, the Pridneprovskaya Railway. The deposit was in service in 1962 - 83. The volume of residual process solutions with an activity of 1.8x10¹¹ Bq in the productive horizon amounted to 6035 thousand m³. The predicted self-purification time for the water-bearing horizon is 280 years at a natural underground water velocity of 20 m/y. The 15-m-thick productive horizon is at a depth of 60 - 65 m.

An underground leaching ground on the Bratskoe deposit is in the Nikolaev Region 10 km from the Bratskoe settlement. The deposit was in operation during 1971 - 89. The volume of residual process solutions with an activity of 1.9x10¹¹ Bq in the productive horizon amounted to 5200 thousand m³. The predicted self-purification time for the water-bearing horizon is 280 years at a natural underground water velocity of 20 m/y. The 15-m-thick productive horizon is at a depth of 94 - 100 m.

The surfaces of the two UL grounds were remediated. The remediation works included removal of 142.6 thousand m³ of soil with an activity of (1.6 - 1.8)x10¹¹ Bq and its subsequent burial in 2.8 -3.5-deep trenches.

At present the Association incorporates mining enterprises, an HMP, a plant for production of sulfuric acid and some service enterprises.

The top-priority lines in the Association's activities are mining of uranium and iron ores as well as production of iron ore and uranium concentrates and sulfuric acid.

The Industrial Association "Eastern Combine for Rare Metals" (IA "Vostokredmet") was established on the basis of the Leninabad Mining and Chemical Combine which is situated in the western part of the Fergana Valley, one of the most picturesque areas of Central Asia.

The Association includes an HMP, an engineering plant, research laboratories of chemical processes and automated management systems, an instrumentation and automatic equipment laboratory, a geological maintenance and repair shop and a construction and mounting department. The IA "Vostokredmet" is one of the leading enterprises in the field of underground and heap leaching of metals.

The combine was established in 1945 as a large-scale uranium mining enterprise on the basis of uranium deposits situated in Tajikistan, Kyrgyzstan and Uzbekistan. As the country's first raw materials base, the Combine incorporated seven mines and five plants, including plant V with a hydrometallurgical shop and the Tabashar, Adrasman, Mailisui, Uigur and Tyuya-Muyun mines.

The settlement of Chkalovsk was built 10 km apart of the city Khodzhent (Leninabad). Later the Combine's basic HMP was built in Chkalovsk to process uranium ores from the different deposits. A pilot hydrometallurgical shop in Tabashary (40 km away from Chkalovsk) was reconstructed to a pilot HMP where ores from the Meilisui, Uigur, Adrasman and other deposits have been processed in addition to the Tabashary ores.

Throughout the period of the Combine's activities 34907 thousand m³ of low-level radioactive waste was accumulated in its territory. The waste are stored in 9 tailings dumps (a total area of 1741 thousand m²) and 21 dumps of unamenable ores (a total area of 2241741 thousand m²) in the mining and processing enterprises (Table 1.11).

In two mining departments which extracted uranium by the UL method the volume of residual process solutions having an activity of 4.0x10¹² Bq in the productive horizons occurring at a depth of 450 - 600 m amounted to 14754 thousand m³.

Table 1.11

Radioactive waste accumulated in the IA "Vostokredmet" as of January 1, 1990

The dumps of unamenable ores and barren rocks are disposed over the vast territory of the Combine. Twelve dumps of mining department 2 are arranged on the terraces of the Chauli-Sai river 0.3 - 6.5 km away from the town of Khodzhent. The quantity of radwaste accumulated within the period of operation of the dumps (1953 - 1980) whose area is 156.6 thousand m² and having an activity of 4x10¹² Bq is 469.8 thousand tons. The EDR within the SPZ is 200 - 600 mR/h.

Eight dumps 1 - 10 km away from the settlement of Charkassar were formed within the operation period of the Adrasman mine in 1954 - 89. Their total area is 34 thousand m²; the quantity of radwaste with a total activity of 5.4x10¹¹ Bq is 292.1 thousand t. The EDR within the SPZ varies from 70 to 100 mR/h. On the site of the mine at a distance of 50 m from the settlement there is a tailings dump of an ore mining enterprise. The tailings dump that occupies an area of 34 thousand m² was in operation in the period of 1949 - 1958. The volume of waste in it is 102 thousand m² at a total activity of 2.4x10¹² Bq. The EDR within the SPZ is 50 - 60 mR/h.

A storage of poor ores with a volume of 1195 thousand m³ and an activity of 2.5x10¹² Bq remained in the site of the Tabashar mine 4 km distant from the settlement Tabashar after the 15-year operation of the mine (1950 - 1965). The EDR within the SPZ is 40 - 100 mR/h. Four tailings dumps with a total volume of 4547 thousand m³ and a total area of 573.8 thousand m² were formed at different times during the operation of a pilot HMP (1949 - 1965). The total activity of waste in the tailings dumps is 3.6x10¹³ Bq. The EDR within the SPZ is 40 - 60 mR/h.

In the valley of the Maili-Su River 15 km away from the town of Mailisai a HMP tailings dump was in operation from 1947 to 1962. At present the surface of the tailings dump is isolated from the environment by a 0.5-m-high soil layer. The volume of waste in the tailings dump is 1340 thousand m³; the activity is 1.9x10¹³ Bq. The EDR on the surface of the tailings dump is up to 30 mR/h.

A tailings dump for the waste of hydrometallurgical processes (from the GMP-1 plant) has been in operation since 1963 in the Digmai cavity 4 km away from the town of Gafurov. The tailings dump occupies a space of 692 thousand m² and is filled with 19200 thousand m³ of waste. The activity of the waste amounts to 1.56x10¹⁴ Bq. The EDR within a 1-km-radius SPZ varies from 40 to 250 mR/h.

Since 1949 to 1967 an HMP tailings dump with an area of 267 thousand m² at a distance of 2 km from the town of Gafurov was in operation. The volume of waste is 2600 thousand m³; the activity of waste is 2.9x10¹³ Bq. A 0.5-m-high soil layer covers the surface of the tailings dump. The EDR in the vicinity of the tailings dump varies within 20 - 60 mR/h.

A tailings dump in the town of Gafurov was operated in 1945 - 1950. It was intended for a pilot plant for hydrometallurgical processing of uranium ores. The tailings dump (an area of 39 thousand m²) is disposed within the area of service and pilot production buildings. It was completely dried and in 1963 its surface was covered with a 1.0-m-thick layer of inert soil. The radon concentration in the air directly above the dump was 2 - 5 Bq/m³; the release of radon to the atmosphere from the entire surface of the dump is about 2.96x10¹² Bq/y. A decision on the on-site burial of the tailings dump was made in 1991. The most effective measures were chosen to ensure the reliable disposal of the tailings dump and the radiation cleanness of the surrounding areas. Under study is the choice of an appropriate material for the covering of the dump surface. The covering must reduce the release of radon from the surface down to 0.05 - 0.1 Bq/(m²s). It is suggested to use for this purpose loessial loams with subsequent compacting. The height of the loam layer must be 1 - 2.5 m to ensure that the time of radon diffusion to the surface would be at least 30 days until the almost complete decay of the radon.

The Industrial Association "Southern Combine for Polymetals" (IA "Yuzhpolimetall" was established on the basis of the Kirgiz Mining Combine founded in the 60s. The Combine mined and processed uranium ores from the Southern Kazakhstan ore region.

Throughout the period of the Combine's activities 18 dumps of unamenable ores and barren rocks with a total volume of 55436 thousand m³ and 4 tailings dumps containing a total of 35695 thousand m³ of radioactive pulp were formed on its sites (Table 1.12). In the depths of two depleted UL grounds 2009 thousand m³ of residual process solutions is left. The solutions contain the natural radionuclides of the uranium series and high concentrations of chemical components. The dumps of unamenable ores and rocks are at a distance of up to 80 km from populated areas. All of the dumps had been taken out of operation by 1991. No data on the rehabilitation of the spaces occupied by the dumps is available. Three tailings dumps at a distance of 2 - 11 km from the settlement of Minkush were taken out of service within 1960 - 1969. A 0.5-m-thick layer of loam was filled and compacted on the surfaces of the tailings dumps as an environmental protection measure. The EDR within the SPZ is no more than 25 - 30 mR/h.

Table 1.12

Radioactive waste accumulated in the IA "Yuzhpolimetall" as of January 1, 1990

An on-site tailings dump of the Kara-Baltinskii Mining Combine (an independent industrial enterprise since 1992) has been in service since 1955 to the present day. The beach of its embankment is 65% formed from loam and 35% covered with polyethylene film. As of 1995, the tailings dump was filled to 54% of the design capacity. At present the tailings dump is used in reprocessing of molybdenum-tangsten-bearing raw materials and radioactive waste in an HMP.

The Industrial Association "Dnieper Chemical Plant" started to process uranium-containing raw materials from iron ore deposits of the Krivorozhskii field in 1948. In 1948 - 1954 uncontrolled tailings dumps were created in natural clay pits within the SPZ of the enterprise,

Throughout the enterprise's activities 13663 thousand m³ of HMP tailings was accumulated in the tailings dumps (Table 1.13).

Table 1.13

Radioactive waste accumulated in the IA "DCP" as of January 1, 1990

The tailings dumps have no protective barriers. Another tailings dump ("D") of the plain flooding type with a capacity of 10 million m³ and an area of 76 ha was put into service in 1954 in the Dnieper flood lands to store radioactive waste from the hydrometallurgical production of uranium. The tailings dump also has no waterproofing means. Its embankment is made of waste from a by-product coke plant, that is, of crushed stone, gravel and silty soils from coal, clay and mica shales. Since 1970 after compaction of its beaches the tailings dump had been filled with phosphogypsum from processing of apatite.

The first section of a flooding-type tailings dump ("C") with a capacity of 8.7 million m³ at a distance of 14 km from the city of Dneprodzerzhinsk was put into service in 1968. An asphalt-bitumen impervious blanket is used as an antiseepage measure. The tailings dump was operated with the use of a circulating water supply without discharge of wastewater into the hydrosphere. The second section with a capacity of 19.2 million m³ and antiseepage protection was put into service in 1983 after the first section was completely filled. The reliability of the antiseepage measures was confirmed by full-scale studies and regime observations.

A radioactive tailings dump (DP-6) is made in the form of a trench 54 x 121 m in size where the remains of a blast furnace melting uranium ores in 1948 - 1964 were buried. The trench was covered with solid rubble and a 1.5 - 2.0-m-thick chernozem layer as well as sowed with grass for turfing. The archival materials of the enterprise which are not complete were used to calculate the total activity of the tailings dumps. The survey work is under way now to determine reliable data on the activity of the tailings dumps.

Data on two uranium mining and processing enterprises disposed in the Russian Federation were included in a simple operational database "Radleg" [1.15]. The prototype for development of the above database use was made from a departmental database on radwaste storage and disposal facilities in NFC enterprises that is based on the materials of radwaste inventories carried out in 1990 and 1993.

The reference tables of fields to the database list the field numbers and names for the fields related to NFC enterprises (PREDPR), storage and subsurface disposal facilities (OBJEKT), and sources of information (ISTOK).

Information on the enterprises located in the territories of the CIS countries - the Republic of Ukraine, the Republic of Uzbekistan, the Republic of Kazakhstan, the Republic of Tajikistan and the Republic Kyrgyzstan will be included in the database in the second phase of the project.

CONCLUSIONS

As a result of many years operation of enterprises of uranium ore mining and processing complex great volumes of low-level RW, containing natural radionuclides of ²³⁸U and ²³²Th families, have been generated in the form of rock dumps (138 millions m³), tailings dumps of hydrometallurgical plants and mine waters’ pools (543 millions m³). The total area of lands under these structures is 130 km².

The wastes of both mining and processing of the ores contain long-lived radionuclides: ²³⁸U (T_1/2 = 4.47 × 10⁹ years), ²³⁰Th (T_1/2 = 7.7 × 10⁴ years) and ²²⁶Ra (T_1/2 = 1.6 × 10³ years), transforming to continuously to ²²²Rn (T_1/2 = 3 × 8 days). That is why, due to presence of the above mentioned radionuclides the radiation background in underground uranium mines, quarries, at industrial sites of ore processing enterprises and adjacent areas by several times exceeds the natural background.

The main source of radioactive contamination ore wastes, which are generated as a result of ore processing and collected in tailings dumps. Within the nuclear fuel cycle as a whole the contaminating impact of the tailings dumps on the environment is comparable with the impact of NPPs and exceeds tens and hundreds times the environmental impact of mining works per se. As a source of radioactive contamination the tailings dumps have characteristic features distinguishing them from other industrial sources of contamination. First of all, a tailings dump is a surface formed from finely divided dusty materials (sands, sludges). For this reason the rules for operating the tailings dumps involve measures on reducing the area of dusty surfaces (slopes of embankments, dried surfaces, etc.). Data on the environmental radiation impact of different wastes discharged by the uranium mining industry are given for comparison in Table 3.

To meet standards for the residual radiation level (0.2 Bq m^-2 s^-1) the approximate depth of remediation layer for reliable isolation of the RW from the environment must be not less than 1.0-2.0 m for dumps of barren rocks and 2.5-3 m for tailings dumps. All objects of storage of uranium ore mining and processing RW need continuous monitoring. In the limits of radiation control SPZ and SZ of these objects are conducted.

A Federal Program on "Management of Radioactive Waste and Spent Nuclear Materials, Their Utilization and Disposal for 1996 - 2005" (named hereinafter the Program) was approved by the resolution of the RF Government in 1995 to solve, on the comprehensive basis, radwaste management problems as well as to construct long-term storage or disposal facilities for reliable isolation of radwaste from the biosphere. For uranium mining and processing facilities the Program envisages:

• a comprehensive study of the environmental impact of uranium mining facilities and the laying-up or, if necessary, disposal of decommissioned mines, open pits and tailings dumps;
• development of plants for decontamination and processing of liquid and solid radioactive waste produced in uranium ore mining and processing;
• development of plants for reprocessing of waste from enriched uranium production to extract useful elements and reduce the volume of the waste.

During the abandonment of and putting in a stand-by mode the uranium mining and processing enterprises their personnel and the population must be protected from the action of the factors of radiation hazard. Among the factors of highest significance are releases of mine waters and the liquid phase of the HMP ore pulp to the hydrosphere, releases of radon and products of its decay into the atmosphere, and dusts from dumps of unamenable ores, enrichment tailings and host rocks. For this purpose "Sanitary Regulations on Abandonment, Laying-up and Conversion of Radioactive Ore Mining and Processing Enterprises" have been worked out and approved. This document establishes the permissible residual levels of radiation contamination of the facilities to be abandoned or laid up (Table 1.14). The standards worked out for the residual radiation contamination assure that the radiation risk to the personnel of these facilities and the population working or living in the neighbouring regions will be limited. In addition to the reduction in the activity of the corresponding radiation source, of extreme importance is reliable isolation of radioactive waste, especially its solid phase, from the environment. For this purpose, dumps of barren rocks, unamenable ores, radiometric enrichment tailings and heap leaching tailings as well as HMP tailings dumps must be reliably covered with a remediation layer of inert rocks (Table 1.3). In so doing, the residual radon release must not exceed 1 Bq/(m²s) for stand-by enterprises and 0.2 Bq/(m²s) for abandoned enterprises.

To ensure the radiation safety in the abandonment, stand-by mode and conversion of uranium mining and processing enterprises the following measures must be implemented:

• radiation-ecological survey of the actual state of the enterprises;
• research and development work involving the assessment of the environmental impact of the enterprases;
• development of abandonment (stand-by) projects including both the assessment of environmental damage and the feasibility study of planned environmental protection measures.

The concepts, methods and normative criteria of radiation safety give a guarantee for the timely and reliable execution of abandonment, stand-by and conversion works as well as the recommissioning of the enterprises.

Table 1.14

Residual radioactive contamination of some objects in uranium mining and processing enterprises to be abandoned

REFERENCES

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1.2. A.KKruglov, Development of Nuclear Industry in the USSR. Moscow, TsNIIAtominform, 1995.

1.3. V.F.Zaitsev, P.P.Savva et al, "Radioecological problems of mining and processing of uranium ores", The 2nd Conference of the Nuclear Society on Radioactive Waste: Problems and Solutions, .Part I, pp.138-142, Moscow, 1991.

1.4. V.N.Mosinets, "Radioactive waste of uranium mining plants and its ecological impact", The 2nd Conference of the Nuclear Society on Radioactive Waste: Problems and Solutions, Part I, pp.79-87, Moscow, 1991.

1.5. V.N.Mosinets, "Radiation safety in abandonment, laying-up and conversion of uranium mining enterprises", The 2nd Conference of the Nuclear Society on Radioactive Waste: Problems and Solutions, Part I, pp.116-121, Moscow, 1991.

1.6. A.F.Iskra, I.K.Lutsenko, "Ecological, technological and economic criteria for use of water resources and protection of surface and underground waters from exposure to radioactive and toxic substances", The 2nd Conference of the Nuclear Society on Radioactive Waste: Problems and Solutions, Part I, pp.181-189, Moscow, 1991.

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1.8. Documentation on Departmental Inventory of Radioactive Waste and Its Storage and Disposal Sites as of 01.01.90. VNIIKhT Files. Moscow, 1991.

1.9. Documentation on Departmental Inventory of Radioactive Waste and Its Storage and Disposal Sites as of 01.01.93. VNIIKhT Files. Moscow, 1994.

1.10. A Federal Special Program on "Management of Radioactive Waste and Spent Nuclear Materials, Their Utilization and Disposal for 1996 - 2005 ". Approved by a decision of the Russian Federation's Government No. 1030 of October 23, 1995.

1.11. Sanitary Regulations on Abandonment, Laying-up and Conversion of Radioactive Ore Mining and Processing Enterprises (SPLKP-91) No. 6028-91. Moscow, USSR Ministry of Health, 1991.

1.12. An Interdepartmental Instruction on Protection of the Earth Surface and Rehabilitation of Areas Damaged in Mining and Processing of Radioactive Ores (MI ORZ-94). Moscow, Minatom RF, 1994.

1.13. The"Atomredmetzoloto" State Concern. An advertising booklet. The Central Research Institute of Management, Economy and Information of the RF Minatom, 1993.

1.14. The Final Technical Report on the ISTC Project #245 "Radleg". Phase I. "The creation of a simple operational database with connection to GIS, including presently available data on the radiation legacy of the ex-USSR", Moscow, 1996.

1.15. The simple operational database "Radleg", tables 1, 2, 3, 4, 6, 10, 11, 12, Moscow, 1996.