3. Environmental impacts

(September 1995) Uranium ore is produced in open pit or underground mines. The ore grades often are only 0.1 %; large amounts of ore have to be mined to obtain the amounts of uranium required. In the early years after World War II, uranium was mostly mined from deposits located close to the surface, while mining later continued into the deeper underground. With the decline of uranium prices on the world market, underground mining became too expensive for most deposits, and many mines have been shut down since then.

During the active mining period, large amounts of air contaminated with radon and dust are blown into the open air, for example 7426 million m³ (i.e. 235 m³/s) of contaminated air alone at Schlema-Alberoda (Saxony, Germany) in 1993, with average radon concentrations of 96,000 Bq/m³. While lowering the doses for the miners, these ventilation efforts increase the levels for residents living near the ventilation shafts. These high levels continue after the shutdown of the mines, as long as they are still ventilated during decommissioning works and not yet flooded. In April 1992, the radon levels for residential areas of the town of Schlema in Saxony were significantly lowered by a change of the ventilation shaft: the contaminated air is now blown into open air at a remote place.

In Bulgaria, a shut-down uranium mine is located immediately neighbouring the village of Eleshnitza. It causes high radon concentrations in free air. It is anticipated that 0.3 to 1 lung cancer incidences annually are caused by the mine in the 2600 residents of the village. [Vapirev1994]

From the shutdown uranium mine of Zirovski Vrh in Slovenia, air containing radon concentrations of 5000 Bq/m³ flows into the surrounding valleys and causes high doses for residents, when air exchange is low due to climatic conditions [Peter1994].

Radon and dust, blown out by the mine's ventilation, do not only cause direct dose loads for the residents by inhalation: an investigation of various food samples grown in the Ronneburg (Thuringia) uranium mining district showed that by the consumption of local food the highest dose by far of 0.33 mSv (33 mrem) per year is caused from wheat grown near a ventilation shaft [Schmidt1994].

Large amounts of groundwater are pumped out of the mines, to keep them dry during mining operations. The water is released into rivers, creeks and lakes. In the sediments of rivers in the Ronneburg area, concentrations of radium and uranium around 3000 Bq/kg were found, indicating up to 100-fold increases over natural background [Hanisch1994].

In the Czech Republic, a continued contamination of the sediments of the Ploucnice river was caused from the insufficient water treatment of the Hamr I uranium mine water releases before 1989. The river sediments and flooding areas are contaminated over a length of approximately 30 km [Andel1993]. The doses received from gamma radiation, reach peak levels of 3.1 Gy/h; that is 30 times background levels.

In the Lergue river in France, the waste waters of the Le Bosc uranium mining complex (Hérault) have caused concentrations of radium-226 in sediments of 13,000 Bq/kg; that corresponds to the concentrations found in uranium ores [Descamps1988]. From the reference it cannot be concluded whether these levels are caused by the mines themselves, by the uranium mill, or by the uranium mill tailings deposits.

In the old mining areas in the Ore Mountains, the problems resulting from uranium mining are commingled with those resulting from historic mining - mining haven taken place in the medieval age. In Schneeberg for example, extremely high concentrations of radon are found in homes: in living rooms, 20,000 Bq/m³ are not uncommon, while up to 100,000 Bq/m³ are found in basements [Keller1991]. These levels are, in part, caused by the direct access to former underground mine workings existing in the basements of many houses, or by other radon pathways from the mines to the basements. Since there is no scientific consensus on the lung cancer risk from such elevated radon levels in homes, a number of epidemiologic studies are being performed worldwide on this subject at present. First preliminary investigations in the East German uranium mining province show elevated lung cancer incidences with men in several towns; they are attributed to occupational exposure in the uranium industry. But, in Schlema and Schneeberg, elevated incidence rates of lung cancer were also found with women [Heinemann1992]. Therefore, a detailed investigation is now being undertaken on the lung cancer risk in homes in Thuringia and Saxony [Heinrich1992].

In the Dresden-Freital area, hard coal containing uranium was mined for fuel use from 1542. From 1952-1955 and 1967-1989, the same coal was mined by Wismut for uranium. Consequently, there is also a problem of both wastes from uranium mining, and from historic mining in this area, especially from the coal ashes.

Waste rock is produced in open pit mines when removing the overburden, and in underground mines when driving galleries through non-ore zones. Piles of so-called waste rock often contain elevated concentrations of radionuclides compared to normal rock. Other piles contain low grade ores, with grades too low for processing in a mill. The transition between waste rock, low grade ore, and ore is fluent and depends on the technological and economic constraints.

All these piles present hazards to residents and the environment, even after the shutdown of the mines, due to their release of radon gas into the air, and to their release of toxic and radioactive contaminants by seepage into groundwater.

The waste rock piles of the uranium mines in the Schlema/Aue area contain a volume of 47 million m³ and cover an area of 343 hectares. The waste rock often was dumped on the valley's slopes. In many instances, they are located in the immmediate neighbourhood of residential areas. Consequently, high radon concentrations in free air around 100 Bq/m³ are found in large areas of Schlema, in some quarters even above 300 Bq/m³. The independent Ecology Institute has calculated a lifetime excess lung cancer risk of 20 cases (and 60 cases respectively) per 1000 inhabitants from these concentrations [Küppers1994]. This is the extra risk caused from radiation, in addition to the risk caused from natural background or other sources. Moreover, much higher peak concentrations of radon may result from climatic inversion conditions in the narrow valleys.

For the southern parts of the town of Ronneburg, the Ecology Institute calculated a lifetime excess lung cancer risk of 15 cases per 1000 inhabitants. Since radon spreads rapidly with the wind, the risk must also be considered for the residents in the wider surroundings: the Ecology Institute calculated an excess lung cancer incidence of 6 cases per year within a radius of 400 km. [Küppers1994]

Seepage is another problem presented by the waste rock piles; in some cases, even creeks were simply buried under the piles. The seepage releases of the waste rock piles in the Schlema/Aue area are estimated at 2 million m³ per year, half of which flows into groundwater. Only a small fraction of the other half is captured at the foot of the piles.

So-called waste rock was often processed into gravel or cement for use in road and railroad construction. The Saxonian Hartsteinwerke Oelsnitz alone, for example, have processed 7.58 million tonnes at uranium concentrations of up to 100 g per tonne. Baukombinat Zwickau used 14.4 million tonnes of material from the waste rock pile of the Crossen uranium mill for road construction, at uranium concentrations of up to 150 g per tonne and radium concentrations of up to 1.3 Bq/g [BT1992a]. The radioactivity thereby was dispersed over large areas. For some part of the material, a follow-up of the use is not possible.

In Czechoslovakia, material at uranium concentrations up to 200 g per tonne, and radium concentrations of up to 2.22 Bq/g, was approved for road construction until 1991 [Andel1994].

In some instances, low grade ores are processed in the heap leaching technology; it is used if the grade is too low for a cost-effective treatment in an uranium mill. The leaching liquid (often sulfuric acid) is pumped to the top of the piles, from where it percolates through the ore and reaches a liner installed under the pile. From there, the uranium bearing liquid is captured and conducted to a processing plant. At the site of Le Cellier (Lozère, France), the leaching process was accelerated, and the uranium recovery was enhanced, by injection of the leaching liquid directly into the piles.

Heap leaching of low grade ores was performed on a large scale at Wismut's Gessental-pile at Ronneburg (7 million tonnes) and in Königstein (2 million tonnes); and at the Hungarian site of Pécs (2-3 million tonnes); and also on a small scale also in Mähring in Bavaria (15,000 tonnes), among others.

During operation, these heap-leaching piles present hazards due to the release of dust, radon gas and, possibly, leaching liquid seepage. After termination of the operation, a permanent hazard may persist due to natural leaching processes taking place, if the material piled up contains the mineral of pyrite (FeS₂): Then, precipitation together with inflow of air can cause the continuous formation of sulfuric acid within the pile, leading to a permanent leaching of uranium and other contaminants, presenting a groundwater hazard for centuries.

In the case of in-situ leaching, the uranium-bearing ore is not removed from its geological deposit, but a leaching liquid is injected through wells into the ore deposit, and the uranium bearing liquid is pumped from other wells. The leaching liquid contains the leaching agent ammonium carbonate for example or - particularly in Europe - sulfuric acid. This method can only be applied if the uranium deposit is located in porous rock, confined in impermeable rock layers.

In-situ leaching gains importance with decreasing uranium prices. For economic reasons, it is the only technology used in the United States today (for example), the country with the highest cumulative uranium production so far. In Saxony, an underground mine converted to an in-situ leaching facility was in operation at Königstein near Dresden until end 1990. On a small scale, in-situ leaching was also used in the Ronneburg (Thuringia) uranium province. In the Czech Republic, in-situ leaching was used on a large scale at Stráz pod Ralskem in North Bohemia. In Bulgaria, in-situ leaching was in use at 8 locations.

The advantages of this technology are:

• the reduced hazards for the employees from accidents and radiation,
• the low cost;
• no need for large uranium mill tailings deposits.

The disadvantages of the in-situ leaching technology are:

• the risk of spreading of leaching liquid outside of the uranium deposit, involving subsequent groundwater contamination,
• the unpredictable impact of the leaching liquid on the rock of the deposit,
• the production of certain amounts of waste slurries and waste water during recovery of the uranium from the liquid,
• the impossibility of restoring natural groundwater conditions after completion of the leaching operations.

In the case of Königstein, a total of 100,000 tonnes of sulfuric acid was injected with the leaching liquid into the ore deposit. At present, 1.9 million m³ of leaching liquid are still locked in the pores of the rock leached so far; a further 0.85 million m³ are circulating between the leaching zone and the recovery plant. The liquid contains high contaminant concentrations, for example, expressed as multiples of the drinking water standards: cadmium 400x, arsenic 280x, nickel 130x, uranium 83x, etc. This liquid presents a hazard to an aquifer that is of importance for the drinking water supply of the region.

Groundwater impact is much larger at the North Bohemian in-situ leaching site of Stráz pod Ralskem: 28.7 million m³ of contaminated liquid is contained in the leaching zone, covering an area of 5.74 km2. This zone contains a total of 1.5 million tonnes of sulphate, 37,500 tonnes of ammonium, and others. In addition to the chemicals needed for the leaching operation (including 3.7 million tonnes of sulfuric acid, among others), 100,000 tonnes of ammonium were injected; they were a waste product resulting from the recovery of uranium from the leaching liquid. Moreover, the contaminated liquid has spread out beyond the leaching zone horizontally and vertically, thus contaminating another area of 28 km2 and a further 235 million m³ of groundwater. To the southwest, the groundwater contamination has already reached the second zone of groundwater protection of the potable water supply of the town of Mimon. In southeastern direction, the contaminated groundwater is still at a distance of 1.2 - 1.5 km from the second zone of groundwater protection of the Dolánky potable water wells, which supply 200 l/s for the city of Liberec [Andel1993]. The migration of the contaminated liquids in a easterly direction towards the Hamr I underground mine is at present intercepted by a hydraulic barrier: decontaminated water is injected into a chain of wells to prevent further migration of the contaminated groundwater.

In Bulgaria, a total of 2.5 million tonnes of sulfuric acid was injected into the ore deposits treated by in-situ leaching [Vapirev1994]. Some in-situ leaching facilities (for example Okop-Tenebo) are located close to drinking water wells. It seems that the environmental impacts of in-situ leaching of uranium have not drawn much attention so far in Bulgaria.

The uranium ore produced in open pit and underground mines is processed in uranium mills to recover the uranium. These mills are, in most cases, built near the mines and comprise a mechanical and a chemical treatment. In the first step, the ore is crushed and ground, then it is leached in a hydrometallurgical process. In most cases, sulfuric acid is used as a leaching agent, but carbonate (alkaline) leaching is also used. Since the leaching agent leaches not only uranium from the ore, but also other constituents such as molybdenum, vanadium, selenium, iron, lead, and arsenic, the uranium has to be recovered from the liquid by ion exchange. The final product of the milling process is Yellow Cake, a compound containing uranium in the form of U³O8 and impurities. This final product is packed in casks and shipped to the customers for further processing.

During operation, uranium mills present a hazard, in particular due to the release of radioactive dusts.

During the decommissioning of uranium mills, large amounts of radioactively contaminated metal scrap have to be dealt with and must be disposed of safely. In the case of the decommissioning of the Crossen uranium mill, Wismut plans to dump large amounts of metal scrap in the Helmsdorf uranium mill tailings deposit, to save cost. But, due to chemical reactions taking place between tailings and scrap, gases develop and may deteriorate the safe long-term disposal of the tailings. A further 20,000 tonnes of metal scrap, at a surface contamination of less than 0.5 Bq/cm², are to be smelted like normal scrap and are to be recycled.

The residues of the milling process, the uranium mill tailings, have the form of a slurry. They are usually pumped to settling ponds for final disposal.

An exception is the Bukhovo mill in Bulgaria, where the slurries were simply dumped in a glen between 1947 and 1958; the finer particles flew into a nearby river. During heavy precipitation, the dumped material was spread over a wider area, contaminating an agricultural area of 120 hectares. Gamma dose rates of up to 1000 µR/h were monitored; this is about hundredfold times the background value. After 1958, the most severely contaminated areas were fenced. But the fences deteriorated later, and the areas were in part reused for agriculture. Radium concentrations of up to 1077 Bq/kg were found in cereals grown on these areas. [Vapirev1994], [Dimtchev1991]

According to the calculating rules prescribed by the radiation protection regulations effective in the Western part of Germany, consumption of these cereals would result in an annual dose of 74 mSv (7400 mrem), while the admissible dose in the German uranium mining area is 1 mSv (100 mrem).

Settling ponds for uranium mill tailings are either installed in existing depressions, or, dams are built for that particular purpose. In France, the tailings are often dumped in former open pit uranium mines.

The largest such settling ponds in Europe are the Culmitzsch tailings dam near Seelingstädt (Thuringia), containing 90 million tonnes of solids, and the Helmsdorf tailings dam in Oberrothenbach near Zwickau (Saxony), containing 50 million tonnes of solids. The Culmitzsch dam was erected on the site of a mined-out open pit uranium mine, the capacity of which was enlarged by additional dams. The Helmsdorf dam was erected as a barrier on the place of the village by the same name, which was completely destroyed for the dam. In the Western part of Germany, there exists only one small tailings dam with a content of 170,000 tonnes, at the Ellweiler uranium mill.