M. DIMITROV
Nuclear Power Plant at Kozloduy, Kozloduy E.I. VAPIKEV, L. MINEV, T. BOSHKOVA Faculty of Physics, Sofia University, Sofia Bulgaria
Abstract
The paper presents a summary of the environmental restoration process in Bulgaria before the termination of the uranium industry (August 1992) when some sites due to depletion had been closed and also the restoration procedure which are currently applied. The methods for
rehabilitation depend on the type of site and therefore the uranium mines, the milling plants and the auxiliary units are discussed separately. At present all sites have been ecologically assessed and for most of them the restoration technologies are selected. Part of the land is restored and returned to its owners. For the in-situ leaching sites long term monitoring of underground water is necessary. The restoration activities must be synchronized since residual ore has to be processed and waste has to be dumped in tailing ponds and underground mines.
It has been pointed out that there is a need for cheap and proven technologies since the closed uranium industry has to provide the funding for the restoration process and there are
difficulties due to the general reduction of industrial production in the country.
1.Introduction - review of the uranium industry in Bulgaria [1,2]
The uranium industry in Bulgaria started immediately after the II World War with classical underground mining and hydrometalurgical processing of the ore to uranium concentrate. The total amount of uranium concentrate produced in the period 1947-1992 is approximately 35000 t or 800 t/annually in the last years before the closure of the uranium industry.
Approximately 34 uranium mining sites exist which include 4 open pit mines, under-ground mines and in situ-leaching mines (after 1968-69).
The total amount of tailing pond wastes of the two milling plants in Buhovo and Eleshnitsa (3 tailings) is 16 000 000 t and approximately 3.1 PBq of stored activity.
The total number of the waste heaps is 298 with approximately 13 720 000 t of dumped mass which covers approximately 845 000 square meters.
Up to 1958 no tailings pond existed at the Buhovo plant and the result is 1 200 000 square meters contaminated with radium land along the rivers Yanishtitsa and Lesnovska.
Along the valleys of the rivers Maritsa, Tundzha and Struma approximately 15 low grade ore deposits were processed by in-situ leaching with sulfuric acid. The surface communications (tubes) cover approximately 16 000 000 m2 agricultural land and for-ests. Some of the heaps of the underground mines have been processed by combined in-situ leaching technologies.
The total contaminated area affected by the uranium industry is approximately 20 000 000 m2, including 4 000 000 m2 forest.
At present the uranium industry is terminated by a government decision and the necessary funding for restoration of the former uranium sites is expected to be raised by selling of equipment.
2.Technologies and procedures for environmental restoration applied before the termina-tion of the uranium industry.
A number of uranium sites were closed before the decision for total termination of the ura-nium industry (see Table 1 in [1] ). Many mines have been closed in the Buhovo region, mines near the towns of Sliven and Melnik, near the Haskovo mineral baths, above the Rila monastery. In-situ leaching sites have been also closed - near the village of Prepechene and Zlatolist in South-West Bulgaria (along the Struma river), some sites of the mine "Pioneer"
near the village of Orlov dol and also sites in the Upper Tracian Plane.
A common feature for all sites is that no environment remediation actions followed after the technical closure. In some cases the monitoring had also been terminated. The environmental monitoring was resumed within the procedures for radioecological assessment and decision taking for site remediation.
The only procedure which has been in implementation is the closure of the entrances of shafts and adits but long afterwards poorly closed exits used to emerge as caving or downfalls occurred.
There are still abandoned trolleys, broken equipment, repair shops, administrative buildings.
Only some reloading sites being close to railroad stations have been cleaned-up.
The operation of the first tailing pond of the Buhovo plant has been terminated long before the closure of the uranium industry but no actions followed - no fence was built and it often served as pasture ground for cattle. The migration of water due to tailing seepage is con-trolled by regular sampling of water in control shafts down the tailing pond. Control of the water is necessary since no tailing impoundment (liners, cover layers) had been implemented when the pond was built.
No water treatment facility has been built after the closure of any site, no actions were taken against wind and sheet and rill erosion of the waste heaps. Only some sorption facilities for excess water have been used during the operation of several mines in order to extract the uranium from water which otherwise will be lost ("Deveti septemvri", "Druzhba", "Dospat" ).
In the period 1985-1990 remediation procedures were applied for closed sites of the mine
"Pioneer" according to a method developed in the Institute of Soil "N.Pushkarov" (Sofia).
The method is intended for a period of approximately 5 y and includes radioecological survey, cleaning-up, neutralization, intensive natural fertilization.
Before the termination of the uranium industry a project was started for restriction of the propagation of the contaminated underground water of sites "Okop" and "Tenevo" (mine
"Pioneer") and site "Cheshmata" (Mine "Parvi mai"). The project has been developed in the former USSR and included pumping of chemical agents - e.g. sodium silicate solution (soluble glass) around a leaching site in order to "seal" the underground contaminated water.
The project was not realized , only some preliminary experimental observations can be used for further estimation for the migration velocity of contaminated water.
S.Technologies for environmental restoration applied after the total termination of the urani-um industry.
At present all uranium industry sites are radioecologically assessed and most of summary information was reported in the previous meetings [1,2].
Most of the restoration work has been carried out for the sites of in-situ leaching. Data on rented areas, remediated areas up to 1 of January 1992 and projected areas for remediation after January 1992 are summarized in Table 1.
During the operation of sites of in-situ leaching the humus layer had not been removed along the piping and the boreholes and therefore detailed radiometric mapping and sampling for chemical analysis is necessary. Only the forest lands of the in-situ leaching sites (approxi-mately 25%) cannot be restored and it is useless to restore them.
According to us the most serious hazard comes from the chemical contamination of subsur-face layers and contamination of water. The most dangerous sites are "Cheshmata"
(Haskovo) and "Tenevo-Okop" (Topolovgrad) near which there are catchment facilities for drinking water. In all hydroecological assessments passive systems for monitoring of the underground migration of contaminated water are suggested hoping that the hydrobarriers Table 1
Rented land, remediated land and returned to the owners land up to 1 of January 1992 and projected land for remediation after January 1992, square meters.
SITE
will seal the water layer and consequently the contaminated water will be desalted. We are also afraid that the calculated rates of migration are optimistic although we understand that construction of adequate purification facilities for enormous water volumes is very expensive and there are no sound arguments that they are absolutely necessary.
Data on quantity of uranium and specific activity of radium in water from different mines (Table 2) show that uranium is below the accepted limit for surface water (0.6 mg/1) but the activity of Ra is generally above the limit (0.15 Bq/1). Continuous observations show that sev-eral years after the termination of mining there is a trend for water purification and Ra re-duction since Ra is transported by the mechanical particles.
At the present moment (end of 1994) two projects are being financially supported within the PHARE programme - restoration of the tailing pond region of Eleshnitsa and restoration of the Bay of Vromos radioactively contaminated by dumping of slurry of copper mines [1]. The projects are in very initial stages and neither the methods nor the organization which will per-form the restoration have been selected.
Table 2
Content of uranium, mg/1, and specific activity of radium, Bq/1, in uranium mine waste water mine N*
A small experimental facility for bacterial sulfate reduction for the excess water from the tail-ing pond in Buhovo is now in the process of construction [3]. The bacterial removal of sul-fates from the washwater results also in simultaneous precipitation of heavy metals.
There are also other propositions but a major obstacle is the lack of financing.
Another major obstacle for accurate assessment of the impact of radioactive contamination is the lack of national levels for natural radionuclides in soil, plants and animal products. Only lately such a project is under development - development of levels and criteria for protec-tion of the populaprotec-tion which live in regions with increased natural radioactivity.
4.Technologies for environmental restoration of uranium mining and milling sites
The methods for rehabilitation depend on the type of site and therefore the uranium mines, the milling plants and the auxiliary objects will be discussed separately. All methods which are implemented or are intended to be implemented are "classical" and described in earlier publications [4,5]
The restoration activities must be synchronized since:
all existing ore and ion-exchange resins have to be processed in the milling plants;
radioactive waste has to be dumped in tailing ponds;
part of the mined rock and equipment can be dumped in underground mines before seal-ing.
4.1. Uranium mines - -underground mines, open pit mines, in-situ leaching sites.
4.1.1. Underground mines.
The methods for restoration include:
closure of adits, shafts, ventilation shafts;
transportation of mined ore (if any) to the chemical plants;
water precipitation or purification,;
heap stabilization , leveling and afforestation., or leveling , isolation and afforestation.
In the case of heap leaching , a neutralization is necessary;
ban on house building on the heaps, prevention on the use of rock material for use in buildings, especially for houses for living, possible use as rock for roads.
There are different alternatives for heap stabilization. For the isolation technologies because of the large total area (845 000 m2) the experts are looking for cheaper covering material which has been experimentally verified.
4.1.2. Open-pit mines.
The methods for restoration include:
site leveling, filling when possible;
treating of the water collected in the region - precipitation or purification;
ban on house building,
use of the pit, if possible, for lake for recreation activities.
4.1.3.In-situ leaching sites
The main method for leaching in Bulgaria is the acid method, the soda methods had been applied only in experiments. For the in-situ leaching additional reagents have been used for intensification of the process - iron sulfide, potassium permanganate, sodium nitrite. Some metals - Mo, Cu, Zn, Ni, W, Cr, Fe, Al, V, and also rare earths - La, Ce, Yb, are also present in the solutions.
The methods for restoration include mechanical and biological technologies:
removal of radioactive wastes of contaminated earth;
deep sealing of boreholes in order to prevent direct water contact;
neutralization of the contaminated with acid or soda areas (liming);
leveling and intensive fertilization with natural fertilizer;
"green" fertilization - ploughing of lucerne etc. before ripening;
crop rotation, e.g. corn-rye-sunflower-rye etc.;
drying or irrigation;
grass, or planting fruit trees;
The methods for water restoration include:
recycling of the solution for increasing the pH;
neutralization of the water in the layer or on the surface;
salt purification;
generation of hydrochemical barriers;
control of the eventual spread of contamination;
ban on hole drilling for irrigation or drinking water.
4.2.Uraniwn milling plants.
The milling plants process ore and the ion exchange resins from the in-situ leaching sites.
The wastes - slurry and water are deposited in the tailing ponds. The rehabilitation pro-cedures concern the plant site and the tailing pond. For the specific case of the Buhovo
plant, the Yana-Bogrov region needs remediation and counter-measures because of the con-tamination of large areas with Ra [1].
The methods for restoration of the plant site include:
cleaning-up of the radioactive wastes and dumping the wastes in the tailing pond;
deactivation of the plant premises;
disassembling of filters, mills, transport belts etc.;
The methods for restoration of the tailing pond include:
strengthening of the tailing dam wall;
routing of the clean water away from the tailing pond;
covering the pond with a layer for prevention of radon exhalation - clay, asphalt, poly-mers;
covering the isolation layer with soil;
planting of grass or trees;
management of the tailing seepage of surface or underground water - neutralization (if necessary), purification for sulfates, heavy metals, radium;
creation of a system for long term monitoring.
The methods for restoration of the radium contaminated areas of the Yana, Gorni Bogrov, Dolni Bogrov region [1 ] include:
removal of the most radioactive spots;
afforestation of the contaminated areas;
covering with soil of tailing pond wastes;
control of utilization of the low contaminated areas.
4.3. Auxiliary sites - warehouses for ore and chemicals, repair shops, transport units, re-search laboratories, drill core samples store.
The remediation measures are site-specific but the most common procedures are:
clean-up of the sites of radioactive wastes;
transportation of highly radioactive ores, solutions, resins, drill cores etc. to tailings ponds;
disassembly of contaminated facilities;
deactivation of buildings;
excavation and transportation of sludge from purification facilities to tailing ponds or underground mines;
planting of grass or trees;
5. The case of the Bay of Vromos - coastal radioactive contamination from copper floatation plant
The case of the Bay of Vromos has been described in [1]. During the period 1954-1977 the waste from a flotation plant which concentrates the ore from a copper mine has been dumped in the sea near the coast. The total waste is estimated to be approximately 8 000 000 t. On the coast the waste is 1300 m long, 120 m wide and the thickness of the layer is 2 - 3 m. The increased exposure rate is associated with increased content of U-238 (by a factor of 10 - 300 the natural concentrations) and Ra-226 ( 5 - 200 ). The measured exposure rates are shown in Table 3.
In 1991 a project started (partially supported by the PHARE programme) for recycling the dumped mass since preliminary experiments showed it will be economically profitable. The sand mass is recycled in the copper plant and the results is a copper concentrate (13-15%), iron concentrate (55%), gold (4-5 g/t). The waste varies within 70-85% from the initial mass
Table 3
Exposure rate and associated area in the Bay of Vromos exposure rate,
/jSv/h area,m^
max 2 200
>1 7000
>0.3 208000
[6], The preliminary experiments confirmed the assumption that natural processes have "en-riched" the dumped mass.
The mass which is expected to be reprocessed is 216 000 t, from which —700 t copper and — 32 000 t iron will be obtained.
The sand is transported to the copper concentration plant by trucks, the sand from the sea (10-20 m) will be dragged by chain-drag.
The measured values of the exposure rate shows that already from the places where the dump has been reprocessed the background is reduced twice.
6. Conclusion
The procedures for environment restoration of the uranium industry sites have been started.
The first steps are radioecological and hydroecological assessment. Some of the sites are hi the process of restoration but for the further actions there is not enough funding - the uranium industry after its termination with a government prescription is expected to supply the neces-sary financing. Due to the general reduction of industrial production, classical mining is also in a difficult position and therefore there is no buyer for the equipment from uranium mining industry.
International projects can help the restoration process especially by exchange of knowledge on experimentally verified cheap restoration procedures.
REFERENCES
[l]Vapirev, E.I., Dimitrov, M., Minev, L., Boshkova, T., Pressyanov, D., Guelev, M., Radioactively Contaminated Sites in Bulgaria, Proc. of Workshop, IAEA Regional Project for Central and Eastern Europe on Environmental Restoration, Budapest, Hungary, 4-8 October
1993.
[2] Dimitrov, M., Vapirev E.I., Uranium Industry in Bulgaria and Environment: Problems and Specific Features of the Period of the Technical Close-out and Remediation of the Nega-tive Consequences, Proc. of Workshop, IAEA Regional Project for Central and Eastern Eu-rope on Environmental Restoration, Piestany, Slovak Republik, 11-15 April 1994.
[3] Somlev, V., Tishkov S., Anaerobic Corrosion and Bacterial Sulfate Reduction: Application for Purification of Industrial Wastewater, Geomicrobiology J., V.12, (1994) 53-60.
[4] Management of Wastes of Uranium Mining and Milling, Proc. of a Symposium Jointly Organized by IAEA and NBA (OECD), Albuquerque, USA, 10-14 May 1982.
[5] Current Practices for the management and Confinement of Uranium Mill Tailings, Techn.Rep.Ser. No.335, IAEA, Vienna 1992.
[6] Bonev, I.,, Tomov, G., Conkov,T.,Kostov K., Estimation of the of the status (15.09.93) and project for cleaning-up of the coastal line of the Bay of Vromos from radioactive floata-tion waste, 1993, (in Bulgarian).
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