RECOLECCIÔN DE DATOS PRESENTACI6N DEL INSTRUMENTO.

91

MANAGEMENT OF RADIOACTIVE RESIDUES AND WASTE

92

TABLE 1. CONTAMINATED MATERIAL GENERATED AND ITS RADIOLOGICAL CHARACTERISTICS

Accumulated amount Radiological characteristics Seepage and pore water to be

treated

17.4 million m³ (annual volume for 2015)

– U_nat: 2–50 mg/L – Ra-226: 1–5 Bq/L Water treatment residues Uranium: 40 t (800 t in 1991)

Precipitates: ~30,000 t, (500 000 t in 1991)

– U-238: 10–100 Bq/g – Ra-226: 1–20 Bq/L Scrap from demolition and

dismantling

260 000 t (cumulative total at end of cleanup)

Total alpha surface activity:

0.01–50 Bq/cm² Debris from demolition and

dismantling

865 000 t (cumulative total at end of cleanup)

– U-238: 0.2–10 Bq/g – Ra-226: 0.2–10 Bq/g Excavated soil from area and

waste rock pile remediation

14.5 million t (cumulative total at end of clean-up)

– U-238: 0.2–10 Bq/g – Ra-226: 0.2–10 Bq/g 2. METHODS

Handling of the contaminated material has to be performed in compliance with the provisions contained in mining and radiation protection legislation and soil protection and water legislation of the Federal Republic of Germany. Furthermore, the German law on closed cycle management — the core of German waste management regulations — has to be observed. This law stipulates that residues and waste have to be recycled whenever possible. Such requirement is in accordance with IAEA standards and recommendations on the management of NORM.

The principal methods for the management of solid radioactive residues and waste are:

– Use as a by-product;

– Recycling, followed by use as a by-product;

– Disposal;

– Sale.

Contaminated water has to be collected and treated prior to discharge into receiving water bodies with due regard to regulatory limits on concentrations and loads.

2.1. Contaminated seepage and minewater

Wismut operates water treatment plants at the Schlema, Königstein, Helmsdorf, Pöhla, Ronneburg and Seelingstädt sites with treatment capacities ranging from 50 to 1100 m³/h. With the exception of the Königstein plant, lime precipitation processes tailored to site specific conditions are used to separate the radiologically relevant constituents Unat, ²²⁶Ra, ²³⁰Th, ²¹⁰Pb and ²¹⁰Po. Because of the high uranium levels in the minewater to be treated at the Königstein site, uranium is separated prior to the subsequent lime precipitation. For the separation, an ion exchange process is applied.

2.2. Water treatment residues

Wismut sells the separated uranium from the first process stage of the Königstein water treatment plant at a break even price to a nuclear sector company which assumes responsibility

93 for the transport and sale of the uranium on behalf of Wismut. The weighing and sale of uranium are monitored by Euratom, the competent European authority.

Sludge generated at the various sites by water treatment precipitation processes is treated with respect to its consistency (water content, particle size), chemical composition and hydrochemical and geochemical properties to render it suitable for safe disposal. In addition to the aforementioned properties, the site specific sludge treatment is also determined by technologies and requirements to be met for on-site disposal. For example, sludge at the Schlema–Alberoda site are dewatered (thickener, filter presses) and subsequently embedded within a cement based matrix. The resulting earth-moist cement solidified residue is disposed of in an engineered cell within waste rock pile No. 371 at the Schlema site and capped with a multiple layer cover. Residues are placed between layers of impermeable material and provided with drainage systems. The conceptual design and technical specifications of the engineered cell are in compliance with the requirements for a modern hazardous waste disposal facility.

In addition to residue disposal within waste rock piles, water treatment residues at Wismut are also disposed of in beach zones of tailings facilities, within an engineered cell on top of the reclaimed Lichtenberg open pit mine, as well as in specific disposal facilities for immobilized residues. With regard to their design and safety, these facilities also meet the requirements for hazardous waste disposal facilities. All disposal facilities are monitored for environmental impacts during residue placement and following closure.

2.3. Metallic scrap from demolishing and dismantling of buildings and facilities

According to a recommendation issued by the German Commission on Radiological Protection, scrap with a total alpha surface activity less then 0.05 Bq/cm² may be released for unrestricted use. In cases where a batch of scrap metal exhibits a total alpha surface activity exceeding 0.5 Bq/cm², the scrap may be recycled by melting for use in steelmaking. Scrap metal exhibiting higher levels of contamination has to be safely disposed of. In line with these requirements, Wismut has adopted the following course of action:

(1) Scrap metal classified as uncontaminated for plausibility reasons (e.g. because of its origin) is sold directly to scrap dealers.

(2) Scrap metal classified as moderately contaminated by reason of its origin is scrubbed and to some extent also decontaminated. The decontamination process uses high pressure water jetting and mechanical abrasion in a rotating container filled with small steel balls. After such treatment, the surface activity concentration of the scrap metal is measured prior to release. For that purpose, Wismut applies a screening measurement technique based on beta surface activity and a follow-up calibration of beta data versus alpha surface activity. Screening data are statistically evaluated. A batch of scrap metal may be released when the upper confidence limit of lognormally distributed data is less than 0.5 Bq/cm². Figure 1 illustrates a typical statistical distribution of screening data of total alpha surface activity of a batch of scrap metal. In the case under consideration, the mean of the recorded 223 measuring data is 0.14 Bq/cm². As the upper limit of the confidence interval (95th percentile) is 0.17 Bq/cm² the scrap metal may be recycled for steelmaking.

(3) Scrap metal unfit for release is deposited in engineered disposal cells within waste rock piles or in beach areas of tailings management facilities and subsequently capped.

94

FIG. 1. Statistical distribution of total alpha surface activity of a batch of scrap metal.

2.4 Debris from the demolition of buildings and facilities

In accordance with mining legislation, uncontaminated demolition debris must not be delivered to disposal sites operated by Wismut. It has to be deposited at municipal landfill sites.

Contaminated demolition debris is deposited in engineered disposal cells within waste rock piles or in beach areas of tailings management facilities and subsequently capped. The disposal cells are partly sealed at the bottom by a compacted low permeability soil layer. The purpose of the bottom seal and the overlying cap is to ensure that water infiltration and seepage-borne release of contaminants into the environment are as low as reasonably achievable.

2.5 Surplus excavated soil from the remediation of industrial areas and waste rock piles

Highly contaminated excavated soil is treated similarly to contaminated demolition debris and deposited in engineered disposal cells within waste rock piles or in beach areas of tailings management facilities and subsequently capped. For moderately contaminated excavated soil and surplus excavated materials from waste rock pile remediation, the Wismut Environmental Restoration Project provides two options for use as a by-product:

(a) Placement into interim covers of large scale tailings management facilities for regrading and contouring of the tailings surface to enhance precipitation runoff from the final cover;

(b) Use for refilling of surface subsidence and for the stabilization of slopes and dams.

3. RESULTS

Wismut’s management of radioactive residues and waste originating from remediation work has contributed to the gradual decline in environmental impacts at the sites under remediation. By way of example, the introduction of efficient water treatment processes has diminished annual uranium releases to surface water bodies from 27 t originally to less than 1.9 t at present.

95 Residues and waste that fail to meet the requirements for by-product use or recycling are put into safe long term storage. In accordance with legal provisions, their environmental impacts have to be reduced by technical measures to a reasonably low level.

Release of scrap metal for recycling has not only a positive environmental impact; it is also a success from an economic point of view. In line with the current trend, more than half of the estimated volume of 260 000 t of scrap metal originating from or still being generated by the Wismut Project is anticipated to be released for by-product use, recycling or sale.

4. DISCUSSION AND CONCLUSIONS

Environmentally responsible and economic management of residues and waste generated during the remediation of complex uranium mining and processing legacies poses a challenge to national authorities and operators associated with large scale remedial projects. Development and implementation of technologies have to comply with conditions specific to the site. At the same time, national laws and regulations have also to be observed.

In Germany, operators have to take into consideration the requirement for by-product use or recycling of radioactive material generated during remediation. However, German mining legislation, as well as radiation protection legislation applicable to the Wismut project, imposes restrictions on the by-product use of contaminated material. Material with an activity concentration of the dominant radionuclide (usually ²²⁶Ra) exceeding 0.2 Bq/g is regarded as radioactive. Waste rock, most of which has an activity concentration less than 1 Bq/g must not be used outside the Wismut property, for example as material for road foundation purposes.

This is in contrast to more recent approaches to the management of NORM, as also recommended by the IAEA.

Nevertheless, the Wismut case study provides ample basis for sharing experience on the management of large amounts of radioactive residues and waste. In the meantime, remedial technologies and approaches developed by Wismut are being applied to uranium mining remedial actions at sites outside of Wismut.

96

RADIONUCLIDE BEHAVIOUR IN POTENTIAL