Environmental Risk and Costs/Benefits of the WISMUT Remediation
Authors: Jakubick Alexander T. , Hagen Manfred 
Published: March 2009

The Uranium mining and milling activities in Eastern Germany before reunification produced more than 232 000 t of U. Following reunification, £ 6.6 billion were committed to remediation of the left behind liabilities. The inventory of the liabilities comprises operations areas (37 km2), waste rock dumps (311 M m3), tailings (160 M m3), an open pit (84 M m3) and five large underground mines (1.53 M m3). The specific activities are 0.5 to 1 Bq/g for the waste rock, 10 Bq/g for the tailings, up to 500 Bq/g for the water treatment residues and 0.2 to 1 Bq/g for scrap metal. The remediation of the risk associated with this inventory is carried out by WISMUT GmbH. The legal framework of the remediation is set by the Federal Mining Act, the Atomic Act, the Radiation Protection Ordinance and the Water Resources Management Act. The large number and variety of objects that release contaminants at very different rates require, remedial measures to be planned and optimized in an integral way for each site. The integration is done on the basis of Conceptual Site Models (CSM). The CSM helps to balance among the objects the remedial effort, the allocation of resources and allows to flexibly adapt remedial measures to the site/object-specific conditions while maintaining conceptual consistency and focus on the overall remediation goals without compromising essential details. The remediation necessity of individual objects or areas is investigated, justified and the type of remedial measures selected on the basis of Remedial Investigation/Feasibility Studies (RI/FS). In the RI/FS the calculated individual effective dose to the public caused by the object/area in the nonremediated and remediated state is compared with the reference level of 1 mSv per year. Based on RI/FS contaminated areas are remediated either for unrestricted or for restricted use. Waste rock piles are remediated by covering in situ, by relocation and/or by backfilling into an open pit. Currently, approximately 40,000 tons of waste rock are backfilled into a pit per day. Backfilling follows a geochemically optimized placement procedure. In cases where the remediation object was judged vulnerable, remediation was supported by risk assessment. A probabilistic risk assessment was used to justify the dry remediation of the tailings ponds. Technically, the most challenging part of dry tailings remediation is the stabilization of the soft, under-consolidated slimes having a high excess pore water pressure and very low shear strengths. Because total cleanup and relocation of contaminants are not always feasible, the remediation is commonly done by covering of the contaminated object or area, i.e. by confinement. The covers used are either barrier covers that limit infiltration by having a low permeability layer incorporated or an evaporative cover which maximizes infiltration storage till it is removed by evapotranspiration. The largest sources of contaminant release are the discharges from flooded mines and from dewatering of the tailings ponds. Discharge rates vary from 30 m3/h to 1000 m3/h. Because the contaminants load in the discharging mine water decreases with time causing the conventional water treatment to become uneconomic, various alternative water treatment technologies are tested at WISMUT to identify suitable and cost efficient replacement options. Considerable amounts of contaminated debris and scrap metals arise from decommissioning and demolition of the structures. The aim is to categorize and recycle the uncontaminated portion of the scrap metal. The categorization of the scrap metal into contaminated and uncontaminated is by measuring the beta-count rate in the field. To improve the selectivity of the field monitors, specially prepared standards reflecting the operational history of the metal at the particular site are used to calibrate the instruments. Approximately £ 3.9 billion were invested into the remediation by end of 2002. A rough calculation of the specific costs of WISMUT remediation when using re-assessed total costs turned out to be approximately £ 22.6 per kg of U3O8 produced. Considering that this sum includes the indirect costs, the specific remediation costs appear in an international comparison very reasonable.