Stephan R. Halaszovich, Josef Wolf
Forschungszentrum Juelich GmbH
52425 Juelich 

TIA-DE is the Decontamination Division of the Operation Management Technical Infrastructure and Site Planning at Research Center Juelich. It is in charge of the centers waste management activities including radioactive waste treatment and interim storage. 

Besides routine services the activities of the decontamination division in the past few years have been focused on facility upgrading to meet current technical standards in radiation protection and on the adaptation of advanced chemical engineering to site-specific conditions in order to reduce final waste volume. Since underground final disposal sites as well as those near the surface are becoming more and more expensive, the reduction of final waste volume has become an important tool for the reduction of waste management costs. 

As a result of the latest amendment of the German Radiation Protection Ordinance a number of licenses have expired. The Research Center Juelich applied for new licenses and initiated an extensive upgrading of the waste treatment facilities. On this occasion waste conditioning processes and equipment were modified in order to achieve the above mentioned objectives. 

Acceptance criteria developed for German final disposal sites include a detailed declaration form concerning more than sixty radionuclides. Therefore the design of the new process lines considers sampling and other methods suitable for nuclide detection. 

Almost all kinds of radioactive waste materials, i.e. non-burnable solids, burnable solids and liquids, waste water, end up in dry, thermally stable supercompacted products. The previously applied cementation will only be used exceptionally in special cases. About 80 % of the final waste volume and consequently of the transportation and disposal costs can be cut by this means. 

The paper will give an overview of the different waste treatment lines and how they link together. It will show the cost savings in more detail. The new waste water treatment technique will be described in particular underlining its main characteristics: 

• tank storage site
• circulating evaporator for large batches of low-concentrated waste water
• preparation vessel for small batches of evaporator concentrates, precipitates, sludges and inhomogeneous dry concentrates
• sampling and radionuclide declaration
• two-stage fluidized bed drier to convert sludges etc. into thermally stable dry products to be supercompacted. 

In the TIA-DE decontamination division there are three main process lines for treatment of radioactive materials and conditioning of radioactive waste: 

• dismantling and decontamination
• incineration of low-level radioactive solid and liquid waste
• evaporation and drying of low-level radioactive waste water and sludges 

Figure 1 shows how the different process lines are linked together and their throughput per year working one shift per day.

Due to the amendment of the Radiation Protection Ordinance and to more stringent standards related to air pollution control almost the entire equipment for waste treatment had to be reconstructed. On this occasion, the equipment was adjusted to new parameters such as the changes in waste generation, current acceptance criteria for final disposal and strict control on waste management. As part of this adjustment the new REBEKA facility was constructed for the treatment of large components and for waste conditioning. 

Except for a very few special cases, like cementation of small amounts of intermediate-level liquid waste or smelting of radioactive scrap metal, all waste treatment operations end with supercompaction, achieving the smallest possible final waste volume. Eliminating cementation, which was previously the usual waste solidification process, the final waste volume will be reduced to 20 % of the cement product. 

In view of increasing disposal costs, the reduction of waste volume is indispensable. In Germany all categories of radioactive wastes have to be disposed of in deep underground disposal sites. The customers are charged with all costs related to the construction,operation and safe closure of the disposal sites. The waste producers share an advance every year related to the total waste volume each of them is expected to accumulate until the year 2080. Upon delivery a disposal fee per cubic meter of waste package volume has to be paid. 

In the case of the ERAM site, located at Morsleben, which is in operation for non-heat-generating waste, the disposal fee is 12,500 DM/m. The site will be shut down on June 30, 2000 if the license cannot be extended. 

The Konrad site for non-heat-generating waste is expected to start operation in 2003. The disposal fee currently calculated is 25,000 DM/m. In contrast to ERAM the Konrad site requires containers in the form of final waste packages instead of drums. Placing drums into a container increases the volume by about 66 %. 

No disposal fee has yet been announced for the Gorleben site, which is due to start up in 2012. This site is designed for all waste categories both non heat generating and heat-generating. 

The amount of waste to be incorporated in cement is limited for reasons of product chemistry. Therefore only about 60 kg of dry waste, i.e. salts or ashes, can be mixed into 200 liters of cement product, but up to 360 kg of supercompacted dry waste fits into the same volume. Drying 74 tons of concentrates and sludges per year produces about 24 tons of dry waste. Supercompaction of this amount saves about DM 2.8 million per year calculated according to the Konrad figures in terms of disposal fees.  

The main design objectives of the aqueous liquid waste treatment facility are

• versatility of tank storage
• treatability of waste water and sludges with the solid content ranging between 0.4 % and 40 %
• homogeneity of the product
• constancy of product composition throughout processing
• representative sampling
• dry thermally stable compactable final product.

The waste water store includes 17 tanks with 825 m total volume to buffer waste water concentrates and sludges before evaporation or drying. All the tanks except one have a volume of 50 m but most of them are divided into two 25 m chambers. They are interconnected with a network of pipes allowing a versatile transfer of liquids but prevents contamination of lower level zones with liquids from higher level ones. 

The liquid waste is treated first in the evaporator. It is possible to feed it directly into the feed vessel of the drier bypassing the evaporator. Figure 2 shows the basic flow sheet of evaporation.

Fig. 2. Principle Flow Sheet of Evaporation 

Waste waters from different laboratories, usually delivered in small portions, often contain significant amounts of mercury. In these cases mercury will be precipitated prior to evaporation. 2.4.6-Trimercaptotriazine (C₃N₃S₃Na₃) dissolved in water is used as a precipitant added to the pH 8 waste water. An additional flocculating agent enhances precipitation. 

The feed is held in two parallel feed vessels. While being pumped into the evaporator, nitric acid is added to adjust the pH to 3 - 4. After evaporation has been completed sodium hydroxide will be added to the evaporator in order to neutralize the concentrate. Five tons of water are evaporated per hour until the solid content in the batch amounts to a maximum of 40 %. The distillate is pumped back into a clean vessel in the waste water store. It can be recycled into the evaporator for further decontamination if necessary. The concentrated batch is released into a buffer vessel. 

All kinds of radioactive concentrates, precipitates and sludges, for example also radioactive sludges from the ponds of the sewage treatment plant, will be dried and heat-treated in the two-stage drier as shown in figure 3.

In the 6 m supply vessel of the drier the feed will be homogenized by circulation and stirring to maintain homogeneity and constancy of product composition. 

Samples are taken out of the supply vessel in order to obtain radiological data such as easily detectable main radionuclides and the scaling factor necessary for the calculation of the undetected radionuclides. These data are used for quality assurance and for the extensive declaration of radionuclides contained in the final waste package as required by the German Bundesamt für Strahlenschutz (Federal Office for Radiation Protection). This declaration is part of the waste package documentation submitted for approval prior to waste shipment to the final disposal site.  

The homogenized feed enters the fluidized bed drier where 0.08 m per hour is evaporated. Heated air with its oxygen content reduced to 4 % is both the fluidizing and heating medium. The dry granules produced in this stage will be heated to 350°C in the subsequent pipe-type fluidized bed heater. At this temperature residual organics and nitrates in the granules will react and be converted into the thermally stable final product. The final product passes through a cooler into the collecting vessel. 

Unlike cemented dry concentrates, noncemented ones are thermodynamically unstable. Laboratory experiments have shown that a self-sustaining exothermal reaction starts as the product's temperature exceeds about 200°C. 

Differential thermal analysis of non-heat-treated and heat-treated products underlined the experimental results. 

Thermal stability of the product is essential to supercompaction because frictional heat could ignite a thermally non-stable product. It is further important because acceptance criteria for final disposal include the demand for the final product to resist 300°C. Consequently non-stable products have to be insulated against heat, for example by concrete so that the size and weight of the waste package are increased. Production of stable products avoid-additional costs for vessel fabrication transport and final disposal fees.

BACK