Treatment and conditioning of radwaste in nuclear power plants

Processing of radwaste from Slovak plants

   
In March 1994, the government of the Slovak Republic approved the Concepts of the management of radwaste from nuclear power installations and other working places with the sources of ionization radiation. Based on these Concepts, a subsidiary of the utility Slovenské elektrárne (Slovak Electric) Inc. named Decommissioning of Nuclear Power Installations, Management of Radioactive Waste and Spent Fuel (SE, Inc. - VYZ, o.z.) was established on the sites of the Bohunice nuclear power plant and the Mochovce plant on January 1, 1996. The VYZ plant is responsible for the preparation of decommissioning projects for the A-1 Bohunice plant, for the treatment and conditioning of radwaste from nuclear power plants, for long-term storage of conditioned radwaste in the Republic Repository in Mochovce, for the safe storage of spent nuclear fuel and disposal of all sorts of institutional radwaste in Slovakia.  
    

  
Among the important technology facilities operated by the VYZ plant, bitumination facility, vitrification facility, full-scale decontamination facility, high-pressure compaction facility, cementation facility, evaporation facility, incineration facility (the latter four facilities for radwaste conditioning are situated in the Bohunice Radwaste Treatment and Conditioning Center), interim storage facility for spent nuclear fuel in Bohunice, and the Republic Radwaste Repository in Mochovce belong.  

   
In the VYZ plant, a number of methods for the conditioning of radwaste from nuclear power plants are used, such as bitumination, cementation and vitrification. In the bitumination facility, liquid radioactive concentrates are boiled off in a film rotor evaporator and mixed together with asphalt. The resulting mixture is then filled into 200-liter barrels. After filling up, the barrels are closed and transported into the interim radwaste storage. These barrels will be inserted into concrete container, filled with cement paste and transported into the Republic Radwaste Repository in Mochovce for ultimate disposal.    

  
By vitrification, treatment of a special liquid radwaste (chrompik) is carried out at the VYZ plant. Chrompik was used at the A-1 Bohunice plant for the cooling of fuel assemblies. Chrompik is injected from a dosing tank directly into the evaporator of a boiler type and then thickened. Vitrification of the mixture of glass and radioactive concentrate is carried out in medium-frequency inductive furnaces. The vitrified liquid picked up in a metal package (cartridge) is later stored in the interim storage facility of vitrification products. It is transported by means of special transport containers.

   
Currently a trial active operation started of the Bohunice Radwaste Treatment and Conditioning Center on the site of the nuclear power plant. The center will be used for the conditioning of the most of solid and liquid radwaste generated during the A-1 plant decommissioning, and from the operation of the V-1 and V-2 plants. Also institutional waste from various Slovak organizations will be conditioned there.  
    

  
The Bohunice Radwaste Treatment and Conditioning Center includes a sorting facility, an incineration facility of solid and liquid radwaste, a high-pressure press for solid compressible radwaste, a facility for thickening waste, and a cementation facility.   
   
   
   
   
The incineration of solid and liquid radwaste will proceed at the temperature of 1000 °C and the generated gaseous flue gases will be cleaned by scrubbing in water and by filtering at HEPA filters.
The compaction of suitable solid radwaste is carried out prior to its insertion into concrete containers.
    

The volume reduction of liquid radwaste is performed by its thickening at a facility for concentration. After thickening the radwaste will be mixed with cement at the cementation facility. The resulting mass will be filled into fiber reinforced concrete containers or will fill solid radwaste in barrels inserted into fiber reinforced concrete containers.
   

  
The cementation facility is designed to fix concentrates of radioactive ash, used scrubber water from the incineration facility, radioactive slugs and sorbents. It also serves for the production of a cement mixture that is poured into barrels filled by mouldings from the press and by non-combustible liquid radwaste in fiber reinforced concrete containers.

   
Besides the above mentioned facilities, other parts of the Bohunice Radwaste Treatment and Conditioning Center are the sorting facility, transport systems, systems for the supply of operational fluids, equipment for the laboratories of chemical and radiation control, including monitoring systems.   

  
Besides the VYZ facilities in operation, other facilities operated by the Nuclear Power Plant Research Institute Trnava Inc. are located on the Bohunice site. It is the experimental incineration facility, bitumination facility and cementation facility. The incineration facility for low-level active radwaste was designed as an experimental facility. Currently it is in operation and it is expected that following the commissioning of the Bohunice Radwaste Treatment and Conditioning Center, its operation could be terminated and it would be used for research purposes only.
    

The bitumination facility of the VÚJE Trnava was also originally built for the needs to investigate possibilities for bitumination technologies. Its focus was gradually reoriented on the verification and application of the technology of dowtherm bitumination and of simultaneous bitumination of dowtherm and radioactive concentrates.
  

  
On the site of the Mochovce nuclear power plant, technologies for processing of radwaste have been prepared. The basic objective is to ensure the treatment of various forms of mainly liquid radwaste into a form suitable for ultimate disposal in the Republic Radwaste Repository in Mochovce. Selected sorts of solid radwaste will be also prepared for transport to the Bohunice Waste Treatment and Conditioning Center where their processing into an ultimate form will be done. The most significant installation in the Complex for Radwaste Processing in Mochovce will be a cementation facility with the resulting cemented products inserted in fiber reinforced concrete containers.    

   
As a conclusion it can be said that mainly the operation of the Bohunice Radwaste Treatment and Conditioning Center due to its comprehensiveness will contribute significantly to the resolution of issues related to the processing of radioactive waste in Slovakia. In our conditions, the amount of radwaste generated under normal nuclear power plant operation has a decreasing tendency. The provisionally increased amounts of both liquid and solid radwaste have been caused by the ongoing gradual reconstruction of the V-1 Bohunice plant that will be completed in 2000.