Progress in dismantling of the WAK Pilot Reprocessing Plant: Vitrification of the HLLW

Full text: In the past international nuclear safeguards was focused on operating facilities and in these facilities namely on the product streams. The amount of nuclear material in waste was regularly measured or estimated by the plant operator but normally accepted by the IAEA without verification, if certain limits were observed. With the additional protocol in force, safeguards measures are applied on (in a technical sense) decommissioned plants and it seems that the conditioning of waste will be safeguarded by the IAEA to a higher degree than in the past. This paper will describe in detail the situation at the Wiederaufarbeitungsanlage Karlsruhe (WAK). The German pilot reprocessing plant was commissioned in 1971 and finally shut down at the end of 1990. During 31 campaigns 210 Mg of uranium and 1100 kg of plutonium originating from different German reactors were reprocessed. All separated plutonium and uranium were shipped off site. Starting in 1996, the process building has been totally dismantled and all liquid and solid wastes of low and medium level activity were shipped to the waste treatment and intermediate storage facility at the Research Centre Karlsruhe (FZK). In a separate building (LAVA) approximately 60 m3 of high level liquid waste (HLLW) with a total radioactivity of nearly 8E17 Bq are stored as 'retained waste' to be conditioned on site. This vitrification project also has been established in 1996 and a new building for the Verglasungseinrichtung Karlsruhe (VEK) is finished and equipped, now waiting for the licence of hot operation in the beginning of 2007. An overview of the WAK dismantling project has been given. The vitrification of the HLLW is an essential step for the total dismantling and demolition of WAK. The VEK facility is only planned, constructed and licensed for this specific task that should be terminated within two years. Looking at the vitrification, it is straight forward process: receiving a volume of 1.6 m3 HLLW from LAVA, the solution is poured continuously on the surface of the melted glass. The raw glass itself is dosed batch wise as small pearls of glass frit. The HLLW is dried, calcinated and its chemical elements are incorporated as oxides into the glass matrix. The glass will be filled in four steps of 100 kg into stainless steel canisters and cooled down for several days. Then a lid is welded remotely on the canister, the canister is decontaminated and neutron as well as beta and gamma doses are measured prior buffer storage. When 28 canisters are filled they will be loaded to a CASTOR cask. In total 130 canisters will be produced and five CASTOR casks will be transported together to an intermediate storage facility. The design of VEK has been already described in detail. Concerning the safeguards relevance of the process and the glass product, the IAEA may accept that a credible diversion path does not exist for the nuclear material. The nuclear material content of the HLLW is well known to the IAEA. The vitrification process itself has no possibilities of recovering U and Pu and, furthermore, on the sites of FZK and WAK reprocessing capabilities do not exist anymore. As a consequence, the design verification of VEK, sealing of back transfer lines from VEK to LAVA (necessary for safety reasons), and the authentication of the operator measurements on the product canisters should be sufficient for a statement of compliance with the safeguards rules. Of course, WAK is open for any additional safeguards measure that does not modify the licensed status of VEK or will be intrusive during the two years period of facility operation. (author)