Planning for the Decommissioning of the ASTRA-Reactor

After 39 years of successful operation the ASTRA Reactor, a 10 MW multipurpose MTR research reactor at the Austrian Research Center Seibersdorf is to be decommissioned. The possible options and the required stages for decommissioning and removal of the radioactive components were evaluated. Of the removal of high-level waste from the site, succeeded by an immediately following, continued dismantling to stage 2 of these guide-lines (restricted site use) was identified as the most reasonable and under present auspices optimum choice. The reasons for this couice are described in detail. In the decommissioning study a preliminary evaluation of the arising radioactive waste was performed. The estimates amount to approximately 320 kg of medium-level radioactive waste and about 100 t of activated and about 60 t of contaminated low level radioactive waste. More details of the structure and activity concentrations to be expeeted in the various components, including irradiation and experimental facilities, are presented in the paper. The influence of permissible levels for unrestricted unse of components and waste on the amount of radioactive waste produced by the decommissioning procedure is discussed. Methods and precedures are further described which are foreseen to result in a minimal radiation exposure of the employed staff and minimize the arising amounts of waste. The choice and deployment of these methods is based on long experience at the ASTRA-reactor with the removal of highly-radioactive structures, experimental facilites and beam tubes. An outline of this experience will be given.