Decommissioning of a MOX Facility in Germany: Applied Techniques for Minimisation and Optimisation of Loading Containers With Nuclear Grade Waste for Final Repository

The Siemens mixed oxide fuel (MOX) facility in Hanau, Germany, processed approx, 8500 kg Plutonium and is now decommissioned. The dismantling of the 235 glove boxes started in September 2001 and is scheduled for completion in 2004. Several dismantling techniques have been developed and established to perform the decommissioning. The residuals have been estimated to about 80 kg of Plutonium. Therefore plutonium-contaminated wastes with a high content of fissionable material must be treated for storage in the German planned repository Konrad. For waste minimisation it is essential to exploit the marginal values of the repository. At the same time it is necessary to minimize the steps to be taken during conditioning for health physics aspects. For this reason different measurement devices are used during decommissioning of the Hanau MOX plant. For determination of the amount of fissile material in small packages a measurement system, optimised for small items, is used. As mainly larger components from glove boxes need to be decommissioned, these components are cut to 200-l drum size and are controlled for maximum allowed Pu-content (50 g fissile material/drum) with a Slab Counter during filling of the drum. The total drum is measured in a device especially designed for 200-l drums. Another transportable measurement device is used for larger components. These items are placed directly into Konrad containers without further treating or cutting. The determination of the plutonium content is based on the measurement of the coincident neutrons from the spontaneous fission of plutonium combined with the determination of the isotopic composition by high-resolution gamma spectrometry. The coincident neutrons emitted from the even plutonium isotopes ²³⁸Pu, ²⁴⁰Pu and ²⁴²Pu are measured with ³He-tubes, and the ²⁴⁰Pu_equivalent is measured. Knowing the isotopic composition, the absolute plutonium content of the item can be determined. The conditioning methods of the individual waste streams for final repository are qualified on a campaign-by-campaign basis. The responsibility for the approval of the applied conditioning-method is with the Federal ordinance for radiation protection (BfS). An essential part of the qualification of the waste is a reliable determination of the activity respectively of the quantity of fissile material, which has to meet the repository’s requirements on the inventory of fissile material. All measurement techniques for the considered procedures are qualified by BfS. All used methods were monitored by experts; for qualification of the applied processes related to final repository aspects the expert organization TU¨V Hannover/Sachsen-Anhalt e. V. is commissioned by BfS. During the process of conditioning performed by Siemens the conditioning itself, the measurement systems as well as the evaluation process are optimized. Therefore, without additional conditioning steps the repository demands for instance for the limitation of the fissile material can be fulfilled easily. For this reason the Konrad container can be equipped with different items to exploit the marginal values of the repository.