Electrochemical Decontamination Methods Applied At Paks Nuclear Power Plant In Hungary

摘要

During the decontamination activities at the Hungarian nuclear power plant at Paks several decontamination methods are applied. Apart from mechanical, ultrasonic and chemical applications decontamination by submersion or the moving cathode electrochemical method are also frequently used. These last mentioned methods are the theme of this presentation. In the submersion method electrolyzing baths of about 1m~3 net volume are used to decontaminate different equipment parts. For example this method is used for those parts of the main circulating pump and the main closing valve that are in direct contact with the primary coolant during operation. A special application of the submersion method is the use of an electrolytic cell that can be mounted onto the drive to decontaminate the labyrinth seals of the CR drives. This method is used not only for equipment for further use, but also for decommissioning. In recent years more than a hundred CR drives have been discarded which were then decontaminated in a special electrochemical bath. The moving cathode electrochemical decontamination method can be manually operated or robotized. The latter is especially useful and beneficial from radiation protection point of view, as the operator needs to remain in the high radiation zone only for a short period of time. The manual method is primarily used to decontaminate the highly contaminated areas of the CR drives before dismantling for maintenance. The casings of the main circulating pumps and the main closing valves are decontaminated by the robotics method. These pieces of equipment cannot be dismantled therefore a special device is used, that can be installed into the casing and operated remotely from the reactor hall. In conclusion, both the submersion and the moving cathode electrochemical decontamination methods are widely used for maintenance and decommissioning purposes at the Paks Nuclear Power Plant.