Electrochemical decontamination of the main gate valve housing in the Nuclear Power Plant Paks.
The upper and lower part of the main gate valve (MGV) housing is decontaminated by different equipment. The pictures show the part of the equipment, which works in the lower part of the MGV housing. This robot is also controlled by a PC-installed program by the help of which cleaning heads automatically follow the accessible internal surface of the MGV housing, cleaning it electrochemically. Because of the very complex geometry of the housing (upper figure), the robot applies three cleaning heads (denoted by H1, H2, and G, see figure in the middle).
The head H1 decontaminatestaminates the upper cylindrical part of the housing, and the internal surface of the rib guide. Head H2 cleans the external cylindrical part of the protruding nozzles. Head G is suitable for decontamination of spherical surfaces. In this way 70 % of the total internal surface can be cleaned. The half of the uncleaned surface can be decontaminated manually, but that of the other half cannot be realized even by hand, because of very complicated and inaccessible surfaces.
During decontamination the operator should take care of draining the electrolyte accumulated at the bottom of the housing. If there is no problem in the operation, the operator shall not intervene into the decontamination process. As the robot is equipped with 2 video cameras, the decontamination process can be monitored from a place with low radiation level. A local cable-phone system makes the work of the operators more comfortable.
During the decontamination process the cleaning head is pressed by pneumatic cylinders against the surface providing a compensation of surface inaccuracy. The total decontamination time in case of continuous, automatic operation is 3.5 hours. The electrolyte consumption is 20-25 l for the decontamination of one MGV housing.
The figure at the bottom shows the equipment for the electrochemical decontamination of the upper part of the MGV housing. The part of the equipment that makes the decontamination has to be placed in the upper part of the MGV housing. Subsequently, the volume has to be filled with electrolyte. The equipment can be operated automatically. The total decontamination time is less than half an hour. The total dose exposure of the operational stuff is minimized.