Dismantling and removal of acid-recovering vaporizer in Tokai Reprocessing Plant

The acid-recovering vaporizer is the equipment for heating and vaporizing nitric acid solution containing a small amount of nuclear fission products discharged from the separation and refining facilities. The vaporized nitric acid is recovered in the acid-recovering rectification column of the next process, and sent to reagent preparation process to use it again. The acid-recovering vaporizer is installed in the acid-recovering cell. It is a convection type vaporizer made of stainless steel, but later, the material was changed to Ti-5Ta. On August 24, 1978, the solution in the acid-recovering vaporizer leaked into the heating steam condensed water system, and the overall test of the reprocessing plant as the last stage of the trial operation was interrupted. Consequently, after the required procedure for changing the acid-recovering vaporizer, it was renewed. In this report, among the works of the renewal, the dismantling and removal are described. The works of dismantling and removing a large equipment in a hot cell for the first time in Japan was finished in about three months, shortening the expected period by two weeks. The outline of the cell, the condition of radiation, the opening of the cell, the reinforcement of scaffolds, dismantling and removal, the container for waste preservation, exposure control, protectors and the mock-up test are reported. (K.I.)