[en] 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.)

[en] The nitric acid solution dissolving nuclear fuel material is transferred with the three way valve called VCV (VCV: vide-casse-vide in Fr.) using vacuum in the Tokai Reprocessing Plant. The initial VCV was not reliable because it had broken with in 1 or 2 years. The cause of failure was damage of the plastic diaphragms in the moving parts. Then, the new VCV valve with stainless-steel bellows was developed. There is no failure in moving parts in 20 years, therefore reliability is significantly improved. (author)

[en] At the Tokai Reprocessing Plant (TRP), spent fuels are dissolved in nitric acid and the dissolved liquid is fed to the extractors (mixer settlers). In the mixer settlers, both uranium and plutonium are extracted by the solvent that contains tri-butyl phosphate. It is important to control the interface between organic and aqueous phase in the settlers And the interface is controlled by the flow control valve. This valve has maintainability problems because it takes a fair amount of time to maintenance. In addition, this is imported product, the production costs are high, and the delivery period for this valve is long. Therefore, we have tried to ohtain same type of valves with the confines of the country. This paper describes the trials and same experimental results. (author)

[en] The automatic inspection system for the instrumentations of the Tokai Reprocessing Plant can automatically conduct inspection activities, including stopping of measurements, preparing of interlock, input of imitation signal, collecting and making of inspection data and resumption of measurements after the inspection, etc. in accordance with pre-established condition and procedure inputted through key board operation. The test of the system connected to 14 instrumentation-loops shows that it is as good as the former manual inspection. In addition, the automatic inspection system brings reduction of inspection time and man power, prevention of human error and speed up of data analysis. (author)

[en] Negative atmospheric pressure is an isolation technique used in nuclear facilities including vessels and hot-cells to prevent release of radioactive materials. In the related system, differential pressure switches are very important function for process monitoring such as liquid level and negative pressure in a reprocessing process. Although air-tight switches have been using to avoid radioactive contamination, such type of switch have not meet requirements for precise operation under deep negative pressure. Therefore, we have been investigation an improved types of switches to overcome the problem. We have developed a prototype switch and made some vibration and endurance tests. Their results are described in this paper. (author)

[en] The air purge method is applied to measure a liquid level and its density of a radioactive solution in a tank in the Tokai reprocessing plant. In this method, air purge tubes soaked in nitric acid solution are often blocked by depositing salt of nitrate. Dried air is usually used for the air purge system and this can be one of the reasons for generating salt on the tube point. Therefore, a series of experiment using a humidifier to humidify the air has been performed to prevent the blocking with salt, and the effect has been experimentally confirmed. (author)

[en] IAEA proposed the Safeguards Improvement Plan (11 tasks) for the TRP aim for more strict and efficient SG in 1995. Development and installation on the Solution Measurement and Monitoring System (SMMS) is one item of them and carried out under the JASPAS program (JA-6). Following the installation and IAEA's acceptance test of the SMMS, a field test of this system has been going on. The main purposes of this system are to establish the IAEA's independent monitoring system, and to establish the confirmation of plant operation and C/S. Input and output accountability tanks (FKMP), 7 Pu storage tanks (IKMP) and a pot attached to the Pu storage tanks are monitored continuously by this system, and the solution level, density and temperature data are transmitted to the inspector office. The authentication of this system has been kept by its detection and record function for system failure. (author)