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In this paper, the decontamination features of the low-pressure arc-discharge method for radioactive waste generated in the operation and maintenance of nuclear power plants were examined. The low-pressure arc-discharge method was applied to type 304 stainless-steel, type 316L stainless-steel, alloy 600 and carbon-steel covered with radioactive corrosion products. Approximately, 80% of the radioactivity build up on stainless-steels could be removed by the low-pressure arc discharge.

The application of a chemical cleaning process to dissolve and remove scale and sludge by chemicals is being planned for Japanese pressurized water reactor (PWR) plants in order to maintain a high heat transfer condition and to prevent the SG tubing degradation. In this paper, the effectiveness of the EPRI process and the KWU process to maintain integrity of SG tubing were investigated under accelerated IGSCC conditions. IGSCC susceptibility and propagation ratio of degraded SG tubing with chemical cleaning, were the same as those of tubing not subjected to the chemical cleaning process. Neither the EPRI nor the KWU process adversely affected tubing integrity.

The application of the chemical cleaning process to dissolve and remove scales and sludge by chemicals is being planned at the Japanese pressurized water reactor (PWR) plant in order to maintain a high heat transfer condition and to prevent the steam generator tube degradation. In this paper, fundamental characteristics and cleaning effectiveness of the EPRI process and the KWU process, which are typical cleaning processes, were investigated. Both processes showed a satisfactory cleaning effectiveness for sludges and scales, and the cleaning effectiveness of the standard KWU process was improved by tailoring it to crevice cleaning conditions.

平成元年に一部の柱上トランスに使用されている再生絶縁油中に極微量 (50mgPCB/kg絶縁油未満) のPCBが混入していることが判明し, 早期に安全な無害化処理方法を確立することが望まれている。トランス構成材に付着・含浸している再生絶縁油およびPCB (以後PCB等という) を除去し, トランス構成材を無害化する方法の一つとして真空条件下でPCB等を加熱・蒸発・分離させる真空加熱分離法が有望視されている。実際に使用されているワニスレスおよびワニス含浸の柱上トランスを用い, PCB等を除去するための基本的な真空加熱分離条件の選定を行った後, 実証試験設備を設計・製作し真空加熱分離法の適用性実証試験を行った。その結果, 同法の標準的な適用条件を真空度0.05torr以下, 加熱温度200℃, 真空保持時間10時間とすることによりトランス構成材中の残留PCB量をほぼ定量下限値 (0.05mgPCB/kg構成材) 未満にでき, かっ設備や処理方法が環境へ影響を与えないことを明らかにした。

In 1989, PCB was found in recycled insulation oils used in some pole transformers at a concentration of 50 mg per kg of insulation oil, prompting quick establishment of their safe separation method. One of the prospective methods for removing, for example, recycled insulation oils attached to and impregnated into the transformer coils, may be a vacuum heating separation method which heats and vaporizes PCB under vacuum conditions for separation. A proving test for the applicability of the specific vacuum heating separation method was carried out with actually used transformers, which confirmed that residual PCB on coils was minimized to less than the quantitative determination threshold of 0.05 mg per kg of insulation oil under the following standard applicable conditions: vacuum lower than 0.05 Torr; heating temperature 200 °C; and vacuum holding time 10 hours. Thus, the reduction of effects on the environment was verified. © 1997 Scripta Technica, Inc. Electr Eng Jpn 120(3): 17–28, 1997