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We investigated a dry surface decontamination technology using low-pressure arc plasma for radioactive corrosion product films. The low-pressure arc plasma is produced with a transferred-type DC arc discharge that operates under reduced pressure; here, the cathode is the object to be treated. The cathode spots formed inside the low-pressure arc plasma can melt away the metal oxide film on the surface of the object without significantly damaging the metal substrate. One of the major advantages of this technology is its potential to reduce the amount of secondary waste compared with existing technologies, e.g., decontamination with chemical solutions, because it eliminates the need for a medium. In this report, the dependence of the decontamination performance on the type of plasma source gas was investigated. Argon, hydrogen, chemically active carbon monoxide, and a mixed gas of CF 4 /O 2 were selected. Consequently, a higher Cobalt-60 removal ratio was obtained with smaller electric charges in the hydrogen low-pressure arc plasma. The low-pressure arc plasma was also applied to pipe-shaped test pieces with a corrosion product film. And eventually, a Co removal ratio exceeding 90% was achieved. The applicability of the dry surface decontamination technology with low-pressure arc plasma for radioactive metal waste with a corrosion product film is demonstrated.

The application of chemical cleaning for dissolving and removing scale and sludge is being planned in the Japanese pressurized water reactor (PWR) plant in order to maintain high heat transfer performance and to prevent steam generator (SG) tube degradation. In this paper, the effectiveness of the Electric Power Research Institute (EPRI) and German Kraftwerk Union (KWU) processes on the integrity of structural materials other than SG tubes and the comprehensive applicability of chemical cleaning are discussed. The integrity of structural materials such as carbon steel, low-alloy steel and stainless steel was maintained after the EPRI and KWU processes. KWU chemical cleaning tailored for crevice cleaning has been studied to improve its cleaning effectiveness in crevices and to control the corrosion depth of structural materials less than the criterion for corrosion depth.

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 designed heat transfer condition and to prevent the steam generator (SG) tube degradation. In this paper, the affects of the EPRI process and the KWU process on the long term integrity of SG tubing were investigated under the simulated SG condition using a SG model boiler test facility. No adverse effect of the both chemical cleaning processes on the long term integrity of SG tubing were observed.

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.

有機金属化学蒸着 (MOCVD) 法により, Fe, CrおよびNiを含む種々の複合酸化物皮膜をステンレス鋼表面に形成し, 高温水中での耐食性および放射性腐食生成物の蓄積挙動に及ぼす皮膜の種類と成膜温度の影響について検討評価した. BWRおよびPWR一次系模擬条件での浸漬試験の結果, MOCVD法により形成した酸化物皮膜は高温水中で安定であった. Cr2O3皮膜付試験片の放射能の蓄積量は, 成膜温度が高いほど小さくなった. XRDスペクトルの観察結果から, 皮膜の結晶性の向上が, 耐食性を向上させるとともに, 放射能の蓄積量を低下させると推測された. 一方, NiO-Fe2O3皮膜は, 放射性核種である60CoがNiFe2O4構造を有する酸化物皮膜へ取り込まれるため, 放射能の蓄積量を低下させることが出来なかった. 以上の結果より, 結晶性に優れたCr2O3皮膜を形成することにより, BWRおよびPWR一次系環境中でステンレス鋼の腐食を抑制し, 放射能の蓄積量を低減できることが明らかとなった.

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

This paper describes a new vacuum thermal recycling (VTR) method for treating discarded polychlorinated biphenyls (PCB)-contaminated capacitors and pressure-sensitive paper. Based on results demonstrating an exceptionally high PCB separation efficiency and recovery ratio from capacitors containing high-concentration PCBs, i.e. > 99.9%, respectively, the presented VTR method is verified to effectively remove PCBs. In addition, associated safety aspects of the employed procedure were confirmed.

In 1989, it was discovered that the recycled insulation oil in pole transformers for electric power supply was contaminated with trace amounts of polychlorinated biphenyls (PCBs; maximum 50 mg-PCB/kg-insulation oil). In order to remove the PCBs from transformer components using n-hexane as a solvent, we investigated the relationship between progressive stages of dismantling and cleaning results. The results are summarized as follows: (1) Based on the cleaning test results, we made an estimate of the residual PCB amount on iron and copper components. By dismantling the test pole transformers into the "iron core and coil portion" and cleaning the components, we achieved a residual PCB amount that was below the limit of detection (0.05 mg-PCB/kg-material). To achieve a residual PCB amount below the limit of detection for the transformer paper component, it was necessary to cut the paper into pieces smaller than 5 mm. We were unable to achieve a residual PCB amount below the limit of detection for the wood component. (2) Compared to Japan's stipulated limited concentration standard values for PCBs, the results of the cleaning test show that cleaning iron or copper components with PCBs only on their surface with the solvent n-hexane will satisfy the limited concentration standard values when care is taken to ensure the component surfaces have adequate contact with the cleaning solvent.

The characterization of radioactive corrosion pro-ducts and the distribution of 60Co on specimens taken from the Pipe of the Ōarai Water Loop of the Japan Material Testing Reactor, with and without...