A variety of technologies are applied to the decontamination of radiocesium from water using inorganic adsorbents such as zeolites, Prussian blue (PB) and its analogues. However, these adsorbents are difficult to apply. Although zeolites work as good adsorbents for cesium (Cs) in freshwater, their adsorption ability is extremely low in seawater and fly ash extracts with a high salt concentration. In contrast, PB and its analogues maintain their selective adsorption ability for Cs even in water containing salts, but a high level of cyan remains in the treated water. In this study, we introduce a new technology that utilizes complexes between PB and hydroxides of transition metals (PB-X) for the decontamination of Cs from water and report results of demonstration tests on simulated seawater and fly ash extract. Furthermore, the excellent results of the PB-X method applied to the extracts from fly ash contaminated with radiocesium (more than 8000 Bq/kg) are also shown. It has been proved that radiocesium activities are not only below the detection limit (<10 Bq/kg) and the content of cyan can be controlled under the regulation value of tap water in the water treated with PB-X.
The glove box (GB) is a device with some plastic components and is used for the containment of radioactive materials. In a MOX fuel fabrication facility, MOX is also handled in the GB. Since the plastic panel, which has the largest area in the GB, is used over a long period, it is exposed to a high dose of MOX continuously. In this study, to confirm whether the containment capability of GB can be maintained even under external thermal stress, the effects of gamma ray irradiation with 60Co on the pyrolysis properties of the common panel materials were investigated by TG-DTA. As a result, polymethylmethacrylate showed a large peak of the mass loss rate at about 260 degrees under the nonirradiation and air condition, but it separated into lower and higher temperature sides above 25 kGy. This effect was not observed up to 10 kGy for polymethylmethacrylate and up to 880 kGy for polycarbonate. By comparison with the estimated total dose of the GB panel irradiated in the operation period, it was found that the irradiation from MOX does not significantly affect the pyrolysis properties of the GB panel in the actual facility.
Although the reliability and safety level of tasks have been improved by using operation manuals, analyses of problems recently experienced in the nuclear energy industry imply that the cause of these problems is attributable to the content and presentation of operation manuals. The importance of operation manuals has also been pointed out in relation to the Fukushima Daiichi nuclear power plant accident. Operation manuals that are effective for both normal and extreme conditions are desirable. The purpose of the present study is to investigate the effect of the manner of rule presentation on human task performance under both normal and extreme conditions. A cognitive experiment using a simulation environment has been conducted. A smart grid simulator has been adopted as an example task. Two operation manuals (manuals A and B) are prepared. Manual A describes the required operations in detail. Manual B describes the meaning of the operations with their underlying knowledge. Subjects have been divided into two groups (A Group and AB Group). Subjects in the A Group can rely on manual A. On the other hand, subjects in the AB Group can rely on both manuals A and B. Results of cognitive experiments imply that, under both normal and extreme conditions, subjects in the AB group have better performance.
An accident of evaporation to dryness by boiling of high-level liquid waste (HLLW) is postulated as one of the severe accidents to occur as a result of the loss of cooling function at a fuel reprocessing plant. In this case, a large amount of ruthenium (Ru) is volatilized and transferred to the vapor phase in the tank, and could be released to the environment. Therefore, the quantitative estimation of the amount of released Ru is one of the key issues in the assessment of the accident consequence. To resolve this issue, an empirical correlation for the rate of Ru transfer to the vapor phase with the temperature, nitric acid mole fraction and activity of HLLW has been developed using the data obtained from the accelerated experiments using simulated HLLW. A simulation study with the developed correlation demonstrated that the estimated amount of Ru transferred to the vapor phase was in good agreement with that obtained from the long-term experiment using actual HLLW.
The upgrade of JT-60U to the superconducting tokamak “JT-60SA” has been carried out as a combined project of JAEA's program for national use and the Satellite Tokamak Program in collaboration with EU and Japan fusion communities. The JT-60U torus was dismantled so as to install the new JT-60SA torus at the same position in the torus hall. JT-60U used deuterium for 18 years, so the neutron yield reached about 1.5×1020 (n) in total. The dismantling project of JT-60U was the first decommissioning experience of a fusion device with radioactivity in Japan. The project was intended to demonstrate decommissioning technologies and work activities, and to acquire experience and data on the technologies as well as to implement the dismantling project safely. Moreover, all disassembled components were stored with the data such as dose rate, weight and kind of material being recorded, so as to apply the clearance level regulation in the future. The lessons learned from the dismantling project indicated that the cutting technologies and storage management of disassembled components were the key factors in conducting the dismantling project efficiently. After completing the dismantling project, efforts have been made to analyze the data for characterizing disassembling activities, so as to contribute to the estimation of manpower needs and the radioactivity of the disassembled components from other fusion devices.