Earticle

The usefulness of the magnetic force control technology has been recognized as MS (magnetic separation) technology in the fields of environment remediation and resource recovery. Especially the use of the superconducting magnet is expected to develop the application fields using MS technology. Since 2011, the researchers from China, Korea and Japan started and have been holding in every year the IFMFC (International Forum of Magnetic Force Control) to develop the application of the magnetic force control technology and exchange the experiences. Recently the United Nations is asking each country to contribute the global issues such as SDGs 2030 and carbon neutral 2050. This review reports the activities of IFMFC since 2011 as to the MS technology application.

In this study, we investigated high-gradient magnetic separation as a method for separating crud in high-temperature, high-pressure water inside a nuclear reactor. Corrosion products in the coolant circulate through the system and attach to the reactor core, where they are activated by neutron irradiation. The activated corrosion products then desorb from the core and circulate through the cooling system again. The corrosion product in the reactor water or piping system is called crud. Crud is the main source of radiation exposure for radiation workers. Removal and recovery of crud is important in decommissioning plants that have been in operation for service life, and new technologies are also desired. A method for separating activated ions adsorbed on ion exchange resins in nuclear reactors using magnetic separation is developed. In this method, the ion exchange resin is washed with acid, the activated ions are adsorbed from the washing water using adsorbents, and then separated magnetically. Rudimentary experiments were conducted to investigate the possibility of this method.

A large amount of cesium-contaminated soil was generated as a result of the decontamination work following the accident at the Fukushima Daiichi Nuclear Power Plant. To reduce the final disposal volume of contaminated soil, it is necessary to separate the contaminated soil into low- and high-dose soil components and reuse the low-dose soil under 8000 Bq/kg. We have investigated a magnetic separation technique to reduce the volume of the contaminated soil. Magnetic separation is a volume reduction technology that utilizes these differences in magnetic properties. However, the high-gradient magnetic separation technique (HGMS) we have been studied has problems such as clogging of filters and low separation accuracy due to the passage of 2:1 type clay minerals with small particle diameters. In this study, we propose a new separation method using a cyclone-type magnetic separator that focuses not only on magnetic susceptibility but also on differences in particle size. The cyclone-type magnetic separator can separate 2:1 type clay minerals from 1:1 type clay minerals by inducing 1:1 type clay minerals with large particle diameters to the outside of the cylinder and 2:1 type clay minerals with small and large particle diameters to the inside of the cylinder through the difference in the combined magnetic and centrifugal forces acting on soil particles. Separation accuracy was evaluated using simulated soil consisting of vermiculite and kaolinite. Based on these results, the reduction rate of the radioactivity concentration was estimated, and the design guidelines of the device for practical use were discussed.

The core of a High Temperature Superconducting (HTS) cable lies eccentrically inside the inner pipe of the cryostat in the absence of any supporting structures or spacers. This eccentricity may result in non-uniform cooling of the superconducting tapes. In this paper, three types of spacers with different geometries are designed with the aim to position the cable core centrally within the inner vessel of the cryostat. An optimum distance to be maintained between two such consecutive spacers is proposed. For an allowable radial deflection of 1.5 mm, the distance required to be maintained between two adjacent spacers was found to be 1.553 m. The spacers have been designed and studied structurally to operate at cryogenic temperatures. The pressure drop due to the presence of these spacers has been computed numerically and a comparison has been made between different types of spacers. It was found that amongst the three spacers designed, though spacer type B offers minimum pressure drop per unit length, spacer type C offers maximum surface area available for cooling the superconducting elements of the HTS power cable.

We fabricate high-entropy alloy (HEA) Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 superconducting (SC) thin films via a pulsed laser deposition method. Two targets are prepared using arc melting, each followed by sintering at different temperatures: 550°C and 700°C for 12 hours. The films, HEA550 and HEA700, are deposited on c-cut Al2O3 substrates at a substrate temperature of 520°C, using the targets sintered at 550°C and 700°C, respectively. The SC transition temperature (Tc) of HEA700 is 6.88 K, slightly higher than that of HEA550 (= 6.27 K). Both films exhibit similar upper critical field (Hc2) at 0 K, with 11.34 T for HEA550 and 11.40 T for HEA700. Notably, HEA700 exhibits a large critical current density (Jc) of approximately 4.4 MA/cm2 and 3.5 MA/cm2 at 2.0 K and 4.2 K, respectively, accompanying by a predominance of normal point pinning. These results indicate that the targets prepared by arc melting are beneficial for achieving a large Jc in HEA SC thin films, thus providing new avenues for improving SC critical properties of HEA thin films for their practical applications.