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The Fukushima power station in Japan was affected by a major earthquake and tsunami in March 2011, inspecting the primary containment vessel remains difficult due to high radioactivity. Long-reach robot arms are useful in inspecting such hazardous environments, and a coupled tendon-driven mechanism enables realizing a long, light-weight, and thin manipulator. However, high elastic elongation of tendons due to gravity may lead to unstable joint control. In this paper, we introduce dynamics-based control as a feasible strategy for a long-reach tendon-driven robotic arm. Additionally, a planning method to identify the joint angle path ensuring stability is proposed. Considering stability analysis, the potential due to the tendon elasticity and gravity is evaluated and used as an index of joint stability. The rapidly exploring random tree is used as the planning algorithm. The effectiveness of the proposed method was demonstrated through the successful manipulation of a 5-kg payload by a 10-m long robotic arm. [ABSTRACT FROM AUTHOR]

After the Fukushima nuclear accident in Japan, whether the structural safety of the nuclear power plant (NPP) can be guaranteed under an earthquake has been of wide concern. Automatic seismic trip systems (ASTS) have been deployed in NPPs. There are generally two units or more double units on the one NPP site, and the vibration energy of the structure can certainly affect its adjacent structures through the soil, and there is energy transfer and conversion between adjacent structures. At present, the distance between two reactors of NPPs of different reactor types is generally 100–200 m (this distance is referring to the distance between the centers of two reactors, which is slightly different for different reactor types). In the past, seismic instruments were used in the ASTS and the setting of shutdown threshold, so the impact of only one unit was considered in the structural analysis of NPPs, and the interaction of two reactors through site conditions was not considered. In addition, as the site conditions of NPPs become more and more complex, it is necessary to consider the impact of one reactor structure on another reactor structure through the soil on the same site under an earthquake. In order to analyze the influence of structure–soil–structure interaction (SSSI), a three-dimensional refined finite element model of NPPs is established in this paper. The soil–structure interaction (SSI) is considered by using viscoelastic boundary. The seismic responses of different positions of the raft foundation and NPP structure, under the conditions of considering SSI effect (one reactor) and SSSI effect (two reactors), are compared. The influence of SSSI effect on the seismic responses of the raft foundation and NPP structure is revealed. It is proposed that SSSI effect should be reasonably considered according to the site conditions for the structural analysis of NPPs for the NPP ASTS. [ABSTRACT FROM AUTHOR]

After the accident at the Fukushima nuclear power plant in Japan, a large amount of radioactive contaminated soil was generated, which brought great challenges for treating and disposing of the soil. The recycling of slightly polluted soil can reduce the amount of contaminated soil. This paper analyzes the main exposed scenes of 137Cs polluted soil used in the construction of highway subgrade, soil bag handling and paving. The Monte Carlo algorithm (MCNP) and RESRAD-ONSITE program are used to simulate the two scenes respectively, and the concentration of 137Cs is derived in the soil at the effective dose of 1 mSv per year. It is concluded that: the annual effective doses of porter and paver are 0.41 mSv per year and 0.23 mSv per year respectively caused by 1 Bqg-1 137Cs contaminated soil; the activity of 137Cs are 2.44 Bqg and 4.26 Bqg-1 respectively in the soil at 1 mSv per year for porter and paver; the calculated results are consistent with those reported by the Japan Atomic Research Agency. Also, they are lower than the activity concentration corresponding to the effective dose con- trol level of 1 mSv per year under low-probability events in IAEA No. RS-G-1.7 slightly. [ABSTRACT FROM AUTHOR]

The decommissioning of the Fukushima Daiichi Nuclear Power Plant, the plant affected by the Great East Japan Earthquake, will continue for a long time to come, but few young people are willing to take on the challenge because they tend to have the impression that decommissioning work is a post-accident cleanup. However, decommissioning is the most important issue for Fukushima and is of global importance. Therefore, the National Institute of Technology, Fukushima College (Fukushima KOSEN), which is located closest to the Fukushima Daiichi Nuclear Power Plant, established a council of cooperation and started the Creative Robot Contest for Decommissioning in cooperation with other National Institute of Technologies (KOSEN) to increase the awareness and interest in decommissioning among the young. The robot contest, themed on issues related to the decommissioning of the Fukushima Daiichi Nuclear Power Plant, has been held annually since 2016 for students of KOSEN across Japan, and the 7th Creative Robot Contest for Decommissioning is scheduled to be held in December 2022. Although the ideas and robots developed by KOSEN students from all over Japan to solve the problems involved in the decommissioning will not directly contribute to future decommissioning work, the ideas and technologies learned can be used in other fields, and the participating students are expected to be active in a wide range of fields as well. This special issue contains review papers of the Creative Robot Contest for Decommissioning, development reports, and research papers on the robots developed. A total of eight papers are included: two review papers, two research papers, and four development reports on decommissioning robots designed by students. At the same time, we hope that young people in Japan and abroad will also become interested in the robots introduced in this special issue, and that the decommissioning work of Fukushima Daiichi Nuclear Power Plant will proceed safely and securely by combining the wisdom of the whole world. [ABSTRACT FROM AUTHOR]