The Fukushima Daiichi Nuclear Power Plant accident, triggered by the Great East Japan Earthquake and the tsunami, has had a major impact on societies across the world. The subsequent focus on decommissioning efforts has attracted worldwide attention. It has been consistently asserted since the aftermath of the accident that the decommissioning of the Fukushima Daiichi Nuclear Power Plant will take approximately 30 to 40 years. The promotion of decommissioning work means that we will continue to face the problems with uncertainties in the work, as sometimes referred to as Unknown Unknowns.

Typical elemental technologies required in remotely operated robotic systems for decommissioning include mobile mechanisms and their control, handling mechanisms and their control, information communication, operation interface (information presentation and command input), shielding (radiation resistance) and so on. Although many tasks using remotely operated robotic systems have been carried out with noteworthy results, there are lingering issues yet to be clarified. To ensure the safe and effective execution of various types of decommissioning tasks over a period of several decades, continuous research and development of each elemental technology are imperative, and these technologies must be integrated into a system appropriately to the assumed tasks. In addition, human resource development and the transfer of knowledge and experience are also important issues.

From such viewpoint, this special issue is titled “Robotic, Mechatronic and Information Systems for Decommissioning.” It contains papers and development reports on robotics, mechatronics, information processing, and information systems technologies relevant to decommissioning work. It also features recent activities of nuclear emergency response organizations.

We hope this special issue will acquaint readers with the latest research and development results and organizational activities related to decommissioning. At the same time, we hope that we were able to provide readers interested in robots, mechatronics, and information technology with an opportunity to become aware of the issues and necessary perspectives related to decommissioning and nuclear disasters.

Lastly, we would like to thank the editorial board of the Journal of Robotics and Mechatronics, the editorial team of Fuji Technology Press, and the reviewers for their support in the planning and publication of this special issue. Their dedicated efforts are deeply appreciated.

The most challenging task in the decommissioning of the Fukushima Daiichi Nuclear Power Station is to retrieve molten and solidified fuel debris, including in reactor internals. The International Research Institute for Nuclear Decommissioning (IRID) has developed various robots that can investigate the interior of a primary containment vessel (PCV) to clarify where fuel debris has accumulated and how it has formed. The scenarios of each unit caused by the accident are different; therefore, IRID has developed robots to satisfy the requirements of each unit. The robots can be categorized into three types: non-submersible robots driving through air, submersible robots swimming underwater, and investigation robots with arms that can extend to enter the PCV. This review focuses on the technological development of robots based on their functionality. Most of the robotic technology is acquired and utilized based on the results of subsidy projects for countermeasures for decommissioning and contaminated water granted by the Japanese government.

The exploration and inspection of narrow spaces in nuclear facilities require the use of long-reach manipulators. Coupled tendon-driven manipulators can realize lightweight and slender arms by positioning actuators, such as motors, at the base. Currently, we are developing a coupled tendon-driven super long-reach articulated arm, which we name “Super Dragon.” Super Dragon is a robot arm with a total length of 10 m, a maximum arm diameter of 0.2 m, and 10 joints. In this paper, we focused on the elasticity and elongation of ropes. The joint actuation of Super Dragon utilizes synthetic fiber ropes characterized by their high strength and flexible bending. However, when these ropes are used over long lengths, wire elongation occurs, thus causing the joint angles to exhibit unintended and unstable behavior. Therefore, we focused on a specific posture and employ a double pulley as a mechanical solution to suppress unstable behavior. We introduced stability criteria and performed parametric searches to obtain the appropriate double pulley radii. Subsequently, we identified the position and radius of the introduced double pulley that can be analytically stabilized. By installing a double pulley in the actual machine and conducting experiments, we successfully suppressed the unstable behavior.

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.

Remotely controlled robots are required to operate in human-inaccessible environments, such as the decommissioning of nuclear power plants. In our previous studies, we proposed a modularized rail structure for such environments. In long-term decommissioning work at a nuclear power plant, robots are controlled by inexperienced operators who have limited knowledge of the design details of the robots. In this study, we developed a remote construction system for supporting inexperienced operators by transmitting the status information of the constructor robot to the operator during the remote construction of a modularized rail structure. The proposed remote construction system was designed based on a human information-processing model. Experiments were conducted using the developed remote construction system. The proposed method achieved a success count of inexperienced operators equivalent to that of skilled operators. Furthermore, a questionnaire administered to participants showed that their cognitive, psychological, and physical loads during construction were sufficiently low during the experiment.

In the teleoperation system of a dual-arm manipulator developed to retrieve fuel debris and reactor interior structures at the Fukushima Daiichi Nuclear Power Plant, we used software in which an obstacle avoidance function (trajectory planning) was implemented to conduct a mock test simulating obstacle removal operations in narrow spaces. The test results confirmed the validity of the obstacle avoidance function, the executability of a series of necessary tasks, and the improved operability. In addition, issues were identified using the test data.

In the decommissioning of the Fukushima Daiichi Nuclear Power Station, radiation dose calculations necessitate a 3D model of the workspace are performed to determine suitable measures for reducing exposure. However, the construction of a 3D model from a 3D point cloud is a costly endeavor. To separate the geometrical shape regions on 3D point cloud, we are developing a structure discrimination method using 3D and 2D deep learning to contribute to the advancement of 3D modeling automation technology. In this paper, we present a method for transferring and fusing labels to handle 2D prediction labels in 3D space. We propose an exhaustive label fusion method designed for plant facilities with intricate structures. Through evaluation on a mock-up plant dataset, we confirmed the method’s effective performance.

To measure and analyze the distribution and criticality of submerged fuel debris “in situ” in the decommissioning process of the Fukushima Daiichi Nuclear Power Station (1F), we developed a system for remote measurement using multiple sensors consisting of the neutron sensor, the sonar, and the sub-bottom profiler (SBP) mounted on a small remotely operated underwater vehicle (ROV). First, the locations presumed to contain fuel debris were explored based on the information of the water bottom shape obtained using the sonar and the bottom surface substructure obtained using the SBP. Second, the system identified the location of fuel debris by detecting neutrons emitted by spontaneous fissions of fuel debris using the neutron sensor with diamond elements. Simulated fuel debris was placed at the bottom of a test water tank that simulated the pedestal. In the primary containment vessel (PCV) of 1F, and a verification test of remote measurement was conducted using the ROV mounted on the multiple sensors. The desired results were obtained.

A prototype system based on a combination of 4π sensitive gamma imaging and simultaneous localization and mapping (SLAM) was developed to find unknown radiation source(s) rapidly. The system consisted of a spherical visible camera, a three-dimensional light detection and ranging, a CdTe pixel array detector for 4π gamma imaging, a portable battery, and a control laptop personal computer; these were mounted on an unmanned vehicle. In a search area of 16 × 16 m² with a height of 3 m, the prototype system successfully demonstrated the finding of a ¹³⁷Cs point source with an activity of 0.67 MBq in the surrounding thin walls.

The radiation tolerance of a microcontroller (Raspberry Pi) required for the development of decommissioning robots was investigated. We found that the flash memory needed to boot the microcontroller had particularly low-radiation tolerance, significantly reducing the operation duration of the microcontroller in a radiation environment. We also found that certain high-performance flash memories have high radiation tolerance. Investigation of the process by which flash memory becomes inoperable revealed that internal memory information is rewritten owing to irradiation, leading to limited lifetime for memory.

In response to the imperative need for robotic involvement in the decommissioning of the Fukushima Daiichi Nuclear Power Plant, a proactive initiative was undertaken. This initiative led to the organization of the “7th Decommissioning Creative Robot Contest,” in which pivotal challenges related to nuclear plant decommissioning were addressed. Recognizing inaccessible areas within a decommissioned plant, the primary objective of this study was to develop a remotely operated robot capable of executing decontamination tasks in such environments. Two distinct locomotion systems were designed: mecanum wheels and crawlers. The mecanum wheels, characterized by their ability to execute approximately 100 mm vertical movements, facilitated the robot to surmount obstacles, particularly by negotiating 100 mm steps by engaging the tracks. Simultaneously, to address decontamination tasks at elevated locations, a threefold expandable ladder truck system was integrated, augmenting the operational range of the robot. Participation in the contest provided a platform for showcasing the developed technologies and validating their practicality. Despite encountering challenges during competition, such as damage to one locomotion system, the other locomotion system can be used to reach the destination. Experience serves as a crucial means of verifying technological advancements. Issues such as malfunctions in the range of motion control due to faulty limit switch contacts and unexpected loads on the tire elevation motors were noted, which hindered the achievement of the anticipated results. Despite these drawbacks, the adopted structural design demonstrates notable advantages, particularly in terms of maneuverability. The combination of mecanum wheels and crawlers along with a ladder truck system demonstrated adaptability to various scenarios. This adaptability holds significant promise for future nuclear power plant decontamination applications. While the competition may not have yielded the desired outcome, the lessons learned and the verified practicality of the developed technologies reinforce their potential utility in addressing the future challenges of nuclear plant decommissioning.

The transfer of stagnant water from the basement floor of the waste treatment building at the Fukushima Daiichi Nuclear Power Station is planned because of the possibility of water flowing out of the building if another tsunami occurs. However, the basement floor is installed with high-dose zeolite sandbags as adsorbents for radioactive materials, which renders their removal challenging. In this study, we conduct a field survey and field reproduction as well as develop a robot that can perform zeolite removal based on the results obtained. In addition, we perform verification tests in a full-scale mock-up test environment and extract issues for application to actual equipment.

During the decommissioning activities, a movie was shot inside the reactor building during the investigation of the primary containment vessel by applying photogrammetry, which is one of the methods for three-dimensional (3D) reconstruction from images, to the images from this movie, it is feasible to perform 3D reconstruction of the environment around the primary containment vessel. However, the images from this movie may not be suitable for 3D reconstruction because they were shot remotely by robots owing to limited illumination, high-dose environments, etc. Moreover, photogrammetry has the disadvantage of easily changing 3D reconstruction results by simply changing the shooting conditions. Therefore, this study investigated the accuracy of the 3D reconstruction results obtained by photogrammetry with changes in the camera angle of view under shooting conditions. In particular, we adopted 3D computer graphics software to simulate shooting target objects for 3D reconstruction in a dark environment while illuminating them with light for application in decommissioning activities. The experimental results obtained by applying artificial images generated by simulation to the photogrammetry method showed that more accurate 3D reconstruction results can be obtained when the camera angle of view is neither too wide nor too narrow when the target objects are shot and surrounded. However, the results showed that the accuracy of the obtained results is low during linear trajectory shooting when the camera angle of view is wide.

Naraha Center for Remote Control Technology Development was established for the development and demonstration of remote control equipment and apparatus to promote the decommissioning of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc. The center has been in operation since 2016. The mission of the center is to contribute to the decommissioning of the Fukushima Daiichi Nuclear Power Station and the reconstruction of Fukushima Prefecture. This report describes the center’s full-scale mock-up test facility, component test equipment for the development of remote control equipment and apparatus, and virtual reality systems and their utilization for the realization of the mission.

This article describes the German emergency response organization for nuclear accidents “Kerntechnische Hilfsdienst GmbH (KHG)” and informs about its tasks, structures, and working methods. At the end the current status of radiation campaigns, a component of a remote controlled systems is reported.

After the nuclear accidents of Chernobyl and Fukushima, several countries concerned with nuclear energy production set up robotic accident intervention groups with the aim to intervene in place of humans in hostile environments with high levels of contamination or irradiation. It is the case of France. The operational feedback of such robotic groups may be of interest for teams performing decommissioning on nuclear facilities. In this aim, a comparative analysis of robotic intervention contexts was undertaken between training contexts and a real operating situation. This allowed us to confirm determinants of performance already identified in the literature and highlighted new determinants of performance for intervention in nuclear environments.

Here, an automatic design method for a serial link mechanism is proposed. This method outputs all kinematic parameters of joints, position, orientation, number, and type of joint (revolute or prismatic). Several studies have been conducted on optimizing only the positions and directions of joints for a desired path. However, automatically determining the numbers and types of joints requires an excessive calculation time owing to the complicity of kinematics. To handle heavy computation, a virtual screw joint (VSJ) is introduced based on a screw axis and the product of exponentials formula. Screw joints have the advantage of including both rotation and translation. First, an additional joint is optimized as a VSJ. Then, adopting its position and orientation and selecting a revolute or prismatic joint facilitate an efficient design process. To demonstrate the effectiveness of this study, two task motions addressed in a related work are adopted as target paths. Consequently, the proposed method automatically generates serial linkages that contain both revolute and prismatic joints and can follow along desired paths.

There is a need to create a well-being oriented society to improve people’s lives by enhancing their mental satisfaction. In this study, we examined the changes in human emotions based on human–robot interaction by using a communication robot called babypapa. We defined KANSEI as the sensitivity of emotional change to the robot’s behavior and established a KANSEI model. Specifically, to clarify the behavior that the robot should exhibit to make children feel close to it, we conducted play experiments between the robot and 3–4 year-old children to investigate the relationship between the robot’s behavior and the feeling of closeness. The results of the experiment showed that contact and noncontact behaviors of the robot contributed to the feeling of closeness. We demonstrated a certain tendency of closeness and robot behavior.

The introduction of ICT into education in educational settings has become increasingly common. Among these, the research and development of educational support robots have attracted attention. Conventional robots provide academic support through button operation by the learner. However, it has been reported that excessive requests for academic support can be problematic in environments in which learners can freely request academic support. To solve this problem, we developed a perplexion estimation method that estimates the state of perplexion from the learner’s facial expression. When educational support is provided using the proposed method, the robot can autonomously provide academic support. Simulation experiments demonstrated that the perplexion estimation method has the potential to accurately estimate the learner’s state. However, there is still no dedicated model for educational support robots that utilizes the perplexion estimation method. Therefore, this paper proposes an apprenticeship promotion model that integrates a learning support method based on cognitive apprenticeship theory and our perplexion estimation method. We then verified the learning effects of the robot equipped with the proposed model on the learner through participant experiments. The experimental results suggest that the robot equipped with the proposed model not only provides the same learning effect to university students as a conventional robot, but also can autonomously provide academic support at the optimal timing.

In rapidly aging societies, the application of robots has spread from industry to nursing and social welfare. As the designs of industrial and non-industrial robots are different, numerous robot components with various shapes and stiffness are required for different tasks. In this study, we attached a variable-stiffness link based on a shape-memory alloy (SMA) and the jamming transition phenomenon to a robot arm and evaluated its pick-and-place motion for various objects with different shapes and weights. The link can be fixed in an arbitrary shape and then restored to its initial shape via the shape memory effect. The objects were picked up and moved by a prototype link, which consisted of four SMA wires inserted in the jamming mechanism. We compared two states of the link, namely with and without deformation of the link into a shape (the centerline and the cross section) to suit the target object using a mold. Experiments confirmed that changing and fixing the link shape to suit the target object increased both positioning accuracy and weight capacity.

This study proposes a simultaneous localization method of a group of autonomous underwater vehicles (AUVs) based on one-way signals to realize distributed oceanographic surveys. Each AUV group consists of a single high-performance AUV (parent AUV) and the other AUVs (child AUVs). The child AUVs estimate their states (position and heading) based on the parent AUV as a positioning reference. By assuming a situation in which many AUV groups are deployed, the child AUVs can receive positioning signals from multiple parent AUVs. Although only the direction information of the parent AUV can be obtained from a signal from one parent AUV, the child AUVs can estimate their states by receiving signals from different parent AUVs. Sea experiments were conducted using an autonomous buoy and an AUV. The effectiveness of the proposed method was evaluated through a navigation simulation based on the sensor data obtained from the experiments.

During the period from sowing and planting to harvesting, outdoor crops are directly affected by the natural environment, including wind, rain, frost, and sunlight. Under such circumstances, vegetables change their growth conditions, shape, and flexibility daily. We aimed to develop an agricultural work-support robot that automates monitoring, cultivation, disease detection, and treatment. In recent years, many researchers and venture companies have developed agricultural harvesting robots. In this study, instead of focusing on intensive harvesting operations, we focused on daily farm operations from the beginning of cultivation to immediately before harvest. Therefore, gripping and cutting are considered basic functions that are common to several routine agricultural tasks. To find the assumed objects from a camera image with a low computational load, this study focuses on branch points to detect and identify even if the stems, lateral branches, and axillary buds are swaying in the wind. A branch point is a characteristic part close to the working position, even when the wind blows. Therefore, we propose a method to detect the assumed branch points simultaneously and divide each branch point into the main stem, lateral branch, and axillary bud. The effectiveness of this method is demonstrated through experimental evaluations using three types of vegetables, regardless of whether their stems are swaying.

Most research on automating gravel pile transport using wheel loaders has been performed primarily through simulations. Thus, studies should evaluate the usefulness of automatic gravel pile transportation by demonstrating it with an actual wheel loader. This study demonstrates automatic driving control using a retrofitted 3-ton wheel loader for gravel pile transportation. The driving model of a retrofitted wheel loader, in which multiple control systems are interlocked, is considered a simple control model with one input and one output for the pedal and vehicle velocity as well as for the steering wheel and steering angular velocity. In this study, we propose a simple and practical method for constructing a driving model via simple response analysis using an actual machine by constructing a feedforward control model based on control input/output using step responses. In this study, feedforward control was applied to the translation of the vehicle, which has a large dead time. By generating the path following the target point from the vehicle predicted position after the dead time from the driving model, the appropriate control input value calculation considering the dead time was performed. By applying the proposed method to a retrofitted wheel loader in a real environment and evaluating the control performance through control experiments, the effectiveness of the proposed method in practice was demonstrated.

Ocean waves play a significant role in coastal dynamics and the management of coastal development activities. However, there are limited instruments to measure the wave height, particularly in developing countries. This study introduces a novel instrument design for simple and cost-effective wave height measurement. The proposed instrument combines a Hall-effect sensor and an accelerometer to capture the rise and fall of a buoy in response to wave movements. The Hall-effect sensor as a rotary encoder detects the rotation of the buoy while the accelerometer measures the tilt of the instrument caused by ocean waves. The instrument is constructed using PVC pipes and incorporates long-range (LoRa) communication technology for real-time monitoring. Experimental tests were conducted at a study site in Banyuwangi Regency, Indonesia, where the performance of the instrument was compared with an ultrasonic sensor-based instrument. The results validate the effectiveness of the proposed instrument design for wave height measurement. The collected data were transmitted via the LoRa communication system, enabling convenient monitoring and analysis of sea-level changes. The valuable contribution of the instrument to the field stems from its precision in measuring the wave height, adaptability to diverse conditions, and potential applicability in shallow waters.