- Development Report
- Open Access
Unitization for portability of emergency response surveillance robot system: experiences and lessons learned from the deployment of the JAEA-3 emergency response robot at the Fukushima Daiichi Nuclear Power Plants
© The Author(s) 2017
- Received: 23 August 2016
- Accepted: 28 January 2017
- Published: 16 February 2017
It was cleared that transportability of emergency response robots system had been very important. Therefore, RESQ series robots, which were developed by Japan Atomic Energy Research Institute (present, Japan Atomic Energy Agency: JAEA), were installed or stored in containers for easy transportation to the accident site. After Fukushima Daiichi NPPs’ accidents occurred, JAEA modified a RESQ-A robot in order to meet the situation of the accidents with consideration of transportation. However, actual situation was beyond the anticipation, and unitization was required to deploy JAEA-3 robot to Fukushima daiichi NPPs. The actual confused situation was many rubble were scattered and temporary cables and hoses were constructed in the reactor buildings, so that reconnaissance robots should be conveyed by operators through limited route, should be reassembled in short time. JAEA modified again in order to unitize JAEA-3 robot system in Fukushima daiichi NPPs. It was lesson learned that emergency response robot system needed to be unitized for increase of portability, and that “Unitization policy for emergency response robot system” was developed.
- NPP accident
- Emergency response
- Robot system
- Unitization policy
Development of nuclear emergency response robots after the JCO criticality accident
The JCO criticality accident occurred on September 30, 1999 when technicians making nuclear fuel using unapproved processes, poured too much around 20% enriched uranium nitrate into a precipitation tank. Stopping the criticality subjected workers to higher than normally approved radiation doses and it was recognized that nuclear emergency response robots were needed to respond to future accidents.
Three organizations developed nuclear emergency response robots: Nuclear Safety Technology Center, Japan Atomic Energy Research Institute [JAERI, now reorganized to Japan Atomic Energy Agency, (JAEA)], and Manufacturing Science and Technology Center (MSTC). The Nuclear Safety Technology Center developed the Monirobo-A and Monirobo-B for outdoors reconnaissance . JAERI developed the RESQ series robots which included two RESQ-A, a RESQ-B, a RESQ-C, and a RaBOT for indoors reconnaissance [2, 3]. MSTC developed the SMERT-K, SMERT-M, SWAN, MARS-A, MARS-T, and MENHIR robots for indoor tasks [4, 5].
JAEA’s response to the Fukushima accident using nuclear emergency response robots
When the accidents at the Fukushima Daiichi Nuclear Power Plants (NPPs) occurred on March 11, 2011, the RESQ series robots were not mission ready. Due to lack of budget, the robots which were still stored in their containers were not maintained and there were no trained operators. The RaBOT robot had been abandoned. JAEA contacted the original manufacturer of the robot for help getting the RESQ robots operational. The original manufacturer was unable to support the need because their facilities had also been damaged by the earthquake and the original engineering was not accessible. In addition, the original engineer was no longer with the company and since the RESQ robots were over 10 years old, some components in the robots were no longer available. After the initial inability to get RESQ robots operational it became apparent that the RESQ robots would not have been suitable for the conditions at Fukushima.
Preparation of the JAEA-3 robot system
The JAEA-3 Robot system was prepared and which system consisted of JAEA-3 robot, the newly developed Gamma Eye, and accessory components. The mission of the system was planned to find out the hot spot on the floor or wall of reactor buildings. Gamma Eye was designed to be remotely operated and to be small and light enough for small reconnaissance robots like JAEA-3. Other modifications on the JAEA-3 robot were done to increase radiation resistance and to waterproof JAEA-3 for water spray decontamination. To increase the radiation resistance of JAEA-3, electronic circuits like servo drives were moved from the robot and into the controller. Long cables connect the controller to JAEA-3. Moving electronic components from the robot to the robot controller increased the radiation resistance of JAEA-3 robot by more than an order of ten thousand Sievert. High pressure water spray was planned for decontamination of the robot itself and the robot was required to be waterproof. However the rubber cables and tires were expected to be difficult to decontaminate with high pressurize water, because small pores on the surface of the rubber would trap small particles of radioactive Cesium. Alternative tires and cables were prepared for use during maintenance to reduce radiation dose to the technicians. The alternative cable for maintenance was short, which made it easier to handle during maintenance.
The RC-2 was a tracked vehicle with: a remotely operated lift for robot deployment, a shielded operation BOX for reducing operators’ radiation exposure during robot operations, an area camera for easy robot operation, dose rate meter, a smaller gasoline generator with 100 VAC output, a 6 MPa water spray and so on. All components were installed or stored on the RC-2, to assure transportability of the JAEA-3 robot and accessory components.
The modification and preparation was started at the beginning of May 2011, and was completed near the end of May, and ready to deploy to unit 2 of the Fukushima Daiichi NPPs.
Actual situation and requirements for deployment at Fukushima Daiichi Nuclear Power Plants
The radiation level was so high the JAEA-3 operator would be exposed to, too much radiation if the robot control vehicle RC-2 is used in the truck-lock of unit 2 of the Fukushima Daiichi NPPs.
In order to deploy JAEA-3 robot to survey for hot spots using Gamma Eye in unit 2 of the Fukushima Daiichi NPPs, operators would have to carry robot and accessory components from the turbine building to the reactor building.
There is a long corridor the from turbine building to reactor building where there were temporary cables and hoses that were used to stabilize and cool the reactor cores. A temporary walkway covered the cables and hoses and let operators walk over the cables and hoses.
The smallest opening was 700 mm wide × 700 mm high.
The floor of the turbine building was contaminated and components temporarily put on the floor while being transported through the building would become contaminated.
The turbine building did not have sufficient ventilation for an internal combustion engine to be run inside the building.
Operations, including carrying units, disassembly, and reassembly, would require operators and technicians to be in a radiation protection suit with full face mask for 3–4 h.
Disassembly and reassembly requiring special operator’s skill or tools would require more time that operators and technicians need to be in radiation protective gear.
A deployed robot would become contaminated.
Unitization policy for the JAEA-3 robot system
Unitization should be completed in 1 month.
Support would not be available from the maker.
It would be difficult to procure special parts.
Each unit should weigh less than 25 or 35 kg, so that one operator could carry it.
Each unit should be smaller than 400 mm depth, 600 mm width and 1000 mm high, to allow the unit to be carried through the 700 mm wide × 1000 mm high opening.
Each unit should fit on a three-wheel-carrier (Fig. 8) to limit the contamination of the unit and to make the units easier to carry and back pack.
Each unit should be assembled with waterproof connectors and without special tools.
Units of the JAEA-3 robot system
Consists of the area camera, a camera tripod, and a cable from the camera to the controller. JAEA-3 did not have a robot mounted camera, but the operator could watch JAEA-3 on the area camera while viewing the output of Gamma Eye. After the robot operational test, the operator could operate the robot using the area camera.
In addition, servo drives for the motors of the JAEA-3 robot were also located inside the control station. It was difficult to find servo drives compatible with the motors from the RESQ-A robot. Many servo drive suppliers were affected by the earthquake and tsunami and were unable to provide servo drives to JAEA. Sawamura Denki Corporation was able to supply servo drives which were almost completely compatible with the JAEA-3 motors. These servo drives had low radiation resistance and it was decided the servo drives should be located in unit 2.
Unit 3 was a 50 m cable to connect the robot and the controller. A single cable with all the conductors could not be manufactured in the short time frame. Several cables were tied together and covered by heat-shrink tube.
Unit-4 was a battery module instead of the gasoline generator to supply power. The battery module was rated for the motor surge currents, could be easily recharged, and powered the Gamma Eye and area cameras.
Unit 4 was the same type of lead-acid battery that is used in cars and an inverter to convert 12 VDC to 100 VAC. All equipment was designed for 100 VAC.
Unit 0: JAEA-3 robot equipped with Gamma Eye
The most difficult equipment to unitize was the JAEA-3 robot equipped with the Gamma Eye, gamma ray imaging and measuring device.
One option was to disassemble Gamma Eye from JAEA-3 and then reassemble the Gamma Eye to the robot. Reassembly would require making mechanical and electrical connections and then precisely aligning and adjusting Gamma Eye, while wearing one cotton glove and three rubber glove for radioactive contamination control. This is very difficult and would potentially expose the operators to high radiation doses.
Contents of each unit
Equipped with “Gamma Eye”
Picture as shown in unit 2 on monitor
Includes servo divers, camera control units and monitors and PC for gamma camera
Consists of multi-line cable, a twisted pair cable and a stainless steel wire
Consists of two 12 V lead acid batteries and DC/AC inverter
Deployment of the JAEA-3 robot system
By dividing the JAEA-3 robot system to five units, it was possible for operators to carry the units and deploy the robot.
Importance of portability of nuclear emergency response robots
As mentioned above, it had been recognized that transportability to an accident site was important. Portability of the robot which allows operators to carry the robot system into buildings for deployment is also recognized as important.
Emergency response robots and the process for deploying the robots should be considered as a system. The system should consider storage in a robot control vehicle in order to allow immediate transportation to an accident site. By unitizing the system into units that can be carried by one or two operators the emergency response team can bypass obstacles like debris and stairs to deploy the robot deep inside a building.
Development of a general unitization policy for portability of nuclear emergency response robot systems
Divide the robot system including the robot itself and accessory components into units weighing less than 25–35 kg, so that each unit could be carried by a single operator.
Sometimes a unit weight of 35 kg or less is not possible. For unit weights of 35–70 kg, add hand holds and carry straps to allow two people to carry the unit. For unit weights over 70 kg, additional solutions should be evaluated.
Limit contamination of each unit to make decontamination of the units easier. For example, units could be transported on a cart, so that contamination is limited to the cart wheels.
To minimize radiation dose to maintenance personnel, remove contaminated components that are not easily decontaminated. For example, temporarily replace the robot cable and wheels.
Units should be easy to reassemble without special tools. For example, tool free connectors could be used.
Avoid build-to-order parts or custom-made parts. Store common parts like tool free and waterproof connectors, so that operators can modify or optimize the system quickly.
The unitization policy would help the robot emergency response team immediately deploy a robot system in response to a nuclear emergency.
SK carried out the total engineering of the dividing and designed the dividing except video system, participated in the sequence alignment and drafted the manuscript. RM carried out designed and participated in the dividing of video system, HA conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Tsutomu Tanaka, Kagekiyo Oikawa and Naoto Yagi for deployment of the JAEA-3 robot system in the Fukushima Daiichi Nuclear Power Plants, Sawamura Denki Corp for supplying servo drives compatible with JAEA-3 robot motors quickly during a very challenging time.
The authors declare that they have no competing interests.
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