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 [1]. 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].
It was also recognized that it is important that the nuclear response robots can be immediately transported to the accident site. The outdoor reconnaissance robots were designed to be stored in a transport and control vehicle. The transport and control vehicle delivers the robots to the site and the robots are controlled from inside the vehicle. The indoor reconnaissance and task robots were designed to be stored and transported in containers. For the indoor reconnaissance and task robots there were additional containers for storage and transportation of the control systems. The containers were also designed to be the operator stations. For example, a RESQ system consisted of two containers (Fig. 1) with the two RESQ-A (Fig. 2), the RESQ-B (Fig. 3), the RESQ-C (Fig. 4), the robot controls, and accessory items. The list of accessory items included two diesel generators (Fig. 5). It was expected that the containerized systems could be delivered to the accident site as soon as trucks, trailers, and drivers could be arranged.
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.
In order to support the emergency efforts at Fukushima, JAEA decided to modify the RESQ robots and a Brokk-40 robot which they also owned. The Brokk-40 was modified to the JAEA-1 robot by adding a blade for moving concrete rubble created by the hydrogen explosions. The blade was to be used to clear the way for small reconnaissance robots. To decontaminate floors in the reactor buildings, JAEA repaired and modified one RESQ-A robot to the JAEA-2. The main modification on JAEA-2 was a water sprayer. To detect hot spots on reactor building floors, the second RESQ-A was repaired and modified to the JAEA-3. The main modification on JAEA-3 was a gamma ray imaging and measurement device called Gamma Eye. JAEA also built robot control and transport vehicles RC-1 and RC-2. Each RC transports a robot and accessory components including a shielded operation box, area camera, radiation dose meter, a smaller gasoline drive generator, and so on [6, 7] (Figs. 6, 7).
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.
