|Fig. 1: Kozloduy Nuclear Power Plant - Control Room of Units 3 and 4. (Source: Wikimedia Commons)|
Many countries that do not have domestic natural gas or oil supplies must rely on nuclear energy. A nuclear power plant is a highly engineered machine that provides electricity efficiently. While the nuclear power plant has various practical advantages, it has a critical disadvantage: Due to the danger of radiation exposure, it is hard for human beings to inspect and maintain the plant. Fig.1 shows a control room of the Kozloduy nuclear power plant and how complex the nuclear power plant is. In response to the increased demand, researchers have developed robots for nuclear power plants.
In 1992, Yamamoto published a paper about an inspection robot system.  The team started to build the robot from 1980. The goal of the robot was following: (1) Reducing the burden on workers, (2) Protecting workers from the tasks in hazard areas, (3) Improving operational efficiency. The main challenge was that the robot needed to observe and inspect the inside of the Primary Containment Vessel (PCV). PCV contains high radiation during boiling water reactor plant operation, so a human cannot and should not enter the area. The PCV area is composed of many pipes, valves and other structures. To make the robot move safely and reliably in the narrow environment, Yamamoto used a monorail system for the robot.
Yamamoto sorted all of the inspection tasks in the nuclear power plant. As the result, 68.3% of the tasks were vision-based, such as reading analog meter and checking valve positions. 19.3% were sound-based, such as listening for abnormal sounds and hearing vibrations from the system. 4.7% were checking the temperatures in the environment. Based on the statistical data, Yamamoto decided to use three types of sensors for the robot: a camera, a microphone, and an infrared camera. Cameras were used for inspecting the environments by eyes, microphones were used for detecting general sounds and vibrations, and infrared cameras were used for checking temperatures. The authors argued that the three types of sensors could cover more than 90% of all inspection tasks. The robot was installed and tested in the Fukushima Daini Nuclear Power Station #3 PCV.
While Yamamoto chose a monorail mechanism robot for reliability, other researchers investigated different robot mechanisms to enlarge the inspection working space of the robots. Briones et al. developed a wall-climbing robot using suction cups and pneumatic cylinders.  Luk et al. developed a four-legged robot for rough and uneven terrain in nuclear power plants. 
© Inrak Choi. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 S. Yamamoto, "Development of Inspection Robot For Nuclear Power Plant," IEEE 220030, 12 May 92.
 L. Briones, P. Bustamante, and M.A. Serna, "Wall-Climbing Robot for Inspection in Nuclear Power Plants," 351292, 8 May 94.
 B. L. Luk et al., "Intelligent Legged Climbing Service Robot for Remote Maintenance Applications in Hazardous Environments," Robot. Auton. Syst. 53, 142 (2005).