|
|
| Fig. 1: Fukushima Daiichi Nuclear Power Station. (Source: Wikimedia Commons) |
On March 11, 2011, a 9.0 earthquake struck 80 miles off the coast of Japan, resulting in a series of 50 foot tsunami waves that washed over the northeast coast of Japans main island. [1] The country was physically and financially devastated; the cost of the disaster was estimated in 2016 by the Japanese government to be approximately $202.5 billion. [2]
Among the resulting wreckage was the Fukushima Daiichi nuclear plant (Fig. 1), which houses six BWRs (boiling water reactors) and is operated by the Tokyo Electric Power Co. (TEPCO). Of the six BWR units at Daiichi, four were completely destroyed. Now, thousands of fuel rods remain onsite, as well as concrete and steel debris, and water contaminated with radioactive particles. Immediately following the disaster, the meltdown of these reactors caused a massive release of radioactivity into the environment. One of the main priorities in the decontamination process, therefore, is to minimize the release of any additional radiation. A particular concern facing TEPCO is the release of contaminated water into the ocean or groundwater. As the plant sits on a slope, precipitation runoff flows into the reactors, and additional water is circulated daily through the facility as coolant. As of March 2019, the store of contaminated water totals approximately 1 million tons and grows by 100 tons a day. Although precautions have been taken to contain the radioactivity, such as paving around the facility and erecting an underground barrier of frozen soil, groundwater near the plant continues to be contaminated. To avoid any further release of radioactive material, TEPCO is turning to robotics to clean up the facility as quickly as possible. Since most of the material onsite is too radioactive for humans to be near, creative solutions for imaging, scoping, and cleanup robots are necessary and emerging. [2]
The environment inside a melted-down nuclear reactor presents unique challenges to robotic scientists. The high gamma radiation levels found within Daiichi scramble the electrons inside semiconductors of hi-tech robots, eliminating them from possibility. Autonomous robots would face an environment so unpredictable and unknown to the developers that they would quickly get ensnared by an unforeseen obstacle. In addition, the molten fuel rods found inside the reactors are extremely volatile and require a degree of agility and maneuverability from the robot in order to avoid disturbing the material. The robotics teams tasked with clean-up had their work cut out for them, but the solution was not immediately clear. One analyst from ABI Research, Rian Whitton, says about the challenge, "Fukushima was a humbling moment. It showed the limits of robot technologies." [1]
Over the past few years, a series of robots have been sent into the reactors in an attempt at observation and data collection with varying degrees of success. Even some of the world's leading robotics companies are struggling to build for the hostile environment. In December 2016, Toshiba sent in the Scorpion, a two-foot long robot equipped with two cameras and a radiation sensor. Toshiba spent over two years developing the robot, and specifically designed it to overcome the challenges presented by the landscape of the reactor. After just two hours of its mission, however, the robot became stuck in debris. The Scorpions failure highlighted just how difficult this mission is. Since then, many iterations of the reconnaissance robot have been tested, each giving researchers more and more pieces of the puzzle through images, temperature readings, and radioactivity levels at different places in the reactor. [1]
In January 2018, Toshiba had a big breakthrough in Unit 2, one of the messiest reactors onsite. The robot, one foot long, four inches wide, and weighing about two pounds, carried a single pan-and-tilt camera. [1] Its simplistic design appeared to be advantageous, as the robot was able to be easily lowered into the containment vessel, offered the researchers a bird's eye view, and survived deadly-high levels of radioactivity. The robot's findings revealed a complicated mix of debris and melted fuel. In February 2019, a new version of the same robot returned, and was able to touch the materials, giving researchers valuable data on the nature of the deposits, as well as hints on how easily the deposits will be able to be moved by robots in the future. [1]
Although there is still much work to be done to complete the cleanup of Daiichi, the recent successes in robotics offer a little hope, and not a moment too soon. In 2016, the Japanese government increased its cost estimate to approximately $75.7 billion. In addition, TEPCO estimates the job will take 30 to 40 years to complete. [2] In light of these costly figures, the existence of nuclear power plants in Japan is in jeopardy. Some key players in the debate over Japanese nuclear energy, including Kiyoshi Kurokawa, a professor at the National Graduate Institute for Policy Studies, make the argument that instead of protecting nuclear plants with flawed defenses against earthquake damage, the government should invest in developing alternative power sources. As the difficult cleanup continues, Japan must weigh the benefits of nuclear energy with the growing costs of maintaining plants like Fukushima Daiichi. [3]
© Julia Grace. 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.
[1] R. Cheng, "The Fukushima Nuclear Meltdown, Eight Years On," CNET, 4 Mar 19.
[2] T. Hornyak, "Clearing the Radioactive Rubble Heap That Was Fukushima Daiichi, 7 Years On," Scientific American, 9 Mar 18.
[3] M. Rich, "New Quake Tests Resilience, and Faith, in Japan's Nuclear Plants," New York Times, 22 Nov 16.
