In 2011, an unusually high magnitude earthquake off the shore of Japan produced a major tsunami which hit the shore of Eastern Japan with great force. The original earthquake and the resulting tsunami flooded the site of the Fukushima Nuclear Facility. Cooling systems went off line and emergency power systems were crippled as well, making it impossible to effectively cool the reactors. Emergency generators and pumps helped to eventually cool the overheated reactors with sea water. Partial melt down of reactors occurred, but sufficient cooling was restored to prevent additional melt down. Radioactive plumes were released from the facility and fallout occurred both on land and at sea. Citizens in fallout areas were evacuated. Many were able to return to obtain some uncontaminated belongings, but have not been able to stay permanently. Over the following year or so the site was cleaned up and Tokyo Electric declared the site stable (but not without substantial oversight).
Tokyo Electric has estimated a timeline of 40 years for complete clean-up and decommissioning of the site. Several of the reactors are still aglow and need to be watered down constantly to prevent further melt down. Cooling continues constantly while cooling water is recaptured and stored. Overall, neverending vigilance is required to keep the site stable. The cooling water is collected. It is radioactive and currently stored in large tanks, a thousand of which have been installed. The tanks also need to be monitored regularly for leaks. Cooling water also accumulates at lower levels in the facility and leaks underground and into the bay. These leaks are being lowered as increased efforts are made to prevent further release of radioactivity into the sea. Flounder caught in Fukushima Bay generally cannot be consumed as they are too radioactive to be eaten.
Systematically all six reactors at the Fukushima facility will need to be decommissioned. This may take at least 40 years. Almost any work at the site is too dangerous for humans to do directly. The inner regions of the site are so contaminated that just the light work of scraping walls cannot be done without being exposed to life threatening levels of radioactivity. The Japanese are developing highly specialized robots to do this work?
Chernobuyl can’t really teach us much about how to proceed with Fukushima other than the fact that a melt down at a nuclear power plant is a dangerous thing. But we knew that already. Subsequent to a melt down the clean up will not be done until the melted down core is taken apart, dispersed and safely buried. Nevertheless, the unstable melted cores at Chernobuyl and Fukushima have to be dealt with differently. The Chernobyl reactor is buried in concrete and it may be rather a long time before anything resembling clean up can occur at the site. Fukushima can be cleaned up. It may take 40 years or longer, and robots, many of which still need to be invented.
At Fukushima, a five stage process is envisioned.(1) The first step is to remove debris from the walls of the entire facility. Robots are required even for this process. The levels of gamma radiation are too high, and a human working for only a short period would be exposed to more radiation than he or she would normally be allowed to take in safely in a year. Nevertheless simple robots should be able to scrub down the walls and take away the radioactive debris. (2) Robots will be sent in to map invisible hot spots in the facility. They can likely solve the problem of bent and twisted steel and concrete that interferes with sending in something or someone much larger. They also have to be booked to cables that don’t get caught in the twisted materials. (3) Once hot spots are mapped hot spots can be divided into multiple kinds, but generally at least it will be possible to differentiate between those that may be easy to remove vs. those which are not. Robots may be able to use high pressure water to break apart some of the hotspots, and afterward removing the fragmented pieces. (4) The next step is to begin to remove spent fuel rods. The are at least 1500 of these and it may take a year to remove them all. (5) The next step is to remove the damaged nuclear core elements. Again new robotic machines may need to be invented.
Interestingly, Japan has shifted and presumably will continue to shift away from nuclear power. Many reactors have been shut down. However, given their economic situation they may start up a few reactors — not necessarily all of the them. However, they have 40 years at least of major clean up at Fukushima in front of them, and a major concern is that an additional seismic even could destabilize an already precarious situation still further. One hopes this does not occur. If it were to happen, the stability at the Fukushima site could be compromised again. Once the melted cores have been removed there should be less chance of destabilization. Until then destabilization could lead to further major releases of radioactivity.