The 9.0 magnitude Tōhoku earthquake that occurred in Japan in 2011 and the tsunami after it caused major damage to the cooling system of the Fukushima I nuclear power plant, and with the explosion experienced after the melting of the three reactor cores, serious radioactive material was released into the atmosphere. This nuclear disaster was described by experts as the second largest nuclear disaster in history after the Chernobyl disaster in 1986.

After more than 10 years since the Fukushima disaster, which is described as the most complex nuclear accident to date, the remains of nuclear fuel, which melted and fell to the bottom of the reactor, which was the most damaged at the power plant, were successfully captured for the first time. An investigation has been launched in the area to find out more.

Nuclear fuel residues have been attempted to be imaged before

Most of the highly radioactive fuel in the explosion fell to the bottom of the containers in which they were stored, thus made it extremely difficult to get it out of the ground. Today, approximately 900 tons of molten nuclear fuel still remains in the facility’s three damaged reactors, including 280 tons in Unit One. Authorities predict that it will take 30-40 years to remove these remains.

A small robot equipped with cameras was sent to Unit 1, which is covered with 2 meters deep radioactive water, in 2017; This attempt was a failure due to high radiation and internal structural damage. But for the first time, a ROV-A robot equipped with small cameras has managed to take pictures of structures submerged in molten fuel and cooling water, plant operator Tokyo Electric Power Company (TEPCO) said on Thursday. In the statement, it was stated that the robot acquired interior images of the primary containment container during its mission to pave the way for the probes.

Company spokesperson Kenichi Takahara noted that piles of debris had risen from the bottom of the container, some of which were inside the plinth, a structure just below the core, where they were molten fuel falling into the area. Takahara added that further research will be needed to confirm what the objects in the images are.

On the other hand, Takahara stated that at one point the robot measured a level of radiation that was deadly to humans. Previously, the annual exposure limit for plant workers was 50 millisieverts.

The information obtained will be used for the safe removal of molten fuel

TEPCO noted that after analyzing the initial data and images collected by the robot, additional probes will be made. Also, five other robots, developed jointly by Hitachi-GE Nuclear Energy and the International Nuclear Decommissioning Research Institute, a government-funded consortium, will be used in the investigation, which will continue over the next few months.

TEPCO officials stated that the investigation at Unit 1 aimed to measure molten fuel piles, map them in three dimensions, analyze isotopes and their radioactivity, and collect samples. These data, which are crucial for developing equipment and strategy for the safe and efficient removal of molten fuel, will also allow for the eventual decommissioning of the reactor. In addition, TEPCO plans to use a robotic arm later this year to extract a ladle of melted fuel for the first time from Unit Two, the unit where internal robotic probes have made the most progress.