A remote-controlled robot has dived into the radiation-riddled waters of the Fukushima power plant and captured images of melted nuclear fuel laying along the murky depths of a reactor. 

As part of the clean-operations at the Fukushima Daiichi Nuclear Power Station in Japan, engineers sent down a remotely operated submarine into the bowels of Unit 1 on February 9, according to plant operator Tokyo Electric Power Company Holdings (TEPCO).

The Fukushima nuclear disaster unfolded on March 11, 2011. After being struck by an earthquake and a 15-meter (49-foot) tsunami, three reactors at the Fukushima Daiichi nuclear power plant in northeastern Japan suffered catastrophic meltdowns, in what became the most severe nuclear disaster since the 1986 Chernobyl event. Due to the harmful radioactive isotopes that were spewed into the surrounding environment, nearly 160,000 residents were promptly evacuated and Japanese authorities implemented a 30-kilometer (over 18 miles) exclusion zone around the power plant.

When the catastrophe struck, Units 1, 2, and 3 were busy working and had fuel in their reactors. The tsunami knocked down the power sources and cooling systems used to control the temperature of the fuel, which resulted in a colossal amount of heat to melt the fuel and the reactor. Eventually, this melting slurry of radioactive fuel and equipment cooled down and solidified into the radioactive debris that the engineers are currently figuring out how to remove.  

The aim of the latest mission was to gain information about Unit 1’s primary containment vessel, as well as locate the tons of melted nuclear fuel debris that still lies in the submerged highly radioactive waters. The plan is to eventually remove this radioactive debris, but the team is currently just surveying the size of the melted debris and analyzing the isotopes being emitted.

Robots are used to this job because levels of radiation in the depths of the plant are too dangerous for humans. As per the Associated Press, some areas the robot explored pick up radiation levels of two sieverts, an ionizing radiation dose that is fatal for humans.

With the help of the robot submarine's camera, the team installed special guide rings around the building, which will help steer the path for future probes. The camera also managed to capture some snaps of nuclear fuel that melted and fell to the bottom of the damaged reactor.

TEPCO, together with the International Research Institute for Nuclear Decommissioning (IRID) and Hitachi-GE Nuclear Energy, is tasked with clearing up and "decommissioning" the power plant. Some of the efforts will be geared towards the removal of this physical nuclear debris, but they also have the problem of dealing with the highly radioactive waters that flooded the power plant. As it stands, the plan is to dump some of this contaminated water in the Pacific Ocean, although this idea has kicked up a storm of controversies. In total, the whole decommissioning process is not expected to be finished until 30 to 40 years from now.