Tokyo Electric Power Company (TEPCO) began their exploration of reactor 3 on Wednesday, July 19 to determine the conditions in the Primary Containment Vessel (PCV) of Fukushima Power Plant. For the first time, TEPCO seems to have found evidence of resolidified melted fuel in the submerged reactor.

Primary Containment Vessel Exploration

On July 19, TEPCO began a multi-day exploration of Unit 3 at Fukushima Daiichi with the help of a swimming robot. This is a part of the long-term efforts the company is making in preparation for an eventual fuel debris removal as a result of the March 2011 meltdown.

Prior to the exploration, initial photographic investigations suggest that excessive heat may have caused the fuel assemblies to melt and drop from their intended positions to the pedestal area. As it turns out, there may be some truth to the hypothesis as the recent robotic exploration seems to have captured images of icicle-looking objects hanging onto the control rod drive.

Further, the robot also captured images of solidified lumps by the wall of the pedestal in the pressure vessel.

Melted Objects

According to the schedule for the investigation, photographs and videos are to be taken on the first day of the investigation, and depending on the footage review the next day, the robot will once again be used to focus on points of interest.

"From the pictures taken today, it is obvious that some melted objects came out of the reactor," said TEPCO spokesman Takahiro Kimoto. "In that sense, it is possible that the melted objects found this time are melted fuel debris or probably around it," he continued, pointing to the possibility that the extremely high temperatures may have caused the fuel to melt its surrounding structure, therefore mixing with them.

This is the first time that TEPCO has found evidence of likely melted debris in their explorations after the investigation earlier this year when they found black lumps in reactor 2, but were said to be difficult to identify.

Remotely Operated Vehicle

The robot TEPCO used for the investigation is a Remotely Operated Vehicle (ROV) just 11.9 inches (30 centimeters) long and 5.1 inches (13 centimeters) wide. It was designed to navigate underwater with its thrusters that allow it to move in different directions, while at the same time capturing images with its front and back cameras.

To conduct the exploration, it was inserted into the PCV through a pipe which was designed to prevent any radioactive gas escaping from the reactor.

No radiation impacts were recorded after the July 19 investigation, and another will be conducted on Saturday, July 22.