Nuclear fuel located inside reactor: TEPCO

Images captured by the Little Sunfish robot between July 19 and July 21 of the inside of reactor 3 at Fukushima No.1 Nuclear Power Plant. The branchlike structures at upper left of the lower, larger image (and the lower left corner of the 4th image in the gallery) is thought by plant operator TEPCO to be nuclear fuel debris that melted to the bottom of the reactor following the March 2011 nuclear disasters at the plant. Other materials in the photos are thought to be various components of the reactor that melted and collected at the bottom of the reactor vessel - a solidified melted mush sometimes referred to as corium. The oval dial-like component pictured top left, is said to be a part of the reactor's control rod mechanism. All images: TEPCO

Stricken Fukushima nuclear plant operator TEPCO is now claiming that recent images captured by the swimming robot that entered the plant's No. 3 reactor may well show huge deposits at the bottom of the reactor that include clumps of melted nuclear fuel.

TEPCO official Takahiro Kimoto announced late Friday that some of the images taken by the Little Sunfish robot, which began investigations inside reactor 3 at Fukushima No. 1 Nuclear power plant on July 19, showed clumps resembling solidified lava-like rock  that may prove to be remnants of the nuclear fuel.

Kimoto said at a press conference in Tokyo that this is the first time "such clear images of what could be melted fuel” have been taken. “We believe that the fuel melted and mixed with the metal directly underneath it," he added. "It is highly likely that we have filmed that on Friday.” 

The fragments pictured are thought to be located among rubble collected at the bottom go the reactor that measure as much as 2 meters in depth. The rubble is located at the base of a structure called the pedestal, which  sits underneath the core inside the reactor's primary containment vessel. 

Images of what was thought to be melted fuel debris were first noticed on Friday and the search for confirmation continued Saturday, the final day of the Little Sunfish's three-day probe inside  reactor 3. There was, however, some confusion in reports about how the pictured nuclear fuel appeared, some saying it was in large clumps, others that it was hanging in icicle-like shards.

Previous searches for melted fuel debris inside two of the other destroyed reactors, (reactors 1 and 2),  produced inconclusive results, and further analysis of the imagery collected this time will be required to gain conclusive evidence that it is in fact melted fuel. At present it remains little more than speculation by TEPCO that it is in fact fuel debris.

Locating the fuel debris in the plant’s three wrecked reactors is said to be a crucial step in the decommissioning of the Fukushima plant, a process that is estimated to take up to 40 years. Without such location and analysis the removal of the highly radioactive fuel will be hazardous, especially as the reactors are in such a damaged, treacherous state only accessible by robots. A novel method to remove the fuel debris was recently reported as being presented by a company helping with the decommissioning process.

One thing that has become clear from this recent find is that, should indeed the fuel debris be a part of the matter shown in the pictures, extracting it from the reactor could be an even more complex process than originally thought. Shown among the items that  have ended up in the bottom of the vessel and are mixed up with what is claimed to be the fuel debris are metal components of the grid used to keep the reactor's control rods in position. 

In other Fukushima related news, TEPCO's announcement last week that it plans to dump more than huge amounts of radioactive water into the Pacific Ocean has caused a stir among residents.

Fishermen and other residents in Fukushima have expressed concern about the planned dumping of 770,000 tons of contaminated water into the sea, saying the announcement is premature and first requires the green light from government and other official bodies.
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​Source: TEPCO, NHK, Mainichi