First step of decommissioning?

July 22, 2017

Images of fuel debris 1st step in deactivating Fukushima plant

http://www.asahi.com/ajw/articles/AJ201707220018.html

THE ASAHI SHIMBUN

The discovery of apparent icicle-shaped melted nuclear fuel within a reactor at the stricken Fukushima No. 1 nuclear power plant could be an important first step toward decommissioning the facility.

Images taken July 21 by a submersible robot that was remotely controlled to a position directly under the pressure vessel of the No. 3 reactor showed what appeared to be fuel debris that had melted through the vessel and later solidified, hanging like an icicle from the bottom of the pressure vessel.

Another pile of solidified material had also accumulated like lava on a structure below the vessel. The material was orange and gray.

The images provided the first confirmation of sizable amounts of solidified material although robots have been sent into three reactors at the No. 1 plant. In other "expeditions," high radiation levels crippled the robot activity and prevented further study.

Operator Tokyo Electric Power Co. said the manner in which the solidified material was found within the No. 3 reactor suggested the material is fuel debris.

"It clearly appears to be something that solidified after melting out of the pressure vessel," said one official. "We believe the material emerged after nuclear fuel mixed with structural matter within the pressure vessel."

Past analysis of the No. 3 reactor led to the assumption that almost all the nuclear fuel had dropped through the pressure vessel after burning a hole in the bottom and dripping down. The latest robot survey confirms that is what likely happened.

TEPCO officials plan to deploy the submersible robot July 22 to an even greater depth within the containment vessel that holds the pressure vessel. It aims to ascertain the amount of fuel debris that has spread at the bottom of the containment vessel.

Images taken by the robot over the two days of study will be analyzed, along with other data, to gain a firmer understanding of what the material is.

That could prove important in deciding how to proceed with decommissioning.

Possible melted fuel seen for first time at Fukushima plant

https://mainichi.jp/english/articles/20170722/p2g/00m/0dm/003000c#cxrecs_s

July 22, 2017 (Mainichi Japan)

TOKYO (AP) -- An underwater robot captured images of solidified lava-like rocks Friday inside a damaged reactor at Japan's crippled Fukushima nuclear plant, spotting for the first time what is believed to be nuclear fuel that melted six years ago.

Plant operator Tokyo Electric Power Co. said the robot found large amounts of lava-like debris apparently containing fuel that had flowed out of the core into the primary containment vessel of the Unit 3 reactor at Fukushima. The plant was destroyed by a massive earthquake and tsunami in March 2011.

Cameras mounted on the robot showed extensive damage caused by the core meltdown, with fuel debris mixed with broken reactor parts, suggesting the difficult challenges ahead in the decades-long decommissioning of the destroyed plant.

Experts have said the fuel melted and much of it fell to the chamber's bottom and is now covered by radioactive water as deep as 6 meters (20 feet). The fuel, during meltdown, also likely melted its casing and other metal structures inside the reactor, forming rocks as it cooled.

TEPCO spokesman Takahiro Kimoto said it was the first time a robot camera has captured what is believed to be the melted fuel.

"That debris has apparently fallen from somewhere higher above. We believe it is highly likely to be melted fuel or something mixed with it," Kimoto said. He said it would take time to analyze which portions of the rocks were fuel.

In an earlier survey Wednesday, the robot found severe damage in the vessel, including key structures that were broken and knocked out of place.

The robot, nicknamed "the Little Sunfish," on Friday went inside a structure called the pedestal for a closer look. TEPCO plans to send the robot farther down on Saturday in hopes of finding more melted fuel and debris.

Experts have said the melted fuel is most likely to have landed inside the pedestal after breaching the core.

Kimoto said the robot probe in its two missions has captured a great deal of useful information and images showing the damage inside the reactor, which will help experts eventually determine a way to remove the melted fuel, a process expected to begin sometime after the 2020 Tokyo Olympics.

"It's still just the beginning of the (decades-long) decommissioning. There is still a long way to go, including developing the necessary technology," he said. "But it's a big step forward."

Locating and analyzing the fuel debris and damage in each of the three wrecked reactors is crucial for decommissioning the plant. The search for melted fuel in the two other reactors has so far been unsuccessful because of damage and extremely high radiation levels.

The submersible robot, about the size of a loaf of bread, is equipped with lights, maneuvers with five propellers and collects data with two cameras and a dosimeter. It is controlled remotely by a group of four operators. It was co-developed by Toshiba Corp., the electronics, nuclear and energy company charged with helping clean up the plant, and the International Research Institute for Nuclear Decommissioning, a government-funded consortium.

Images show possible fuel debris

https://www3.nhk.or.jp/nhkworld/en/news/20170722_04/

Engineers at the Fukushima Daiichi nuclear power plant are working to scrap the facility's damaged reactors. For the first time, they've found what's likely to be fuel debris in one of them.

The engineers have been trying to locate molten fuel in the No.3 reactor. The fuel is thought to have melted and fallen to the bottom of the containment vessel.

They lowered a submersible robot into the 6-meter-deep cooling water in the vessel. The image sent back by the robot shows an orange substance on a device that operates the fuel control rods. Objects shaped like icicles are also visible.

The engineers plan to use the robot to look for fuel debris at the bottom of the containment vessel.

Removing the molten fuel from the reactors is the biggest hurdle to decommissioning them.