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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Decommissioning heavy challenges

March 9, 2017

Engineers Face Big Challenges



- Yoshihito Kametani


Engineers are trying to solve one of the biggest challenges involved with decommissioning the crippled Fukushima Daiichi nuclear power plant. They need to invent machines that can remove the melted fuel rods.

Earlier this year TEPCO sent cameras into the containment vessel of the No.2 reactor. One image they recorded shows a steel grating covered in a yellowish substance, and some parts of the floor that have caved in. The findings surprised some experts.

"I did expect to see a hole on the floor, but there are details which I didn't imagine," says Toru Ogawa, director at the Collaborative Laboratories for Advanced Decommissioning Science. "We see so much of something, sticking all over the floor -- this is what I didn't expect."

But he says it's difficult to tell what it is.

TEPCO had hoped to locate melted nuclear fuel. Removing it will be the biggest hurdle in the decommissioning process, but they've admitted that they still aren't sure where it is.

"We have yet to come to any conclusion about the exact location of the melted fuel. We intend to examine the information we have collected up until now, and then we'll come up with a more detailed judgment," says Yuichi Okamura, a TEPCO official.

High radiation levels have prevented anyone from going inside the containment vessels in the reactor buildings.

Researchers, including at Mitsubishi Heavy Industries in western Japan, are rushing to develop robots to help workers involved in the decommissioning. The company is testing a 7-meter-long robotic arm that can be remotely controlled. It may eventually be used at the crippled plant. But there are still many challenges ahead.

"We need to carry out maintenance remotely in the event of trouble. That's one of the toughest challenges," says Kenichi Kawanishi, an official at the company. "The most important thing is to find out how much and to what extent the fuel melted and spread."

TEPCO will inspect another reactor this month to try to find clues about the whereabouts of the molten fuel. They'll send this new robot with a small camera to the bottom of the containment vessel.


see also :


video : Decommissioning Fukushima Daiichi

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March 9, 2017


video : New Decommission  Technology

A testing facility for decommissioning work in the town of Naraha, less than 20 kilometers from the Fukushima nuclear plant, is being used to help develop robots and virtual reality programs that will be used in the project.

The evacuation order was lifted in Naraha a year and a half ago, and the facility was built to help research how to decommission the crippled plant. It’s run by the Japan Atomic Energy Agency, and all kinds of technologies are being brought in to come up with solutions for tackling the unprecedented nuclear accident.

Overcoming debris has been a hurdle for robots to do any work inside the reactor buildings. People can’t go inside of those buildings yet because of the high radiation levels, so it’s crucial for robots to find out what’s really happening.

Some of the tests involve robots that can function under water. They will be needed to explore parts of the reactors that are immersed in water to keep the melted fuel rods cool.

It's still unclear exactly where the melted fuel is. Technology to uncover those details is being developed as well because that's a crucial part of the decommissioning.

Eventually, the day may come when human researchers are finally able to go inside the reactor buildings. In order to get ready for that moment -- a virtual reality system is a crucial part of the preparations.

By wearing special glasses, researchers can experience in 3 dimensions what it’s like to actually move around inside the nuclear plant, avoiding poles and pillars that could get in the way when they try to bring in tools and equipment.

A lot of the work will be done in the dark at the Daiichi plant, which is why they practice moving around with a flashlight. Because of the high level of radiation inside, they have limited time to be inside, so at the top right hand corner of the screen in the simulation, participants can check how long they have been inside and how much radiation they have been exposed to.

The visuals used for training that we were shown are not what staff train with. There's another version that’s actually based on data brought back by cameras they’ve sent into the reactor buildings at the Daiichi plant, but that version is classified.

Hiroyuki Daido, director of the Naraha Remote Technology Development Center, speaks with anchor Minori Takao.

Takao: What part of the reactor building have you recreated so far?

Daido: Stairways around the containment vessel. Getting closer to the core is important for decommissioning, and using robots for that process.

Takao: But we know that the radiation level is way too high there now. So this training is about years into the future. What needs to happen to get to that stage?

Daido: We need to continue to get more data about the state of the inside of the buildings. Our cameras are already giving us a clearer picture, so hopefully if we keep advancing our robots, the day humans can get inside will get closer.

Takao: Despite all of the unanswered questions surrounding the plant, people are trying to plan ahead, in order to keep the already heavy damage from the accident to a minimum.

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