Probe shows challenges posed by melted fuel at Fukushima plant

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The rod-like probe outfitted with a tong-like pinching device that was used to touch melted nuclear fuel debris at the bottom of the No. 2 reactor at the Fukushima No. 1 nuclear plant
February 18, 2019
A specially designed, remotely controlled probe touched melted nuclear fuel debris at the bottom of a ruined reactor at the Fukushima No. 1 nuclear power plant in the first successful operation to inspect radioactive debris through direct contact.
The plant’s operator, Tokyo Electric Power Co. (TEPCO), lowered the rod-like probe outfitted with a tong-like pinching device into the primary containment vessel of the No. 2 reactor at the crippled plant and used the machine to successfully lift pieces of the debris several centimeters.
The removal of the fuel debris is the biggest challenge in the long process of decommissioning the reactors, which will take at least three to four decades. The lifting of debris is a ray of hope in the grim battle to overcome the formidable challenge.
But the success was tempered by the fact that there were large chunks with slick surfaces the robot’s pinchers were unable to grab. The probe found that deposits in various conditions lie scattered about the bottom of the vessel. Some pieces are apparently entangled in the surrounding equipment.
Tasks in and around the No. 1 to No. 3 reactors at the nuclear plant cannot be carried out by humans because of dangerously high radiation levels. Nuclear fuel in the core of these reactors overheated and melted down after towering tsunami triggered by an epic earthquake knocked out vital cooling systems on March 11, 2011.
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TEPCO to survey suspected fuel debris in reactor

 

February 7, 2019
 
The operator of the crippled Fukushima Daiichi nuclear power plant says it will conduct the first contact survey on suspected fuel debris inside one of the reactors. The device has a maximum length of 15 meters, making it possible to reach the area directly below the reactor core where the suspected fuel debris is located.
 
TEPCO says it can plan a sampling survey if the debris may be moved. TEPCO says the tip of the device will touch and pinch the debris. The company says it hopes to assess how hard the debris is and whether it can be moved.
 
TEPCO says it will begin a comprehensive debris retrieval operation in 2021. The firm adds that the information obtained will be used to assemble removal equipment even if the debris cannot be moved.
 
Tokyo Electric Power Company said on Thursday that it will insert the measurement device into the containment vessel of the No.2 reactor next Wednesday.
 
The firm plans to decide by March of next year which reactor it will first work on.
 

 

One more expensive robot to go probe in and to get fried

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Toshiba Corp.’s energy systems unit group manager Jun Suzuki shows a remote-controlled melted fuel probe device at its facility in Yokohama, near Tokyo, Monday, Jan. 28, 2019. Toshiba unveiled the device carrying tongs that comes out of a long telescopic pipe for an internal probe in one of three damaged reactor chambers at Japan’s
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A remote-controlled melted fuel probe device is unveiled by Toshiba Corp. at its facility in Yokohama, near Tokyo, Monday, Jan. 28, 2019. Toshiba unveiled the device carrying tongs that comes out of a long telescopic pipe for an internal probe in one of three damaged reactor chambers at Japan’s tsunami-hit Fukushima nuclear plant – this time to touch chunks of melted fuel.
Toshiba unveils robot to probe melted Fukushima nuclear fuel
Jan. 28, 2019
YOKOHAMA, Japan (AP) — Toshiba Corp. has unveiled a remote-controlled robot with tongs that it hopes will be able to probe the inside of one of the three damaged reactors at Japan’s tsunami-hit Fukushima nuclear plant and manipulate chunks of melted fuel.
The device displayed Monday is designed to slide down an extendable 11-meter (36-foot) long pipe and grip highly radioactive melted fuel inside the Unit 2 reactor’s primary containment vessel.
An earlier robot captured images of pieces of melted fuel in the reactor last year, but other details of the fuel’s status remain largely unknown.
Toshiba’s energy systems unit said experiments with the new probe planned in February are key to determining the technologies needed to remove the fuel debris, the most challenging part of the decades-long decommissioning process.
Robot to examine fuel debris in Fukushima unit
29 January 2019
Toshiba has developed a remotely-operated robot to investigate debris in the bottom of the primary containment vessel (PCV) of unit 2 at the damaged Fukushima Daiichi nuclear power plant in Japan.
The device developed by Toshiba for examining debris in unit 2’s PCV (Image: Toshiba)
A pre-investigation of the area directly below the pressure vessel – known as the pedestal – was carried out in January 2017 at Fukushima Daiichi 2 using a remotely operated camera on a telescopic probe. Photos taken during that investigation showed a black mass and deposits near a grating in the pedestal area, possibly melted nuclear fuel.
The following month, Tokyo Electric Power Company (Tepco) sent a “scorpion-shaped” robot – developed jointly by Toshiba and the International Research Institute for Nuclear Decommissioning (IRID) – into the PCV of unit 2. Although the robot was unable to reach the part of the vessel directly under the reactor pressure vessel, the company said the information it gathered would help it determine how to decommission the unit.
In January 2018, an internal investigation of the PCV of unit 2 using a suspended pan-tilt camera attached to a telescopic guiding pipe identified deposits and fuel assembly components at the bottom of the pedestal area.
Yesterday, a robotic device developed by Toshiba Energy Systems & Solutions Corporation was unveiled that will be used to explore these deposits. The device – approximately 30cm in length and 10cm in width – features a camera, LED lighting, a pan-tilt mechanism, finger drive mechanism (tongs), radiation dosimeter and a thermometer.
“Using know-how cultivated through previous investigations at the Fukushima Daiichi nuclear power plant, Toshiba ESS added a finger drive mechanism for touching the deposits to investigate their condition to the telescopic guiding pipe developed last January,” the company said.
“Until now we have only seen those deposits, and we need to know whether they will break off and can be picked up and taken out,” Jun Suzuki, a Toshiba ESS group manager for the project, told Japan Today. “Touching the deposits is important so we can make plans to sample the deposits, which is a next key step.”
The robotic device is scheduled to be deployed to investigate the interior of unit 2’s PCV next month.
Tepco has also carried out robotic surveys of the PCVs of units 1 and 3 at the Fukushima Daiichi plant.
In March 2017, Tepco carried out an investigation of the PCV of unit 1 using the PMORPH robot developed by Hitachi-GE Nuclear Energy and IRID. Equipped with a dosimeter and waterproof camera, it took radiation readings and digital images at ten different measurement points within that unit’s PCV.
In July that year, it inserted a screw-driven submersible robot developed by Toshiba and IRID into unit 3’s PCV.
Goro Yanase, vice president of Toshiba ESS’s Nuclear Energy Systems & Services Division, said: “We will continue to advance technology development and contribute to investigation of the interior of the Fukushima reactors.”

Toshiba unveils device for Fukushima nuclear reactor probe

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Toshiba Corp. unveiled a pan-tilt camera which it jointly developed with the International Research Institute for Nuclear Decommissioning (IRND), to inspect the interior of the damaged primary containment vessel of Fukushima Dai-ichi Nuclear Power Station Unit 2 in Yokohama, Friday, Dec. 22, 2017. The device shown to media Friday is 13 meters (43 feet) long and designed to give officials a deeper view into the nuclear plant’s Unit 2 primary containment vessel, where details on melted fuel damage remain largely unknown.
By Mari Yamaguchi | AP December 22 at 10:10 AM
YOKOHAMA, Japan — Toshiba Corp.’s energy systems unit on Friday unveiled a long telescopic pipe carrying a pan-tilt camera designed to gather crucial information about the situation inside the reactor chambers at Japan’s tsunami-wrecked Fukushima nuclear plant.
The device is 13 meters (43 feet) long and designed to give officials a deeper view into the nuclear plant’s Unit 2 primary containment vessel, where details on melted fuel damage remain largely unknown.
The Fukushima plant had triple meltdowns following the 2011 quake and tsunami. Finding details about the fuel debris is crucial to determining the right method and technology for its removal at each reactor, the most challenging process to safely carry out the plant’s decades-long decommissioning.
Japan’s stricter, post-Fukushima safety standards also require nuclear plant operators elsewhere to invest more time and money into safety measures.
On Friday, Kansai Electric Power Co. announced that it would decommission two idle reactors at the Ohi Nuclear Power Plant in western Japan, citing the difficulty of adding all the safety requirements at the nearly 40-year-old reactors that would be needed to get approval for their restart.
Reports have said it would cost about 58 billion yen ($500 million) and take 30 years to decommission a reactor, about half the estimated cost to restart one.
Also Friday, Japan Nuclear Fuel said that it was postponing the planned launch of its trouble-plagued spent fuel reprocessing plant by three more years until 2021. It cited delayed approval by the authorities. It also said it was postponing the planned manufacturing of fuel from recycled plutonium and uranium.
The mission involving Toshiba’s new probe at Fukushima’s Unit 2 reactor could come as soon as late January. Company officials said the new device will be sent inside the pedestal, a structure directly below the core, to investigate the area and hopefully to find melted debris.
The device looks like a giant fishing rod about 12 centimeters (4.7 inches) in diameter, from which a unit housing the camera, a dosimeter and thermometer slowly slides down. The probe, attached by a cable on the back, can descend all the way to the bottom of the reactor vessel if it can avoid obstacles, officials said.
Two teams of several engineers will be tasked with the mission, which they will remotely operate from a radiation-free command center at the plant.
A simpler predecessor to the pipe unveiled Friday had captured a limited view of the vessel during a preparatory investigation in February. A crawling robot sent in later in February struggled with debris on the ground and stalled in the end due to higher-than-expected radiation, its intended mission incomplete.
The upgraded probe has been co-developed by Toshiba ESS and International Research Institute for Nuclear Decommissioning, a government-funded unit of construction and nuclear technology companies over the past nine months.

Inside Fukushima Daiichi Unit 3 Robot Probe Inspections

TEPCO released three videos of its robot probe inspections inside unit 3. The videos provided some interesting information, showing some unexplained “blobs”, thick adhered substances, concrete spalling seen in fires, possible melted fuel formations, and thought to be solidified melted fuel around the lower end of a control rod.

TEPCO think the graphite gaskets sealing the control rod holes in bottom of the reactor vessel melted allowing molten fuel to flow through these holes to drip down into the reactor pedestal. Structures in the pedestal show some of the patterns created by the thick substances that appear to have splattered around the containment structures.

TEPCO cites 364 tons of fuel debris (melted fuel, internal reactor parts and control rods) to be expected at unit 3. The videos only show very small views of the damage found making it difficult to determine how much fuel debris was actually found inside unit 3’s pedestal.

 

 

 

Source : Tepco

http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=qf64ne97&catid=61785

http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=o6lm23vu&catid=61785

http://www.tepco.co.jp/en/news/library/archive-e.html?video_uuid=u10b97j8&catid=61785

Fukushima Unit 2 Radiation Readings Revised

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TEPCO revised unit 2’s containment inspection radiation readings done earlier in 2017, claiming a set of instrument and calibration errors caused the inaccurate readings.

TEPCO claims that their camera based radiation estimates were too high due to an oversight where they forgot to reset the sensitivity threshold on the equipment that was reading camera interference.

The final claim made in the report for downgrading the radiation readings was that one of the 4 sensors was reading considerably higher than the other 3. When they took that sensor out of the readings the other 3 sensors read considerably lower.

Source : Tepco’s handout

http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170727_03-e.pdf

Likely Melted Fuel Heap Found Inside Fukushima Daiichi’s Reactor 3 Shows Future Removing Difficulties

Underwater robot finds likely melted fuel heap inside Fukushima reactor

melted fuel 23 july 2017 3.This image captured by an underwater robot provided by International Research Institute for Nuclear Decommissioning on Saturday, July 22, 2017 shows heaps of solidified lava-like rocks believed to be nuclear fuel.

 

TOKYO (AP) — Images captured by an underwater robot showed massive deposits believed to be melted nuclear fuel covering the floor of a damaged reactor at Japan’s crippled Fukushima nuclear plant.

The robot found large amounts of solidified lava-like rocks and lumps in layers as thick as 1 meter on the bottom inside of a main structure called the pedestal that sits underneath the core inside the primary containment vessel of Fukushima’s Unit 3 reactor, said the plant’s operator, Tokyo Electric Power Co.

On Friday, the robot spotted suspected debris of melted fuel for the first time since the 2011 earthquake and tsunami caused multiple meltdowns and destroyed the plant. The three-day probe of Unit 3 ended Saturday.

Locating and analyzing the fuel debris and damage in each of the plant’s 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.

During this week’s probe, 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.

TEPCO spokesman Takahiro Kimoto said it would take time to analyze the debris in the images to figure out debris removal methods.

http://mainichi.jp/english/articles/20170723/p2g/00m/0dm/033000c

 

Melted nuke fuel images show struggle facing Fukushima plant

melted fuel 23 july 2017 2What is believed to be nuclear fuel debris has accumulated at the submerged bottom of the containment vessel in the No. 3 reactor at the Fukushima No. 1 nuclear power plant in an image taken on July 22. Part of the collapsed metal scaffolding is seen at back right.

 

Images captured on July 22 of solidified nuclear fuel debris at the bottom of a containment vessel of the crippled Fukushima No. 1 nuclear power plant show the enormity of decommissioning of the facility.

Plant operator Tokyo Electric Power Co. said it will closely study the images from the No. 3 reactor’s containment vessel to determine the spread and amount of nuclear fuel debris.

After analysis, TEPCO will decide on a policy to retrieve the fuel debris.

The government and TEPCO plan to start the retrieval process in one of the three crippled reactors at the plant from 2021.

It will be a formidable task, given that a method of recovering debris that is stuck to the floor has yet to be considered.

The recent images were taken by a submersible robot, which was sent into the containment vessel on July 19, 21 and 22.

The No. 3 reactor’s containment vessel is filled with water to a depth of 6.4 meters.

On the final day, the remote-controlled robot was dispatched to the deepest part of the containment vessel.

The images showed that pieces that fell from the structure and deposited material accumulated to a height of about 1 meters at the bottom of the containment vessel.

In particular, what is believed to be nuclear fuel debris is scattered in the form of rocks in the area directly beneath the pressure vessel.

The latest investigation has confirmed TEPCO’s assumption made through analyses that most of the reactor’s nuclear fuel melted through the pressure vessel and accumulated at the bottom of the containment vessel.

It also discovered that the nuclear fuel debris has spread throughout the containment vessel.

The images marked the first confirmation through a robot probe of a large amount of nuclear debris in any of the embattled No. 1 through No. 3 reactors.

http://www.asahi.com/ajw/articles/AJ201707230012.html