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Unclear debris map casts shadow over decommissioning of Fukushima plant

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Pebble-like sediment believed to be nuclear fuel debris is lifted by a special device inside the No. 2 reactor containment vessel at the Fukushima Daiichi Nuclear Power Station.
April 9, 2019
TOKYO — The government and Tokyo Electric Power Co. (TEPCO) are set to launch full-scale probes of the inside of the No. 1 through No. 3 reactors at the disaster-stricken Fukushima Daiichi Nuclear Power Station this fiscal year, in an attempt to determine which reactor to work on first to remove fuel debris — a critical step for decommissioning the facility.
However, the interior of the No. 2 reactor, which is most likely to be the first to go through the debris removal process, has turned out to be different from what had originally been expected, underscoring the difficulties entailing the removal work. Since many companies are involved in the process, how to pass down the know-how acquired over the course of the more than 30 year-decommissioning process also poses a challenge.
“At present, it is difficult to clearly say we are going to remove all fuel debris,” said Akira Ono, who leads the decommissioning project, at a regular press conference by TEPCO on March 28, while noting that the utility will not back down from its ultimate goal of full debris removal.
If TEPCO fails to take out all debris from the nuclear plant, the very premise for dismantling the facility and returning the plot to its original state will be undermined. Such a scenario would adversely affect the disaster recovery plans envisaged by the national government and the Fukushima Prefectural Government. While awareness about the difficulty of debris removal has been shared among concerned parties, the actual dismal situation had not been recognized until TEPCO conducted the first debris survey at the No. 2 reactor on Feb. 13.
In that survey, a remotely controlled special device that was injected into the No. 2 reactor’s containment vessel succeeded in lifting portions of sediment accumulated at the bottom, which were believed to be fuel debris. Officials involved were relieved because they “had been worried the material would not move at all,” according to Ono.
The radiation level of the material, measured at a distance of some 30 centimeters, was 7.6 sieverts per hour, far less than anticipated. If the sediment contained a good portion of nuclear fuel, the radiation doses ought to have been several hundred sieverts per hour, even eight years after the 2011 nuclear meltdowns.
This finding suggested that the sediment that TEPCO came in contact with in the survey was not the main nuclear fuel debris it was looking for. Many speculate that the surface of the sediment may mainly consist of metals including cladding tubes that used to cover nuclear fuels.
The question now is whether fuel debris exists beneath the surface of the sediment or if nuclear fuel still remains within the reactor pressure vessel, or even somewhere else. There are currently no prospects for TEPCO to ascertain an accurate distributions of debris.
The material that was lifted in the survey mostly comprised pebble-like sediment, weighing less than 1 kilogram in total. Meanwhile, fuel debris generated in the core meltdowns is estimated to total 237 metric tons at the No. 2 reactor alone and a combined 880 tons at the No. 1 through No. 3 reactors.
At the No. 2 reactor, TEPCO will conduct a more detailed survey on debris possibly in the latter half of this fiscal year and attempt to collect small amounts of samples. At the No. 1 reactor, several apparatus including a robot submarine will be used to launch a full-scale survey inside the reactor to try to collect debris this fiscal year. As for the No. 3 reactor, the power company is apparently planning to prioritize removal of spent fuel, as related devices have gone through a series of glitches.
Unlike the other reactors, the No. 2 reactor did not suffer a hydrogen explosion in the 2011 disaster. Therefore, the No. 2 reactor remains the primary candidate for the first full-scale debris removal work, which is hoped to start in 2021.
With regard to the No. 1 and No. 3 reactors, the utility has yet to be able to reach materials appearing to be debris. The decommissioning of the nuclear plant is scheduled to be completed in 2051, a full 40 years after the triple meltdowns, but a concrete path toward that goal is not yet in sight.
“We have no choice but to remove whichever debris we can,” said a senior official with the Ministry of Economy, Trade and Industry.
Naoyuki Takaki, professor of nuclear engineering at Tokyo City University, commented, “There could ultimately be a decision to stop debris removal after pulling out as much debris as possible. In that case, we would have no option but to consider building a sarcophagus like the one at the Chernobyl nuclear plant.”
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April 14, 2019 Posted by | fukushima 2019 | , , , | Leave a comment

Tepco to temporarily stop injecting water at Fukushima reactor

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November 9, 2018

Tepco to temporarily stop injecting water at Fukushima reactor
The operator of the Fukushima Daiichi nuclear power plant plans to temporarily stop injecting water into one of its damaged reactors to test the cooling of fuel debris.
Tokyo Electric Power Company announced it will conduct the 7-hour test at the No.2 reactor as early as March next year.
The unit is one of 3 in the 6-reactor facility that suffered a meltdown after the March 2011 earthquake and tsunami. The damaged reactors contain a mixture of molten nuclear fuel and structural parts.
TEPCO officials say water injections keep temperatures stable in the 3 reactors at around 30 degrees Celsius.
The planned experiment is aimed at checking how the debris is being cooled. It will be the first time to halt water injections into the reactor since they were stabilized after the accident.
TEPCO’s assessment says the reactor temperature would rise by around 5 degrees per hour if injections were halted by accident. But it says the rise will be limited to about 0.2 degrees per hour when natural heat radiation is taken into account.
TEPCO officials say they will begin cutting back on water injections by around half to 1.5 tons per hour for about a week as early as in January, before halting them completely in March after checking the results.
TEPCO estimates the 7-hour stoppage may raise the reactor temperature by about 1.4 degrees but says water injections will resume if the temperature rises more than 15 degrees.
Company officials say they want to assess changes in the temperature so they can use the data in future emergency cases, including earthquakes and tsunamis.
https://www3.nhk.or.jp/nhkworld/en/news/20181109_10/

November 17, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Fuel debris possibly found in Fukushima Daiichi’s Reactor 3

Images show possible fuel debris

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.

https://www3.nhk.or.jp/nhkworld/en/news/20170722_04/
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TEPCO surveys bottom of reactor containment vessel

The operator of the Fukushima Daiichi nuclear power plant has carried out another robotic survey in one of the damaged reactors. The probe is meant to confirm the existence and status of fuel debris consisting of molten fuel and reactor parts.

Officials of Tokyo Electric Power Company, or TEPCO, say the probe took place at the bottom of the containment vessel in the No.3 reactor on Saturday. The vessel’s bottom is thought to hold much fuel debris.

TEPCO used a robot designed to move through cooling water in the vessel.

The survey follows Friday’s release of photographs taken during the previous underwater robotic probe of the same vessel. The robot did not reach the vessel’s bottom during the first probe.

The images show rock-like lumps located near walls of a reactor-supporting structure and various other parts of the vessel.

TEPCO officials say it is very likely the lumps are fuel debris created after nuclear fuel in the reactor melted, mixed with reactor parts, and fell. If confirmed, this would be the first time fuel debris has been found in the No.3 reactor.

Robotic probes have so far failed to provide clear evidence showing the existence and status of fuel debris in other 2 damaged reactors.

Removing the fuel debris is one of the major hurdles to decommissioning the reactors which continues to emit extremely high levels of radiation.

https://www3.nhk.or.jp/nhkworld/en/news/20170722_22/

 

 

 

July 22, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Debris extraction method at Fukushima nuclear plant to be revealed

A state-backed entity is expected to soon compile a plan for decommissioning the crisis-hit Fukushima nuclear power plant, unveiling how to extract fuel debris from three reactors for the first time, sources close to the matter said Tuesday.

The Nuclear Damage Compensation and Decommissioning Facilitation Corp., tasked with providing technical support for decommissioning the complex, is mulling proposing a method to remove nuclear debris without fully filling their reactor containment structures with water, the sources said.

It means the debris inside the Nos. 1 to 3 reactors at the crippled Fukushima Daiichi complex is likely to be shaved off gradually with a drill or laser equipment, while pouring water shower under a remotely controlled operation, the sources said.

A method to fulfill reactor containers with water first is effective in blocking radiation from spreading but the entity decided not to adopt the approach as the three reactor containers are believed to have been damaged and water would likely leak.

july 5 2017 fuel debris removal.jpgShown in red is melted nuclear fuel, or nuclear debris. Shown in black is a drill or laser for scraping off the debris.

 

Under the method the entity currently envisions, some part of debris would remain in the air during the operation so a major challenge facing the debris extraction work is how to shield radiation and prevent debris from flying off.

While debris in the reactors has yet to be directly confirmed and information on the exact locations and conditions is limited, the extraction work, the most difficult part of the decommission project, is expected to proceed in stages from the side of the bottom part of each reactor container while ensuring safety measures, the sources said.

Based on the decommission plan to be compiled by the entity, the government and the plant operator Tokyo Electric Power Company Holdings Inc. are expected to determine a debris extraction scheme for each reactor building this summer and possibly review a road map for decommissioning the complex as well, the sources added.

Decommissioning the crippled reactors is expected to take at least 30 to 40 years.

The current road map calls for completion of a plan on how to extract debris from each reactor this summer and finalizing a detailed method for at least one of the three units in the first half of fiscal 2018 to begin the extraction operation in 2021.

Following a magnitude-9.0 earthquake in March 2011, tsunami waves inundated the six-reactor plant, located on ground 10 meters above sea level, and flooded power supply facilities. Reactor cooling systems were crippled and the Nos. 1 to 3 reactors suffered fuel meltdowns, while hydrogen explosions damaged the buildings housing the Nos. 1, 3 and 4 units.

At least 150,000 people in Fukushima were forced to live as evacuees amid radiation fears. While some have returned to their homes, the utility known as Tepco and the government face enormous challenges in scrapping the crippled reactors.

The Nuclear Damage Compensation and Decommissioning Facilitation entity was established after the Fukushima crisis, the worst nuclear disaster since Chernobyl, to help the utility pay damages for the calamity. The state-backed entity holds a majority stake in Tepco.

https://english.kyodonews.net/news/2017/07/ddee4ff9fec7-debris-extraction-method-at-fukushima-nuclear-plant-to-be-revealed.html

 

July 6, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Fuel debris extraction plan for crippled Fukushima reactors to be revealed soon: sources

n-fukushima-a-20170706-870x328.jpgA series of photos taken on Jan. 30 shows the inside of the Fukushima No. 1 nuclear plant’s reactor 2 pressure vessel. A specific method for removing debris is set to be revealed soon

 

A state-backed entity is close to completing a plan for decommissioning the crisis-hit Fukushima nuclear power plant, detailing for the first time how it hopes to extract fuel debris from three reactors, sources said.

The Nuclear Damage Compensation and Decommissioning Facilitation Corp., tasked with providing technical support for decommissioning the complex, may propose a method to remove nuclear debris without completely filling the reactor containment vessels with water, the sources said Tuesday.

The plan means the debris inside reactors 1, 2 and 3 at the crippled Fukushima No. 1 complex is likely to be shaved off gradually with a drill or laser equipment as a shower of water is poured remotely, the sources said.

Filling reactor containment vessels with water before removing the debris is seen as effective in blocking the spread of radiation, but the entity decided not to adopt the approach because they fear water may leak from the damaged structures, the sources said.

In the method currently being weighed, some debris would remain in the air during the operation, posing a major challenge in efforts to block radiation and prevent debris from flying off, the sources said.

While debris has yet to be directly confirmed and information on exact locations and conditions is limited, the extraction work — the most difficult part of the decommissioning project — is expected to proceed in stages from the side of the bottom part of each reactor containment vessel, the sources said.

Based on the plan, the government and the plant operator, Tokyo Electric Power Company Holdings Inc., are expected to determine a course of action for each reactor building this summer, possibly reviewing a road map for decommissioning the entire complex as well, the sources added.

Decommissioning the crippled reactors is expected to take at least 30 to 40 years.

The current road map calls for a debris-extraction plan for each reactor by this summer, with a detailed plan for at least one of the units ready in the first half of fiscal 2018. Extraction work would begin in 2021.

Following a magnitude 9.0 earthquake in March 2011, tsunami waves inundated the six-reactor plant, located on ground 10 meters above sea level, flooding power supply facilities. Reactor cooling systems were crippled and reactors 1, 2 and 3 suffered fuel meltdowns, while hydrogen explosions damaged the buildings housing reactors 1, 3 and 4.

At least 150,000 people in Fukushima were forced to live as evacuees amid radiation fears. While some have returned to their homes, Tepco and the government face enormous challenges in scrapping the reactors.

The Nuclear Damage Compensation and Decommissioning Facilitation entity was established after the crisis, the worst nuclear disaster since Chernobyl, to help the utility pay damages. The state-backed entity holds a majority stake in Tepco.

http://www.japantimes.co.jp/news/2017/07/05/national/group-mulls-fukushima-no-1-melted-fuel-debris-extraction-without-filling-containment-vessels-water/

 

July 6, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

‘Dry retrieval’ plan for nuclear fuel debris at Fukushima plant set to be adopted

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A public-private organization decommissioning the stricken Fukushima No. 1 nuclear power plant is poised to adopt a “dry” nuclear fuel retrieval method — extraction without filling the containment vessels with water — for the three reactors at the station that melted down in March 2011, the Mainichi Shimbun has learned.

Sources close to the Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF) say the method will be incorporated into the strategic plan for decommissioning that will soon be announced to the public. The government and Fukushima plant operator Tokyo Electric Power Co. (TEPCO) will establish fuel retrieval plans based on consideration of this method, and will deliberate a revision to the decommissioning road map as early as this summer.

Until now, the NDF had considered employing the submersion fuel retrieval method — filling the containment vessels with water — alongside the dry method. In the submersion method, water shields plant workers from radiation. The NDF, however, determined that repairing all damaged areas of the containment vessels in order to be able to fill the reactor wells to the top with water would be too difficult. Instead, for the time being, the NDF decided to prioritize dry removal of the nuclear fuel debris using robotic arms.

“It isn’t that we’ve decided to completely do away with the submersion method, but we have to think about how best to distribute the technological resources we have,” said one source closely involved with the NDF.

When using the dry nuclear fuel retrieval method, it is crucial to implement measures to prevent microscopic radioactive substances from spreading in the air. To counter this, the NDF is considering spraying water on the fuel as robotic arms are used to sever and retrieve the fuel debris.

The damage differs from reactor to reactor at the Fukushima No. 1 plant. Probes of the reactor interiors conducted by TEPCO have yet to directly observe the nuclear fuel, meaning that the shape and distribution of the debris remain unknown. Fuel removal methods specific to the state of each reactor must be decided before moving ahead.

In the No. 1 reactor, much of the nuclear fuel is believed to have melted through the pressure vessel onto the floor of the reactor containment vessel. Inserting a robotic arm through the side of the containment vessel to remove the melted fuel is under primary consideration to deal with this situation.

http://mainichi.jp/english/articles/20170705/p2a/00m/0na/008000c

 

 

July 5, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Fukushima Daiichi reactors internal estimates by Tepco

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In dismantling the Fukushima Daiichi nuclear power plant, it is essential to grasp the state of nuclear fuel melted its nuclear reactors, but the radiation is very high and it is difficult to see inside. Under these circumstances, TEPCO announced a new estimate chart for the interior of the three nuclear reactors.
TEPCO announced the estimate inside the nuclear reactors at the International Forum on Waste Plant on the July 3rd, 2017. In the inside of the nuclear reactor of Unit 3, a part of the nuclear fuel collapsed to the bottom of the pressure vessel and is stacked like a garbage while keeping its shape. Meanwhile, it seems that molten nuclear fuel has fallen to the bottom of the storage container beneath, but when analyzing the data at the time of the accident again, it is said that there is a possibility that it is eroding the concrete on the floor of the containment vessel .
Estimates were obtained reflecting computer simulations and recent internal surveys, etc. Based on these estimates, the government decided how to remove “fuel debris”.

https://headlines.yahoo.co.jp/videonews/nnn?a=20170703-00000081-nnn-soci

July 5, 2017 Posted by | Fukushima 2017 | , , | Leave a comment

Preventing Recriticality in Fuel Debris at Fukushima Daiichi Nuclear Power Station

 

This video released on July 16, 2016 by Tepco intends to explain the conditions of the fuel retained in the reactors of Units 1-3 at Fukushima Daiichi Nuclear Power Station, and TEPCO’s measures to prevent recriticality- return to a point at which a nuclear reaction becomes self-sustaining- in the fuel debris there.

July 17, 2016 Posted by | Fukushima 2016 | , , , | Leave a comment

NRA commissioner suggests plan to remove all fuel debris at Fukushima plant may not be best option

FUKUSHIMA – A Nuclear Regulation Authority commissioner has suggested that removing all fuel debris from reactors at the meltdown-hit Fukushima No. 1 nuclear power plant may not be the best option.
“I wonder if the situation would be desired that work is still underway to extract fuel debris 70 or 80 years after” the nuclear disaster, NRA Commissioner Toyoshi Fuketa told reporters Friday.
“There are a variety of options, including removing as much fuel debris as possible and solidifying the rest,” he added.
Fuketa and another NRA commissioner, Satoru Tanaka, visited the complex Friday, the last of the commissioners to do so ahead of the fifth anniversary of the March 11, 2011, earthquake and tsunami that triggered to the triple meltdowns at the atomic plant.
His remarks could affect the decommissioning plan drafted by the government and the plant’s operator, Tokyo Electric Power Co. Under that scenario, fuel debris is to be disposed of over the course of 30 to 40 years.
Fuketa said that unlike the disaster at the Chernobyl nuclear power plant, it is “not realistic” to construct concrete buildings to cover reactors at the Fukushima No. 1 plant because the situation is different.
The commissioner also questioned whether construction of an underground ice wall around the reactor buildings to prevent radioactive water buildup will prove effective.
http://www.japantimes.co.jp/news/2016/02/20/national/nra-commissioner-suggests-plan-remove-fuel-debris-fukushima-plant-may-not-best-option/#.VsijEubzN_m

February 20, 2016 Posted by | Fukushima 2016 | , , | Leave a comment