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High-level radiation at Fukushima Daiichi No.2 reactor

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February 4, 2020

Japan’s nuclear regulators say high-level radiation was detected last month in the No.2 reactor building of the crippled Fukushima Daiichi nuclear plant.

The Nuclear Regulation Authority last October resumed its probe into what caused the accident at the plant following the March 2011 earthquake and tsunami.

The results of a survey carried out last Thursday on the top floor of the building were disclosed at a meeting of commissioners and experts on Tuesday.

A meltdown took place at the reactor after the 2011 accident.

A robot on the floor directly above the reactor detected 683 millisieverts of radiation per hour.

The plant’s operator, Tokyo Electric Power Company, had also detected high levels of radiation there after the accident.

The site remains inaccessible to humans nine years later.

Commissioners and experts were also shown video of the No.4 reactor, which avoided a meltdown but experienced a hydrogen explosion. The video shows a steel frame believed to have been exposed by the blast.

The regulation authority plans to compile the data into a report this year, not only to determine the cause of the accident but also for work to decommission the reactors.

https://www3.nhk.or.jp/nhkworld/en/news/20200204_41/

February 6, 2020 Posted by | Fukushima 2020 | , , | Leave a comment

Radiation levels in one Fukushima reactor high enough to kill a human in two minutes

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December 9, 2019

The radiation levels in ‘s unit two reactor are so high they could kill a human in two minutes, according to data collected by a robot.

Tokyo Electric Power, the company which operates the nuclear plant in Fukushima, carried out a robotic survey of the area around the core that melted six years ago, following the earthquake and tsunami that triggered the .

But the scorpion robot Sasori got stuck inside the reactor after its crawling functions failed while climbing over highly radioactive debris and had to be abandoned inside the reactor.

It recorded radiation measures in the area of 210 sieverts per hour, which are lethal enough to kill a human within two minutes.

This is not the first time a robot has become inoperable after entering the reactor.

During a previous survey, another robot designed to clean the debris for Sasori’s passage had to return halfway through when two of its cameras failed after being exposed for two hours to radiation and reaching its maximum tolerance of 1,000 sievert. Such an exposure to  can kill a human within seconds.

Despite the dangerously high levels of radiation, company officials said it was not leaking outside the reactor.

The high radiation and inadequate cleaning of the reactors could also limit the scope of future investigations and the company may have to develop more radiation-resistant cameras and equipment.

The probe was specially developed for surveying the interior of the crippled reactor and collect data that will assist in removing the melted fuel.

But the level of radiation and the presence of debris seem to have brought the decommissioning project to a standstill.

https://insiderfinancial.net/radiation-levels-in-one-fukushima-reactor-high-enough-to-kill-a-human-in-two-minutes.html

December 17, 2019 Posted by | fukushima 2019 | , , | Leave a comment

‘Scorpion‘ robot mission inside Fukushima reactor aborted

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December 8, 2019

A “scorpion” robot sent into a Japanese nuclear reactor to learn about the damage suffered in a tsunami-induced meltdown had its mission aborted after the probe ran into trouble, Tokyo Electric Power company said Thursday.

TEPCO, the operator of the Fukushima nuclear plant, sent the remote-controlled device into the No. 2 reactor where radiation levels have recently hit record highs.

The “scorpion” robot, so-called because it can lift up its camera-mounted tail to achieve better viewing angles, is also designed to crawl over rubble inside the damaged facility.

But it could not reach its target destination beneath a pressure vessel through which nuclear fuel is believed to have melted because the robot had difficulty moving, a company spokeswoman said.

“It‘s not immediately clear if that‘s because of radiation or obstacles,” she said, adding that TEPCO is checking what data the robot was able to obtain, including images.

A massive undersea earthquake on March 11, 2011 sent a huge tsunami barrelling into Japan‘s northeast coast, leaving more than 18,000 people dead or missing, and sending three reactors into meltdown at the plant in the worst such accident since Chernobyl in 1986.

The Japanese government said in December that it expects the total costs — including compensation, decommissioning and decontamination — to reach 21.5 trillion yen ($189 billion) in a process likely to take decades as high radiation levels slow operations.

The robot, 60 centimetres (24 inches) long, is made by Toshiba and equipped with two cameras and sensors to gauge radiation levels and temperatures.

“Scorpion‘s mission is to take images of the situation and collect data inside the containment vessel,” TEPCO spokesman Shinichi Nakakuki said earlier.

“Challenges include enduring high levels of radiation and moving on the rough surface,” he said.

Radiation levels inside the reactor were estimated last week at 650 sieverts per hour at one spot, which can effectively shut down robots in hours.

But the probe — designed to withstand up to 1,000 sieverts of radiation in total — would not sustain severe damage because it was unlikely to remain for too long at a single point, Nakakuki said.

https://livingstonledger.com/scorpion-robot-mission-inside-fukushima-reactor-aborted/

December 8, 2019 Posted by | fukushima 2019 | , , | Leave a comment

Robot pulled from Fukushima reactor due to radiation

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December 6, 2019

Cleaner robot pulled from Fukushima reactor as record radiation levels damage its camera

A remote-controlled cleaning robot sent into a damaged reactor at Japan‘s Fukushima nuclear plant had to be removed before it completed its work because of camera problems most likely caused by high radiation levels.

It was the first time a robot has entered the chamber inside the Unit 2 reactor since a March 2011 earthquake and tsunami critically damaged the Fukushima Da-ichi nuclear plant.

Tokyo Electric Power Co. said it was trying to inspect and clean a passage before another robot does a fuller examination to assess damage to the structure and its fuel. 

WHAT HAPPENED? 

The robot went only part way into a space under the core that TEPCO wants to inspect closely. 

It crawled down the passage while peeling debris with a scraper and using water spray to blow some debris away. 

The dark brown deposits grew thicker and harder to remove as the robot went further.

After about two hours, the two cameras on the robot suddenly developed a lot of noise and their images quickly darkened — a sign of a problem caused by high radiation.

 

The second robot, known as the ‘scorpion,‘ will also measure radiation and temperatures.

Thursday‘s problem underscores the challenges in decommissioning the wrecked nuclear plant. 

Inadequate cleaning, high radiation and structural damage could limit subsequent probes, and may require more radiation-resistant cameras and other equipment, TEPCO spokesman Takahiro Kimoto said.

We will further study (Thursday‘s) outcome before deciding on the deployment of the scorpion,‘ he said.

TEPCO needs to know the melted fuel‘s exact location and condition and other structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. 

It is part of the decommissioning work, which is expected to take decades.

During Thursday‘s cleaning mission, the robot went only part way into a space under the core that TEPCO wants to inspect closely. 

It crawled down the passage while peeling debris with a scraper and using water spray to blow some debris away. The dark brown deposits grew thicker and harder to remove as the robot went further.

After about two hours, the two cameras on the robot suddenly developed a lot of noise and their images quickly darkened — a sign of a problem caused by high radiation.

Operators of the robot pulled it out of the chamber before completely losing control of it.

The outcome means the second robot will encounter more obstacles and have less time than expected for examination on its mission, currently planned for later this month, though Thursday‘s results may cause a delay.

Both of the robots are designed to withstand up to 1,000 Sieverts of radiation. 

The cleaner‘s two-hour endurance roughly matches an estimated radiation of 650 Sieverts per hour based on noise analysis of the images transmitted by the robot-mounted cameras. 

That‘s less than one-tenth of the radiation levels inside a running reactor, but still would kill a person almost instantly.

Kimoto said the noise-based radiation analysis of the Unit 2‘s condition showed a spike in radioactivity along a connecting bridge used to slide control rods in and out, a sign of a nearby source of high radioactivity, while levels were much lower in areas underneath the core, the opposite of what would normally be the case. 

He said the results are puzzling and require further analysis.

TEPCO officials said that despite the dangerously high figures, radiation is not leaking outside of the reactor.

Images recently captured from inside the chamber showed damage and structures coated with molten material, possibly mixed with melted nuclear fuel, and part of a disc platform hanging below the core that had been melted through. 

https://insiderfinancial.net/robot-pulled-from-fukushima-reactor-due-to-radiation.html

December 8, 2019 Posted by | fukushima 2019 | , , | Leave a comment

Radiation levels inside Fukushima high enough to kill robot sent to clean

serveimage

December 6, 2019

A remote-controlled cleaning robot sent into a damaged reactor at Japan‘s Fukushima nuclear plant had to be removed Thursday before it completed its work because of camera problems most likely caused by high radiation levels.

It was the first time a robot has entered the chamber inside the Unit 2 reactor since a March 2011 earthquake and tsunami critically damaged the Fukushima Da-ichi nuclear plant.

Tokyo Electric Power Co. (TEPCO) said it was trying to inspect and clean a passage before another robot does a fuller examination to assess damage to the structure and its fuel. The second robot, known as the “scorpion,” will also measure radiation and temperatures.

Thursday‘s problem underscores the challenges in decommissioning the wrecked nuclear plant. Inadequate cleaning, high radiation and structural damage could limit subsequent probes, and may require more radiation-resistant cameras and other equipment, TEPCO spokesman Takahiro Kimoto said.

“We will further study (Thursday‘s) outcome before deciding on the deployment of the scorpion,” he said.

TEPCO needs to know the melted fuel‘s exact location and condition and other structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. It is part of the decommissioning work, which is expected to take decades.

The remote-controlled “cleaning” robot, bottom, was sent in to inspect and clean a passage for another robot in the damaged nuclear facility. (TEPCO/Associated Press)

During Thursday‘s cleaning mission, the robot went only part way into a space under the core that TEPCO wants to inspect closely. It crawled down the passage while peeling debris with a scraper and using water spray to blow some debris away. The dark brown deposits grew thicker and harder to remove as the robot went further.

More obstacles for second mission

After about two hours, the two cameras on the robot suddenly developed a lot of noise and their images quickly darkened — a sign of a problem caused by high radiation. Operators of the robot pulled it out of the chamber before completely losing control of it.

The outcome means the second robot will encounter more obstacles and have less time than expected for examination on its mission, currently planned for later this month, though Thursday‘s results may cause a delay.

Both of the robots are designed to withstand up to 1,000 Sieverts of radiation. The cleaner‘s two-hour endurance roughly matches an estimated radiation of 650 Sieverts per hour based on noise analysis of the images transmitted by the robot-mounted cameras. That‘s less than one-tenth of the radiation levels inside a running reactor, but still would kill a person almost instantly.

Kimoto said the noise-based radiation analysis of the Unit 2‘s condition showed a spike in radioactivity along a connecting bridge used to slide control rods in and out, a sign of a nearby source of high radioactivity, while levels were much lower in areas underneath the core, the opposite of what would normally be the case. He said the results are puzzling and require further analysis.

TEPCO officials said that despite the dangerously high figures, radiation is not leaking outside of the reactor.

Images recently captured from inside the chamber showed damage and structures coated with molten material, possibly mixed with melted nuclear fuel, and part of a disc platform hanging below the core that had been melted through.

https://livingstonledger.com/radiation-levels-inside-fukushima-high-enough-to-kill-robot-sent-to-clean/

December 8, 2019 Posted by | fukushima 2019 | , , | Leave a comment

Regulator: Venting at Fukushima reactor failed

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Thursday, Nov. 28
Japan’s nuclear regulator says it believes that the operator of the crippled Fukushima Daiichi nuclear plant failed to properly vent a vessel containing one of the plant’s reactors in the days after the March 2011 accident.
Tokyo Electric Power Company attempted to vent the containment vessel of the No.2 reactor to lower interior pressure and prevent equipment from being damaged.
The Nuclear Regulation Authority said on Thursday that its analysts examined parts of piping used in the venting.
They said no significant contamination was found on the piping, showing that radioactive gas was not released through the pipes.
The regulator says it believes the venting was not conducted as planned due to unknown reasons.
An investigation by TEPCO also showed a similar result.
It is believed that a massive amount of radioactive gas was released from the No.2 reactor into the environment, but the source of the leak has not been determined.
The regulator plans to look into the level of radioactivity inside the No.3 reactor next month.

December 2, 2019 Posted by | fukushima 2019 | , , | Leave a comment

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.
Read more:

February 23, 2019 Posted by | fukushima 2019 | , , , | Leave a comment

TEPCO finds some debris in Fukushima N°2 reactor could be removed

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February 14, 2019
TOKYO (Kyodo) — The operator of the disaster-hit Fukushima Daiichi nuclear power plant said Wednesday its latest probe has found that debris inside one of the reactors can be lifted, raising hopes for progress in its bid to remove melted fuel and decommission the complex.
During the around eight-hour examination on Wednesday, TEPCO inserted the probe, equipped with a camera, radiation meter and tong-like grips to hold objects, through a penetration hole that provides access to the primary containment vessel.
Of the six locations that were surveyed, the probe, which is 30 centimeters tall and 10 cm wide, successfully moved gravel and a stick-like structure in deposits in five areas. The tong-like grips were able to lift up to 5 cm of some of the deposits, according to TEPCO.
In the remaining area that resembled clay, however, the probe could not pick up any of the deposited material, indicating it was relatively hard.
“As we have found that we can move (the deposits), we proved that extracting fuel debris is possible. But for objects that cannot be grasped, we need to develop new equipment,”
Read more:

February 23, 2019 Posted by | fukushima 2019 | , , | Leave a comment

Fukushima Daiichi: probe touched suspected fuel debris in reactor#2

Images have been released of the reddish-brown amorphous mass. But its level of radioactivity is still unknown, which means that TEPCO has not even reached the earliest stage of its reactor decommissioning process.
I am acutely reminded again of the magnitude of this irreversible mess.
The technology we are left with is an out-of-control monster. And so long as nuclear power plants remain in operation, there is no guarantee that the same nightmare will not recur–even as we speak.

TEPCO: Probe touched suspected fuel debris
February 13, 2019
The operator of the damaged Fukushima Daiichi nuclear plant says a probe made direct contact with substances believed to be fuel debris at one of the plant’s reactors.
Tokyo Electric Power Company, or TEPCO, conducted its first contact survey of suspected fuel debris at the Number 2 reactor on Wednesday.
TEPCO has already confirmed the existence of deposits believed to be a mixture of molten nuclear fuel and structural parts at the bottom of the reactor’s containment vessel.
In Wednesday’s survey, a pole that can extend to 15 meters was sent under the reactor, and the probe was lowered from the end of the pole.
TEPCO plans to take out a small amount of the deposits with a different device in the latter half of the next fiscal year to use them as samples for study.
Officials say the probe was able to touch the deposits without any major trouble.
This is a key survey for devising a way to remove radioactive deposits.
They say they looked into the deposits’ hardness and whether they can be moved.
 
1st contact made with melted nuclear fuel at Fukushima plant
February 14, 2019
“The probe lifted pebble-like nuclear fuel debris and structural parts up to 8 cm in diameter at five spots in the 2,500-square-cm area that was investigated. It failed to pick up debris at one spot.
TEPCO said the probe could not lift clay-like debris likely because it had adhered to the bottom of the containment vessel.
The probe also touched nuclear fuel debris lying at several spots on the lattice-shaped scaffold for workers directly below the reactor’s pressure vessel.
The previous investigation of the No. 2 reactor in 2017 located melted fuel debris on the scaffold. But a robot deployed for a further investigation broke down on its way to the debris.
In a survey last year, the utility used the rod-like probe to take images of the inside of the reactor.
TEPCO is expected to remove a small amount of nuclear fuel debris in the second half of fiscal 2019 as part of preparations for full-scale retrieval.”

February 18, 2019 Posted by | fukushima 2019 | , , , | Leave a comment

Fukushima Unit 2 Refueling Floor Work Poses Risks

Work has begun on the unit 2 refueling floor at Fukushima Daiichi. Previously, TEPCO installed a controlled building on the side of unit 2. This building provides filtered ventilation and a staging area. It will allow workers to send equipment into the reactor building refueling floor. The wall between the two buildings was opened earlier this spring.
After the initial disaster it that unit 2 was creating the most significant radiation releases to the environment.  The highest of the three units that melted down. In 2012 an obvious steam leak from the reactor well was discovered via TEPCO images.
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TEPCO eventually put a filtration system on the building. This prevented radiation releases to the environment. The future plans for this unit include removing the entire refueling floor level. The roof and walls down to the refueling floor deck are to be removed. Then a new cover building with replacement systems will be installed. Workers are still unable to enter the refueling floor area. High radiation levels prevent human entry. Only robots have entered. TEPCO has not addressed this radiation risk during the demolition and construction phase. Earlier reporting mentioned the planned use of dust suppressants during the demolition work. There is no management plan for potential radiation releases from the reactor well.
TEPCO’s schedule shows they may begin removing equipment from inside unit 2’s refueling floor as early as mid-July. The building demolition and spent fuel removal schedule is still somewhat vague. This is dependent on other work completion.

August 1, 2018 Posted by | Fukushima 2018 | , , , | Leave a comment

Gov’t, TEPCO consider starting removal of debris from 2nd reactor at Fukushima nuke plant

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The inside of the containment vessel of the No. 2 reactor at the Fukushima No. 1 nuclear plant is seen in this frame grab from video provided by the International Research Institute for Nuclear Decommissioning (IRID).
TOKYO — The government and Tokyo Electric Power Co. (TEPCO) are considering starting the removal of molten nuclear fuel from the No. 2 reactor of the Fukushima No. 1 Nuclear Power Plant, people familiar with the matter have told the Mainichi Shimbun.
Three of the four reactors at the plant in the northern Japanese prefecture of Fukushima suffered core meltdowns after the reactors’ cooling systems shut down due to tsunami triggered by the Great East Japan Earthquake of March 2011.
According to the sources, an on-site inspection of molten fuel debris inside the reactor’s containment vessel using remote control equipment will be conducted this fiscal year. Data from the test, such as the hardness of the debris and whether it is movable, will be used to develop equipment to remove and store the highly radioactive materials.
Under the road map for decommissioning the power plant revised in September last year, the government and TEPCO are to decide on a reactor on which to start debris removal and determine how to carry out the procedure by March 2020, the end of next fiscal year. Actual removal is scheduled to begin in 2021.
In January of this year, the government and TEPCO managed to insert a pipe with a camera into the No. 2 reactor’s containment vessel and captured the image of gravel- or clay-like deposits believed to be fuel debris on the floor.
According to the people familiar with the matter, the government and TEPCO have judged that it is necessary to further examine the conditions of the No. 2 reactor as a possible starting point for fuel debris removal, since inspections needed for such an operation have progressed further on the No. 2 unit more than on the other two reactors that suffered core meltdowns in 2011.
The government and TEPCO will carry out the new probe in the fall or later of this year by inserting a camera-equipped pipe attached with a device capable of directly touching the debris, which will gather data on the reactor’s current conditions. The debris is not taken out of the containment vessel at any point of this survey. In the next fiscal year starting April 2019, they will consider examining wider areas inside the containment vessel and recovering a small sample of molten fuel for analysis ahead of full-fledged extraction in 2021.
As for the other reactors, the No. 3 unit has water inside the containment vessel, the removal of which is difficult, although images of what appeared to be fuel debris were captured inside the reactor in July 2017. The No. 1 reactor, meanwhile, will receive another probe to determine the existence of molten fuel inside because an inspection carried out in March last year failed to spot any debris.
TEPCO will shortly submit a plan for the examination of the No. 1 and No. 2 reactors’ interior for fiscal 2019 and later to the Nuclear Regulation Authority.
(Japanese original by Toshiyuki Suzuki and Ei Okada, Science & Environment News Department)

August 1, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

TEPCO to gauge radiation in reactor building

 

June 21, 2018
The operator of the crippled Fukushima Daiichi nuclear power plant intends to send a robot into the No.2 reactor building as early as next week to measure interior radiation levels in detail.
 
It is a key step toward removing all 615 nuclear fuel rod units that remain in a storage pool in the building, and eventually decommissioning the reactor.
 
The pool is located on the top floor of the building. The No.2 reactor experienced a meltdown after the major earthquake and tsunami that hit eastern Japan in 2011.
 
Tokyo Electric Power Company, or TEPCO, plans to transfer the fuel units to reduce the risks posed by possible earthquakes and other factors.
 
TEPCO needs to map radiation levels and other detailed conditions inside the building before retrieving the fuel units.
 
The utility on Thursday finished breaching a wall of the building to allow entry to a robot and heavy machinery. Work on the 5-meter wide and 7-meter high hole started last month.
 
TEPCO plans to send a robot fitted with a camera and a radiation measurement device through the opening as early as next week.
 
And TEPCO could start removing the fuel around fiscal 2023 based upon the survey results.
 
TEPCO also seeks to begin retrieving nuclear fuel from the No.1 reactor around fiscal 2023 and from the No.3 reactor as soon as this autumn. Both reactors had a meltdown following the natural disaster.

 

June 26, 2018 Posted by | Fukushima 2018 | , , | 1 Comment

TEPCO prepares to remove fuel from damaged reactor

 

May 28, 2018
The operator of the damaged Fukushima Daiichi nuclear power plant has started laying the groundwork to retrieve fuel from one of the plant’s reactor buildings. It’s a crucial step toward scrapping the complex.
 
Tokyo Electric Power Company began the work on Monday to move 615 fuel rod units from a storage pool on the top floor of the No. 2 reactor to a more secure location.
 
The No. 2 reactor is one of 3 at the plant that melted down in the 2011 accident. Radiation levels inside the reactor building remain high.
 
TEPCO will open a hole measuring 5 by 7 meters in the building’s wall and send a robot through it to measure radiation levels inside.
 
A section of the wall will be divided into 29 blocks, each with a handle to facilitate its removal.
 
From a control room some distance from the reactor building, TEPCO officials will remotely operate a machine to remove the blocks.
 
The work is expected to continue until mid-June.
 
The plant operator will measure radiation levels before deciding how to retrieve the fuel rods. The company plans to start retrieving the fuel in fiscal 2023.
 
TEPCO official Hiroshi Noda says that although the decommissioning work for the No. 2 reactor has just started, it’s a major step forward.
 
He says the company will make sure that the work will have no impact on the environment.

 

June 5, 2018 Posted by | Fukushima 2018 | , | Leave a comment

New Data for Unit 2’s Missing Fuel

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TEPCO published a Roadmap document right before leaving for Golden Week vacation. In this document is a 30+ page section of new data for unit 2’s missing fuel.
 
TEPCO has given varying explanations for unit 2’s meltdown and fuel location. Two muon scans have been completed for unit 2. The first found no fuel remaining in the RPV. A second scan by TEPCO claimed to have found some fuel in the bottom of the RPV, our analysis of the scan found otherwise. It is likely that all of the fuel inside the reactor vessel melted and all of it except for some residues is no longer in the RPV.
 
Fuel debris volume:
The volume of fuel debris inside unit 2 is difficult to calculate due to a number of factors. The debris is spread between multiple areas including the floor grate level, the pedestal floor and whatever debris may have burned down into the pedestal floor. The total volume of the fuel core is known for unit 2 but the exact size of the pedestal diameter is not known.
 
A fuel debris volume estimate was made for unit 1 based on known data and meltdown events at that reactor. Unit 1 is smaller than unit 2 in both fuel core size and size of the reactor structures. The general reactor building sizes and the fuel core sizes should be something that could roughly scale up for unit 2. Unit 1 estimate showed a fuel volume of all of the fuel and related melted structural materials as 60-100 cm deep.
 
Inside unit 2 about 50% of the pedestal floor was found to be covered with 70 cm of fuel debris. Additional fuel debris in an unknown volume is on the floor grate level. An unknown amount is burned down into the pedestal concrete basemat. Further fuel debris may be in lower reactor piping systems or the outer drywell floor. Unit 2’s fuel debris volume would also be reduced as the control rod drive array and bottom head of the reactor vessel are still intact. That large amount of metal structural material is known to not be part of the melted fuel debris in unit 2.
 
What has been found on inspection may be all of the fuel debris for unit 2 if a portion of the material is burned down into the pedestal basemat concrete. In most meltdown scenarios that is a given assumption unless the containment structure was heavily and repeatedly flooded with water at the time the fuel first dropped into the pedestal. With unit 2 that is an unlikely scenario.
 
There is an alternative possibility that a large amount of the radioactive materials in the fuel vaporized during the meltdown and escaped containment. This concept requires more investigation to confirm vaporization but this possibility for unit 2 is not completely ruled out. Fused microparticles containing nuclear fuel and other meltdown related materials have been found over a wide swath of Fukushima and beyond. Unit 2’s refueling floor blow out panel and reactor well containment gasket are one escape path for micro materials, steam and other gasses. Unit 2’s venting attempts are another concern. TEPCO has claimed the direct drywell venting of unit 2 didn’t work and the rupture disc for this system did not break as intended. TEPCO has provided no conclusive proof of this claim such as photos, video or other tangible evidence for this claim. Due to this, there is still the possibility that unit 2’s venting released some of these fused microparticles of fuel.
 
Radiation levels:
The radiation levels found in unit 2’s pedestal including a reading close to the fuel debris pile were between 7-8 Sieverts/hour. The high reading found along the CRD rail in 2017 was between 200-300 Sieverts/hour. These pedestal readings are drastically lower than what would be expected near an unshielded large pile of fuel debris.
By comparison, radiation levels along the outer containment wall in 2012 were within a similar range of the lower readings found on the CRD rail in 2017.
 
The elephant’s foot at Chernobyl, measured within the first year of the disaster, converted to Sieverts was 100 Sievert/hour.
 
Underwater readings in unit 1’s torus room near what is suspected fuel debris, taken in 2012 were 100,000 to 1 million Sieverts/hour.
 
Radiation levels near the fuel debris indicate that the top layers of debris may be mostly metallic materials with little fuel.
 
Radiation levels indicate that fuel bearing debris is not in the visible layer in the pedestal. (other possible locations – vaporized/vented, beneath the metallic layer, sml amounts in piping).

Roadmap document, section on unit 2:
http://www.tepco.co.jp/nu/fukushima-np/roadmap/2018/images1/d180426_08-j.pdf#page=3

TEPCO photo page for unit 2 findings:
http://photo.tepco.co.jp/date/2018/201804-j/180426-01j.html

May 10, 2018 Posted by | Fukushima 2018 | , , | Leave a comment

Lethal radiation detected at Fukushima plant reactor 2

 

 
 
The operator of the crippled Fukushima Daiichi nuclear power plant has released the results of its latest probe of the site.
 
A remote-controlled inspection of the Unit 2 reactor containment vessel last month detected a maximum of 8 sieverts per hour of radiation.
 
Experts say exposure to such radiation for about an hour would be fatal.
 
Officials from Tokyo Electric Power Company, or TEPCO, released the results on Thursday.
 
They said the radiation reading was taken near what appeared to be fuel debris, the term used to describe a mixture of molten fuel and broken interior parts.
 
The finding shows that nearly 7 years after the meltdowns, radiation levels remain so high that they present a major challenge to decommissioning work.
 
During the probe, 42 sieverts per hour of radiation was also detected outside the foundations of the reactor.
 
But officials said they have doubts about the accuracy of the reading because a cover had not been removed from the measuring instrument at the time.
 
They added that they don’t know why radiation levels were lower near the suspected fuel debris than around the foundations.
 
They gave a number of possible reasons, such as that cooling water may have washed radioactive materials off the debris.
 
TEPCO’s Chief Decommissioning Officer, Naohiro Masuda, says the company will develop debris-removal technology based on the outcome of the investigation.
 
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February 1, 2018 Posted by | Fukushima 2018 | , , | Leave a comment