The corium of reactor 2 of Fukushima Daiichi is clearly visible
Fukushima Unit 2 in the News Again
From Majia’s Blog
TEPCO tells us they have identified the remains of “part of a nuclear fuel assembly” scattered at the bottom of unit 2’s containment vessel:
CHIKAKO KAWAHARA January 20, 2018 Melted nuclear fuel seen inside No. 2 reactor or at Fukushima plant. The Asahi Shimbun http://www.asahi.com/ajw/articles/AJ201801200017.html
A remote-controlled camera captured what appears to be melted fuel inside a reactor of the stricken Fukushima No. 1 nuclear power plant, operator Tokyo Electric Power Co. said. The released footage showed pebble-like nuclear fuel debris and part of a nuclear fuel assembly scattered at the bottom of a containment vessel, located just below the pressure vessel.
Where is the rest of the fuel?
Fukushima’s reactor 2 held quite a bit more than a single fuel assembly. According to a November 16 report by TEPCO titled, ‘Integrity Inspection of Dry Storage Casks and Spent Fuel at Fukushima Daiichi Nuclear Power Station,’ as of March 2010 the Daini site held 1,060 tons of spent uranium fuel. The total spent uranium fuel inventory at Daiichi in March 2010 was reported as 1,760 tons. The 2010 report asserts that approximately 700 spent fuel assemblies are generated every year. The report specifies that Daiichi’s 3,450 assemblies are stored in each of the six reactor’s spent fuel pools. The common spent fuel pool contains 6291 assemblies.
Unit 2 has been in the news. Last February, Akio Matsumura described a potential catastrophe at Unit 2:
Akio Matsumura (2017, February 11). The Potential Catastrophe of Reactor 2 at Fukushima Daiichi: What Effect for the Pacific and the US? Finding the Missing Link, http://akiomatsumura.com/2017/02/the-potential-catastrophe-of-reactor-2-at-fukushima-daiichi.html, accessed November 20, 2017
It can hardly be said that the Fukushima accident is heading toward a solution. The problem of Unit 2, where a large volume of nuclear fuels remain, is particularly crucial. Reactor Unit 2 started its commercial operation in July 1974. It held out severe circumstances of high temperature and high pressure emanating from the March 11, 2011, accident without being destroyed. However, years long use of the pressure vessel must have brought about its weakening due to irradiation. If it should encounter a big earth tremor, it will be destroyed and scatter the remaining nuclear fuel and its debris, making the Tokyo metropolitan area uninhabitable.
Unit 2 has been in the news because of persistent high radiation levels. In Feb 2017, TEPCO reported measuring radiation levels of 530 SIEVERTS AN HOUR (10 will kill you) and described a 2-meter hole in the grating beneath unit 2’s reactor pressure vessel (1 meter-square hole found in grating):
Radiation level at Fukushima reactor highest since 2011 disaster; grating hole found. The Mainichi, February 2, 2017, http://mainichi.jp/english/articles/20170202/p2g/00m/0dm/087000c
TOKYO (Kyodo) — The radiation level inside the containment vessel of the No. 2 reactor at the crippled Fukushima Daiichi nuclear complex stood at 530 sieverts per hour at a maximum, the highest since the 2011 disaster, the plant operator said Thursday.
Tokyo Electric Power Company Holdings Inc. also announced that based on image analysis, a hole measuring 2 meters in diameter has been found on a metal grating beneath the pressure vessel inside the containment vessel and a portion of the grating was distorted.
…The hole could have been caused by nuclear fuel that penetrated the reactor vessel as it overheated and melted due to the loss of reactor cooling functions in the days after a powerful earthquake and tsunami on March 11, 2011 hit northeastern Japan.
According to the image analysis, about 1 square meter of the grating was missing.
This extraordinarily high radiation in unit 2 was reported by the Japanese media in January 2017 as presenting a barrier to the decommissioning timeline:
MASANOBU HIGASHIYAMA (January 31, 2017) Images indicate bigger challenge for TEPCO at Fukushima plant. The Asahi Shimbun, http://www.asahi.com/ajw/articles/AJ201701310073.html
If confirmed, the first images of melted nuclear fuel at the Fukushima No. 1 nuclear plant show that Tokyo Electric Power Co. will have a much more difficult time decommissioning the battered facility.
The condition of what is believed to be melted fuel inside the No. 2 reactor at the plant appears far worse than previously thought.
…High radiation levels have prevented workers from entering the No. 2 reactor, as well as the No. 1 and No. 3 reactors at the plant.
UNIT 2 HISTORY
Looking back at testimony by Masao Yoshida, Fukushima’s plant manager, and media coverage of that testimony, I see that unit 2 was identified as posing the greatest immediate risk, although the explosion at unit 3 was clearly larger (this discrepancy is perplexing). Here is an excerpt of the testimony published by the Asahi Shimbun:
Yoshida feared nuclear ‘annihilation’ of eastern Japan, testimony shows. (September 12, 2014) THE ASAHI SHIMBUN http://ajw.asahi.com/article/0311disaster/fukushima/AJ201409120034
Plant manager Masao Yoshida envisioned catastrophe for eastern Japan in the days following the outbreak of the Fukushima nuclear disaster, according to his testimony, one of 19 released by the government on Sept. 11. . . .
. . . In his testimony, Yoshida described the condition of the No. 2 reactor at the Fukushima plant between the evening of March 14, 2011, and the next morning: “Despite the nuclear fuel being completely exposed, we’re unable to reduce pressure. Water can’t get in either.”
Yoshida recalled the severity of the situation. “If we continue to be unable to get water in, all of the nuclear fuel will melt and escape from the containment vessel, and radioactive substances from the fuel will spread to the outside,” he said. Fearing a worst-case scenario at the time, Yoshida said, “What we envisioned was that the entire eastern part of Japan would be annihilated.”
You can read more excerpts from the 400-pages of testimony published by the Asahi Shimbun, which both applauds and critiques the panel investigation of the disaster that produced the testimonies:
The Yoshida Testimony: The Fukushima Nuclear Accident as Told by Plant Manager Masao Yoshida The Asahi Shimbun http://www.asahi.com/special/yoshida_report/en/
Although the panel interviewed as many as 772 individuals involved, it failed to dig deep into essential aspects of the disaster because it made it a stated policy that it would not pursue the responsibility of individuals.
What is true about unit 2? Yoshida provides this account from the article cited immediately above:
At around 6:15 a.m. on March 15, 2011, four days after the Great East Japan Earthquake and tsunami, a round table presided by Yoshida in an emergency response room on the second floor of the Fukushima No. 1 nuclear plant’s quake-proof control center building heard two important reports, almost simultaneously, from front-line workers.
One said that pressure in the suppression chamber, or the lower part of the containment vessel for the No. 2 reactor, had vanished. The other said an explosive sound had been heard.
Question: Well, this is not necessarily in the No. 2 reactor, but sometime around 6 a.m. or 6:10 a.m. on March 15, pressure in the No. 2 reactor’s suppression chamber, for one thing, fell suddenly to zero. And around the same time, something …
Yoshida: An explosive sound.
http://majiasblog.blogspot.fr/2018/01/fukushima-unit-2-in-news-again.html
Fukushima Daiichi Reactor 2: new investigation
Tepco’s full report of 19 January 2018
Source : http://www.fukushima-blog.com/2018/01/reacteur-2-de-fukushima-daiichi-nouvelle-investigation.html
Special thanks to Pierre Fetet of the Fukushima Blog
Translation Hervé Courtois (Dun Renard)
TEPCO claims to have found ‘fuel debris’ in No. 2 reactor
Tepco to resume attempt to probe damaged reactor at Fukushima No. 1 plant
Fukushima Unit 2 Radiation Readings Revised
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
Search for melted nuclear fuel at Fukushima plant’s No. 2 reactor faces obstacles
Although nearly six years have passed since the nuclear disaster at the Fukushima No. 1 Nuclear Power Plant in 2011, the search for the melted nuclear fuel inside the plant continues.
The operators of the plant, Tokyo Electric Power Co. (TEPCO), deployed over 800 workers inside the No. 2 reactor at the No. 1 plant between December 2016 and February 2017 — but so far, they have been unable to identify the location of the melted nuclear fuel.
TEPCO also plans to conduct studies inside the No. 1 and No. 3 reactors, but they are surely headed for a rough road as the search for the melted nuclear fuel continues to be extremely difficult. It is likely that struggles in that search will have a negative effect on the government and TEPCO’s target of completing the Fukushima decommissioning work between 2041 and 2051.
Apart from humans, robots have also been involved in the search. In the case of the No. 2 reactor for example, robots have been used in the following way.
The mission to get a good look inside the No. 2 reactor containment vessel had four steps; first, workers would drill a hole measuring 11.5 centimeters in diameter into the containment vessel wall, allowing robots to enter the vessel; then workers would insert a pipe with a camera into the hole so that the situation inside the vessel could be observed; a cleaning robot would then be sent inside the vessel to clear away any sediment in the way for the next robot; and finally a self-propelled, scorpion-shaped robot would travel to the area directly below the nuclear reactor, in search of the melted fuel. However, a number of unexpected problems emerged along the way.
Heavy machinery giant IHI Corp.’s Keizo Imahori, 38, who oversaw the mechanical boring of the containment vessel in December 2016, explains that, “A number of unexpected dents were found on the floor of the nuclear reactor building.” This was a surprising discovery for Imahori and his team. The presence of the dents meant that it would be difficult for machines to get sufficiently close to the necessary areas to drill a hole, which in turn has a detrimental effect on the entire search for melted nuclear fuel.
As an emergency measure, 1-meter by 1-meter iron sheets were used to cover the dents, but workers involved in laying the sheets were exposed to extra radiation because of this additional work.
In addition to the dents, the No. 1 to No. 3 reactors at the Fukushima plant, which first started operating in the 1970s, had many parts that have undergone repair work not reflected in their original construction plans. It was impossible to check such changes in the structure beforehand due to high levels of radiation.
There was another problem — the machines could not be attached to the side of the containment vessel, which meant workers were unable to carry out drilling work. This was caused by the containment vessel’s paint peeling away. The problem was solved after workers peeled off the paint by hand, but this also caused them to be exposed to more radiation.
The hole-boring process at the No. 2 reactor took approximately 20 days to complete — during which, workers involved in the project were exposed to approximately 4.5 millisieverts of radiation on average. Based on national guidelines, many companies involved in decommissioning work set the annual upper radiation dose at 20 millisieverts for their workers. Therefore, workers can only be involved in this project up to five times before their level of radiation exposure exceeds the limit. However, as Imahori points out, “We have no way of knowing the situation unless we actually go in there.”
Nevertheless, in order to ensure that highly-skilled professionals with expert knowledge in nuclear power plants continue to be involved in the search for the melted nuclear fuel, it is necessary to use robots as much as possible to reduce the amount of radiation to which humans are exposed.
At the same time, with the Fukushima No. 1 Nuclear Power Plant being somewhat like a “burning house,” manpower is also required to make effective progress with the search. Yasuo Hirose, of IHI Corp., states, “If we completely rely on robots for the decommissioning work, they will not be able to deal with any unexpected problems. The decommissioning process is likely to be a very long task.”
http://mainichi.jp/english/articles/20170227/p2a/00m/0na/011000c
Pics from Fukushima robots not enough to devise fuel-removal plan for reactor 2: Tepco
Members of the media take in the No. 1 reactor at the Fukushima No. 1 power plant in Fukushima Prefecture on Thursday.
OKUMA, FUKUSHIMA PREF. – While a recent investigation found what may be melted nuclear fuel rods in reactor No. 2 containment vessel at the Fukushima No. 1 plant, that information isn’t nearly enough to devise an effective method for removing it, the chief of the plant told reporters during a media tour Thursday.
“We put in cameras and robots and obtained valuable images, though they were partial . . . but it’s still unclear what is really going on there,” said Shunji Uchida, who became chief of the crippled plant last July. “We first need to know the situation of the debris.”
Last month, the utility inserted a 10.5-meter rod with a camera on its tip into a hole in the No. 2 reactor’s primary containment vessel and discovered black lumps sticking to the grating directly underneath the suspended pressure vessel, which holds the core.
Tepco claims it is still unsure whether the lumps are really melted fuel that burned through the bottom of the pressure vessel. Although it is still years away from actually trying to remove the fuel, Tepco, the government and related parties are planning to decide on a basic strategy this summer and go into more detail next year.
Uchida described last month’s surveillance operation as “just peeking.”
Engineers are playing with the idea of refilling the primary containment vessel with water during debris cleanup operations to reduce the intensity of the radiation, but since the PCV was probably damaged during the meltdown crisis in March 2011, the water that’s being pumped in 24/7 to keep the fuel cool is just leaking back out.
According to past analyses, some of the melted fuel rods penetrated the pressure vessel and fell into the containment vessel surrounding it after the March 11 quake and tsunami caused a station blackout at the plant, crippling all cooling functions.
Radiation levels at Fukushima reactor puzzle nuclear experts
It is unclear why there is less radioactivity under the reactor vessel, when it is where there should be the most.
A robot was expected to solidify ways to clean up the No. 2 reactor at the Fukushima No. 1 nuclear plant, but its short-lived mission raised puzzling questions that could derail existing decommissioning plans.
The robot, Sasori, was abandoned in the melted-down reactor after it became stuck in deposits and other debris that are believed to have interfered with its drive system.
But it did take radiation measurements that indicate Tokyo Electric Power Co., operator of the plant, was too optimistic about the state and location of the melted fuel within the reactor. The melted fuel, in fact, may be spread out all over the reactor’s containment vessel.
Scientists had believed the melted nuclear fuel fell through the reactor’s pressure vessel and landed on metal grating and the floor of the containment vessel.
The results of Sasori’s investigation, coupled with previous data taken from possible images of the melted fuel, show the situation within the reactor is much worse than expected. And a fresh investigation into the reactor is now nowhere in sight.
A remote-controlled video camera inserted into the reactor on Jan. 30 took what are believed to be the first images of melted fuel at the plant, which suffered a triple meltdown after the March 2011 Great East Japan Earthquake and tsunami.
Based on the images, TEPCO estimated 530 sieverts per hour at a point almost halfway between the metal grating directly beneath the pressure vessel and the wall of the containment vessel. Black lumps on the grating are believed to be melted fuel.
A different robot sent in on Feb. 9 to take pictures and prepare for Sasori’s mission estimated 650 sieverts per hour near the same spot.
Both 530 and 650 sieverts per hour can kill a person within a minute.
Sasori, equipped with a dosimeter and two cameras, on Feb. 16 recorded a reading of 210 sieverts per hour near the same location, the highest figure measured with instruments in the aftermath of the disaster.
Sasori was supposed to travel along a rail connecting the outer wall of the containment vessel with the metal grating to measure radiation doses and shoot pictures inside, essential parts of work toward decommissioning the reactor.
After traveling only 2 meters, the robot became stuck before it could reach the metal grating.
TEPCO at a news conference repeatedly said that Sasori’s investigation was not a “failure” but had produced “meaningful” results.
However, an official close to TEPCO said, “I had great expectations for Sasori, so I was shocked by how it turned out.”
Hiroaki Abe, professor of nuclear materials at the University of Tokyo who has studied TEPCO’s footage, tried to explain why high doses were estimated between the pressure vessel and the containment vessel.
“Instead of directly landing on the rail, the melted nuclear fuel may have flown off after it reacted violently with the concrete, which had a high moisture content, at the bottom of the containment vessel, just like what happens when lava pours into the sea,” Abe said.
But he said this scenario raises a puzzling question, considering the estimated radiation readings near the area below the pressure vessel were down to 20 sieverts per hour, according to an analysis of the video footage.
“If nuclear fuel debris had splattered around, the radiation levels at the central area below the pressure vessel must be extremely high,” he said. “In addition, deposits on the rail would have taken the shape of small pieces if they were, in fact, flying nuclear fuel debris. The findings are puzzling.”
Images by the remote-controlled camera also showed that equipment in the lower part of the pressure vessel was relatively well preserved, indicating that the hole at the bottom of the vessel is not very large.
“How to remove nuclear fuel debris will all depend on how much remains inside the pressure vessel and how much fell out,” Abe said.
Toru Obara, professor of nuclear engineering at the Tokyo Institute of Technology, stressed the need to retrieve substances from the bottom of the robots or elsewhere.
“We could get clues as to the state of the melted nuclear fuel and the development of a meltdown if we could figure out which materials mixed with the nuclear fuel,” he said.
The surveys by the camera and robots were conducted from a makeshift center at the No. 2 reactor. The center’s walls are made from radiation-blocking metal.
TEPCO and the government plan to determine a method to remove nuclear fuel debris in fiscal 2018 before they proceed with the actual retrieval process at one of the three destroyed reactors.
One possible method involves filling the containment vessels with water to prevent radioactive substances from escaping.
http://www.asahi.com/ajw/articles/AJ201702190042.html
Robot stuck in Fukushima No. 2 reactor on 1st try, abandoned. Damage inside No. 2 reactor building at Fukushima plant greater than expected
The Sasori robot is stuck inside the containment vessel of Fukushima No. 1 nuclear power plant’s No. 2 reactor on Feb. 16. (Provided by International Research Institute for Nuclear Decommissioning)
Robot stuck in Fukushima No. 2 reactor on 1st try, abandoned
In the latest hitch in efforts to decommission reactors at the Fukushima No. 1 nuclear power plant, a robotic surveyor became mired in deposits and was lost on its maiden journey on Feb. 16.
Tokyo Electric Power Co., which operates the plant in Fukushima Prefecture, had to abandon the Sasori (scorpion) robot after it became stuck inside the containment vessel of the power station’s No. 2 reactor that morning.
The highly touted probe was specially developed for the important task of surveying the interior of the crippled reactor and collecting data to assist in removing the melted fuel.
But with the environment inside too treacherous for a key component in the process, TEPCO’s decommissioning project seems to have come to a standstill.
According to the utility, the robot entered the containment vessel around 8 a.m. It traveled along a 7.2-meter-long rail connecting the outer wall of the containment vessel with its central portion immediately beneath the pressure vessel.
But about 5 meters into its mission, the robot’s controls started to become less responsive. TEPCO believes it was due to deposits and other debris that are blocking the rail entering its drive system.
The operator tugged on the electrical cable connected to the robot and had it pull back to an area along its path with less obstacles, but it ultimately became stuck there.
The robot measured the radiation levels in the area at 210 sieverts per hour, which is lethal enough to kill a human in two minutes. Earlier, the company had estimated the level in the area at 650 sieverts per hour from video footage captured on Feb. 9 by another robot that paved the way for the Sasori.
With the robot completely immobilized, TEPCO gave up on retrieving it around 3 p.m. The operator cut the electric cable and closed the tunnel bored into the wall of the containment vessel, entombing the robot inside.
The probe was cast aside to the edge of the 0.6-meter-wide rail so that it would not impede future surveyor robots.
Had everything gone according to plan, TEPCO would have sent the Sasori onto the grating in the heart of the containment vessel, which is covered in black chunks believed to be melted fuel rods that fell from the pressure vessel above.
The utility had hoped to measure the dosage of these radioactive lumps, as well as capture images of the underside of the pressure vessel, which contains holes from when the nuclear fuel burned through it in the meltdown that was triggered by the Great East Japan Earthquake and tsunami in 2011.
http://www.asahi.com/ajw/articles/AJ201702170048.html
Damage inside No. 2 reactor building at Fukushima plant greater than expected
Damage within the No. 2 reactor building at the Fukushima No. 1 Nuclear Power Plant was found to be greater than expected, based on images sent back by a robot sent into the structure by plant owner Tokyo Electric Power Co. (TEPCO) in a mission that concluded Feb. 16.
The operation used a self-propelled scorpion-shaped robot, with the goal of investigating the inside of the reactor’s containment vessel and the area directly beneath the reactor, but the area under the reactor was not reached. The No. 2 reactor building was thought to be comparatively undamaged compared to the No. 1 and No. 3 reactor buildings, where hydrogen explosions occurred. Worse damage than expected was discovered, however, such as holes in the grating foothold inside the containment vessel.
At a press conference, TEPCO official Yuichi Okamura stressed, “This investigation was the first of its type in the world and uncovered information about the debris inside. The mission wasn’t a failure.”
The robot’s camera also took footage of the condition of pipes in the structure, and image processing could make these pictures clearer. However, the robot’s treads stopped moving after it proceeded over 2 meters along a rail, and TEPCO was not able to use it to check the melted nuclear fuel.
TEPCO plans to decide as early as this summer on how to remove the melted fuel from the No. 1 through No. 3 reactors and start the decommissioning process in earnest. The results of the investigation were to be used as base data for the decommissioning, but with it having not produced an overall understanding of the No. 2 reactor building’s interior, a new investigation will probably be sought.
However, no plan for the next investigation has been decided, and it may begin with the development of a new robot. TEPCO plans to send in a different robot to the No. 1 reactor building next month. For the No. 3 reactor building, a robot capable of moving in water is being developed because there is a large amount of contaminated water at the bottom of its containment vessel.
http://mainichi.jp/english/articles/20170217/p2a/00m/0na/011000c
Fukushima Unit 2 Scorpion Probe Dies But Sends Back Some Data
While the press reported Scorpion’s mission as a failure, it provided useful data before being abandoned. It collected some radiation readings and a number of useful images.
The robot seems to have become stranded on a pile of debris on the rail. Radiation data from along this inspection route provided only one radiation reading, no telemetry as other videos had. Tepco’s video is heavily edited but still provides some useful information.
A reminder, these readings are the result of venturing into the more deadly areas of the reactor where they have been unable to previously, no resulting from an increase of radiation. While this is much lower than the earlier camera estimates of radiation it is still extremely high and quite deadly.
Arond the same area where the high radiation source was found, TEPCO stated they found a 210 Sv/h reading with the on board radiation sensor.
New images from inside the pedestal were obtained as were some images looking up into the containment structure.
Image below from TEPCO. White ghosting on the image is likely due to radiation levels rather than steam. The existing melt hole in the pedestal floor grate can be partially seen in the upper mid section of the image. A very thick amount of fuel debris can be see in the lower right section of the image. The mark “clean” on this image with an arrow indicates an area where the floor grate may have failed after the molten fuel had splattered on the area. Further below, more fuel debris and structures can be seen.
The red circle shows an area where it appears fuel debris was moved or blocked by a fallen piece of sheet steel.
In both images, sections of light colored piping can be seen below the area where the grate is missing. On the far left of the image a partially melted section of flexible conduit can be seen.
This appears to indicate that high temperatures within the pedestal were very localized.
Sources:
TEPCO handout for this work
http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170216_01-e.pdf
Reactor 2’s Platform has 3 Holes
Tepco released a new image of the reactor 2: at least three holes in the platform and still no corium.
The platform is made of metal (grating), just below the tank, intended to access the control rods. The bottom of the containment is a little over 3 m below.
Tepco’s document in Japanese:
http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_08-j.pdf
Latest probe of reactor 2 fails after Fukushima robot blocked by obstacles
A robot shown in this photo by the International Research Institute for Nuclear Decommissioning was put inside reactor 2 at the Fukushima No. 1 nuclear plant on Thursday
Robot stops working in Fukushima reactor
The operator of the crippled Fukushima Daiichi nuclear power plant says it suspended a survey by a robot at one of its reactors after the device stopped working.
Tokyo Electric Power Company, or TEPCO, sent the scorpion-shaped robot into the containment vessel of the plant’s No. 2 reactor on Thursday.
The company believes fuel in the reactor melted through its core during the 2011 accident and accumulated at the bottom of the facility’s containment vessel.
The survey was aimed at getting a close look at what could be fuel debris — a mixture of nuclear fuel and melted parts of the reactor.
The robot was also expected to measure radiation and temperatures there to gather data for scrapping the reactor.
TEPCO officials say the device was advancing on a metal rail leading to a central area below the reactor’s core, but stopped moving before it could reach the center.
The officials say they decided to give up the robot and cut its remote-control cable.
TEPCO plans to analyze data collected by the robot and figure out how to carry out future probes.
https://www3.nhk.or.jp/nhkworld/en/news/20170216_34/
Robot survey of crippled Fukushima reactor ends in failure
The operator of the crisis-hit Fukushima Daiichi nuclear power plant said Thursday its attempt to take a close look at the crippled No. 2 reactor using a scorpion-shaped robot ended in failure due to a technical flaw.
A track glitch meant the self-propelled robot was unable to climb over obstacles, Tokyo Electric Power Company Holdings Inc. said. It gave up on retrieving the robot by cutting its remote control cables.
TEPCO, however, said, “We have received new important information about the radiation level and temperature inside the (reactor) containment vessel,” emphasizing it did not view Thursday’s survey as a failure.
http://english.kyodonews.jp/news/2017/02/459048.html
Latest probe of reactor 2 fails after Fukushima robot blocked by obstacles
A renewed attempt to survey reactor 2 at the damaged Fukushima No. 1 nuclear power plant failed Thursday when the latest robot probe became obstructed.
The robot was inserted into the primary containment vessel at around 7:50 a.m. to approach the metal grating directly underneath the pressure vessel, where a black mass has been found.
Tokyo Electric Power Company Holdings Inc. had hoped to take a closer look at what could be melted nuclear fuel, but it was forced to abandon the operation shortly after 3 p.m.
The robot didn’t reach its objective, Tepco said, and the utility eventually severed its controller cable.
Having detected an extraordinarily high radiation level —estimated at 650 sieverts per hour — in a preparatory survey, Tepco had hoped to obtain more precise readings, images and data needed to remove fuel and other debris to decommission the plant.
In previous surveys, the utility found deposits on the grating believed to be nuclear debris and a 1-sq.-meter hole believed to have been created by molten fuel escaping from the pressure vessel.
Challenges dogged the latest attempt from the start. There was little clear surface for the robot to move around, and the radiation could kill the unit as with the preliminary surveys.
Next month, Tepco plans to survey the No. 1 reactor.
Operation of communication about the “scorpion” robot which will be sent to the confinement enclosure of reactor n ° 2
TEPCO and its partners launched a communication operation about the “scorpion” robot, which will be sent to the containment reactor of reactor n ° 2 in an attempt to locate the corium, ie the highly radioactive molten fuel, mixed with debris. It is not certain that the mission will be a success, the cleaning robot having lasted only two hours in this enclosure because of the extreme radiations, without being able to finish its task.
A press release announces what we already know and insists on the challenges: “every step is a new challenge for TEPCO, but TEPCo welcomes the challenges”. The company would be almost happy with the accident? It is accompanied by a promotional video with a comparison to the kendô fights posted on its Facebook page.
http://www.tepco.co.jp/en/press/corp-com/release/2017/1377951_10469.html
https://www.facebook.com/OfficialTEPCOen/videos/1346869308705698/
The Japanese nuclear industry wants to place itself on the decommissioning market and highlights the technologies being developed. This robot was designed by IRID, Toshiba and TEPCO. IRID benefits from public funds. As for Toshiba, it is almost bankrupt because of its nuclear branch and TEPCO is financially in a bad shape.
The press release and the video do not provide any relevant information and are in complete discrepancy with reality.
1. Current conditions of Unit 2 Primary Containment Vessel (PCV)
Nuclear fuel in the Primary Containment vessel (PCV) was exposed to the air and melted from the impact of March 2011 Great Earthquake.
As a result of the accident analysis, it was found that a portion of melted nuclear fuel might have been fallen inside the pedestal.
To remove fuel debris, it is necessary to investigate the PCV and clarify the conditions of debris and surrounding structures.
2. Outline of Unit 2 PCV investigation
[Purpose]: To obtain feedback information (deformation of platform, etc.) for the design and
development of next investigation devices inside the pedestal
To inspect conditions on the platform inside pedestal, fuel debris fallen to the CRD housing, and conditions of structures inside pedestal.
[Investigation point]: Platform and Control Rod Drive (CRD) will be investigated from the platform inside pedestal
3. Work steps for Unit 2 PCV investigation
4. Preparatory investigation results from X-6 penetration to CRD rail
4. Preparatory investigation results at the entrance of pedestal area
4. Preparatory investigation results of pedestal area
5. Additional results expected from the self-propelled investigation device
6. Investigation by the self-propelled investigation device to the end of CRD rail
6. Investigation by the self-propelled investigation device to the end of CRD rail
Reference: Investigation results on the platform inside the pedestal
Technical information for the media is available here:
In Japanese about the upcoming mission http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_08-j.pdf
And in English http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_01-e.pdf
And about radiation protection measures http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_09-j.pdf
And in English http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_02-e.pdf
Translated from L’ACROnique de Fukushima http://fukushima.eu.org/operation-de-communication-sur-le-robot-scorpion-qui-va-etre-envoye-dans-lenceinte-de-confinement-du-reacteur-n2/
Clean-up robot pulled from Fukushima Reactor 2 due to extremely high radiation
Cleaner Robot Pulled From Fukushima Reactor Due to Immense Radiation
The camera on the bot was compromised by the high levels of radiation.
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. 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.
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.
Extremely high radiation breaks down Fukushima clean-up robot at damaged nuclear reactor
A clean-up mission using a remotely operated robot at Japan’s crippled Fukushima nuclear plant has had to be aborted, as officials feared they could completely lose control of the probe affected by unexpectedly high levels of radiation.
The robot equipped with a high-pressure water pump and a camera designed to withstand up to 1,000 Sieverts of cumulative exposure had been pulled off the inactive Reactor 2 at the Fukushima Daiichi nuclear complex earlier this week, The Japan Times reported Friday, citing the plant operator, Tokyo Electric Power Company (TEPCO). The device reportedly broke down just two hour into the probe.
The failure led experts to rethink estimated levels of radiation inside the damaged reactor.
While last week TEPCO said it might stand at 530 Sieverts per hour – a dose that can almost instantly kill a human being, following the latest aborted mission a company official has said a reading of up to 600 Sieverts should be “basically correct.”
Even despite the considerable 30-percent margin of error for the revised estimate, the latest probe left no doubt that radiation levels are at record highs within the reactor. Even though it cannot be measured directly with a Geiger counter or dosimeter, the dose is calculated by its effect on the equipment.
Last month, a hole of no less than one square meter in size was discovered beneath the same reactor’s pressure vessel. The apparent opening in the metal grating is believed to have been caused by melted nuclear fuel, TEPCO then said.
The recent mission has demonstrated that the melted fuel is close to the studied area.
While extreme radiation levels have been registered within the reactor, officials insist that no leaks or increases outside have been detected.
The failure might force Japan to rethink the robot-based strategy it has adopted for locating melted fuel at Fukushima, according to The Japan Times.
The robot affected by radiation was supposed to wash off thick layers of dirt and other wreckage, clearing ways for another remotely controlled probe to enter the area, tasked with carrying out a more proper investigation to assess the state of the damaged nuclear reactor. Previously, even specially-made robots designed to probe the underwater depths beneath the power plant have crumbled and shut down affected by the radioactive substance inside the reactor.
The Fukushima Daiichi nuclear power plant suffered a blackout and subsequent failure of its cooling systems in March 2011, when it was hit by an earthquake and tsunami. Three of the plant’s six reactors were hit by meltdowns, making the Fukushima nuclear disaster the worst since the Chernobyl catastrophe in Ukraine in 1986. TEPCO is so far in the early stages of assessing the damage, with the decommissioning of the nuclear facility expected to take decades.
https://www.rt.com/news/377025-fukushima-radiation-breaks-robot/
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https://mainichi.jp/english/articles/20201229/p2a/00m/0na/032000c
December 30, 2020 (Mainichi Japan)
Tsuboi released comments expressing his joy after he
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Still, each time I have met Tsuboi, he has
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