Tokyo Electric Power Company announced on February 23 that it had completed a robot probe survey lasting five days in the reactor containment vessel of Fukushima Daiichi nuclear power plant Unit 1.
Its goal was to confirm the whereabout of the melted nuclear fuel, but it was blocked by piping and could not put the camera in athe place where nuclear fuel could be seen.
Information necessary for taking out the nuclear fuel to decommission the reactor remains inadequate, and some voices began to question the robot conducted investigation method.
During the 5-day survey, there was also a point where the measuring instrument with an camera and a radiation dosimeter integrated together was hung up in a range from 0 to 3 meters from the bottom of the containment vessel, pipes and debris blocking its path in many points. The radiation dose in the water is from 3.0 to 11 Sv. Per hour. It was not possible to directly check the melted nuclear fuel.
TEPCO and the country are facing the decommissioning of a furnace …
A photo taken by a robot on Wednesday shows an underwater image of water pool on the bottom of the containment vessel of the reactor 1 at the Fukushima No. 1 plant
Tokyo Electric said Thursday that it failed to get any photos of potential fuel debris during a five-day probe of the primary containment vessel at reactor 1 of the Fukushima No. 1 power plant.
Tokyo Electric Power Company Holdings Inc., however, stressed that the investigation was worthwhile because its robot was able to take underwater images in the pool of water at its bottom and gauge its radiation level, which will help it estimate where the melted fuel lies.
The monstrous tsunami of March 11, 2011, tipped reactors 1, 2 and 3 into core meltdowns. The molten fuel rods then penetrated their pressure vessels before apparently dropping to the bottom of the giant containment vessels.
There is about a 2.5-meter deep water pool at the bottom of the primary containment vessel of reactor 1, and Tepco believes most of its melted fuel rods fell into it. Thus the main mission of the robot investigation this time was to capture underwater images.
The robot traversed gratings set up several meters above the vessel’s bottom and lowered a wire with a camera and dosimeter on its tip at 10 locations in the water.
Yet none of the images disclosed by Tepco showed anything resembling fuel debris, while parts of machinery, such as a valve, were captured.
When the robot dangled the camera on spots where Tepco thought there was a higher probability of locating the fuel, it instead found a 90-cm pile of sediment.
Tepco spokesman Yuichi Okamura said the sediment is probably not fuel debris, given the relatively low radiation readings, which ranged from 5.9 to 9.4 sieverts per hour.
Although the readings indicate extreme danger to people, Okamura said the readings would have been much higher had they been melted fuel rods. He said Tepco had no idea what the sediment is but added that there was a possibility it was covering the fuel.
According to Okamura, radiation readings get weaker by a hundredth if blocked by a meter of water. Since the robot detected readings from 5.9 to 9.4 sieverts per hour about 90 cm above the pool’s bottom, there might be something down there emitting strong radiation.
Tepco plans another investigation this month to pick up samples of the sediment.
While no fuel debris was recognized, Okamura said Tepco would review the data and analyze it further. By comparing radiation readings from various locations, the utility might be able to roughly pinpoint where the melted rods lay, he said.
He added that it was an achievement that the robot lasted for five days in the deadly radiation and that Tepco was able to retrieve it.
The PMORPH robot within unit 1’s PCV
A robot has entered into the primary containment vessel of the damaged unit 1 of the Fukushima Daiichi plant and provided Tokyo Electric Power Company (Tepco) with radiation and temperature measurements within it. The company hopes the data, together with video footage, will enable it to locate the molten fuel in the unit.
On 18 March, Tepco inserted the PMORPH robot into unit 1 in the first of a series of four planned robot explorations of the basement area of its primary containment vessel (PCV) around the pedestal, on which the reactor pressure vessel sits. The investigation is part of preparatory work for the eventual removal of fuel debris.
The PMORPH robot was developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning (IRID). It can assume a long, straight shape for passing through narrow spaces, such as pipes. Alternatively, it can rotate its crawlers by 90 degrees in relation to its central body to assume a U-shape, with the crawlers providing better stability when travelling over flat surfaces.
The robot features a combined total of five cameras and also includes a winch used for lowering and raising a sensor unit that incorporates an underwater radiation-resistant camera, LED and a dosimeter.
In the latest investigation, the robot travelled along a section of the first floor grating, on which it measured a radiation dose of 7.8 Sieverts per hour. The robot also lowered its sensor unit into the water that has collected at the bottom of the primary containment vessel. At a height of about 1 metre above the PCV basement floor, Tepco recorded a dose level of 1.5 Sv/h. The robot also recorded temperature measurements within the PCV of 14-23°C.
Last month a “scorpion-shaped” robot developed by Toshiba and IRID was sent into the primary containment vessel of unit 2 of the Fukushima Daiichi plant. “In that case,” Tepco said, “although the robot was obstructed from reaching all the way into the pedestal area, important information was obtained about the conditions at the base of the reactor.” Readings indicate the temperature within the area of the containment vessel where the robot stopped was around 16.5°C and the dose rate was about 210 Sv/h, significantly higher than those measured in unit 1.
Tepco said the latest reading and images obtained from unit 1 will now be examined in greater detail. “The conditions of the PCV basement floor will be examined later,” it noted.
The insertion of the PMORPH robot follows an investigation of the unit’s containment vessel by another shape-changing robot in April 2015. That was the first time a robot had entered the containment vessel of any of the damaged units. However, after taking several images and measurements, that robot got stuck in the grating and stopped working.
Tepco is preparing to conduct similar investigations using a robot in unit 3 at the plant.
Preliminary report of March 12 investigation 1/2
Preliminary report of March 12 investigation 2/2
Impact to the surrounding environment :
The radiation level of 7.8 Sv/h was measured by a dosimeter during the March 18 investigation, but the radiation impact has been reduced by the shielding of PCV concrete walls and steel. No radiation impact has been observed in the surrounding environment.
The investigation is conduced while creating a boundary around the guiding pipe to prevent the air inside the PCV from leaking to the outside.
No significant changes have been observed at the monitoring posts and dust monitors after the investigation, compared to the before.
Real-time data of the monitoring posts and dust monitors along the site boundary are available on the website.
Monitoring of the plant parameters:
Although the radiation level of 7.8 Sv/h was measured by a dosimeter during the March 18 investigation,it does not mean that a new phenominonhas occurred but rather the area that has not been investigated since the March 2011 accident was investigated for the first time.
Plant parameters are monitored all the time during the investigation, and no significant changes have been observed in the PCV internal temperatures after the investigation, compared to the before.
The condition of cold shutdown has not been changed. Temperature data inside the PCV are available on the website.
The operator of the crippled Fukushima Daiichi nuclear power plant says a robotic survey of fuel debris at the No. 1 reactor is being hampered by plumbing and other structures. The utility says it will extend the probe by one day, until Wednesday.
So far engineers have detected strong radiation of about 11 sieverts per hour in the water inside the containment vessel.
Tokyo Electric Power Company on Saturday started sending a remote-controlled robot into the reactor’s containment vessel to look at the state of debris — a mixture of melted fuel and reactor parts. The robot is equipped with a camera and a dosimeter.
The melted fuel is believed to still be at the bottom of the vessel, where about 2 meters of contaminated water accumulates.
TEPCO released the results of the ongoing survey on Tuesday. It said the robot moved to a location believed to be just above the debris and lowered the camera and dosimeter into the accumulated water.
The dosimeter detected radiation of 6 sieverts per hour one meter from the bottom. But piping prevented the device from reaching deeper, and it has yet to confirm the debris.
TEPCO also said the robot recorded about 11 sieverts of radiation per hour about 30 centimeters from the vessel’s bottom at another location. Officials believe the radiation may be coming from contaminated fragments that fell to the bottom, as they expected no debris there.
Through the extended probe, TEPCO hopes to collect more data on conditions inside the vessel.
A robot on March 18 took this image of a valve and a pipe in cooling water at the bottom of the containment vessel of the No. 1 reactor at the Fukushima No. 1 nuclear power plant.
Cooling water in the No. 1 reactor of the Fukushima No. 1 nuclear plant has improved in transparency, which should make it easier to pinpoint the location of melted nuclear fuel, the plant’s operator said.
The improved transparency, compared with the level two years ago, was confirmed on March 18, when a research robot took an image that clearly showed a valve and a pipe in the water at the bottom of the reactor’s containment vessel, Tokyo Electric Power Co. said March 19.
Devices on the robot measured radiation levels of 7.8 sieverts per hour on a metal stage for workers and 1.5 sieverts per hour in the water.
The research robot on March 20 and 21 will study areas where the melted nuclear fuel could exist.
Grating inside the containment vessel of the No. 1 reactor at the crippled Fukushima No. 1 nuclear plant is seen in this handout image captured by a robot Saturday.
Robot makes foray into reactor 1
Tokyo Electric on Sunday confirmed lethally high radiation levels inside the primary containment vessel of reactor 1 at the heavily damaged Fukushima No. 1 nuclear plant but found they were not nearly as high as those recently logged in reactor 2.
Using a camera-equipped robot on Saturday, Tepco logged 7.8 sieverts per hour on some grating inside the vessel and 1.5 sieverts per hour in water pooled at its bottom.
Those figures are far lower than the 210 sieverts per hour measured at one spot in the PVC of the No. 2 reactor last month, but they are still extremely high.
The four-day probe launched by Tepco on Saturday is aimed at locating the melted fuel rods inside the No. 1 reactor building.
The primary mission of the robot is to investigate the bottom of the containment vessel to see if it can capture images of the melted fuel. Debris is believed to have penetrated the vessel and fallen into the surrounding containment vessel as a result of the heavy damage inflicted by the March 2011 tsunami that devastated eastern Tohoku.
The pressure vessel is the main component of the reactor and contains the fuel rod assemblies. Finding the exact location and condition of the melted fuel is considered critically important to dismantling the reactors.
However, the high radiation inside poses a daunting challenge for those involved in the decommissioning work.
In photos handed out to the media, a valve is shown covered in a yellowish substance that the utility said could be rust.
Another photo shows the grating that the robot, which is attached to a cable, was traveling on.
The utility had sent the robot into the PVC of reactor 1 two years ago but it could only capture images of the grating at the time.
Tepco said the robot can withstand up to 1,000 sieverts before malfunctioning. It traveled about 5 meters on Saturday and will eventually make its way to the other side of the concrete structure through a space that runs beneath the pressure vessel, which houses the core.
If the robot reaches its goal, computer simulations by Tepco show that there is a chance that melted fuel rods could be found there, Tepco said.
In January and February, Tepco investigated the containment vessel of the No. 2 reactor.
It is now preparing to conduct a similar robot probe of the reactor 3.
The operator of the damaged Fukushima Daiichi nuclear power plant started a robotic survey inside the No. 1 reactor on Saturday.
Tokyo Electric Power Company send a remote-controlled robot into the reactor’s containment vessel to look at the state of debris — a mixture of molten fuel and reactor parts. The debris is believed to be under contaminated water at the bottom of the vessel.
The utility had originally planned to start the probe on Tuesday. But it called off work when images from a camera to monitor the robot became unavailable.
The company later ascertained the cable connecting the camera to the monitor screen was broken.
TEPCO said it replaced the cable with a new one. It plans to conduct the survey for 4 days using the robot equipped with a camera and dosimeter.
Tokyo Electric Power Co. (TEPCO) said it will send a fishing gear-like robot into the nuclear fuel containment vessel of the Fukushima No. 1 nuclear plant’s No. 1 reactor on March 14 to examine the state of melted nuclear fuel.
This will be the power company’s latest in a series of attempts to find and examine nuclear fuel at the plant using robots. TEPCO plans to spend four days on the search in hopes of ascertaining the state of the fuel for the first time. The melted fuel is believed to be in the bottom of the containment vessel, where radioactively contaminated water has accumulated.
The rod-shaped robot measuring about 70 centimeters long will travel through the water inside the vessel after being dropped in on a cable — like fishing — through a gap in scaffolding at the site.
TEPCO to conduct robotic probe of No.1 reactor
The operator of the Fukushima Daiichi nuclear power plant says it will send a remote-controlled probe into the crippled No.1 reactor next week.
Tokyo Electric Power Company said on Thursday a robot equipped with a camera and dosimeter will be inserted into the containment vessel of the reactor, beginning on Tuesday.
The 4-day probe is part of the utility’s effort to remove melted nuclear fuel from the 3 reactors at the plant that experienced meltdowns following the massive earthquake and tsunami on March 11th, 2011.
TEPCO believes the fuel penetrated the No. 1 reactor’s pressure vessel and has remained at the bottom of the containment vessel as fuel debris.
The robot is 70 centimeters long and about 10 centimeters wide. It will enter the containment vessel through a pipe.
The plan is to lower the camera and dosimeters attached to cables at 5 locations into contaminated water at the bottom, which is about 2 meters deep.
TEPCO officials say that even if the water is too murky to capture images, data from the dosimeter will help them assess the condition and extent of the debris.
They say it will be a delicate operation, citing the possibility that the robot may get stuck in piping or on other structures and become irretrievable.
The latest probe follows a robotic survey into the No.2 reactor earlier this year.
TEPCO to examine inside of Fukushima No. 1 reactor Tues. with robot
The operator of the disaster-struck Fukushima Daiichi nuclear power plant said Thursday it will attempt to examine the inside of the No. 1 reactor next Tuesday using a remote-controlled robot.
The move follows a botched attempt by another self-propelled robot to take a look inside the No. 2 reactor, which also melted down. That robot became unable to move when it encountered debris and eventually could not be retrieved.
These are the first attempts by Tokyo Electric Power Company Holdings Inc. to examine the insides of the wrecked reactors since the nuclear disaster triggered by a massive earthquake and ensuing tsunami on March 11, 2011.
Robot probe of Fukushima reactor halted due to glitch
An operation to prepare to examine the inside of the No. 2 reactor at the disaster-struck Fukushima Daiichi nuclear plant was halted Thursday due to a technical glitch, the plant operator said.
Tokyo Electric Power Company Holdings Inc. said it sent a robot with a high-pressure water nozzle into a containment structure housing the pressure vessel, but suspended the work after video images from a camera on the robot became dark.
TEPCO said high radiation levels may have caused the camera glitch. The camera was designed to withstand cumulative radiation exposure up to 1,000 sieverts. Previously the company said up to 530 sieverts per hour of radiation was detected within the reactor containment structure in late January. The radiation reading during the robot operation Thursday was 650 sieverts, TEPCO said.
In this image released by Tokyo Electric Power Co. (TEPCO), a remote-controlled “cleaning” robot, bottom, enters the reactor containment chamber of Unit 2 for inspection and cleaning a passage for another robot as melted materials are seen at Fukushima Dai-ichi nuclear power plant in Okuma town, Fukushima prefecture, northeastern Japan, Thursday, Feb. 9, 2017. The “cleaning” robot that entered one of three tsunami-wrecked Fukushima reactor containment chambers was withdrawn before completing its mission due to glitches most likely caused by high radiation.
Cleaner robot pulled from Fukushima reactor due to radiation
TOKYO (AP) — 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.
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