Some Nuclear Regulation Authority members are skeptical of continuing to send robots into reactors in the crippled Fukushima No. 1 nuclear plant to collect vital data on the locations of melted nuclear fuel and radiation levels.
These regulators are increasingly calling for a new survey methodology after recent investigations utilizing robots controlled remotely generated few findings and were quickly terminated.
“We should come up with a method that will allow us to investigate in a short period of time and in a more sensible way,” said a senior member of the NRA, the government watchdog.
The suggestion followed the failure of the latest probe from March 18 to March 22 in which a robot was sent in the No. 1 reactor to ascertain the location of fuel debris, information crucial to preparing for the decommissioning.
Tokyo Electric Power Co., the operator of the plant, said on March 23 the robot was unable to deliver a camera to planned spots from where images of nuclear fuel debris could be taken.
The utility cited the piping and deposits of what looked like sand accumulating on the piping as impediments that hindered the robot surveyor’s path.
The survey was designed for the robot to reach numerous locations inside the No. 1 reactor to determine the location of nuclear fuel debris and their radiation levels.
The lower part of the reactor’s containment vessel is submerged in water where deposits of fuel debris are believed to reside below the surface after melting through in the 2011 nuclear disaster, triggered by the Great East Japan Earthquake and tsunami.
At one location, the robot succeeded in placing a camera, which is combined with a dosimeter, to a depth 0.3 meter from the containment vessel floor.
The probe measured underwater radiation levels from 3.0 to 11 sieverts per hour during the five-day survey. But it was unable to take images of the debris in the water.
TEPCO and the government hope to start removing molten nuclear fuel from 2021. But they have yet to collect information on the location, amount and condition of the melted fuel.
In a survey of the No. 2 reactor in February, a robot became stuck in deposits and other debris after traveling only 2 meters inside.
Surveyor robots for the No. 1 through No. 3 reactors have been developed by the International Research Institute for Nuclear Decommissioning since 2014, a project costing 7 billion yen ($62 million) by the end of March 2018.
It takes time to develop such multifunctional robots, but the surveys centering around the robots so far have failed to produce meaningful results.
No survey has been conducted at the No. 3 reactor.
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.
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.
Tokyo Electric Power Company Holdings Inc. (TEPCO) has informally decided to decommission the No. 1 reactor at its Fukushima No. 2 Nuclear Power Plant, it has been learned.
In the wake of the March 2011 Great East Japan Earthquake and tsunami and ensuing meltdowns at the Fukushima No. 1 plant in Fukushima Prefecture, local bodies and residents of the area who suffered extensive damage requested that all four reactors at the No. 2 plant also be decommissioned.
TEPCO had avoided stating a clear position on the No. 2 plant’s reactors, but there had been pressure from the government and ruling coalition for it to make a decision. The company accordingly decided to decommission the plant’s No. 1 reactor, which suffered the most damage, and will consider what to do with the other three reactors in the future.
The No. 1 reactor of the Fukushima No. 2 plant began operating in 1982. It was flooded by tsunami on March 11, 2011, and all four reactors at the plant remain idled. The No. 2 plant suffered less damage than the No. 1 plant, and if it passed screening by the Nuclear Regulation Authority, its reactors could be restarted. But the Fukushima Prefectural Government and all 59 local assemblies have asked TEPCO and the government to decommission all reactors in the prefecture.
TEPCO has remained busy handling compensation claims relating to the Fukushima nuclear disaster and the disaster cleanup. If it were to decommission all of the No. 2 plant’s reactors, they would lose value and it would have to write down huge losses. Company president Naomi Hirose has therefore avoided taking a clear position on the issue, saying, “I would like to consider it and make a decision as a business operator.”
Last year, however, officials decided to create a fund to cover the huge cost of handling the nuclear disaster, which is expected to reach 21.5 trillion yen, nearly double the original prediction. There was accordingly pressure from the government for TEPCO to reach an early decision on the fate of the No. 2 plant’s reactors.
The No. 1 reactor at the No. 2 plant is the oldest of the plant’s four reactors. It temporarily lost its cooling functions in the March 2011 disaster, and suffered the most damage among the four reactors. TEPCO believes that by limiting decommissioning to one reactor for the time being, it will be able to hold the decommissioning cost below 100 billion yen, minimizing the impact on company finances and on decommissioning work at the Fukushima No. 1 plant. However, a decision to decommission only one reactor at the No. 2 plant is unlikely to win public approval.
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 : Tepco denies it plans to scrap reactor at plant close to crippled Fukushima site
TOKYO (Reuters) – Tokyo Electric Power Co Holdings on Friday denied a media report that it was set to decommission a nuclear reactor that suffered only minor damage compared with the nearby Fukushima Daiichi plant that was wrecked after a massive quake in 2011.
The Mainichi newspaper reported earlier that Tepco was likely to decommission the No.1 reactor at the Fukushima Daini power plant as it was the worst-hit of the facility’s four reactors after the quake and tsunami, temporarily losing cooling functions.
Local governments have been calling for the decommission of all four reactors at Fukushima Daini. The government and the ruling Liberal Democratic Party have also pressed Tepco to make a decision on decommissioning the No.1 reactor.
Dozens of reactors elsewhere in Japan are still going through a relicensing process by a new regulator set up after the Fukushima disaster in 2011, the world’s worst since Chernobyl 25 years previously, highlighted regulatory and operational failings by the country’s nuclear utilities.
The operator of the Fukushima Daiichi nuclear power plant has cancelled Tuesday’s operation to send a remote-controlled probe into the crippled No.1 reactor.
Tokyo Electric Power Company began preparations in the morning to send the robot into the containment vessel of the reactor to monitor melted nuclear fuel.
But the company called off the attempt after images on a camera placed outside of the containment vessel to monitor the robot could not be seen on screens in the control room.
The company plans to investigate the cause of the problem and try again on Wednesday or later.
An emergency cooling system for the No.1 reactor at the Fukushima Daiichi nuclear plant was set at a mode that was difficult to start for nearly 30 years until 2010.
The No.1 reactor was the first of the 3 reactors at the plant to melt down in the 2011 accident.
The isolation condenser system was automatically activated after the massive earthquake 6 years ago, and operators used it to cool down the reactor.
However, they failed to make full use of it, and misjudged its operating status after power was lost in the tsunami.
The subsequent meltdown of the No.1 reactor caused a hydrogen explosion.
NHK interviewed officials from Tokyo Electric Power Company and requested the disclosure of information. NHK found that the setting of the emergency cooling system was changed in 1981 to make it difficult to start.
The isolation condenser is supposed to switch on automatically when the pressure inside the reactor rises for some reason. But its settings were altered so that another device for reducing internal pressure would start first.
There is no record of the isolation condenser being used for nearly 30 years, even when problems occurred.
Safety measures were reviewed the year before the 2011 accident, and the cooling system was reset to make it easy to start.
However, it was never actually tested before the 2011 accident.
The utility says it cannot confirm why the setting was changed in 1981 as there are no records, and it was not tested because there was a risk of a radioactive leak if the system became damaged.
The company says employees were told about the isolation condenser in their training courses.
Hosei University Professor Hiroshi Miyano says people cannot use such a device without experience, and this may have been a factor behind the scale of the accident. He says safety equipment testing and training should be reviewed at other nuclear plants.
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.
A new investigative robot, equipped with a censoring unit hanging through metal grating, is scheduled to be send into the No. 1 reactor at the Fukushima No. 1 nuclear power plant in the coming months. (Kohei Tomida)
HITACHI, Ibaraki Prefecture–Another robot has been developed for the elusive goal of locating melted fuel and surveying the interior of the No. 1 reactor at the Fukushima No. 1 nuclear plant.
A team of engineers and researchers from Hitachi-GE Nuclear Energy Ltd. and the International Research Institute for Nuclear Decommissioning revealed the robot on Feb. 3.
Tokyo Electric Power Co., operator of the plant, plans to deploy the robot into the No. 1 reactor before the end of March.
The robot will be fitted with a censoring unit mounted with a camera, dosimeter and lighting. Its purpose is to give TEPCO an idea of the location and condition of the melted nuclear fuel in the reactor.
Most of the melted fuel is believed to have fallen through the reactor’s pressure vessel, landed on the bottom of the surrounding containment vessel, and is soaking in cooling water about 2 meters deep.
The new robot will maneuver around metal grating originally set up for maintenance work about 3.5 meters above the bottom of the containment vessel.
At each of five survey points, the robot will lower the censoring unit through the grating. The unit can operate in water.
In April 2015, TEPCO sent two robots into the No. 1 reactor, but they could not locate the melted fuel.
One of them became stuck, and high radiation levels disabled the camera on the other. TEPCO abandoned the machines in the reactor.
On Jan. 30, a remote controlled video camera sent into the No. 2 reactor took what are believed to be the first images of melted fuel at the plant.
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