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.
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.
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.
TEPCO handout for this work
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.
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.
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.
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.
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 about radiation protection measures http://www.tepco.co.jp/nu/fukushima-np/handouts/2017/images1/handouts_170215_09-j.pdf
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