Swimming robot ‘little sunfish’ to inspect crippled Fukushima plant
Japan has unveiled a small swimming robot that will inspect the damage at the crippled Fukushima nuclear power plant. The device weights 2kg, is 13cm in diameter and will be able to swim deep into the melted reactor, its developers say.
The Japan-based International Research Institute for Nuclear Decommissioning (IRID) unveiled the robot, dubbed ‘mini manbo’ (little sunfish) in the media, together with Toshiba group on Thursday.
The robot “is small enough and resilient enough to enter and inspect the damaged primary containment vessel [PCV] of Fukushima Daiichi Nuclear Power Station Unit 3,” a statement from the IRID said, adding that the device will be deployed this summer.
The device is equipped with two cameras and can be remotely controlled via a wire, while operators can record its progress through the coolant. ‘Little sunfish’ will deliver a video feed that “will clarify damage to the PCV interior and information on how best to retrieve fuel debris,” the IRID added.
The major advantage of the robot is that it “can avoid various obstacles,” Tsutomu Takeuchi, a senior manager at the nuclear energy division of Toshiba, told AP. The company is tasked with helping to clean up the damaged plant.
The device was created for inspection of the primary containment vessel (PCV) of Unit 3 of the crippled plant. Unit 3 was flooded with coolant to a depth of about 6 meters (20ft) and in order to make a proper clean-up, such a coolant must be located and mapped, according to the IRID.
“The penetration hole giving access to the PCV is only 14cm in diameter, limiting the size of any robot that can be deployed,” the IRID added.
Thus, the newly-presented robot seems ideal for the job.
The robot’s radiation resistance is approximately 200 Sievert (Sv), according to its characteristics. For comparison, an exposure of about 1 sievert can cause biological damage to living tissue, according to the International Atomic Energy Agency (IAEA).
“Scientists developed ‘mini manbo’ with the aim of operating in a highly radioactive environment,” Goro Yanase, general manager of Toshiba’s Nuclear Energy Systems & Services Division, said.
“We succeeded in developing a small robot with high-level radiation resistance, and through its deployment we expect to get information that will support the advance of decommissioning,” he added.
The Fukushima Daiichi nuclear power plant suffered a blackout and subsequent failure of its cooling systems in March 2011, when it was struck by an earthquake and tsunami. Three of the plant’s six reactors were hit by meltdowns, making the disaster the worst since the Chernobyl catastrophe in the USSR in 1986.
Japanese authorities have repeatedly sent robots to inspect the contained area of the crippled plant but the devices either broke down or the missions were aborted. In February, such an attempt ended in failure as a clean-up robot stopped working two hours after it was sent to the inactive Reactor 2 at the nuclear complex.
Following the failure, Naohiro Masuda, president of Fukushima Daiichi Decommissioning, said that more creativity was needed to produce robots that can find and assess the condition of melted fuel rods at the high-level radiation site.
Toshiba unveils submersible video robot to probe reactor 3 at Fukushima No. 1 plant
YOKOSUKA, KANAGAWA PREF. – Toshiba Corp. unveiled on Thursday a submersible robot to take live video of reactor 3 at the Fukushima No. 1 power plant to confirm whether fuel debris is sitting at the bottom of a pool of radioactive water inside.
The location and condition of the fuel in the three reactors hit by core meltdowns is critical information for Tokyo Electric Power Company Holdings Inc., which runs the plant. Removing the fuel debris is considered the most difficult part of decommissioning the complex.
Unit 3 has the highest level of water inside at 6 meters. The fuel debris inside is presumed to have melted through its pressure vessel and settled at the bottom of its primary containment vessel.
“Until today, no one has seen the situation inside reactor 3,” said Tsutomu Takeuchi, senior manager at Toshiba’s Fukushima Restoration and Fuel Cycle Project Engineering Department.
“If we can observe the situation inside the reactor, that would be a huge leap in our ongoing effort to extract the debris” and eventually shut down the wrecked plant, he said during a demonstration of the robot at the Port and Airport Research Institute in Yokosuka, Kanagawa Prefecture.
Co-developed with the International Research Institute for Nuclear Decommissioning, the cylindrical 30-cm robot, dubbed the “mini manbo” (miniature sunfish), has a camera that can move 180 degrees vertically on its front and a fixed camera on its rear, allowing it to crawl through the water while capturing images.
Tepco plans to send the remotely controlled robot into the reactor as early as mid-July. A camera inserted into the reactor in October 2015 was unable to reach the bottom of the containment vessel.
No probe has been able to confirm the location or condition of the nuclear debris in any of the three crippled reactors.
Tepco sent a scorpion-shaped robot developed by Toshiba and the institute into reactor 2 in February, but it broke down before reaching its target under the pressure vessel after a tire got stuck.
In March, Tepco’s five-day robot-based investigation failed to capture an image of what was thought to be fuel debris in reactor 1.
A separate Tepco probe in January found black lumps in reactor 2’s pressure vessel but couldn’t immediately confirm they were fuel.
In December, the government estimated that the total cost of the Fukushima disaster would reach ¥21.5 trillion, including ¥8 trillion for decommissioning. That was almost doubled the initial estimate of ¥11 trillion.
Takeuchi of Toshiba did not reveal how much it cost to develop mini manbo.
Tsutomu Takeuchi, senior manager at Toshiba’s Fukushima Restoration and Fuel Cycle Project Engineering Department, shows off a robot it claims can probe water-filled reactor 3 at the defunct Fukushima No. 1 nuclear plant.
Swimming and wriggling robots unveiled for Fukushima clean-up
University and industry scientists have demonstrated new robots specialised for moving through and searching scenes of destruction that are impossible or dangerous for humans to enter.
Hardy, agile, remote-controlled robots will be vital for the decommissioning of power plants, particularly in the case of the Fukushima Daiichi Nuclear Power Plant, which suffered a meltdown in 2011 following a devastating tsunami and earthquake.
Robots can spend hours or days in environments so highly radioactive that a human worker would be killed in seconds.
The Japanese government hopes to start the challenging task of removing hundreds of tonnes of melted fuel after the Tokyo 2020 Olympics, potentially beginning work in 2021. For this to be possible, engineers need to know the exact location of the fuel, and understand the extent of the structural damage to the reactors.
Among other efforts, a snake-like robot was used in 2011 to explore the reactors, but was trapped repeatedly by obstacles and its camera was blocked. A “scorpion” inspired crawling robot also failed to navigate the site and was abandoned inside.
Years later, a new version of the snake-like robot has been revealed by Japanese scientists, including a team from Tohoku University in Sendai: a region severely affected by the tsunami and earthquake.
The robot stretches to eight metres in length, has a camera attached to the front and can move at speeds of up to 10cm per second.
It wriggles in a serpentine motion, propelled by the vibrations of the brush-like hairs that cover its body. Unlike any other robot, it can also “rear” its tip like the head of a snake, shooting a small jet of air to lift it. This allows it to climb over obstacles – such as debris in a disaster zone – up to 20cm in height.
According to Professor Satoshi Tadokoro of Tohoku University, the robot could search for people trapped in collapsed homes following earthquakes, and test the structural safety of damaged buildings. The researchers hope to have it ready to assist in search and rescue operations and other tasks within three years of durability testing.
Meanwhile, an alternative disaster relief robot has been unveiled by Toshiba and the public International Research Institute for Nuclear Decommissioning. This swimming robot is the size of a loaf of bread is and fitted with lights, camera and tail propellers.
It is designed specifically to inspect meltdown damage at the Fukushima nuclear plant, and will enter the primary containment vessel of Fukushima’s Unit 3 this summer to locate melted fuel in radioactive water.
On May 25, the Tokyo Electric Power Co. (TEPCO) released a status report on the ongoing decommissioning work at the Fukushima Daiichi Nuclear Power Plants, which suffered a tsunami-caused meltdown in March 2011.
Starting two months ago, in March, a self-propelled robot has been used to investigate the interior of the primary containment vessel (PCV) of Unit 1 at Fukushima Daiichi—a necessary step before fuel debris can be removed. As of April 6, the robot had sampled deposits twice.
Fluorescent X-ray spectroscopy has now confirmed the presence of elements that had originally existed in the PCV, such as iron and nickel within the reactor core internals, stainless steel in the heat-insulating materials, zinc in the paint, and lead in the shielding materials.
Although uranium was confirmed as the primary radioactive nuclide within Unit 1, it is not necessarily part of the fuel debris there, given that that element exists naturally. TEPCO said that it would carry out more detailed analyses to confirm the uranium’s source.
As the water level in the PCV of Unit 3 is higher than that in Units 1 and 2, its so-called “X-6 penetration”—which would give easier access to the inside of the pedestal (under the reactor pressure vessel)—is submerged. TEPCO plans to investigate the interior of that unit’s PCV at an undetermined date this summer using a submersible robot that can both crawl and swim. Earlier this month, the power utility began taking measurements using muon observation technology to determine the location of fuel debris.
Under the “Mid-and-Long-Term Roadmap” toward decommissioning, TEPCO will determine policies on fuel debris removal at each Fukushima Daiichi unit this summer. According to its May 22 report to an expert panel of the Nuclear Regulation Authority (NRA), the power company has already made investigations to determine general conditions inside the individual PCVs.
TEPCO will continue to focus on gathering information during the current fiscal year (ended March 31, 2018), including that on the forms and distribution of fuel debris—necessary to determine the means to remove it—and safety measures for the actual removal work.
A photo capturing contaminated water at the Fukushima No. 1 nuclear plant, which was taken by a robot on March 21, 2017.
Tokyo Electric Power Co. (TEPCO) failed to locate melted nuclear fuel inside the No. 1 reactor at the disaster-stricken Fukushima No. 1 Nuclear Power Plant in a robot probe, though it found higher levels of radiation toward the bottom of the reactor container vessel, the utility said on March 27.
TEPCO made the announcement after analyzing data obtained from a probe conducted from March 18 through 22, in which a remotely controlled robot was sent into the No. 1 reactor’s container vessel for research.
The power company is set to finalize a decision to take out melted fuel from the No. 1 through No. 3 reactors as early as this coming summer, accelerating work to decommission the facilities. Like a similar robot probe inside the No. 2 reactor last month, however, the latest survey on the No. 1 reactor also failed to obtain data necessary to extract melted fuel, such as where the fuel is located. Therefore, the utility is compelled to consider fetching melted fuel in the absence of sufficient data.
TEPCO injected a robot that can move on a running belt into the container vessel of the No. 1 reactor. The robot hung a wire holding a camera and a dosimeter at its tip from a metal grating for workers and measured the condition of the contaminated water below. From March 18 to 22, the robot examined an area near a slot from which the device is injected into the vessel and measured 1.5 to 11 sieverts per hour of radiation. Between March 20 and 22, the robot explored an area around the openings for workers at the bottom of the container vessel, which is close where melted fuel is believed to be situated, and detected measurements of 3 to 9.4 sieverts of radiation.
Sand-like sediment was found to be spreading across the bottom of the container vessel. Because of accumulated sediment near the openings, the robot could gauge radiation doses only up to a height of 90 centimeters from the bottom of the vessel. Compared to the radiation levels at the same height of an area where melted fuel is believed not to exist, the area near the openings showed higher radiation readings.
It is believed that most of the melted fuel at the No. 1 reactor has spread across the contaminated water accumulating at the bottom of its container vessel. TEPCO believes that melted fuel is likely leaking from those openings.
Naohiro Masuda, head of TEPCO’s Fukushima Daiichi Decontamination & Decommissioning Engineering Co., told a press conference on March 7, “The results of this probe will be precious resources for us to make a decision on our plan.”