A Swimming Robot Will Be Sent Into One Of Fukushima's Flooded Reactors Next Month


Jonathan O'Callaghan

Senior Staff Writer

The Little Sunfish robot. IRID/Toshiba

Engineers in Japan are preparing to send a small swimming robot into the radioactive waters of Fukushima, as they attempt to find material from the reactor.

The robot is being developed by the Japan-based International Research Institute for Nuclear Decommissioning (IRID), in partnership with Toshiba. It has been called ‘Little Sunfish’, or ‘mini manbo’.


“We have already developed remotely operated robots for inspections at Fukushima,” said Goro Yanase, general manager of Toshiba’s Nuclear Energy Systems & Services Division, in a statement. “In this case, we had to meet the specific challenges of limited access and flooding, in a highly radioactive environment.”

The robot, called an underwater ROV (Remotely Operated Vehicle), measures just 30 centimeters (11.9 inches) long and 13 centimeters (5.1 inches) wide. It has front- and rear-facing cameras and LED wires, being powered by a long wire. Five thrusters, four at the rear and one at the front, will help it steer through Fukushima.

Little Sunfish will be sent into Unit 3 of the Fukushima Daiichi Nuclear Power Station. Three of Fukushima’s six reactors went into meltdown in March 2011, when a tsunami triggered by an earthquake struck the plant. About 160,000 people were evacuated from nearby as a result of the radiation leak.

This reactor has been flooded with coolant up to a depth of about 6 meters (20 feet). Once operators have been trained, Little Sunfish will be sent into the flooded reactor at Unit 3 next month.


However, the clean-up process cannot begin until the melted fuel from all the reactors is found. Various efforts have been made to do this so far, with some material being found earlier this year. Previous attempts to send robots into Fukushima have failed due to the high radiation levels.

This latest robot is small enough to be able to swim into the flooded primary containment vessel (PCV) of Unit 3, where engineers have created a penetration hole 14 centimeters (5.5 inches) across.

Little Sunfish can handle radiation levels of up to 200 Sieverts per hour. But some parts of the plant have levels of up to 530 Sieverts per hour, more than enough to kill a human, so care will need to be taken when it enters.

As mentioned, though, this is just one small step in a very long process. It has been estimated it will take up until 2021 to find all of the melted fuel from the three reactors. After that, it will take another four decades to completely decommission Fukushima, at a cost of $188 billion.


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  • radiation,

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  • Little Sunfish,

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  • nuclear meltdown