A Japanese robot has begun probing the radioactive water at Fukushima's nuclear reactor.

The marine robot, nicknamed the 'little sunfish', is on a mission to study structural damage and find fuel inside the three reactors of the devastated plant.

Experts said remote-controlled bots are key to finding fuel at the dangerous site, which has likely melted and been submerged by highly radioactive water.

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A Japanese robot has begun probing the radioactive water at Fukushima's nuclear reactor. This image captured by an underwater robot shows a part of equipment housing a control rod drive system of Unit 3 at Fukushima Dai-ichi nuclear plant

'SUNFISH' ROBOT An underwater robot has captured images and other data inside Japan's crippled Fukushima nuclear plant on its first day of work. The marine robot, nicknamed the 'little sunfish', is on a mission to study damage and find resources inside the devastated plant. The probe - about the size of a loaf of bread - is equipped with lights, manoeuvres using tail propellers and collects data using two cameras and a dosimeter radiation detector. During a demonstration of the device at a test facility near Tokyo last month, the probe slowly slid down from a rail and moved across the water. A team operated it remotely, with one guiding the robot while another adjusted a cable that transmits data and serves as its lifeline. Advertisement

The probe - about the size of a loaf of bread - is equipped with lights, manoeuvres using tail propellers and collects data using two cameras and a dosimeter radiation detector.

Plant operators chose to send the robot inside the containment vessel of the No. 3 reactor because it has highest known water levels out of the the three reactors.

The robot entered the structure at 6.30am JST (10.30 BST, 5.30 ET) through a pipe connected to the containment vessel.

The marine machine, which was attached to cables, then swam to the area just below the reactor pressure vessel inside to take images.

New images taken by the robot show how parts of the system, including the control rod, have been damaged by radiation.

On Friday, the robot will continue its travels to the bottom of the containment vessels, where melted fuel deposits are believed to have accumulated.

In 2011, a 10-metre-high tsunami that killed nearly 19,000 people crashed into Japan's Fukushima nuclear power plant, leading to several meltdowns.

Five years after the disaster, researchers are still struggling to clean up the highly dangerous radioactive materials in water of the wasting reactors.

The robot entered the structure at 6.30am JST (10.30 BST, 5.30 ET) through a pipe connected to the containment vessel. This image, captured by the robot, shows a part of a control rod drive of Unit 3 at Fukushima Dai-ichi nuclear plant

The robot is on a mission to study damage and find fuel that experts say has melted and mostly fallen to the bottom of a chamber and has been submerged by highly radioactive water. Shown is a damaged platform inside of Unit 3 primary containment chamber

An underwater robot (pictured) has captured images and other data inside Japan's crippled Fukushima nuclear plant on its first day of work

The 'Little sunfish' (pictured), which is about the size of a loaf of bread, has now begun collecting in the highly radioactive waters

WHY IS THE ROBOT HUNTING FOR FUEL? In 2011, a 10-metre-high tsunami that killed nearly 19,000 people crashed into Japan's Fukushima nuclear power plant. This lead to several meltdowns, allowing harmful radioactive fuel rods and debris to escape from contained areas. Five years after the disaster, researchers are still struggling to clean up fuel in the waters of the wasting reactors. It's estimated that plant officials have only located 10 per cent of the waste fuel left behind after the nuclear meltdowns. And the damaged plant is believed to be leaking small amounts of the radioactive waste into the Pacific Ocean, which could be travelling as far as the west cost of the US. Researchers are now pinning their hopes on the remote-controlled sunfish robot to locate the lost fuel in order to work out the safest way to remove it. Advertisement

It's estimated that plant officials have only located 10 per cent of the waste fuel left behind after the nuclear meltdowns.

And the damaged plant is believed to be leaking small amounts of the radioactive waste into the Pacific Ocean, which could be travelling as far as the west cost of the US.

Researchers are now pinning their hopes on the remote-controlled sunfish robot to locate the lost fuel in order to work out the safest way to remove it.

During a demonstration of the device at a test facility near Tokyo last month, the probe slowly slid down from a rail and moved across the water.

A team operated it remotely, with one guiding the robot while another adjusted a cable that transmits data and serves as its lifeline.

Japan hopes to locate and start removing fuel from the reactors after Tokyo's 2020 Olympics.

In earlier operations, snake and scorpion-shaped robots became stuck inside two reactors.

The scorpion robot's crawling function failed and it was left inside the plant's Unit 2 containment vessel.

Pictured is a front-on view on the 'sunfish' robot. Experts said remote-controlled bots are key to finding fuel at the site

The remote-controlled device, co-designed by Toshiba (whose employees are pictured above), follows in the wake of various other failed robots

The robot (pictured during a test last month) is designed by Toshiba and the International Research Institute for Nuclear Decommissioning

The other, designed for cleaning debris for the 'scorpion' probe, was called back after two hours when two of its cameras stopped working after its total radiation exposure reached 1,000 Sievert – a level that would kill a human within seconds.

The plan had been to use the robot for 10 hours at an exposure level of 100 Sievert per hour.

The swimming robot shown was co-developed by electronics and energy giant Toshiba and the government's International Research Institute for Nuclear Decommissioning.