Six years after a tsunami triggered a triple meltdown at Japan’s Fukushima Daiichi Power Plant in 2011, cleanup teams at nuclear plant have some good news—they have visual confirmation of what appears to be melted fuel debris in one of the plant’s damaged reactors.
This is a significant step forward for the decontamination work, which involves locating and removing 600 hundred tons of melted fuel from three damaged reactors.
Previous attempts to locate any melted fuel had failed. The biggest obstacle to the decontamination efforts is the intense radiation, which destroys the wiring in electronic devices, making it extremely difficult to inspect the reactor cores where the melted fuel is located.
Measurements from a surveillance attempt in March reported that radiation levels inside the reactor reached 530 sieverts, according to the Independent. The specially designed robots, which can take two years to build, can withstand less than 100 sieverts of radiation. Such levels of radiation are fatal to humans; exposure to one sievert will result in radiation sickness and nausea, 10 sieverts would be fatal within weeks.
Tokyo Electric Power Company (TEPCO), the plant’s operator that is leading the decommissioning work, has had to develop all-new technology for the robots to withstand the high levels of radiation. The success of this recent surveillance mission has been encouraging for all involved. “Taking pictures of how debris scattered inside of the reactor was a big accomplishment,” said Takahiro Kimoto, spokesman for TEPCO, at a press conference on July 21.
Footage from a remote-controlled robot, nicknamed the “Little Sunfish,” revealed lava-like icicles, which experts believe resemble the corium they are searching for. Corium is a mixture of melted fuel and surrounding reactor materials that results from nuclear meltdowns. TEPCO is now working on a plan to retrieve some of the material to test for the presence of melted fuel.
As the removal of melted fuel has never been attempted, the success of “Little Sunfish” gives TEPCO greater confidence that their constantly improving robot technology will at least allow investigators to survey parts of the reactor that have previously been inaccessible. “Little Sunfish” is about the size of a loaf of bread, allowing it to maneuver underwater through the tight spaces inside the reactor’s containment vessel.
TEPCO has set itself a 40-year target to decontaminate the site and extract the melted cores from all three of the reactors that went into meltdown when the plant lost power from the 2011 tsunami.
Due to the high level of radiation, fuel removal will start no earlier than 2021. TEPCO aims to have a removal plan confirmed by March 2019.
TEPCO, also Japan’s largest utility, will bear most of the clean up costs after an investigation found that the company had failed to meet basic safety requirements. But the Japanese tax payer has been paying the bill in the short term. The Japan Ministry of Economy, Trade, and Industry estimates that the decommissioning of the reactors will cost US$72 billion, said Bloomberg. But Naoto Kan, Japan’s prime minister at the time of the tsunami, told Foreign Correspondent that he estimated more than $240 billion in cleanup costs.
See “Little Sunfish” in action. The cutting-edge robot was developed by the joint efforts of Toshiba Corporation and the International Research Institute for Nuclear Decommissioning.