Six years after the Fukushima meltdowns engineers at the Fukushima Dai-ichi plant have succeeded in guiding a small robot to the heart of the heavily damaged Reactor 3 reactor and located the fuel which melted onto the floor of the reactor building. Earlier robots had failed, getting caught on debris or suffering circuit malfunctions from excess radiation (see previous blog about this). But the newer version, called the Mini-Manbo, or “little sunfish,” was made of radiation-hardened materials with a sensor to help it avoid dangerous hot spots in the flooded reactor buildings. After three days of careful manoeuvring the robot sent back a video of a gaping hole at the bottom of the reactor and, on the floor beneath it, clumps of what looked like solidified lava but was actually melted uranium fuel.
The Manbo (see photo) used tiny propellers to hover and glide through water in a manner similar to an aerial drone. Uranium fuel rods in three of the Fukushima reactors had liquefied, then dripped to the bottom of the reactor vessels in a molten mass hot enough to burn through the steel walls and even penetrate the concrete floors below.
The Japanese prime minister’s office has set a target date of 2021 – the 10th anniversary of the disaster – when workers begin extracting the melted fuel from Reactor 3. They also hope that beginning the cleanup will help them win the public’s consent to restart Japan’s undamaged nuclear plants, most of which remain shut down since the disaster.
Tepco have just begun began installing equipment to be used for removing fuel from the storage pool of Reactor 3. The equipment, weighing 72 tons, was lifted by two large cranes. The storage pool, located on a floor 36 meters above ground level, holds the remains of 566 spent and unused nuclear fuel assemblies.