Robot captures molten radioactive fuel in Fukushima

The molten nuclear fuel mound at reactor No. 1 (Photo: TEPCO).

The strong earthquake and tsunami in 2011 destroyed the cooling system at the power plant, causing the core of three reactors to melt. Much of the highly radioprotective fuel falls to the bottom of the reactor vessel, making removal extremely difficult. Authorities once tried to put a small robot with a camera in the No. 1 reactor but failed. However, photos taken earlier this week of the ROV-A robot revealed broken structures, pipes, molten fuel mounds and other debris submerged in cold water, according to a February 10 announcement by the operator. The factory is operated by Tokyo Electric Company (TEPCO).

About 900 tons of molten nuclear fuel remained inside the plant's three destroyed reactors, including about 280 tons of fuel in reactor No. 1. Removal became a daunting task, lasting 30 days. - 40 years according to optimistic estimates. The robot, equipped with a number of small cameras, takes pictures of the inside of the reactor vessel during its mission to pave the way for future vessels, TEPCO said.

Kenichi Takahara, a spokesman for TEPCO, said piles of debris protruding from the bottom of the tank, including inside the engine platform directly below the furnace core, indicate that the mounds of molten fuel fell into the area. . According to Takahara, the company will send additional probes to confirm the object in the image. In one location, the robot measured radiation at 2 sieverts, which can be deadly. The annual exposure for power plant workers is 50 millisieverts.

The No. 1 reactor probe robot started operating on February 8 and was the first robot to arrive since 2017. Before that, another robot failed to take pictures of molten fuel due to too high radiation levels. and damage to the internal structure. Fuel in furnace No. 1 is submerged in highly radioactive water, 2m deep. TEPCO said it will proceed with the deployment of other exploration vehicles after analyzing the data and images collected by the first robot.

Another five robots, co-developed by Hitachi-GE Nuclear Energy and the Nuclear Disarmament Research Institute, will be used in the next few months. The research project at reactor 1 is to measure molten fuel mounds, create 3-D mapping, analyze isotopes and radioactivity levels, and collect samples. These are key factors in developing safe and efficient molten fuel removal equipment and methods, allowing for complete decommissioning of the reactor.

TEPCO hopes to be able to use the robotic arm by the end of this year to remove molten fuel at furnace #2, where the rover is furthest away.