The operator of the damaged Fukushima Daiichi nuclear power plant has started preparations to remove nuclear debris from one of the three reactors that suffered a meltdown in 2011.

The debris is a mixture of molten nuclear fuel and parts of the reactor structure. Its removal is the biggest challenge in decommissioning the plant.

The government and the plant’s operator, Tokyo Electric Power Company, plan to conduct a test retrieval of a small amount of debris from the No.2 reactor by March.

Technicians will deploy a remote-controlled robotic arm. But they first need to remove accumulated sediment blocking the pipe to the reactor containment vessel.

On Wednesday, workers used a bar-like tool to break down the sediment at the entrance of the pipe.