TOKYO (Kyodo) -- The operator of the Fukushima Daiichi nuclear complex said Saturday it moved a tiny portion of melted fuel just outside a reactor container as part of its attempt to retrieve the debris for the first time since a nuclear disaster hit the plant over a decade ago.

Tokyo Electric Power Company Holdings Inc. plans to check the radiation level of the 5-millimeter-size debris, possibly on Tuesday, to determine if it can be recovered.

Retrieving highly radioactive melted fuel is a serious challenge in the decades-long decommissioning plan for the Fukushima Daiichi complex, which was damaged by a massive earthquake and tsunami in March 2011.

After experiencing suspensions in the retrieval trial that started at the No. 2 unit in August, TEPCO announced on Wednesday that its recovery device, with claws attached at its tip, grasped a pebble-like piece of debris from the bottom of the reactor's primary containment vessel.

On Saturday morning, the device, together with the debris it is holding, was moved outside the reactor's containment vessel and was placed inside a metal box.

If the debris is found to emit no more than 24 millisieverts per hour from a distance of 20 centimeters, it will be transferred to a sealed "glovebox" inside the building housing the No. 2 reactor for size and weight measurements, before being sent to a research facility for further testing.

If the debris' radiation level is higher, TEPCO will return the object to the reactor's containment vessel and consider extracting a different sample. The threshold is in place to minimize radiation exposure for the workers involved.

An estimated 880 tons of fuel debris remains in the Nos. 1, 2, and 3 reactors, which experienced core meltdowns during the nuclear crisis.