Tokyo Electric Power Co. has begun using a special cement mixture to coat the seafloor of the port at its stricken Fukushima No. 1 nuclear power plant to contain radioactive substances released in the 2011 disaster.

TEPCO said the work was intended to ensure that high concentrations of radioactive materials in the mud and sand do not spread to the open sea.

In going ahead with the operation, officials conceded that it would likely be difficult to later dredge the area to remove the contaminated mud.

“The first priority is to keep the material where it is,” said a TEPCO official. “No decision has been made on whether to recover the (radioactive) mud at some point in the future.”

Highly radioactive water used to cool melted nuclear fuel spilled into the port area after the triple meltdowns triggered by the Great East Japan Earthquake and tsunami.

TEPCO in 2012 coated areas of the seafloor near the outlets of underground tunnels through which the radioactive water was released. Other parts of the port were left untouched until now.

A survey of the site in late February turned up readings of 167,000 becquerels per kilogram of radioactive cesium near the quay where vessels dock, TEPCO said, adding that cesium readings of 2,200 becquerels per kg were detected close to the port entrance and open ocean.

Ships use the port to unload equipment and materials for the plant.

In July, the plant operator began work to coat a 50,000-square-meter area near the quay with a special soil and cement mixture. TEPCO plans to coat the remaining 130,000 square meters in phases.

TEPCO said the process will be done twice to ensure durability. The first part of the operation is scheduled for completion by the end of this fiscal year.