Japanese nuclear regulators have urged the operator of the disabled Fukushima Daiichi nuclear plant to improve the way it manages accumulating waste at the complex.
Most of the radioactive waste generated through decommissioning of the plant is being stored at designated outdoor depots.
But wreckage and other clutter that cannot be quickly transported there is instead being kept at interim sites for up to one year in principle.
The Nuclear Regulation Authority says the volume of waste at the interim sites reached 60,000 cubic meters in July, surging more than eight-fold from the figure in January of last year.
It also says the waste has been kept longer than one year in some sites, and not enough patrols are being conducted.
The plant's operator, Tokyo Electric Power Company, says it could not send the waste to the outdoor depots while work was underway to rearrange containers there. It adds that the containers had to be inspected following leaks of radioactive substances.
The company says it will review the temporary storage arrangements and manage waste properly.
The total volume of radioactive waste at the plant reached about 480,000 cubic meters as of March of this year, 10 years after the triple nuclear meltdown accident.