Tokyo Electric Power Company (TEPCO), the operator of the problematic Fukushima Daiichi nuclear power plant, filed for regulatory approval of its plan to dump treated radioactive water from its stricken nuclear power plant, according to Japanese news agency Jiji Press on Tuesday.

The preparation will fully start once the local authority approves the plan.

TEPCO began a geological survey in late November to prepare for the construction of a 1-kilometer undersea tunnel expected to be used for draining diluted contaminated water into the ocean, starting in the spring of 2023.

About 1.3 million tonnes of contaminated water is being stored in large tanks at the Fukushima Daiichi plant after the cores of three nuclear reactors at the plant melted down following a major earthquake and tsunami a decade ago.

In April, the Japanese government decided to process and discharge the contaminated water into the Pacific Ocean, triggering domestic protests and drastic concern globally.

Read more: TEPCO determined to discharge Fukushima water into Pacific