Japan's Nuclear Regulation Authority on Wednesday formally approved Tokyo Electric Power Company Holdings Inc.'s operation plan for the release of treated water from its disaster-stricken Fukushima No. 1 nuclear power plant into the ocean.

The plan includes standards for the levels of radioactive materials contained in the water when it is released from the plant, the site of an unprecedented triple reactor meltdown in March 2011.

Construction of an undersea tunnel to be used for the water release is expected to be completed by the end of June.