The operator of the crippled Fukushima Daiichi nuclear power plant says there has so far been no trouble with the release of treated and diluted water into the ocean as Thursday marks one week since the start of the release.
The plant suffered a triple meltdown in the 2011 earthquake and tsunami. Water used to cool molten fuel at the plant has been mixing with rain and groundwater.
The accumulated water is treated and stored in more than 1,000 tanks in the plant. They currently hold some 1.35 million tons of treated water, reaching 98 percent of the tanks' capacity.
The water is treated to remove most radioactive materials, but still contains tritium.
Tokyo Electric Power Company has been diluting the treated water before discharging it to reduce tritium concentrations to about one-seventh of the World Health Organization's guidelines for drinking water.
TEPCO says no problems have emerged with discharge or other equipment. It says each day about 450 tons of treated water is mixed with more than 700 times that volume of seawater before being released. The company says it had discharged over 2,900 tons of treated water as of Wednesday.
TEPCO has been taking water samples from the sea within 3 kilometers of the plant daily to check tritium levels since the discharge. It says tritium concentrations have been below the detectable level of 10 becquerels per liter.
Tritium concentrations have also been lower than the detectable level in seawater monitoring conducted by the Environment Ministry and Fukushima Prefecture, and in fish caught in waters near the plant that were examined by the Fisheries Agency.
TEPCO plans to release 7,800 tons of treated water over 17 days in the first round and 31,200 tons through March. The amount is equivalent to that stored in about 30 tanks.
The release of the treated and diluted water is expected to continue for about 30 years.
Local fishers and others are opposed to the discharge, citing concerns about reputational damage. Observers say the government and TEPCO must ensure safety over the long term and provide information with high transparency.