Discharging the water into the Pacific Ocean over the course of a year would amount to between just one-1,600th and one-40,000th of the radiation to which humans are naturally exposed, the Economy, Trade and Industry Ministry, or METI, told a government subcommittee on the issue.
Water used to cool the melted-down cores and groundwater from close to the damaged facility contain some radioactive materials. It is being collected and stored in tanks on the plant grounds, but space is running out and the government is exploring ways to deal with the waste water — which already totals more than 1 million tonnes with the volume increasing by more than 100 tonnes every day.
Tokyo Electric Power Company said in August that the tanks are likely to reach capacity in three years with no solution yet found to the question of what to do with the water.
According to Tepco, Fukushima-Daiichi had 960 tanks containing 1.15 million tonnes of treated water as of mid-July.
The treated water contains tritium and other residual radionuclides from the nuclear station, which was shut down by an earthquake and tsunami in March 2011.
According to an estimate by the ministry, annual radiation levels near the release point after a release would be between 0.052 and 0.62 microsieverts at sea, and 1.3 microsieverts in the atmosphere, compared with the 2,100 microsieverts that humans come into contact with each year in daily life.
In January the International Atomic Energy Agency urged Japan’s government to urgently decide on how to dispose of treated water from the nuclear station.
The water may require further treatment to reduce radionuclides to authorised levels before any of the five disposal methods being considered by the government can be implemented. The methods are ground injection, controlled discharge into the sea, discharge as steam, discharge as hydrogen, and solidification for underground burial.
Releasing treated water into the sea in a controlled manner is common practice at nuclear power plants and was generally considered the most viable option for Fukushima-Daichi because it could be done quickly and would cost the least.
Japan’s Nuclear Regulation Authority has long said that releasing the treated water into the sea is the most reasonable option, but people in Fukushima prefecture, especially fishermen, fear it will damage the region’s reputation, the Japan Times said.