Storage tanks filled with radioactive water at the Fukushima No. 1 nuclear power plant in Okuma, Fukushima Prefecture, in 2019 (Asahi Shimbun file photo)

Tokyo Electric Power Co., operator of the crippled Fukushima nuclear plant where 1.2 million tons of radioactive water produced in the aftermath of the disaster is in storage tanks, offered assurances that the water can safely be discharged into the Pacific Ocean after it has been processed.

But to ensure absolute safety, the process could take as long as 30 years or so.

It is a pressing issue as TEPCO has nearly run out of space to store the water at the Fukushima No. 1 nuclear power complex.

TEPCO said that even though the water contains tritium, a particularly nasty substance that is difficult to remove completely through processing, it would be safe to release because the affected area will be limited to around the nuclear plant.

A TEPCO official stated that the tritium density of the water would "be sufficiently lower than the standard for drinking water."

TEPCO on March 24 for the first time released a prediction of how the processed contaminated water would spread in the sea at the time of its release.

Even if the maximum volume in storage under the current plan was released, it said areas where the density of tritium exceeded the current level in the seawater would range 30 kilometers north to south and extend 2 km offshore.

The central government said it would hold meetings to hear the views of people who feel their economic livelihoods would be affected by the discharge on April 6 in Fukushima Prefecture.

A subcommittee under the Ministry of Economy, Trade and Industry is considering releasing the water into the sea as the technically easiest option.

In February, it proposed two ideas, release into the ocean or the atmosphere, as “realistic options” after it considered five methods of disposal.

First, the contaminated water will be reprocessed with equipment called advanced liquid processing systems, or ALPS. All radioactive materials, with the exception of tritium, will be removed until the level of contamination is lower than existing standards to permit release.

When it comes to dealing with the tritium, the reprocessed water will be diluted with seawater to lower the density of the radioactive substance so that it meets TEPCO's current discharge standard of 1,500 becquerels per liter.

Another option is to release the water into the atmosphere by vaporizing the tritium-laced water into steam and mixing it with air so that it dilutes safely and poses no health hazard to people on the ground.

The total amount of tritium contained in the storage tanks is about 860 trillion becquerels.

TEPCO's forecast looked at four scenarios for releasing the contaminated water into the ocean, ranging from 22 trillion to 100 trillion becquerels annually based on the tritium amount released from nuclear power facility in Japan and abroad.

It calculated how the tritium would spread over a sea area ranging about 500 km from north to south and extending about 600 km offshore.

If 22 trillion becquerels was released per year, it said the areas exceeding the current density levels in the seawater would cover an area about 3 km north to south and extend to about 700 meters offshore.

Even if 100 trillion becquerels was released annually, the area above current levels would cover about 30 km from north to south and extend to about 2 km offshore.

The areas range from borderline between Minami-Soma and Namie in the north to the southern part of Naraha in the south. All these areas were affected by the nuclear crisis triggered by the 2011 earthquake and tsunami disaster.

In the absence of models to show what could happen in the event of an airborne release, TEPCO was unable to make a prediction.

The company pledged to "appropriately compensate" those who suffer financial hardship due to consumer concerns about the safety of produce from Fukushima Prefecture. However, it did not offer details or state who would be compensated.

TEPCO says the nuclear complex will run out of capacity to store any more contaminated water around summer 2022, based on the current plan.