TOKYO >> Japan released a draft report Dec. 31 on how to dispose of treated water at the Fukushima No. 1 nuclear power plant.

The draft includes two methods, narrowed down from five that had been under consideration.

An expert panel, chaired by Ichiro Yamamoto, professor emeritus at Nagoya University, has been calling for the government to decide how and when to dispose of treated water — contaminated water that has undergone purification — at Tokyo Electric Power Company Holdings’ Fukushima plant.

Options discussed: releasing the water into the ocean after diluting it, releasing it through evaporation and a combination of both options.

The operation to cool down the melted nuclear fuel in the reactors generates contaminated water, which is then processed with purification equipment that separates out radioactive contaminants.

About 1.1 million tons of treated water is being stored in nearly 1,000 tanks at the site. Contaminated water is increasing by about 170 tons a day.

Since fall 2016, the panel has been studying possible methods for releasing treated water.

Of the two methods being considered, releasing treated water into the ocean after dilution, at a level within the national safety standard, is already widely practiced at nuclear power plants in Japan.

The other method involves evaporating treated water, which would meet national air safety standards, and releasing it into the atmosphere. A similar method was used after the Three Mile Island nuclear accident in the U.S.

The timeline of the disposal depends on when the process begins and the amount of treated water to be released annually, but the process is expected to take at least 10 years.

“It is necessary to make sure to finish the release of treated water by the time the decommissioning is completed,” according to the draft.

The panel urged the government to listen carefully to the opinions of a wide range of people, including local residents.