Storage tanks containing processed but still contaminated water at the crippled Fukushima No. 1 nuclear power plant (Asahi Shimbun file photo)

Tokyo Electric Power Holdings Co. on Nov. 18 released for the first time an estimate of the annual disposal amount of radioactive tritium from its crippled Fukushima No. 1 nuclear power plant.

The volume will vary from 27 trillion to 106 trillion becquerel, depending on the commencement date and ending time of the disposal process, according to a report the utility presented to a subcommittee of the Ministry of Economy, Trade and Industry.

In comparison, a domestic nuclear power plant in operation usually dumps liquid radioactive waste that contains tritium, a radioactive form of hydrogen, from several hundred billion up to 100 trillion becquerel annually into the ocean, according to the ministry.

In line with the comparison, there will be no health-related problem by being exposed to radiation of the tritium disposed of from the Fukushima plant, the ministry said.

TEPCO made its preliminary calculation in substantiating the impact of the long-term storage of contaminated water.

The estimate set the total amount of tritium contained in the radioactive water stored in the tanks to be 860 trillion becquerel as of January 2020. Four starting dates of the disposal process were set as the beginning of 2020, 2025, 2030 and 2035.

The estimate assumed two ending times for the disposal at the end of 2041 and 2051, based on the progress schedule set by the government and the utility, which predicted the reactor decommissioning to be completed in 30 to 40 years.

The amount of tritium is expected to decay naturally over time. Still, the estimate revealed that the later the starting date is, the more the annual disposal amount will be.

Since the 2011 Great East Japan Earthquake and tsunami crippled the plant in Fukushima Prefecture, TEPCO has processed and stored a large amount of radiation-contaminated water in tanks on the grounds of the plant.

Even after being treated with a filtering system, the polluted water still contains tritium, which will be released when the water is dumped into the ocean or is disposed of in another manner.

The volume of contaminated water has continued to accumulate from the cooling of melted nuclear fuel debris and underground water pouring in.

TEPCO said that it cannot keep installing more storage tanks for the contaminated water due to space limitations of the site and that all the tanks will be full by around the summer of 2022.

If the disposal process hasn't begun by then, TEPCO will have to build more storage tanks, exceeding the limit, which will lead to a delay in the construction of other facilities that are necessary for the decommissioning work of the Fukushima No. 1 plant.