Photo/Illutration(The Asahi Shimbun)

  • Photo/Illustraion

Heeding a government warning, Tokyo Electric Power Co. said it will build a 600-meter-long sea wall to strengthen protection against tsunami at the already battered Fukushima No. 1 nuclear power plant.

TEPCO announced its change in stance on Sept. 14 at a meeting of the Nuclear Regulation Authority, the country’s nuclear watchdog.

The wall will be constructed on the east side of four reactor buildings at the plant, TEPCO said. Details, such as height, construction schedule and costs, have yet to be decided.

The utility built a temporary sea wall after the March 2011 Great East Japan Earthquake and tsunami caused the triple meltdown at the Fukushima plant.

The company had said the temporary wall would provide sufficient protection of the plant from tsunami.

But TEPCO officials had second thoughts after the government’s Headquarters for Earthquake Research Promotion in December 2017 warned that the probability of an extremely powerful earthquake of magnitude 8.8 or higher striking in the Pacific Ocean off Hokkaido within 30 years was 40 percent.

The headquarters called for additional safety measures at nuclear plants, saying the strength of such a quake would be similar to the magnitude-9.0 Great East Japan Earthquake that spawned the devastating tsunami in 2011.

If another huge tsunami hits the plant, it could cause tons of radioactive water to flow out and obstruct work to decommission the nuclear reactors there.

“If another tsunami comes, the measures we have taken for the past seven years will be meaningless,” a TEPCO official said.

Work continues at the Fukushima No. 1 plant to cool the melted nuclear fuel within the heavily damaged reactor buildings. This water, coupled with the tons of daily groundwater that becomes contaminated after entering the reactor buildings, has forced the utility to store tons of radioactive water in tanks on the premises of the plant.

Those tanks and radioactive water accumulating in the reactor buildings could be swept away in a tsunami that hits the plant.

In addition, 1,573 nuclear fuel assemblies are stored in pools in the damaged reactor buildings.

If a tsunami knocks out functions to cool the fuel assemblies, the fuel could melt and release radioactive substances into the atmosphere.

TEPCO constructed the temporary 400-meter-long sea wall on the south side of the No. 4 reactor building in June 2011.

For possible tsunami coming from the east or north sides, TEPCO said waterproof doors on reactor buildings could overcome the problem.

The utility decided that an additional sea wall would be needed after the headquarters’ warning about an earthquake off Hokkaido, which is located north of the Fukushima plant.

TEPCO had considered constructing a sea wall at the site even before the 2011 nuclear disaster. However, it failed to reach a decision on its construction.