The Yomiuri Shimbun Tokyo Electric Power Company Holdings Inc. will strengthen its protections against tsunami at its Fukushima No. 1 nuclear power plant to prevent water contaminated with high levels of radiation from spilling outside the plant, The Yomiuri Shimbun has learned.
During the decommissioning work, contaminated water has accumulated in the basements of the buildings that house the nuclear reactors. If a tsunami were to hit, this water could flow into the sea.
To prevent water from entering the basements, TEPCO will move up the schedule for work to block openings on the surface and the buildings’ ground floors, as well as add more spots to be blocked.
Mega-quake seen as ‘imminent’
The decision to step up tsunami protections was made after the government’s Headquarters for Earthquake Research Promotion released a long-term assessment in December on the possibility of a gigantic earthquake along the Chishima Trench on the Pacific Ocean side of Hokkaido.
The assessment warned that a huge earthquake of magnitude 8.8 or greater was “imminent.”
TEPCO calculated that a tsunami striking the Fukushima plant could be as high as 10.3 meters — which is 1.8 meters higher than the elevation of the site where the reactor buildings and other facilities are located — possibly flooding the site.
About 50,000 tons of water contaminated with high concentrations of radioactive substances have accumulated in the basements of the reactor buildings, turbine buildings and other facilities of reactors Nos. 1-4.
Reactors Nos. 1-3 experienced meltdowns after the 2011 Great East Japan Earthquake. Reactor No. 4 is adjacent to reactor No. 3.
Water could enter the basements of these buildings through stairways, air vents, perforated pipes and other openings. This would cause the level of contaminated water to rise, which could be taken out to sea by a tsunami’s backwash or other means.
To prepare for another tsunami, TEPCO has already closed several openings by blocking them, welding them shut and other measures. In addition, it has built temporary seawalls, moved emergency power sources to higher ground and taken other actions.