TOKYO -- Tokyo Electric Power Co. Holdings began Tuesday the final phase of an underground "ice wall" around the crippled Fukushima Daiichi nuclear power plant intended to reduce groundwater contamination, though experts warn the bold project could be much less effective than once hoped.
At 9 a.m., workers began activating a refrigeration system that will create the last 7 meters of a roughly 1.5km barrier of frozen earth around the plant's reactor buildings, which were devastated by the earthquake, tsunami and nuclear meltdowns of March 2011. Masato Kino, an official from the Ministry of Economy, Trade and Industry supervising the cleanup, spoke cautiously at the occasion, noting that "producing results is more important than the simple act of freezing" that particular segment of soil.
Tepco estimates that roughly 580 tons of water now pass through the ice wall on the reactor buildings' landward side each day, down from some 760 tons before freezing of soil commenced in March 2016. About 130 tons daily enter the reactor buildings themselves, and Tepco hopes completing the wall will bring that figure below 100 tons.
By this math, the near-complete wall blocks only a little over 20% of groundwater coming toward it. But, as Japan's Nuclear Regulation Authority said Aug. 15 when approving the wall's final stage, the barrier is "ultimately only a supporting measure" to other systems preventing contamination. The main line of defense is a so-called subdrain system of 41 wells around the reactor buildings that pump up 400 to 500 tons of water daily, preventing clean water from entering the site and contaminated water from leaving it.
Freezing of earth around the facility has been conducted gradually, amid concerns that highly contaminated water inside could rush out should the water level inside the reactor buildings drop. "Working carefully while keeping control of the water level is a must," said Yuzuru Ito, a professor of civil and environmental engineering at Setsunan University.
It is unclear precisely when the wall will be complete. The plan is to freeze soil 30 meters deep over the course of two or three months, completing the barrier as soon as this fall. But as the gap in the wall narrows, water flows through it more quickly, making soil there more difficult to freeze. "Water is flowing quickly now, and so it is difficult to proceed as we have so far," a Tepco representative said.
Japan has spent some 34.5 billion yen ($315 million) in taxpayer funds on the wall, expecting the icy barrier to put a decisive end to groundwater contamination at the Fukushima plant. It now appears that a dramatic improvement is not likely, though the wall will still require more than 1 billion yen per year in upkeep. "The frozen-earth barrier is a temporary measure," said Kunio Watanabe, a professor of resource science at Mie University. "Some other type of wall should be considered as well."