OKUMA, Japan - A costly "ice wall" is failing to keep groundwater from seeping into the stricken Fukushima Dai-ichi nuclear plant, data from operator Tokyo Electric Power Co (Tepco) shows, preventing it from removing radioactive melted fuel at the site seven years after the disaster.
When the ice wall was announced in 2013, Tepco assured sceptics that it would limit the flow of groundwater into the plant's basements, where it mixes with highly radioactive debris from the site's reactors, to "nearly nothing."
However, since the ice wall became fully operational at the end of August, an average of 141 metric tonnes a day of water has seeped into the reactor and turbine areas, more than the average of 132 metric tonnes a day during the prior nine months, a Reuters analysis of the Tepco data showed.
The groundwater seepage has delayed Tepco's clean-up at the site and may undermine the entire decommissioning process for the plant, which was battered by a tsunami seven years ago this Sunday. Waves knocked out power and triggered meltdowns at three of the site's six reactors that spewed radiation, forcing 160,000 residents to flee, many of whom have not returned to this once-fertile coast.
Though called an ice wall, Tepco has attempted to create something more like a frozen soil barrier.
Using 34.5 billion yen (R3.87-billion) in public funds, Tepco sunk about 1,500 tubes filled with brine to a depth of 30 metres in a 1.5-kilometre perimeter around four of the plant's reactors. It then cools the brine to minus 30 degrees Celsius (minus 22 Fahrenheit).
The aim is to freeze the soil into a solid mass that blocks groundwater flowing from the hills west of the plant to the coast.
However, the continuing seepage has created vast amounts of toxic water that Tepco must pump out, decontaminate and store in tanks at Fukushima that now number 1,000, holding one million tonnes. It says it will run out of space by early 2021.
"I believe the ice wall was 'oversold' in that it would solve all the release and storage concerns," said Dale Klein, the former chairman of the US Nuclear Regulatory Commission and the head of an external committee advising Tepco on safety issues.
"The hydrology of the Fukushima site is very complicated and thus the exact water flow is hard to predict," he said, "especially during heavy rains."