A major problem at Fukushima Dai-ichi is the flow of groundwater through the plant from the surrounding hills. This water flows into the irradiated debris in the basements of the destroyed reactors and then from there into the sea.

Tepco’s answer to this was to build a frozen soil barrier circling the four radioactive reactors. This cost $324 million in public funds. The company sank about 1,500 tubes filled with brine to a depth of 30 meters (100 feet) in a 1.5-kilometre (1-mile) perimeter around four of the plant’s reactors. It then cools the brine to minus 30 degrees Celsius (minus 22 Fahrenheit).

The water inflows often fluctuate with rainfall. The dry month of January averaged 83 tons a day. But when a typhoon struck during the last week of October, 866 tons a day poured into the reactors. This is the peak level shown in the graphic below.

In 2013, Tepco assured skeptics that this barrier would limit the flow of groundwater into the plant’s basements from the site’s reactors, to “nearly nothing.” However, since the ice wall became fully operational at the end of August of last year, 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.

The continuing seepage has created vast amounts of toxic water that Tepco must pump out, decontaminate and store in tanks that now number 1,000, holding 1 million tonnes. It says it will run out of space by early 2021.

The purification process removes 62 radioactive elements from the contaminated water but it leaves tritium, a mildly radioactive element that is difficult to separate from water. Not considered harmful in low doses, tritium is released into oceans and rivers by nuclear plants around the world at various national standard levels.

But local residents, particularly fishermen, oppose ocean releases because they fear it will keep consumers from buying Fukushima products.