Concerns over release of 'treated' Fukushima wastewater

AImost 12 years have passed since the strongest earthquake in Japan's recorded history resulted in a tsunami that killed more than 18,000 people along its north-east coast.

- Justin McCurry

As the country prepares for the 11 March anniversary, one of its most troubling legacies is about to come into view with the release of more than 1m tonnes of "treated" water from the destroyed Fukushima Daiichi nuclear power plant. The tsunami knocked out the plant's backup electricity supply, leading to meltdowns in three reactors, in the world's worst nuclear accident since Chernobyl 25 years earlier.

Much has changed since the Guardian’s first visit to the plant in 2012, when the cleanup had barely begun and visitors were required to wear protective clothing and full-face masks. Atmospheric radiation levels have dropped, damaged reactor buildings have been reinforced and robots have identified melted fuel in the basements.

But progress on decommissioning – a process that could take four decades – is being held up by the accumulation of huge quantities of water that is used to cool the damaged reactor cores.

Now, 1.3m tonnes of water – enough to fill about 500 Olympic-sized swimming pools – is being stored in 1,000 tanks that cover huge swathes of the complex. And space is running out.

Two steel pillars protruding from the sea a kilometre from the shore mark the spot where, later this year, the plant’s operator, Tokyo Electric Power [Tepco], plans to begin releasing the water into the Pacific Ocean, in the most controversial step in the Fukushima Daiichi cleanup to date.