The Japanese government is to spend $320m on a 1.4 kilometre “ice wall” at Fukushima nuclear power plant, as it aims to prevent contaminated radioactive water leaking into the wider environment.

Since 2011, when reactors at the plant were destroyed, water has been continuously pumped into the ruins to prevent radioactive material overheating and potentially catching fire.

Over 300,000 tonnes of contaminated coolant water is now stored in 1,000 tanks on site, with leakages from those tanks posing a hazard to the environment: in August it was found that one tank had leaked 300 tonnes of radioactive water.

The problem is particularly serious as Fukushima is built on a slope, meaning that groundwater flows into the site, mixing with the leaked radioactive water and then potentially flowing into the nearby sea.

Pipes carrying coolant at temperatures as low as minus 40 degrees Celsius will freeze the earth around the plant to a depth of 30 metres, hopefully blocking this flow, but the wall will not be completed until 2015.

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