The clear-up of the Fukushima nuclear disaster will take decades, experts warned.

The Dai-ichi nuclear plant was rocked by explosions and damage to the reactors after systems failed in the face of the 9.0 magnitude earthquake and subsequent 14-metre tsunami in northeast Japan.

A year on, workers have managed to get the reactors into a “stable cold shutdown state”, but it may be a decade before they can get into the reactors themselves and fully decommissioning the site will take 30 to 40 years, experts said. Leeds University’s head of radiation protection Ian Haslam, raised concerns about the contaminated water which has been used to cool the reactors and appears to have been stored in containment ponds which are rapidly filling up.

“If they are filling up, they’re going to have to empty them sometime. Where are they going to go? It’s going to have to go in the sea.”

He said the seas off Fukushima were fertile fishing grounds and discharging the contaminated water into the sea could risk polluting that area with radioactivity.

And he questioned whether the site had been sufficiently secured to withstand the “worst case” scenario of another quake or tsunami.