Japanese nuclear work 'at critical stage'

Workers at the stricken Japanese nuclear plant need to keep up recovery efforts to control the reactors over the next few "critical" days, experts said today.

Workers at the stricken Japanese nuclear plant need to keep up recovery efforts to control the reactors over the next few "critical" days, experts said today.

Frantic attempts to cool down the reactors at the Fukushima plant following the earthquake and tsunami, which damaged the power stations and led to a series of blasts and fires, had to be suspended after high radiation levels were recorded.

Workers who are dousing the reactors with sea water were withdrawn after radiation levels became too high, but have since returned to carry on the work.

Dr Ian Haslam, head of radiation protection at the University of Leeds, said moving the workers away from Fukushima plant after more radiation leaked from the site was a "desperate measure" in response to dangerously high levels of radiation.

But he said the danger of radiation was a local issue.

Laurence Williams, professor of nuclear safety at the John Tyndall Institute for Nuclear Research, said measures of radioactivity outside the plant were not significantly raised.

He also said levels had spiked, allowing workers back in, which suggested that the higher radiation was the result of another release of radioactive steam being vented from the reactor to relieve pressure - rather than sustained releases from a damaged core.

Water is being pumped into the reactor to cool the nuclear rods but high temperatures are leading to high pressures of steam and gas which need to be released.

Dr Haslam raised concerns the radiation would be affecting the recovery efforts at the site.

He said workers would be "dose sharing", rotating people between high dose and low dose areas.

But he said: "If they are saying they have to move everyone out, it's a desperate measure."

He said it indicated extremely high levels of radiation, which could lead to radiation sickness, burns and damage to chromosomes in the body.

"The actual external radiation dose rate that is coming from the core is a local concern. It is going to affect what happens at the site.

"They need to be at the plant to take the measures to keep it under control - if they move away they are not keeping it under control.

And he warned: "If you let it go, it will get hotter and hotter, there's a risk of fire, and you're changing from this present rate of release which is worrying but at a relatively low risk to something that becomes a higher risk both now and in the future - and may cause panic, which is a problem."

But Prof Williams said there was no sustained release of radioactive material, which showed the Japanese workers were doing a good job of controlling what was happening at the plant.

"The longer they can keep some degree of cooling past the fuel rods, sooner or later the temperatures will get to a level where they can flood the core with water."

Currently temperatures are too high to flood the reactor as the water would just turn to steam, but when they can, it will effectively shut the reactor down and give the company time to decide how to eventually decommission the ageing plant.

He said: "We've got a few critical days. If you can keep this going for two, three, four days, as soon as you can remove more heat than is being produced, temperatures come down and you can flood the core."

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