Greenpeace radiation team experts check crops for contamination in Fukushima City, 60km from the Fukushima Daiichi nuclear plant.

Japan nuclear reactor pumped with nitrogen to prevent explosion

Japan nuclear workers are pumping nitrogen into nuclear reactor No.1 to try and prevent an explosive build-up of hydrogen gas.

Fukushima engineers have been working since Wednesday night to pump nitrogen gas into the containment vessel of the nuclear reactor at the plant, which was smashed by a 10-metre tsunami that followed March’s quake.

A Tokyo Electric Power Company (TEPCO) official said it was a precautionary measure and the chances were “extremely small” of a repeat of hydrogen gas explosions that ripped through two reactors early in the crisis.

But while the government says the situation has stabilised at the nuclear plant, 240 km north of Tokyo, it is still far from under control.

“Data shows the reactors are in a stable condition, but we are not out of the woods yet,” Chief Cabinet Secretary Yukio Edano said.

One TEPCO official said 6,000 cubic metres of nitrogen gas would be pumped into reactor No.1 and the utility was preparing gas injections for reactors No.2 and No.3 in the six-reactor plant as a safety precaution.

Engineers have managed to plug a leak at reactor No.2, but they still need to pump 11.5 million litres of contaminated water back into the ocean because they have run out of storage space at the facility. The water was used to cool overheated fuel rods.

Fukushima workers are struggling to restart cooling pumps - which recycle the water -in four damaged reactors. Until those are fixed, they must pump in water to prevent overheating and meltdowns, but have run out of storage capacity for the seawater when it becomes contaminated.

UN Scientific Committee on the Effects of Atomic Radiation chairman Wolfgang Weiss said based on the information he had now, the Fukushima accident was not expected to have any serious impact on people’s health.

Fukushima was less dramatic than Chernobyl in 1986 but “much more serious” than Three Mile Island in 1979, he said.

However, neighbouring South Korea and China are worried about radioactive fallout.  China's health ministry found traces of radioactivity in spinach in three Chinese provinces and South Korean media have reported fears about contaminated rainfall.

Some schools in South Korea have closed because of fears the rainfall across the country could be contaminated. The country’s nuclear safety agency said a small level of radioactive iodine and caesium particles was reported in the south but was not enough to cause public health concern.

Meanwhile, in Washington, Democratic lawmakers raised concerns, in the wake of Japan's crisis, about whether regulators and the nuclear power industry were doing enough to ensure US reactors could withstand worst-case scenarios in the wake of Japan's crisis.

Concerns focused on a Pennsylvania nuclear plant with the same kind of reactor design as the Fukushima facility.

Some lawmakers argued that the US plant could be at risk of meltdown in the case of a severe emergency.

US Nuclear Regulatory Commission (NRC) official Martin Virgilio told a congressional hearing that the NRC did not believe that the core of Fukushima's reactor No.2 had melted down.

Earlier, a Democratic lawmaker had said the NRC informed him the core had become so hot it had probably melted through the reactor pressure vessel.

The NRC is conducting special inspections at two Illinois nuclear plants operated by Exelon Corp after routine checks in February found a problem with backup pumps that would be used to remove heat from the reactors in case of an accident.

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