Japan minister to visit stricken nuclear plant

With Tokyo warning the crisis is far from over, Banri Kaieda will don full protective gear for his brief trip to the damaged Fukushima Daiichi plant, his ministry said.

Kaieda, who has overall responsibility for all of Japan's 50-plus nuclear reactors, will be the first government figure to step inside the compound since the giant tsunami of March 11 knocked out cooling systems.

The visit comes 24 hours after it emerged small amounts of radioactive water spilled from spent fuel cooling pools at another nuclear plant as a powerful aftershock rocked northeast Japan.

The cooling systems at three plants were forced onto back-up power when the 7.1 magnitude tremor late Thursday shut down electricity generation across a swathe of the country.

Yesterday, Tohoku-Electric Power, the operator of the Onagawa nuclear plant, said around four litres (a gallon) of mildly radioactive water had spilled from the spent fuel pool of one reactor.

The entire plant had been shut down since the March 11 disaster and the leak did not present any danger, the company said.

A spokesman for the Ministry of Economy, Trade and Industry said Kaieda wanted to see for himself the work being done at Fukushima.

"He will express his appreciation to the workers at Fukushima Daiichi and will see the situation first hand," the spokesman said.

Kaieda will also visit the "J-Village" sports complex, which is being used as a base for workers at the plant.

The complex lies inside a 20-kilometre exclusion zone around the plant, from which thousands of people were evacuated when levels of radiation in the area soared following the emergency.

The crippled plant has leaked radiation that has made its way into tap water and farm produce, sparking food export bans covering a large area.

Some highly radioactive water has leaked into the Pacific Ocean and this week Tokyo Electric Power Co. (TEPCO) began dumping 11,500 tonnes of low-level radioactive water from the plant into the sea to free up urgently needed storage space, a process they hoped would finish on Saturday night.

Workers at the plant on Thursday began injecting inert nitrogen gas into reactor No. 1 in a bid to head off a possible explosion from a build-up of hydrogen reacting with oxygen from the air.