Japan began pumping nitrogen into one of its crippled nuclear reactors, refocusing the fight against the world's worst nuclear disaster in 25 years on preventing an explosive buildup of hydrogen at the Fukushima Daiichi power complex.

Workers began injecting nitrogen into the containment vessel of reactor No. 1 last night, following a morning breakthrough in stopping highly radioactive water leaking into the sea at another reactor in the six-reactor plant.

"It is necessary to inject nitrogen gas into the containment vessel and eliminate the potential for a hydrogen explosion," an official with plant operator Tokyo Electric Power Co told a news briefing.

The possibility of another hydrogen explosion like those that ripped through reactors 1 and 3 early in the crisis, spreading high levels of radiation into the air, was "extremely low," he said.

But TEPCO suspected that the outside casing of the reactor vessel was damaged, said the official. "Under these conditions, if we continue cooling the reactors with water, the hydrogen leaking from the reactor vessel to the containment vessel could accumulate and could reach a point where it could explode," he said.

Although engineers had succeeded after days of desperate efforts to plug the leak at reactor No. 2, they still need to pump 11.5 million liters of contaminated water back into the ocean because they have run out of storage space at the facility. The water was used to cool over-heated fuel rods.

The growing concerns of nearby South Korea and China about radioactive fallout from Japan were underscored when China's health ministry reported traces of radioactive iodine in spinach.

The two western neighbors of Japan have reportedly complained they have not been fully informed about TEPCO's plans to release radioactive water into the Pacific Ocean.

"We are instructing the trade and foreign ministries to work better together so that detailed explanations are supplied especially to neighboring countries," Chief Cabinet Secretary Yukio Edano told a news conference.

Experts insisted the low-level radioactive water to be pumped into the ocean posed no health hazard. Radioactive iodine detected in the sea has been recorded at 4,800 times the legal limit, but has since fallen to about 600 times the limit. The water remaining in the reactors has radiation 5 million times legal limits.

Spinach radiation in China


A vendor sorts spinach at a vegetable market in Beijing, April 6, 2011. Sample inspections conducted on Tuesday found low levels of radioactive iodine in spinach planted in Beijing, Tianjin and Henan province. (Photo/Asianewsphoto)
Meanwhile, radioactive iodine-131 had been found on spinach in Beijing, Tianjin and Henan, China's National Nuclear Emergency Coordination Committee said yesterday.

But the amounts were one thousandth to three thousandth the legal limit stipulated in China's national radiation safety standard, according to the committee's daily statement, which said the results were based on checks carried out on Tuesday.

The Ministry of Health also issued a statement last night saying that traces of iodine-131 had been found in spinach planted in open fields in the three regions. According to the ministry, it has been proved that washing the spinach in water could effectively remove radioactive material.

It is believed that recent rain in the regions helped the radioactive iodine drop from the air onto the fields, the ministry said.The current trace amounts of radioactive material in food will not pose any threat to public health, and there is no need to take protective measures against contamination, the ministry said.

Meanwhile, Shanghai Center for Disease Control and Prevention officials said yesterday that nothing abnormal had been detected in local food or drinking water.

Gao Linfeng, director of the Shanghai CDC's radiation health department, said the city was regularly checking drinking water sources and food, including green-leaf vegetables, grown on local farms. "We haven't found radioactive substances in our tests," he said.

A total of 14 provinces and municipalities are monitoring drinking water and food for radioactive substances, as required by the Ministry of Health, since March 26, when iodine-131 was first detected in the air above China.

The committee said that all 31 provincial regions on the mainland detected radioactive iodine-131 in the air yesterday. Inner Mongolia Autonomous Region found both iodine-131 and caesium-137, while another 20 regions, including Shanghai, found iodine-131, caesium-137 and caesium-134 from the quake and tsunami damaged Fukushima Dai-ichi nuclear plant in Japan.

People's Daily Online / Agencies