Japan turns to combat-style tactics to cool overheated uranium fuel

Military helicopters dumped loads of seawater onto Japan''s stricken nuclear complex on Thursday, turning to combat-style tactics while trying to cool overheated uranium fuel that may be on the verge of spewing out more radiation.

Plant operators also said they were racing to finish a new power line that could restore cooling systems and ease the crisis at the Fukushima Dai-ichi plant on the country''s northeast coast.

Two Japanese military CH-47 Chinook helicopters began dumping seawater on the complex''s damaged Unit 3 at 9:48 a.m. (0048 GMT, 8:48 p.m. EDT), according to Japan''s defence ministry.

"Thereafter, in total there have been 4 operations conducted by air," Defence Minister Toshifumi Kitazawa said.

Chopper crews were flying missions of about 40 minutes each to limit their radiation exposure, passing over the reactor with loads of about 7,500 litres (about 2,000 gallons) of water.

The water drops were aimed at cooling the Unit 3 reactor, as well as replenishing water in that unit''s cooling pool, where used fuel rods are stored, officials said.

The plant''s owner, Tokyo Electric Power Co., said earlier that pool was nearly empty, which would cause the rods to overheat and emit even more radiation.

Kitazawa told reporters that emergency workers had no choice but to try the water dumps before it was too late.

Meanwhile, a number of water cannons were being prepared for use on the ground.

The troubles at the nuclear complex were set in motion last week''s 9.0-magnitude earthquake and tsunami knocked out power and destroyed backup generators needed for the reactors'' cooling systems.

That added a nuclear crisis on top of twin natural disasters that likely killed well more than 10,000 people and left hundreds of thousands homeless.

Four of the plant''s six reactors have faced serious crises involving fires, explosions, damage to the structures ousing reactor cores or rising temperatures in the pools used to store spent nuclear fuel.

Officials also recently announced that temperatures are rising in the spent fuel pools of the last two reactors.

The top US nuclear regulatory official gave a far bleaker assessment of the situation than the Japanese, and the US ambassador said the situation was "deteriorating" while warning US citizens within 50 miles (80 kilometres) of the complex to leave the area or at least remain indoors.

The Japanese government said it had no plans to expand its mandatory, 12-mile (20-kilometre) exclusion zone around the plant, while also urging people within 20 miles (30 kilometres) to stay inside.