US naval barges loaded with fresh water are speeding towards Japan's overheated nuclear plant to help workers scrambling to stem a worrying rise in radioactivity and remove dangerously contaminated water from the facility.
Workers at the stricken Fukushima Dai-ichi plant have been pumping sea water in a frantic bid to stabilise reactors overheating since a tsunami knocked out the complex's crucial cooling system on March 11.
Plant operator Tokyo Electric Power Company is rushing to use freshwater instead because of the corrosive potential of the salt in seawater, Hidehiko Nishiyama of Japan's Nuclear and Industry Safety Agency said at a briefing.
The switch was the latest tactic in attempts to regain control of the nuclear power plant near the coast, 140 miles north-east of Tokyo.
Low levels of radiation have been seeping from the plant since a magnitude-9 earthquake and tsunami, forcing residents to evacuate areas within 12 miles of the plant.
Elevated radiation have been found in raw milk, sea water and 11 kinds of vegetables, including broccoli, cauliflower and turnips, prompting several countries to halt some food imports from the Fukushima region.
Tap water in several areas of Japan, including Tokyo, also exceeded government standard for infants, who are particularly vulnerable to cancer-causing radioactive iodine.
On Friday, nuclear safety officials revealed that they suspected a breach in one or more of the plant's units, possibly a crack or hole in the stainless steel chamber around a reactor core containing fuel rods or the concrete wall surrounding a pool where spent fuel rods are stored.
Suspicions were aroused when two workers suffered skin burns after unexpectedly encountering water that was 10,000 times more radioactive than levels normally found in the units, NISA said.
Such a breach could mean a much larger release of radioactive contaminants. The most likely consequence would be contamination of the groundwater, experts said.