Japan earthquake: Meltdown alert at Fukushima reactor

Tokyo: Physics professor says another Chernobyl is highly unlikely. Technicians are battling to stabilise a third reactor at a quake-stricken Japanese nuclear plant, after the latest explosion rocked the facility.

Fukushima Daiichi plant's operators said they could not rule out a fuel rod meltdown, after a cooling system broke. They are frantically injecting more water into reactor 2 after its fuel rods became almost fully exposed. A cooling system breakdown preceded explosions at the plant's reactor 3 on Monday and reactor 1 on Saturday.

The latest explosion, said to have been caused by a hydrogen build-up, injured 11 people, one of them seriously, and sent a huge column of smoke billowing into the air. The operators are playing down any health risk and say the thick containment walls shielding the reactor cores have so far remained intact.

But the US said it had moved one of its aircraft carriers from the area after detecting low-level radiation 160km (100 miles) offshore.

The fuel rod exposure at Fukushima Daiichi number 2 reactor is potentially the most serious event so far at the plant. A local government official confirmed the fuel rods were at one point largely, if not totally exposed; but we do not know for how long. Without coolant around the rods, temperatures can rise to hundreds of degrees Celsius, almost certainly resulting in some melting.

This opens the possibility of a serious meltdown - where molten, highly radioactive reactor core falls through the floor of the containment vessel and into the ground underneath. However, engineers appear to have restored some water flow into the reactor vessel and if they are successful, temperatures will begin to fall again rapidly. Tens of thousands of people have been evacuated from a 20-km exclusion zone around the Fukushima Daiichi plant.

Experts say a disaster on the scale of Chernobyl in the 1980s is highly unlikely because the reactors are built to a much higher standard and have much more rigorous safety measures.

In other developments:

• Two thousand bodies have been found on the shores of Miyagi prefecture, Japanese media are reporting
• The government said it would pump 15 trillion yen ($182bn; £113bn) into the economy to prop up markets, but the Nikkei slumped more than 6%
• Prime Minister Naoto Kan postponed planned rolling powercuts, saying they may not be needed if householders could conserve energy