Meltdown Alert at Fukishima

14 March 2011: Satellite photo of the Fukushima Daiichi plant showed the damage done to reactors 1 and 3, where there was an explosion on Monday  Technicians are battling to stabilise a third reactor at a quake-stricken Japanese nuclear plant that has been rocked by a second blast in three days. Sea water is being pumped into reactor 2 at the Fukushima Daiichi plant after its fuel rods were fully exposed twice.

International nuclear watchdogs said there was no sign of a meltdown but one minister said a melting of rods was "highly likely" to be happening. The crisis was sparked by Friday's 9.0-magnitude quake and tsunami.
Thousands of people are believed to have died, and millions are spending a fourth night without water, food, electricity or gas. More than 500,000 people have been left homeless.

On Monday a hydrogen blast at the Fukushima Daiichi's reactor 3 injured 11 people and destroyed the building surrounding it. The explosion was felt 40km (25 miles) away and sent a huge column of smoke into the air. It followed a blast at reactor 1 on Saturday. Chief Cabinet Secretary Yukio Edano said there were signs that the fuel rods were melting in all three reactors."Although we cannot directly check it, it's highly likely happening," he told reporters.
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 exactly 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.

Both explosions at the plant were preceded by cooling system breakdowns but the Tokyo Electric Power Company (Tepco) said neither blast penetrated the thick containment walls shielding the reactor cores.
It said radiation levels outside were still within legal limits. But shortly after Monday's blast, Tepco warned it had lost the ability to cool Fukushima Daiichi's reactor 2.
Officials battled all Monday and into the early hours of Tuesday to try to keep water levels up in order to cool the nuclear fuel rods, but on two occasions the rods have been fully exposed. Exposure for too long a period of time can damage the rods and raise the risk of a meltdown.

Four of the five pumps used to administer cooling sea water were believed to have been damaged by the blast at reactor 3. Nuclear and Industrial Safety Agency official Ryohei Shiomi said reactors 1 and 3 had "somewhat stabilised" but "unit 2 now requires all our effort".
A Tepco official later pointed to some improvement and said the company did "not feel that a critical event is imminent". Pressure has been released from the containment vessel, reducing the risk of a catastrophic explosion, but if the vessel is cracked it could still release radioactive material.
The Japanese government has asked the International Atomic Energy Agency (IAEA) to send a team of experts to help.