The US military has delivered high-pressure water pumps to Japan to help cool Fukushima's crisis-hit nuclear power plant.
The pumps were ferried to Yokota Air Force Base for use at the crippled Fukushima plant, with four additional pumps delivered from Sasebo, in Japan's southwest, the US Pacific Fleet said in a statement.
Rising temperatures caused by damage to the cooling system pumps during Friday's earthquake are cauding the water in the reactor cores to turn to steam, increasing pressure, and exposing the fuel rods.
When the fuel rods become even partly exposed, the temperature increases rapidly, turning more of the water to steam, and increasing pressure even more quickly. When the rods come into contact with steam, rather than water, hydrogen is produced.
With large amounts of hydrogen held in a container whose heat and pressure is increasing rapidly, there is a risk of an explosion, which may damage the containment vessel and allow nuclear fuel to leak out, spreading large amounts of radiation.
The high-pressure pumps are used to re-fill the reactor cores as the water level begins to drop, replacing the water at a speed which cools both the rods and the chamber, reducing pressure and averting the potential for a meltdown.