an interesting post, page-10

In an emergency press conference later Saturday (March 12), chief Cabinet secretary Yukio Edano said a hydrogen explosion had occurred inside the external container structure.

Oxygen explodes when it combines with hydrogen. This can be seen in experiments in which a hydrogen-filled test tube is placed close to a flame, and a popping sound is heard as the two combine.

US space shuttles have used the hydrogen-oxygen reaction to acquire the enormous energy required for space travel.

Why did hydrogen fill the external containment structure before the blast Saturday afternoon?

According to professor Emeritus Keiji Miyazaki at Osaka University, an expert in atomic energy engineering, nuclear fuel is enveloped in a particular type of metal covering. When the fuel reaches an extremely high temperature and then comes into contact with the cooling water, the metal's properties break down the water and generates hydrogen.

The hydrogen can leak from the reactor containment vessel into the outer structure through valves and other gaps.

The hydrogen that filled the outer structure Saturday is believed to have exploded when it mixed with the oxygen in the air, Miyazaki said.

According to a nuclear technology expert with experience designing the same type of reactor as the Fukushima No. 1 plant, neutrons in the reactor's pressure vessel usually collide with water molecules and create hydrogen. It is quite possible that hydrogen derived from water molecules leaked out of the vessel, the expert said.