When the accident at Fukushima happened, the temperatures in the reactor vessels increased and the pressures went up. In order to deal with this, steam was released from the pressure vessels. Water boiling in the reactors exposed the fuel rods, and since the zircaloy cladding of the rods reacts with steam, producing hydrogen, this reaction is the most likely source. This situation is, of course, a meltdown.
The problem with the hydrogen, of course, was that it collected in the reactor buildings, mixed with the atmosphere, and exploded.
Fukushima
Fukushima is not an event that happened, it is a place, a prefecture, or district, in Japan. There are two Fukushima nuclear power plants. The plant where the accident took place, Fukushima Daiichi, is located in Okuma, Fukushima, Japan.
There are two Fukushima nuclear power plants, both of which are in the Fukushima district on the east coast. Fukushima Daiichi, where the meltdowns happened, is at a town called Okuma. Fukushima Daini, is at a town called Naraha.
Naoshi Fukushima was born in 1925.
Yutaka Fukushima was born in 1958.
Masami Fukushima was born in 1929.
Masami Fukushima died in 1976.
Tadashi Fukushima was born in 1964.
Fukushima University was created in 1949.
Kikujirō Fukushima was born in 1921.
Fukushima Masanori died in 1624.
Fukushima Masanori was born in 1561.