This animation was created by the Japan Nuclear Energy Safety Organization, a government corporation under the Ministry of Economy, Trade and Industry (which regulates the nuclear industry), to train Senior Specialists for Nuclear Emergency Preparedness on the severe accident of loss of cooling, using a Mark-1 Boiling Water Reactor.
It was created before the Fukushima I Nuke Plant accident, though there is no information as to when it was created. (The Japan Nuclear Energy Safety Organization itself was created in 2003.)
The accident sequence in the animation:
Control rods are inserted, and the reactor stops.
A big pipe connected to the Reactor Pressure Vessel breaks, and all methods of cooling the reactor fails.
Water starts to leak. Water level in the RPV gets low, exposing the fuel core.
That's exactly what happened at Fukushima I Nuclear Power Plant.
They must have known all along that it was not even a meltdown but melt-through.
Core melts 30 minutes after the loss of coolant accident.
Corium drops to the bottom of the RPV after 1 hour of loss of coolant.
Corium melts through the 15-centimeter RPV bottom after 3 hours, drops to the concrete floor of the pedestal that supports the RPV.
Corium melts through the concrete floor of the pedestal and drops to the floor of the Containment Vessel.
Gas is generated by the corium melting the concrete, and the gas fills the Containment Vessel raising the pressure and the temperature.
Gas starts to leak at the franges of the Containment Vessel and fill the reactor building, necessitating the venting.
The animation has this reassuring message at the end:
"Even if it gets to the worst case scenario (that you've just seen), we are trying our best to learn and upgrade our skills in dealing with nuclear emergencies by training the nuclear emergency specialists, so that the residents near the nuclear power plants can feel safe and secure."
A Senior Specialists for Nuclear Emergency Preparedness is a METI (NISA) official stationed full-time in the area where a nuclear power plant is located.