According to Tokyo Electric Power Company, the explosion happened “near” but not in the Unit 1 reactor. Radiation levels had reached 1,000 times above normal in a reactor control room at the plant, and more troublingly levels had reached 8x normal near the main gate.
The important thing, though, is that it appears that the explosion likely caused by a hydrogen build up only affected the wall around the reactor and not steel container housing the reactor itself. The important thing now is that cooling operations continue unhampered. If the cooling systems are inoperative for several hours, the reactor’s water will boil away and the fuel will begin to melt. When that happens, the situation escalates from “manageable” to “Three Mile Island.” And while there are indications that radiation levels have in fact declined since the explosion, Daiichi is still currently walking that line very tightly.
The 2053 nuclear tests and explosions that took place between 1945 and 1998 are plotted visually and audibly on a world map.
As the video starts out detonations are few and far between. The first three detonations represent the Manhattan Project and the two bombs that ended World War II. After a few representative minutes the USSR and Britain enter the nuclear club and the testing really starts to heat up.
Even though the video does not differentiate between sub-critical “safety” tests and full detonations, you get a good idea of the fever of the nuclear arms race.