Nuclear chain reaction between being slightly subcritical and slightly delayed-supercritical, but must always remain below prompt-critical. It is impossible for a nuclear power plant to undergo a nuclear chain reaction that results in an explosion of power comparable with a nuclear weapon, but even low-powered explosions due to uncontrolled chain reactions, that would be considered "fizzles" in a bomb, may still cause considerable damage and meltdown in a reactor. For example, the Chernobyl disaster involved a runaway chain reaction but the result was a low-powered steam explosion from the relatively small release of heat, as compared with a bomb. However, the reactor complex
Timeline of the Fukushima Daiichi nuclear disaster TEPCO informs the Nuclear and Industrial Safety Agency and the government of Fukushima Prefecture of the results of soil tests for uranium (, and ) carried out around the Fukushima Daiichi plant. The uranium found was considered to be natural, as its isotope ratios were consistent with the natural abundance. At 21:14 a cooling pump at reactor five stops. At 08:12 the next day, work began on a spare pump, and cooling was restored at 12:49. The reactor temperature had risen to 92.2 °C. The cause of the outage is suspected to be motor failure. It is reported that 22