Prompt criticality, which differs from the state of criticality that normally occurs inside a nuclear reactor, is reached when nuclear fission energy is released in one 1,000th of a second.
One expert expressed "shock" at the more dangerous likelihood of prompt criticality at the uranium processing plant run by JCO Co.
Apart from prompt criticality, another state of criticality is delayed criticality, in which energy produced by fission is emitted with long delays, allowing power changes to occur slowly.
Nuclear explosions, on the other hand, are triggered by prompt criticality.
According to an expert, significant proof demonstrating the possible occurrence of prompt criticality is neutron radiation data gathered by a monitoring station of the Japan Atomic Energy Research Institute in the town of Naka, about 1.
The data shows the occurrence of prompt criticality to be extremely likely.