> ...the activity levels (radiation levels) of the steam moving through the main steam lines momentarily rose to about 3 to 4 times higher compared with the nor

> ...the activity levels (radiation levels) of the steam moving through the main steam lines momentarily rose to about 3 to 4 times higher compared with the normal activity level. The momentary increase of the activity level in the main steam lines caused the automatic isolation of the containment, the so-called i-isolation. This is one of the safety functions of the plant, and it's job is to isolate the reactor's containment and the reactor so that no radiation can reach the environment. The i-isolation is designed to operate in the case of an internal pipe leakage or significant fuel damage. In this case, the cause was neither. The i-isolation automatically initiates water spraying in the containment and a reactor trip, among other things. As a result of a reactor trip, all the control rods automatically go inside the reactor, and the chain reaction stops. The way I read this is--there was a very brief rise in the radioactivity of the steam in the pipeline, which kicked off the shut down of the plant. There was no indication of a larger issue, no indication that lives were in danger. In other words, the professionals on the scene had reason to believe it was nothing--and they were correct. While the public certainly have a right to know if they are at risk, plant operators in this situation have an obligation to communicate in very careful manner. After all, in the era of social media, one hysterical politician could set off a mass panic via twitter. Far better, if the situation is in hand, to get things into an easily explainable safe state before communicating with the excitable non-experts.