Three Mile Tokyo

My understanding of the issue here is that the reactors typically take some steps to reduce/stop their power output when bad stuff happens (ie by pushing the control rods completely into the core). This results in reduced power output and lowers the temperature in the core quickly.

The reactors all have emergency cooling systems, however using these would result in the plant completely shutting down. These systems are redundant, and have never failed completely (ie only 1 of 2,3,4+ of the copies of the system need to work to shut the reactor down).

The two scenarios that I think are plausible at this stage are:

• The coolant systems aren't fully functioning (either they don't have power or the pipes are physically damaged). In the worst case here, the reactor core will get fucked up and they'll have to replace it or possibly close the reactor. More likely, as they know there's an issue they'll activate one of the emergency cooling systems to stop the reactor and then the plant will cease producing power. This is probably a worse scenario because its effects are far wider (no electricity to the area).
• The reactor and/or containment structure have been damaged as a result of the earthquake and radiation is being emitted. In the worst case here, moderate amounts of radiation will be released and people in the area may experience health effects in the longer term.

As a sidenote, a nuclear meltdown is a very bad thing, but it's not as bad as a lot of people initially think. Not all meltdowns are Chernobyl, and Chernobyl isn't possible with modern reactors - in fact most meltdowns have been caused by people overriding the safety mechanisms in place to prevent meltdowns (or on other tests, or by improper training/experience).

The TL;DR here is that Chernobyl could not happen in a first world country on a modern reactor. They know that there are problems (which basically means that nothing really bad will happen) and seem to be handling them in a sensible manner. Worst case, the reactor needs to be shut down, power output is interrupted, or there is a small possibility of people being moderately irradiated.

Thanks px1999