Imagine I'm not a nuclear physicist.
What is a meltdown? And what repercussions?
Well, to fully understand what's going on you'd need to be a nuclear engineer and you'd need to be familiar with these particular Boiling Water Reactors (BWR) that are in trouble right now.
Basically, in a nuclear power plant you have fuel rods which undergo nuclear fission. That means that they are comprised of one element and split into smaller elements, and they release a ton of energy in the process. The reaction proceeds until the fuel rod becomes completely spent, meaning there is no more of the original element left to split. These particular reactions require a neutron to initiate, and they give off a few neutrons when they complete. These product neutrons then initiate more and more reactions until you get this uncontrollable chain reaction.
Nuclear power plants impose a restriction to control the chain of reaction. They use control rods next to the fuel rods which soak up a lot of the released neutrons and keep the chain reaction from getting out of hand.
These BWRs use water that gets vaporized by the hot reactor and is then cycled past a turbine to generate electricity, and returned to the reactor after being cooled and re-condensed. The water also acts as the electron moderator instead of control rods. (Maybe they have control rods too, I don't know.) So, basically, when they can't re-condense the water, there are fewer neutrons picked up by the vapor than what the liquid is able to absorb. So those neutrons react with the fuel rods making them get hotter and hotter and making the pressure in the system rise higher and higher until the reactor vessel can no longer hold it.
I guess the fix is, obviously, to get the condensers back up and running, but I think they were also trying to vent the steam and refill with fresh water. The problem with purging the reactor is that all the steam in there is radioactive. That's in addition to the MASSIVE pressure built up in those things. Otherwise, they could just purge it
like they do when they quench superconducting magnets.
I've sent a message asking about this to my friend that's a nuclear engineer at Texas A&M. Let's see what he has to say.