I still remember the voices after Chernobyl: Light water reactors are safe and core meltdown can never happen, because the moderator is water. If it evaporates, the moderator is gone and the core will cool down.
Chernobyl was a graphite moderated reactor. When the core overheated, the graphite melted together with the uranium and the nuclear reaction could not be stopped any more.
Now we see how reliable those reports really are. There is no base for any beliefs, if you ask me.
Hmm, I think it is readily accepted and established that complete loss of coolant in a LWR will lead to meltdown - although I can't comment on whether that was the scientific opinion immediately after Chernobyl.
The problem at Chernobyl is not as you describe. The issue there was that through a process of bad core management, while trying to shut down the reactor and at the same time run an experiment, meant the core ended up in a very unstable state. Mostly the instability was managed automatically but at some point it went wrong; there is much debate over this, though conventionally it is accepted that someone, it is not known who, SCRAMmed the reactor - the poor design of the control rods meant that rather than immediately stop the reaction it actually made things worse as they were inserted, causing the core to overheat causing extreme pressure, cracking the control rods and essentially making the situation unrecoverable. Then a steam explosion broke the pressure seal and the chamber emptied of coolant.
After that the exact mechanics of what happened is somewhat unknown (instrument failure) but the lack of coolant lead to a critical "nuclear excursion"; i.e. essentially the neutron emission becomes so large that the fuel becomes supercritical. The excursion heated the fuel so that it expanded and "exploded" out of the pressure vessel; once that had happened the fuel was dispersed and the nuclear reaction ended.
At that point the graphite was exposed to the air and caught fire; it was this (and the resulting smoke plume) that spread most of the radiation.
I still remember the voices after Chernobyl: Light water reactors are safe and core meltdown can never happen, because the moderator is water. If it evaporates, the moderator is gone and the core will cool down.
You misunderstood. No one reasoned that loss of water coolant would somehow cool the reactor (that's self-evidently absurd); they reasoned, and still reason, that loss of coolant would shut off the fission reaction. This rules out, not meltdowns, but uncontrolled power excursions like the one that created the steam explosion that blew up Chernobyl.
This is the wrong comparison. You can choose the food you eat, but you cannot choose the energy you use. At least not as easily.
But there are similarities: the industry that sells energy wants to go on running their reactors. They advertise and we belief and consume.
There is also an industry (or industries) that tries to control the food market. We belief and consume. Now look at the rate of overweight people and tell me they do a good job.
As much as I like to get healthy (as good as possible) food I also want clean (as good as possible) energy. Japan shows again, that nuclear power is hard to control. And loss of control has devastating consequences.
This is not what the nuclear industry tells us, right? So it is not the right thing to believe. The same with the food industry, as you dug out this comparison.
I consulted Wikipedia about the design of german light water reactors. Bor is used in addition to water. It enables regulation of the power (in some limits). Makes sense to do that. I don't know if this is done in Japan too. It could explain, why the reaction does not stop after the water is gone.
No, I am talking about german news reports. It makes no sense for the soviets to say that light water reactors are safe after a graphite moderated system has gone out of control.
Chernobyl could never happen in germany, because the construction of light water reactors is inherently safe. Thats what the news reported and the politicians claimed.
Do you see what happens now? Something like in Japan can never happen, because we don't have earthquakes and Tsunamis like they have.
These reports are not reliable. The basic idea, that a reactor has to shut down, if it gets out of control, is the right one. But it seems, the idea is not implemented well enough, even in the light water reactors.
Chernobyl was a graphite moderated reactor. When the core overheated, the graphite melted together with the uranium and the nuclear reaction could not be stopped any more.
Now we see how reliable those reports really are. There is no base for any beliefs, if you ask me.