Lakshmi.Jaerik said:
No, they apparently meant some combination of boron... magically disappearing, and water... like, increasing?
Or... a weird situation where the nuclear reactor could "suddenly restart" and go critical again on its own. And then explode?
Also, unicorns.
Well it is technically possible. The reactor wants to startup. It naturally would.
This is why we have control rods. In no normal situation could the reactor be critical with the rods on bottom. Actually even with the most reactive one on top in the absolute worst case possible circumstances the core is made and the fuel is placed in such a way that it couldn't.
The problem comes when the fuel placement and core changes. Ie severe core dmg that ends up melting rods away or melting various peices of fuel that were seperated closer together or away from the rods etc. While more water for moderation would be helpful if melted right wouldn't be necessary. But good luck achieving that much melting with cooling restored and decay heat down to hardly anything now
This is why we have Boron injection. But you inject dissolved boron and it will flow into all those cracks and stick to stuff and add alot more neutron absorption which should keep it from starting back up.
I haven't done much research on the odds of a re-criticality event after boron injection... but that's partly because boron injections are just something that is never done. It's a very overpowering last resort. It works so good it's alot of work to recover so you can restart the reactor on purpose lol. So not sure if it's happened or if much testing has been done on it.
As far as an explosion... well there is enough poisons and such loaded in and made from the running of a reactor in the fuel that nuclear explosion would be impossible. Ever. In fact you a implosion is almost required for that anyways. As far as another steam or hydrogen explosion... doubtful but possible. But last I heard cooling had been restored making it alot less likely