At the start of the event, Reactor #4 was shut down for annual maintenance.
So you’re probably wondering how #4 got into play? My antenna went up last night when someone wrote that #4 was not involved “yet”.
Reactor #4 has a spent fuel rod storage facility next to it (as do #5 and #6, I assume). The WSJ description says the heat of the other reactors caused the fire. I doubt that explanation.
If a spent fuel rod pool loses its water, this is what can happen. How did the fuel rod pool at an idle reactor lose its water?….. explosion of the next door containment building? tsuname damage?
Time will tell, but now things just got much worse.
It is possible the spent fuel pool was cracked or otherwise damaged in the quake. More likely is the water simply boiled off. These are BWRs and likely have an 18 month fuel cycle. Every 18 months, 100 or so fuel assemblies would be offloaded to the spent fuel pool and cool off awaiting the never-to-be final burial/entombment site. The cooling is provided by pumps and heat exchangers in the fuel pool cooling system. If these units have been around for many years, there is a substantial quantity of assemblies needing cooling. Once the power went, the pumps stopped. It would take a few days to heat and evaporate enough fuel pool water to uncover the assemblies. I would have to run some calcs, but it would be pure speculation – we don’t really know what is happening.
A shame. If you stand in the fuel pool building with low or no lighting, the Cherenkov Effect is quite fascinating.
At the time, the first report was that the blast from the explosion of the #3 containment building was the cause. #3 blowing up was much more extensive than #1. Supposedly the fuel storage areas in the containment buildings that blew up are still intact, which is pretty incredible. Another report said it was the heat from the other reactors, which doesn’t make much sense.
The thought crossed my mind (with absolutely no evidence to back it up) that when they lost cooling in the reactors, they might have withdrawn the cooling water from #4 to try to pump it into the other reactors, since it would have been “clean” water instead of sea water…
As briand75 said, the water probably began to boil off over time when the spent fuel cooling system stopped working.
The spent fuel pools have pretty incredible design standards from a seismic standpoint. They have every bit as much design robustness as the reactor does. So it would not surprise me that the pools would ride out the earthquake will no significant structural damage. It is very unlikely that they would be able to pull water from the #4 spent fuel pool to the other units. I am 95% sure that it would be against design standards for system separation.
Salt water is bad in general, but it will be less harmful in the spent fuel pools than in the reactor itself because the fuel cladding temperatures are much lower in the fuel pools. Again they’ll have to add boron to the seawater to ensure that the stored fuel does not return to criticality and begin generating neutrons. (It shouldn’t, but the boron provides absolute assurance.)
If you have Boron laced water, and the water boils off, you need to keep adding boron?
BTW, what are the probability that a radio blog would have >1 person who knows about nucear reactor design…
Yes to the boron question. It’s a bit hard to dissolve in water so you don’t want to rely on it happening just because there’s a bunch of crystals lying around on the floor…
Funny, I was thinking the same thing about nukies and the radio blog. Perhaps that’s an indication that there are far too many skilled people in the U.S. with too much time on their hands? :-)
So what happens if you were trying to mix boron with sea water that’s about 40 degrees F (guess)
I vaguely remember mixing boric acid for something a long time ago – perhaps for irrigating a burn wound? It is a bit stubborn to get into solution.