poto wrote: GIDGE wrote:
poto wrote:The reactor itself at Fukushima is a GE BWR Mark III reactor I believe. In the case of a complete meltdown, they will open the valves designed to vent steam and allow all the water to safely boil off. Then the fuel rods themselves will melt and turn into a shallow pool in the bottom of the containment vessel. Spreading it out will help it cool. Then coolant will be pumped in to further cool it. This will prevent the core from ever exploding and no significant radiation will be released. After a while, the remnants of the core will be collected and shipped to a reprocessing facility. Of course, this worst-case is not going to happen as long as they are able to keep pumping water into the reactors which they have been able to do.
Thanks for the explanation! It's my understanding that the fuel used to power the pumps injecting cool seawater into the reactor has been exhausted.
Could this potentially (probably) present a whole new set of (incredibly dangerous) challenges - from a structural/engineering standpoint?
I was under the impression that they are using diesel fuel to power the new backup generators that were flown or trucked in after the plant's backup generators failed. I haven't heard of any shortage of diesel at the plant, and I imagine that it would be simple enough to transport more fuel to the site fairly quickly.
Even if they run out of fuel to power the pumps, what happens is the water in the reactor eventually boils off and is released via the vents. If there is no water in the reactor to cool the core, eventually the fuel rods will melt completely, but that still does not mean they will lose containment. As I said before, these reactors are designed to contain a complete core meltdown. There is a big catch basin underneath the reactor that is designed to contain a complete meltdown. The containment vessels are still completely intact. Had the earthquake damaged the containment vessels, we might have had some big problems, but this is not the case.
Of course, their engineers are working diligently to keep the reactor cores cool, as preventing a complete meltdown is their top priority right now. They will probably have to keep pumping water for a few months, and periodically releasing steam to control any pressure that is building up.
After a few months the reactors will be cool enough to be passively cooled and that will be the end of it as far as most people are concerned.
My understanding is that all the difficulties so far have to do with this pumping of water to continually cool off the reactor. The fuel rods were inserted immediately, which is good, and which did not happen with Chernobyl. But they've had multiple problems with the pumps. Some parts of the pumping machinary may have been cracked or damaged, there have been problems getting fuel in to the site, for the pumps.
I just listened to Cham Dallas talking on CBS
(he's a supporter of the nuclear industry, not anti-nuclear, and spent years studying Chernobyl to see what went wrong there) and he emphasized the potential for human error here, and also that the Japanese crisis is happening in a disaster zone, following earthquake and tsunami. Little things are going wrong, and right now the biggest problem is with keeping water pumping to cool things down.
The system is designed to be safe, when not damaged. They are not sure at all yet about the extent of damage or what specifically may or may not have been damaged, thus making things less "safe." The recent explosions did not damage the reactor containment vessel (we are told) but all these explosions and quakes (there could be another) can damage the pumping systems.
Pumping then stops, and the reactor heat builds up, melting stuff, making it harder to control.