Is it even possible to handle all contingencies though? I don't know enough to do the maths, but when you've got
four different reactors
an earthquake
followed by a tsunami
followed by loss of electricity for the emergency pumps
followed by parts of the plant blowing up
followed by tons of dust getting in the way
followed by possibly more aftershocks
followed by possibly more tsunamis
followed by possible injuries to the personnel needed to run these operations
considering other equipment can break down
considering political pressures to make certain decisions
considering some of the physics/chemistry here may be entirely novel
...
Think of all the different permutations in those variables, just how many scenarios have been prepared for? It has to be more complicated than just 'if casing 1 fails, casing 2 will stop it, and if casing 2 fails, casing 3 is there'
The first 10 things you have listed there are entirely predictable. Indeed, the emergency procedures were designed to handle them and simply haven't coped.
They were unlucky that the tsunami was slightly worse than they had planned for, which washed away the diesel backup generators. Backups for those generators were quickly brought in, though.
OTOH, they have been very lucky that no aftershocks have caused any tsunamis (yet). If that happened right now then they are screwed.
I haven't seen any evidence of the last two occurring.
"what appears to have happened is the tsunami flooded the basements where these emergency diesel generator connections are at. So, even though they brought in mobile units, new emergency diesel generators, to hook them up to run the safety systems, the basements were flooded, where they needed to do the hook-up."
Yesterday I heard somebody who was responsible for a nuclear power plant in Europe speak on the radio (in Europe too). He said they were prepared for a malfunctioning valve, power outage etc. (predictable events) but they weren't actually prepared for the case that everything happens at once.
I wasn't saying those things were unpredictable, I meant that in combination they could result in so many different scenarios, I wonder if it's even feasible to have a plan for all of them.
The process of nuclear decay is well understood, so you can compute, given any mass of nuclear material, how much heat and for how long that mass will generate sitting in a pile by itself. You do that calculation in the presence of full moderation (all control rods inserted, below the critcial level) and without moderation (control rods out).
Now you design a thermal sink which can absorb that much heat indefinitely when either covered in soil or sitting out in free air (choose the option that has the worst heat conduction) Note that modern reactors like the Pebble Bed can't really do the whole core meltdown thing, but those that can you can design what is essentially a bucket of boron laced sand underneath them such that in the event hell breaks loose with the control rods out, the core will melt and diffuse into the sand which will drop it below critical and now you're solving for "non-critical pile turned off, how much heat from time 0 to n?"
Ok, now lets see what can cause this reactor design to cause any damage. Hmm, well its immune to anything that doesn't hit it directly and destroy the containment vessel.
So basically anything except a direct hit by an asteroid or perhaps a nuclear weapon.
Now if you look at Pebble Bed reactors they take the approach that the fuel itself is in self contained containment vessels, you can dump them out across the floor and they will cool off without doing anything else and without any radiation.
But to re-iterate what others have said, there is a security/hazard/value trade off, airplanes fall out of the sky all the time and yet people still fly, automobiles kill their occupants and yet people still drive, coal miners die trying to dig up coal and yet they keep mining.
Nuclear reactors are no different in this regard, they have a 'worst case' scenario (similar to a plane losing a wing at altitude but we're not all demanding that planes have a parachute under the seat cushion), if we only have to deal with worst case reactor scenarios during 9.0 earthquakes, I'm ok with that. I can understand if you aren't.
It will not be possible ever, to keep handling cases of escalating complexity one of top of other. When things get complex beyond certain level, a kill switch should be triggered. The Kill switch should not depend on If-else cases ...
In what sense is it true that "that hasn't helped"? Are you suggesting that if they'd kept the reactors running things would have been better?
Perhaps what you mean is "hasn't made the impact of a magnitude-9 earthquake and tsunami zero". Honestly, I can't see that that's a reasonable thing to ask for.
It "hasn't helped" in the context of the post I was replying to.
The poster clearly thought that a kill switch would be some kind of magic button that would turn everything off and "make it safe". I'm pointing out that nuclear power stations don't work like that.
Clearly, it is a much better situation now than if they had been going when the tsunami hit.
And your response indicates compelete ignorance of both the situation and nuclear reactions.
There is no kill switch, if they had a "kill switch" and executed it right now, you'd be condemning all the reactors to meltdowns, and you'd be condemning the US Western Coast to dangerous levels of radiation.
The content of the fuel rods take DAYS to become non-radioactive enough for them to not need to be cooled constantly. The very problem that's occuring now is occuring because either the radioactive cesium and iodine is either at risk of not being cooled which will lead to a meltdown and release of them into the atmosphere, or a containment breach with largely the same impacts.
Hmm. What do you envision a "meltdown" to consist of? The system still has a fallback system in the event of a core meltdown that is designed to cool and manage the core without radiation release. Meltdown definitely does not equal to "release of them into the atmosphere".
I'm not overly familiar with this specific reactor design; but usually what happens is they seal the containment as the core melts, flooding the sump (where the slag would collect) with water to cool it down.
Right now they are trying to avoid that because a) there is always a risk of radiation leak from the containment and b) because the cleanup bill would catch quite a few more zeroes. The point is; meltdown is the final failure scenario, if they get to it, well, they get to it. But there is no fallback if something goes wrong at that point; so it is potentially better to try and control it at this stage, while you still have a fallback to implement.
Please don't be overly dramatic ("and you'd be condemning the US Western Coast to dangerous levels of radiation"); this is a bad situation. But at the moment there does not appear to be a major risk to the US Western Coast. As you say, best not to comment in too much depth if you don't know the details.
>The system still has a fallback system in the event of a core meltdown that is designed to cool and manage the core without radiation release.
What do you think is failing and is the entire cause for all of this concern. The fallback system is pumping water into the reactor to keep it cool. Those are the systems that have been failing and have failed (during the explosions/fires) and have caused the (temporary-ish) meltdowns in the last few days.
A full meltdown has the potential to release a significant amount of radiation. A full meltdown increases in possibility as the reactors become harder to control and cool due to explosions and containment failure. It probably doesn't pose a significant risk to CA, but they will receive some radiation if it were actually to experience complete failure.
Meltdown isn't binary. They're experiencing meltdown right now. By definition. That's what the release of radioactive material is. The question is, can they keep it under relative control and prevent further exposure of the still proceeding fuel rods.
They're experiencing meltdown right now. By definition. That's what the release of radioactive material is.
Not really; in this case "meltdown" refers to the actual process of core melting, it is not entirely clear but it does not appear much or any of the cores have melted. Certainly not to the stage I would refer to as a meltdown. They are still in a "struggling to cool it down" stage.
The release of radioactive material is not equatable to a meltdown - all manner of things can lead to such a release, meltdown is just one of them.
If they actually have a full core melt (to the point it drops out of the reactor vessel into the dry well), yes, the risk of release of radioactive material is heightened. But probably not to the level you envision, and it is certainly not a case of "if it melts it's game over".
Explosions within the reactor shell are extremely unlikely, even in the event of a core meltdown, because the system is specifically designed to stop such an event occurring (which is one reason it has not so far happened :)).
Note; containment failure has not occurred, as far as we know, at any stage. The reactors are not being "controlled", the process is stopping by itself. The reactors simply have to be kept cool while that happens.
What do you think is failing and is the entire cause for all of this concern.
There is a different system in such a case (or, rather, a different approach). Essentially they just flood it with water.
With the best will in the world; it is worth reading some of the more technical explanations rather than just the media. They explain the process and the issues much better - even Wikipedia has reasonable material (and is at least a place to start with links)
This is now the second time you've accused me of not knowing what I'm talking about and yet your only difference of opinion is my terminology as to whether it's a meltdown or whether the process of "oh shit, dump water on it" is controlled or not. In fact, most of the information I have on this topic was from spending most of Sunday re-reading Wikipedia on nuclear reactors, but thanks for assuming I watch or read ANY mainstream news.
QUOTE: "A meltdown occurs when a severe failure of a nuclear power plant system prevents proper cooling of the reactor core, to the extent that the nuclear fuel assemblies overheat and melt, either partially or completely"
That has occurred. That's not in dispute, unless I'm just completely 100% off base here. A quick Google search reveals that fuel rods in both reactors were not only uncovered by water at various points, but were also "exposed" which I presume to be through a containment failure, AND there are numerous reports that the parts of the rods have in fact melted.
As I said earlier, this constitutes a meltdown and greatly increases the severity and danger of the problem at hand. It's not a total meltdown, I already "disclaimered" that repeatedly. Those rods melting pose a large risk to containment efforts. If they melt, they can escape much more easily and that means radiation exposure on a much greater level, even if only for workers at the plant.
I don't mean to sound patronising or rude, if that is what came across sorry.
Whilst mostly you're correct, there are some fundamental problems with what you are saying.
It's definitely stretching the definition of a meltdown to refer to this event as such. It's still pretty much unknown if any melting has occurred, and to what extent it has done. Generally a meltdown is as I described it; where the situation is unrecoverable with the standard cooling and you are facing the situation of simple containment.
I suppose technically this could be seen as a partial meltdown; but the truth is that this situation is at the very edge of the margin for such a problem. A meltdown is not a binary thing, but in this case it is not really a meltdown, and that was my main point.
Right now it is absolutely recoverable, and based on the latest data #1 and #3 reactors will be fine from this point on. Certainly if they survive the next couple of days it will all be fine.
but were also "exposed" which I presume to be through a containment failure
No. If this were the case there would be a much serious issue :) It simply means the coolant level dropped so far that they were exposed to the air inside the container.
If they melt, they can escape much more easily and that means radiation exposure on a much greater level, even if only for workers at the plant.
Potentially... but bear in mind that radiation expulsion so far is relatively unrelated to the core; the radiation released so far is included in the steam that is being vented (and then the explosions push it right out). In a proper meltdown situation the risk is that an explosion releases actual core material into the wild, that would be a magnitude worse than the current situation.
At the moment I don't believe the rods are melting, they are being successfully cooled (and for the most part have been).
I don't know, maybe you're right but I continue to see, more and more, evidence that they did melt. I continue to see more and more people placing this between TMI and Chernobyl in severity...
