Skip to comments.Why I am not worried about Japan’s nuclear reactors
Posted on 03/13/2011 9:24:12 AM PDT by Qbert
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The safety systems on all Japanese plants will be upgraded to withstand a 9.0 earthquake and tsunami (or worse)
As far as a seismic standpoint, it appears that these plants withstood far more than they were designed to. From a structural stand point, there does not seem to be a problem. It was the secondary stuff that had a problem.
I would have have assumed that in Japan, the emergency diesels would have been protected from any conceivable tsunami. Apparently not.
Loss of off site power on Gen I and II reactors is a big deal and not unexpected experience. That is why some much emphasis was placed in designing back-up power in the form of those diesels. That the Japanese allowed them to be placed where the tsunami could take them out (or the switch gear for them) is surprising.
I'm guessing, the Japanese with most of their plants located along the coast will require all back up diesel systems to be located well above any conceivable tsunami level in the future. Monday morning quarterbacking, but if they had done that 30 years ago, we wouldn't even be talking about this today.
The newer designs like the passive systems in the AP-1000 could go without power of any sort for days using just natural circulation, but we have what we have now. We just have to make it work.
Not accurate. The 'pressure cooker' is the reactor vessel it self. Outside that is the secondary containment which is steel and concrete. Beyond that, is the building you see from the outside.
Study the drawing.
One reply to the Cesium question is at the link:
“The cesium was in trace amounts and dispersed via the prevailing winds over the ocean. It then reacts immediately with water to produce cesium hydroxide (CsOH) and is dissipated.”
In general you give a much better understanding of the Mark 1 BWR GE reactor, but I have a few comments...
You say it takes about 45 minutes for the Zircaloy cladding to reach the melting point of 2200 C without coolant.
It is my understanding that the fuel rods on all three reactors have been exposed for longer than 45 minutes without coolant. I believe in reactors 1 and 3 at least the top two meters were uncovered for quite a period of time. In fact, reactor 2 is now reported to have no coolant around the rods at all!
So who is to say that we don’t see temps rise to 3000 C at which point the Uranium begins to melt ?
Also, I understand that the Uranium is not really a rod but rather lots of small pellets. If the Zircaloy is gone, what is to keep this big long stack of pellets in place? Won’t they just perhaps topple down and all fall together in a pile at the bottom of the reactor? Could this start the chain reaction again ?
I also understand that Unit 3 uses not only simple Uranium fuel, but the more dangerous kind that either has Plutonium in the mix, or creates Plutonium ?
Finally, when I look at the picture of the plant after the explosion, it seems that you can actually see the RPV between the steel members, which would imply the concrete containment has been breached, and perhaps only the steel RPV still has integrity, although no one has confirmed this absolutely.
Dr. Josef Oehmen is an expert in risk assessment. One problem in risk assessment is outliers. What about the risk of human error shutting a valve, causing a hydrogen explosion, the resulting debris then damaging the torus causing a large radiation release, or explosion damage or human error causing a leak and a resulting fire in the fuel storage pool? Either of these could cause a large enough radiation leak to cause the facility and all cooling efforts to be abandoned. Since the reactors were built so close together, the neighboring one would be abandoned, and cooling failure accidents would then cascade from one to another. Or what about the risk to one’s reputation of posting an optimistic assessment and then having events turn out much worse?
> The earthquake that hit Japan was 7 times more powerful than the worst earthquake the nuclear power plant was built for ... So the first hooray for Japanese engineering, everything held up.
Hooray? They had no idea that 8.4+ richter scale quakes happened more than once in Japan in 20 century? Hooray?
> The temperature at this stage was about 550°C. ...
> The radioactive nitrogen as well as the noble gases do not pose a threat to human health.
> At some stage during this venting, the explosion occurred.
Radioiodine is not a noble gas. No way it can be released from the fuel at only 550°C. Therefore we know that fuel rods went far higher and were damaged *before the venting*.
This is not supposed to happen. Therefore, it is not a normal venting.
Same for hydrogen. It can only be generated in such large quantities if core overheated. Hydrogen explosion is very far from normalcy. Having workers injured by it also can’t be possibly a part of any planned-for failure scenario.
> And this started to happen. ... The nuclear material itself was still intact, but the surrounding Zircaloy shell had started melting. What happened now is that some of the byproducts of the uranium decay radioactive Cesium and Iodine started to mix with the steam. The big problem, uranium, was still under control,
The uranium per se is never a big problem in nuclear accidents, since its radioactivity is very low.
Short- and medium-lived isotopes (radioiodine, caesium, strontium, plutonium...) are far bigger problem, and they did leak in non-minuscule quantities.
> It is confirmed that a very small amount of Cesium and Iodine was measured in the steam that was released into the atmosphere.
“Small amount” caused 40 Roentgen/h fields in places! Yes, this is not a Chernobyl-scale contamination, but it is pretty bad. I can’t believe this is supposed to happen under any planned failure scenario.
> The water used in the cooling system is very clean, demineralized (like distilled) water. The reason to use pure water is the above mentioned activation by the neutrons from the Uranium: Pure water does not get activated much, so stays practically radioactive-free. Dirt or salt in the water will absorb the neutrons quicker, becoming more radioactive. This has no effect whatsoever on the core it does not care what it is cooled by. But it makes life more difficult for the operators and mechanics when they have to deal with activated (i.e. slightly radioactive) water.
Scrammed reactor does not emit neutrons. Therefore it cannot activate salts in the water. Therefore activation is not a concern at all.
he concern is, sea water is corrosive, and also when boiled, it will create deposits which will make reactor unusable for any future normal operation.
> The radioactive Cesium and Iodine will be removed there and eventually stored as radioactive waste in terminal storage.
Radioactive iodine is never stored as “radioactive waste in terminal storage”. The reason is simple: there are no radioactive iodine isotopes with half-life more than 60 days. IOW: radioactive iodine fully decays soon enough to not require storage.
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