It can be hard to sort out exactly what's happening in Japan right now, or what the status of the nuclear situation is. Euan Mearns has done everyone a great service in pulling together a summary of known and unknown and credible, intelligent speculation, while clearly indicating which is which. It is well worth a read. Consider this useful analysis by Joules Burn, quoted in the piece:
Since residual weld stresses and tensile stress in piping, valves, control tubing, etc are always present, Standard Operating Reactor water quality standards require keeping chlorides at parts per billion levels. Seawater has about 3.5% or 35 grams per liter of salinity!!!
I have no way of knowing how many days they have before a stainless steel component suddenly cracks, but, If it were me, I would be advocating an emergency program to get pure deionzied cooling water back into this stainless steel system ASAP. In laboratory tests in boiling chlorides, cracking of stainless in tensile stress can occur within days- They have at most a few months if they keep boiling sea water in this system and yet another disaster occurs. I am sure there are competent scientists in Japan's nuclear industry and government regulators. I hope they are on top of this threat!
It can be very hard to sort out the news details, and I'm grateful to The Oil Drum for providing this kind of useful analysis!
Sharon
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Thanks for sharing this. It is an excellent summary and helps sort out a lot of conflicting reports in the media, that are coming fast and furious.
The primary consideration for such a low chloride content in the BWR water is probably not stress corrosion cracking. The BWR feed water goes through the core, so it is irradiated by neutrons. Chlorine absorbs neutrons and becomes radioactive. That is probably the primary reason for low chloride.
The highest stressed parts of the plant are going to be the turbine blades. They are subject to both stress and fatigue from vibration. The turbines are not in use and will likely never be used again.
Stresses in the piping are mostly due to the internal pressure. Under operating conditions, that was ~1000 psi. The pressure is much lower than that now.
There are probably at least weeks, if not months before stress corrosion cracking would become important except in very specific circumstances. Maybe springs in relief valves? but usually springs use different alloys that are less susceptible (because they are highly stressed).
Sharon, I have respected your opinion for years on preparing for bad times. There is a lot of talk online about the jet stream bringing nuclear fallout to the US. What is your take on this? What can we do to prepare, and what can we do to prepare our livestock? I would really like to know what you think of the risks of this nuclear fallout. How much do I need to be worrying and what can I do? You always look into the real science of issues and I would like to know what you recommend.
If it were me, I would be advocating an emergency program to get pure deionzied cooling water back into this stainless steel system ASAP.
Gosh, WHY haven't those well-trained, professional emergency crews thought of THAT? I'm sure they're just using seawater because it's pretty and green, and not because there's been an epic natural disaster that's eliminated their ability to provide said pure, deionized cooling water.
Today, the German EPA has published a very detailed analysis of the situation in Fukushima: http://www.bmu.de/atomenergie_sicherheit/doc/47088.php Unfortunately, as of now there is only a German version of this report.
Daedalus2u is correct that the main reason for specifying distilled water rather than ordinary tap water is the danger that impurities in the water will absorb neutrons and become radioactive. It's not such a big problem for protons or O16, the nuclei comprising most of the water. Even if one of those nuclei absorbs a neutron (or two, in the case of O16), it becomes H2 or O17 or O18, all of which are stable, and I'm told the cross sections for neutron capture in those cases are low to begin with. But chlorine, for instance, has two stable isotopes (Cl35 and Cl37), so any chlorine nuclei that absorb a neutron (for which the cross section is higher than for H1 or O16) become radioactive. Similar issues apply to many other elements that might be impurities in water. However, seawater is especially corrosive. When I first heard (about Sunday) that they were pumping seawater into the reactors, my reaction was, "They're desperate to keep those reactors cool, to the point that they don't care if they never generate electric power again."
As for radioactive emissions reaching the US (aspiringlady's question): Jeff Masters at Weather Underground has been showing model runs of what would happen. It strongly depends on local weather conditions at the plant when the release takes place: high pressure tends to keep the contaminated air close to the ground (wind speeds are lower there), and precipitation tends to cause particles to rain out. In order for the jet stream to be relevant, the released radioactivity has to get up to that altitude, which requires either (1) rising air ahead of an approaching low pressure system (but not yet arrived as otherwise the particles will rain out) or (2) a major fire/explosion which forcibly propels contaminants to jet stream altitudes. In other words: if you're on the west coast you might want to stock up on potassium iodide, but don't panic yet.
http://mitnse.com/
They explain things pretty well and in context with each issue in its own post and updates when they get them.
Also keep in mind potassium and iodine have their own toxic effects so don't destroy your thyroid if you don't need to.
Getting things exactly right as usual, The Onion reports that U.S. reactors are completely safe ... unless something bad happens. Would be a hell of a lot funnier if I hadn't been hearing just that claim on the radio, (and from some comments on The Oil Drum).
... Living on the west coast, I'm wondering about aspiringlady's question, too. Health Division, however, keeps assuring me it's highly unlikely; we're all perfectly safe (and so are our reactors). Appreciate the link from adela; will go read now.
Also, thanks to Eric Lund, for that concise and clear explanation.