[quote=suziegruber]Dogs,
Thank you for the very helpful information and explanations. You filled in a lot of holes for me in my understanding of this very complex situation.
I just read that there is damage to the “nuclear fuel rods.”
http://www.zerohedge.com/article/asahi-shinbun-confirms-nuclear-rods-pressure-vessels-and-spent-fuel-pools-are-damaged
I have confirmed the translation of this article with a Japanese colleague of mine.
So here’s my question. If one or more of the reactors is damaged such that cooling cannot be stabilized, is their only option to entomb the whole four reactor complex? If so, can you talk a bit about how this mitigates heat decay that will continue to occur? I am guessing that the sand and concrete provides a good enough shield to contain the radiation. Am I correct?
Thanks again for your willingness to enlighten us.
–Suzie
[/quote]
Suzie -
Once the cores were uncovered it was all but certain that core fuel damage occurred. The extent of the damage is where you start getting into 6 degrees of separation. “Meltdown” has such headline grabbing connotation and sensationalism, when the truth is, any core damage is bad. Core damage probably occurred as early as Sunday.
The reactor(s) will stabilize themselves. Decay heat is still being produced and still being dissipated - the preferred method is with cooling water in a controlled evolution. Less desired is manually controlled venting as pressure builds following limited success at getting cooling water into or onto the core. Least desired is letting things run their course with no corrective or mitigating action taken.
So even if nothing is done, eventually the reactor(s) will stabilize themselves. Decay heat won’t be as much of a concern as the radiation levels. It is conceivable that the Japanese will be forced to dump sand and concrete on the complex to knock radiation levels down low enough to allow closer inspections and assessment of the extent of the damage inside unit #4 (and probably #3). If they can get the rad levels down AND confirm that the boundary beneath the plant is intact, then sealing the entire complex in concrete might be the best option. The best scenario is that they can get rad levels under control and “clean up” the site by removing the damaged core(s) and any associated high radiation sources that may have spilled into the complex for storage at a long term disposal facility.
Dogs,
Zero Hedge just published an article indicating that Japan has increased its decontamination threshold to
No surprise there: by now everyone is well aware that the fuel rods are if not completely then certainly partially destroyed. However, the real danger, and explains why we have been following atmospheric conditions over Japan so closely, is that as Kyodo just reported, the rain is now pouring radioactive cats and dogs. But the most troubling development is that instead of being proactive and finally warning its citizens about the dangers, the Japanese government has just raised the decontamination threshold by nearly 20 times from 6,000 cpm to a stunning 100,000 cpmCan you comment on this level based on your experience?
Thanks,
Suzie
This reading itself lacks perfect information but I will try to estimate an answer.
For technical junkies:
100,000 cpm (counts per minute) does not tell us very much by itself. Basically the meter is displaying the number of radiation incidents it detects, also called "counts". No meter reads 100% of the radiation that passes through it so each instrument type has an "efficiency" by which the counts it detects relate to the actual radiation present. Typically ranges between 10-35% for common instrumentation. I suspect the type of instrument they are using at monitoring locations is most likely the ubiquitous GM pancake type probe which has a standard efficiency of 10%. This means the count rate is only reflecting 10% of the Beta and Gamma radiation that passes through it. In other words, 100,000 CPM probably means 1,000,000 DPM (disintegrations per minute). Next we'd have to know the energy of the radiation and the surface area under consideration to arrive at a dose rate which involve still more technical details.
The distilled version:
100,000 CPM is most likely measuring 1,000,000 DPM of activity. There is so much information missing in the quote that I'm reluctant to give an answer, however, a rule of thumb that I have observed for fission products is that for every 50,000 DPM (5,000 cpm) of Beta/gamma activity you will see 1 millirem/hr for typical fission product mixed from power plants. Using that as a guide then 100,000 CPM could approximate to 20 millirem/hr across the area of contamination.
Dose effects
If the above is assumed to be true we are still looking at very low levels in regards to acute dose effects. in other words if you are worried about short term radiation effects in the body, this would occur at several orders of magnitude higher than these levels. I guess you could say that is the happy version of that data. The flip side is, those levels are much higher than what the US allows for Nuclear workers before they should be contaminated. That level is ~1,000 DPM loose contamination (or essentailly non detectable). So, if the information you provided is true, the release criteria is very high by comparison.
Practical matters
In normal, non emergency periods we are able to work with a very low contamination release threshold. In emergency situations you perform a sort of "Triage", prioritizing hazards to the extend you can manage them. You do the best you can with the resources you posses. I suspect the government raised the (already high) decontamination threshold because they simple had to. They are probably decontaminating more people than they really have resources for. If they maintained the lower threshold they would draw personnel away from other vital tasks.
In summary, these are still levels below which the health hazards are so low they are unknown or difficult to estimate. We assume, conservatively, that there is risk in any radiation exposure but we can only estimate true effects by using much higher dose information that we KNOW produces adverse health effects and extrapolate these backward to the lower levels. Having said that, these raised thresholds are troubling. The public should never ever experience contamination such as this.
Follow-on effects
A more worrisome aspect is what this threshold implies. This new threshold implies that members of the public are encountering contamination near these levels with some regularity. That means that contamination is present and well dispersed in some of these regions. That means that livestock and crops in these areas also most likely contain this well dispersed radioactive contamination. That means the contamination will be concentrating into food sources.
For example if a dairy cow were to graze a 5 acre area containing these dispersed contamination levels, that dairy cow would concentrate some of that 5 acres of contamination into its stomach, and consequently into the milk. This same concentration effect occurs in crops which will draw in certain isotopes, unable to distinquish between those that are stable and those that are radioactive. This is why there has been a halt to consumption of Dairy and Spinach in certain regions.
Once again I'm compelled to leave a disclaimer. There is so much information lacking that there's plenty of room for error and innacuracy. However i believe the above is most likely "in the ballpark".
One update I just learned today:“Potassium-iodide pills have been distributed to evacuation centres to protect against the possibility that iodine-131 could be absorbed by a person’s thyroid gland, which is the clearest risk of cancer following this kind of radioactive release. People leaving the 20 kilometre zone to travel through the further ten kilometre zone have been recommended to take the appropriate dose of potassium iodide since 16 March.”
Rick and Chris,
I was blown away by this interview. I feel that I learned a lot more from this than any amount of MSM.
Thank you both!
Lots of good data, here -> http://allthingsnuclear.org/
Useful information about the spent pools… + informed speculation about the explosions.
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