Saturday, March 26, 2011

Don't believe what the press is telling you!

Consider this news story (and accompanying video) from the BBC about radioactivity in the sea within 300 m of the Fukushima nuclear plant:

Levels of radioactive iodine in the sea near the tsunami-stricken Fukushima nuclear plant are 1,250 times higher than the safety limit, officials say.

The readings were taken about 300m (984ft) offshore. It is feared the radiation could be seeping into groundwater from one of the reactors.

But the radiation will no longer be a risk after eight days, officials say. [Emphasis added]

There is no explicit by-line on this article, but the video contains an interview with BBC reporter Chris Hogg in Tokyo that repeats that a half life of 8 days means "that after 8 days the risk will have dissipated".

The reporter is WRONG. Twice, because that is also not what the officials said. His ignorance of basic physics, in this case a topic I always teach in a college general education class, led him to misinterpret what was actually said by a government spokesman and hence mislead the public.

The risk will not dissipate after 8 days.

First, what did the official say? The article reports that
"Generally speaking," spokesman Hidehiko Nishiyama told a news conference, "radioactive material released into the sea will spread due to tides, so you need much more for seaweed and sea life to absorb it." He continued: "And, since [the iodine] has a half-life of eight days, by the time people eat the sea products its amount is likely to have diminished significantly."

This (emphasis added) is correct.

The most significant effect is dilution. Levels will be very high near the source, but get reduced significantly as the source gets mixed into a larger volume of water. (Like smoke when you are a long way from a fire.) It also matters what the ratio is of radioactive iodine to the iodine that is naturally in the water, since the seaweed can't tell the difference.

It is also correct because in 8 days the radiation level in the seawater will be half what it is today. Half. Not "dissipated", half. The radiation level of the iodine in that bay will only fall to 625 times the safe level, not zero, in those 8 days. The risk is reduced, but not gone.

But there are other factors. For example, I have no idea how long it takes from the time seaweed is harvested and when it shows up on shelves all nicely dried and packaged, but it is unlikely to be a few days. Only fresh items like milk and vegetables appear "just in time" in supermarkets. Radiation drops every day it sits in a warehouse. It falls to half after 8 days, one quarter after 16 days, one eighth after 24 days, and one sixteenth after about a month.

The obvious fact (pull out your calculator) is that what remains after a month is still 1250/16 = 78 times the safety limit if all of the iodine stayed in the ocean near the plant. This shows why dilution is so important.

Side comment 1:

The other contaminant in seafood, mercury, does not go away with time and is not as easy to detect and monitor as radiation from I-131. I-131 emits a gamma ray which can be detected through the usual plastic packaging used for seaweed, right on the shelf. Mercury requires a careful (and destructive) chemical test.

Side comment 2:

The reporter quite correctly puts attention on cesium, which has a 30 year half life. Isotopes with very short half lives are "hotter" but go away quickly, so you just have to keep your distance for a month or two. Gram for gram, cesium isn't as hot but you have to avoid it for a longer time. That can be hard to do.

However, this ignores the other significant factor, which is biological activity. Our body needs a regular supply of iodine, so it will go looking for it in anything you eat. (Naturally iodine deficient diets in the Ukraine contributed to the uptake of I-131 after Chernobyl.) Further, it gets concentrated in one place, the thyroid.

Cesium (Cs) is in the same chemical family as sodium (Na), in table salt, and potassium (K), in sports drinks and bananas, which are both essential to the operation of our body. However, since it is much heavier, I doubt if it can substitute for the many ionic processes the body uses Na and K for. Any biologist or chemist know if Cs is concentrated by the body?

By the way, one reason I knew this was a major incident was that Cs-137 could be detected above background in California. You see, it takes a significant release to see it above the Cs-137 that still remains from atmospheric nuclear testing. As big as Chernobyl was, its Cs-137 was barely detectable over the stuff left from weapons tests done decades earlier once it got diluted by one trip around the globe.

Side comment 3:

There has been no new I-131 made since fission was stopped on March 11, fifteen days ago. That means only one quarter of the original I-131 remains in the fuel rods inside the three reactors that had been operating at the time of the quake.

The most important thing in this article might be that the levels in sea water had increased by a factor of 8 in the past week. That means I-131 from inside fuel rods inside the reactor vessel is not only finding its way into the water, but a larger fraction of it has been released from the fuel rods. (There is less I-131 available to leak out, but more of what remains is getting out. Did I say that clearly enough?) This is further indication that the fuel rods have been damaged significantly, which we already knew, but might just result from the iodine -- already vented from the reactor vessel -- being washed out of the containment building as they can now pour more water onto and into the containment building.

Side comment 4:

That observation in the quotation at the top of this article, that radiation "might" be seeping into ground water, struck me as strange. There is I-131 in Tokyo drinking water. This is because Tokyo's water supply comes from surface water (mostly behind dams based on a city water department document I found), which will be contaminated by radioactive rain carrying I-131. But everyone should know that rain also soaks into the ground. Apart from geochemical processes that would capture iodine, it will go into the ground water.

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Wednesday, March 16, 2011

Measuring "pi"

Rhett Allain had an interesting post for "Pi Day" concerning the use of a simple harmonic oscillator consisting of a mass on a spring to measure pi. Clever!

However, he neglected the effect of the spring mass. The correct formula for this problem requires the addition of 1/3 of the mass of the spring to the mass hanging on the spring, which appears inside the square root used to calculate the value that goes on the x axis of his fit. Although it is really hard to tell what his fit looked like or what the mass of the spring might be, including this necessary effect should increase the slope and make his result worse.

Nice idea, however. I'll have to give this a try when we have the lab setup.

That said, I have special praise for his OUTSTANDING blog about how to build you own energy balance thing. I did the human demo in one class before spring break, and might have saved some students some money if the showmen are out on the beaches this week. The plastic version looks like it might make a good demo all on its own ... even without the cute crown with its cell phone re-receiver energy recycling thingy.

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Tuesday, March 15, 2011

From ridiculous to sublime

Time to weigh in, quickly, on the nuclear crisis in Japan.

As I commented on a link dump at Uncertain Principles that points to a half decent article that has since been moved and corrected to some degree, the news reporting about the reactor problems was truly awful for the first day or two. What an abomination.

It has, however, improved a LOT. Tonight I was stunned at how well MSNBC covered the subject. And not just with the experts, who no longer need scare quotes around their titles, but also in a lengthy intro by Rachel Maddow on her show. Yeah, she was still a bit confused by the fact that rust is oxidation (of iron) but the oxidation of zircalloy is not rust, but the presentation was not wrong and well pitched to a (scientifically illiterate) audience.

It is worth watching on Hulu or wherever they archive it.

The real key, however, is that they have real experts. I missed the name of the guy from Sandia who was on an earlier show, but they had Frank von Hippel from Princeton on the Maddow show along with some others of similar quality but whose work is not personally known to me. Clearly a whole bunch of people were as horrified as I was by the junk that was being broadcast and had the pull to get the attention of the networks and change what is out there. It probably also helped the DOE Sec Chu can teach as well as do physics, and did a good teaching job in front of Congress.

The changes are dramatic.

The comparisons to Chernobyl are now rational, rather than nonsensical.

No idiot is out there saying that a scrammed boiling water reactor will go prompt critical if it melts down. The "expert" that didn't seem to know that the heat in the shut down plant comes from internal radioactive decay of fission products is long gone, replaced by one that knows spent fuel rods are also hot -- and "hot" with radioactive elements that live just long enough to be very dangerous if they were to be released.

OK, one Congressman (who as a physicist should know better) was out confusing a civilian nuclear power program that only uses fuel under IAEA supervision with a rogue state operating a clandestine enrichment program probably designed with help from North Korea and Pakistan, but let's ignore that one.

Actual facts, like the location of the spent fuel storage pools 40 feet in the air !! ????? !! above the containment structure in an earthquake zone, are now clearly featured in the stories. Ditto for giving radiation levels in Sv rather than in "chest x-rays" (which deliver much less radiation than they used to). Even Livermore managed to get out the fact that they have a nuclear weather forecasting program for this, and other purposes.

And I am particularly impressed that we are sending some of our specialized monitoring equipment (I'd guess it is the stuff developed to look for weapons or the result of a "dirty bomb" or an event just like this one) to Japan. I hope it works as well as advertised.

That is about all that I have time for tonight, but I will try to blog about some specific details when I get a chance.

I'll close with the most important point that hasn't been emphasized in the reporting so far, and might have confused people about the extent of the radioactive plume. Radiation detection is EXTREMELY sensitive. I heard of a case where the detectors outside of a nuclear plant were set off by the alpha radiation from the Thorium and Uranium in the smoke from a coal plant that had been pushed down to the ground by an inversion layer. A nuclear carrier would have similarly sensitive monitors on the ship, so we would need to be told the level that was detected -- not just the fact that radiation was detected -- to get a sense of what our carrier picked up off the coast of Japan. Further, it can be far more discriminating that a simple Geiger counter. You can tell what radioactive isotope is out there as well as how much, and the specific isotopes tell you where they came from. That is how people know fuel elements have been damaged without being able to see inside the plant.

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Beware the Ides of March!

A belated "Happy Pi Day" and "Happy Einstein's birthday" ...

... as well as my fourth blogiversary (the day before).

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