Monthly Archives: March 2011

Misplaced Angst

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Your iPod is polluting China and L.A.—and Wyoming might be next

You may have been aware too that in manufacturing your electronic marvel, the Shenzhen plant emitted roughly 25 pounds of the greenhouse gas carbon dioxide. It’s even possible that you were aware of the 9-10 pounds of CO2 emitted in transporting the device to you from China.

Oh my GOD! 35 POUNDS of CO2 in getting my iPod delivered to me. That’s horrible!

Um, no, not really.

Bbbbut, 35 POUNDS!

Let’s look at that. Of 35 pounds (16 kg), about 9.5 lbs (a little over 4 kg) is Carbon. Two gallons of gasoline contain 11 pounds of Carbon. It sounds like a lot, but realize that driving 10,000 miles a year in a car that gets 25 mpg you dump 4 tons of CO2 into the atmosphere. Context matters.

Further, the blurb about China burning coal to generate the electricity to do the manufacturing needs to put in context as well. In the United States, the average person uses FOUR TIMES as much electricity as the average person in China. Add to that the China has been aggressively pursuing green energy — they already lead the US in wind energy generation, and are pushing forward in solar while we drag our feet. The US is not “greener than thou” and shifting the blame for pollution/CO2 distracts from the need to get our own house in order.

Interlude

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Just in case world events have you a little down. Here is 30 minutes of “Scenes from a hat”

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Let's Overreact Some More

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There are calls to shut down US reactors owing to earthquake concerns, despite the Japan situation being caused by a tsunami (which resulted from an earthquake).

Global earthquake activity since 1973 and nuclear power plant locations

This map shows a heatmap of 175,000 4.5+ magnitude earthquakes since 1973 based on data from the USGS (United States Geological Survey). And worldwide locations of nuclear power stations using information from the IAEA (International Atomic Energy Agency)

Amazing display revealing where the major fault lines are, along with the realization that there have been more than 175,000 earthquakes above this magnitude (and many more weaker than this) in the last (almost) 40 years and how few reactors are actually near earthquake activity.

Those Procrastinating Radionuclides

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In all the discussion of nuclear power, there’s one bit that hasn’t been discussed in any of the summaries, which may be a good thing because I’m not confident that the general science media would get it right: How can you control the fission reaction in a reactor?

First, a bit of terminology. A critical reactor is one in which each fission result in one neutron, on average, inducing another fission. Which makes the fission rate from this chain reaction constant. So all those times you’ve seen on a TV show or in a movie, where a character shrieks, “OH my GOD! The reactor has gone CRITICAL!” it’s really no big deal. The population of neutrons from fission is constant over some period of time. If you are supercritical this population is increasing, and subcritical means it is decreasing. And the rate of fissioning is proportional to the neutron population.

The neutrons that come from fission (called “prompt neutrons,” for reasons which should become clear shortly) have a lot of energy — an MeV or so, typically, so they are called “fast,” — and they bounce around, scattering off nuclei and losing energy in those collisions. Most of the collisions are with the material that’s there for the express purpose of slowing the neutrons down — the moderator — and if the neutron gets down to thermal energies (“slow” or “thermal” neutrons) before it leaks out of the reactor or gets captured by some nucleus, it can be absorbed by the uranium and induce another fission. And this happens really quickly. A matter of a few tens of microseconds. It’s convenient to look at this in discrete steps, even though the reactions are continuous: each set of fissions releases neutrons which slow down or are lost, and these then induce more fissions. That constitutes a generation with some characteristic lifetime. If the lifetime were that of prompt neutrons alone there’s no way you could ever control a nuclear reactor. Because when a reactor is supercritical, the effect compounds: more than one neutron survives to cause a fission, which means more fissions, which gives you even more neutrons, and so on, ad infinitum. And if your time constant for doing this compounding is 25 microseconds, that’s of order 40,00 generations in just one second. Even if you had just a 0.01% increase in population per generation, you’d increase the population (and power) by a factor of 50 in just one second. There are no systems that could react fast enough to stay within reasonable limits.

But that’s not the whole picture. Not all neutrons come directly from the fission process. Some neutrons appear as the result of beta decays. Beta minus decay occurs in nuclei that have an overabundance of neutrons, and as you look at nuclei that are far from stability (that is, it takes several decays before you would end up with a stable nucleus) there is a tendency for the decays to release more energy and happen quicker.

In beta minus decay, a neutron changes into a proton and a positron and neutrino are emitted from the nucleus. This “reshuffles” the nucleus and the energy states it has; in a lot of cases, the daughter nucleus is not in the ground state, so a gamma is also emitted as it de-excites. For some nuclei far from stability, there is so much energy left over that the nucleus can emit a neutron instead of a gamma. But before this neutron can appear, we have to wait for the beta decay to happen, and that delay is on a time scale best measured in seconds. These are called “delayed neutrons,” and they comprise a little less than 1% of the neutrons from fissions in a critical reactor. But because they take so relatively long to appear, the effective generation time is much greater. Which means only a handful of neutron generations will occur in the time it would take for the system to respond — the reactor is actually subcritical from just the prompt neutrons, and any neutron population increase is relying on decays that won’t occur for around a second.

This works as long as the reactor is subcritical on prompt neutrons. If the reactor went “prompt critical” there would be a spike in power before the system could respond; this is what happened at Chernobyl, because safeguards were intentionally disabled and procedures violated in order to run a test. In a bomb the design is to be highly prompt supercritical using fast neutrons; you aren’t thermalizing neutrons or relying on delayed neutrons for anything. One of many ways a bomb is different from a reactor.

Hey, it's That Thing From That Flick!

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Famous Objects from Classic Movies

It’s done “hangman” (or wheel of morons fortune) style, so you can guess a little. Fun, but I do have to question a couple of the “famous” objects I saw; some are not so iconic that they couldn’t be from more than one movie, or didn’t have a particularly strong association with the movie.

(I mean really, do you associate a coffee cup with one particular movie?)

Is the Shoe on the Other Foot?

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Desmogblog: Are Liberals Science Deniers? Now’s A Good Time to Find Out

A centerpoint of this “nuclear counterargument” was that the left used fears of reactor meltdowns and the escape of radiation to unjustifiably scare the public. And if that’s true, then this is certainly the ideal moment for such misuse of science to occur again. So the question is, will it?

It’s almost like a natural experiment in the politicization of science.

You’re never going to eliminate denialism from either side of the political spectrum, but unlike global warming (the GOP members of the Energy and Commerce Committee just unanimously rejected an amendment acknowledging global warming is even occurring), we have the president already backing nuclear power.

As for the citizenry, I think it will break down the same way — some will throw whatever argument they can find into the breach, because they’ve already made up their minds and facts don’t matter, but most of the others will assess the situation rationally. I agree with Chris here — I think there will be measurably less denialism on the left. In case you couldn’t tell already, I’m not squeamish about nuclear power (up to the point where some tea-partier decides that it should not be regulated by the government because regulation is bad.)

MiniMe, You Retweet Me

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Yesterday I tweeted

Lesson from Japan is not that nuke power is dangerous. Tsunamis are dangerous. Four lost trains are not being used to bash train travel.

and frankly, it got a hell of a response (according to my modest standards) of 28 retweets (and a couple of copy/tweet RTs) at the time of this writing. With that comes a few responses that disagree. I’m not about to get into a discussion on twitter, explaining the details I couldn’t cram into 140 characters, into a series of messages limited to 140 characters.

I have a blog for that.

I was chided for the comparison with the lost trains

People would bash train travel too if one of the lost trains exploded and caused 1250 sq Km evacuation

This misses the point I was trying to make. Trains wreck and even explode (I’ve linked to some spectacular explosions from trains) and yet people are not widely afraid of train travel. In this particular instance, nobody is blaming train travel for the loss of the trains — they blame the tsunami. Why? because train travel is normally quite safe, and it took an unusual event — a rare, massive (especially for that fault line) earthquake followed by a wall of water to cause these events. Nobody has a problem identifying the trigger. The earthquake caused the Fujinuma irrigation dam to collapse. Do we now question the inherent safety of dams? Is there a call to eliminate them? Do dams, or trains, evoke the visceral response that nuclear power does? How much area was evacuated in response to the tsunami warning — was it more than 1250 square kilometers?

The issue is the asymmetric assessment of risk (or complete disregard for risk assessment, in some cases). There is a false premise used by some that if nuclear power is not risk-free then it cannot be permitted. This standard is applied almost nowhere else, because it can’t be. You are at risk if you get out of your bed in the morning, but you’re at risk if you stay in bed — there is always risk. In the time that Fukushima Daiichi reactor #1 has been operating, the US has averaged more than 40,000 automobile deaths per year. Why is that tolerable? It’s because we don’t assess the risk in the same way. A large number of people (potentially) dying all at once evokes a greater emotional response than the same number (or even more) dying over a period of time

Part of it is the same reason behind being willing to seemingly spare no expense to stop terror attacks, despite the relatively few who have died from them. We have a similar reaction to the term “radiation” as we do to “terrorism.” But coal plants are famous for the amount of radioactive material they spew into the environment. Hell, bananas are radioactive, as are people.

The bottom line is that, according to the available information, the almost-40-year-old reactors held up remarkably well to the earthquake itself, and it was the resulting tsunami that took out the backup systems that are now causing the (quite serious) problems. But one has to put this in context of the scope of the devastation, rather than holding the risk up to an impossible zero-tolerance standard. Put another way: how many people died in this tragedy, and what’s getting most of the press?

You Can't Even Hope to Contain Him

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I was dumping some packing peanuts into a trash can and they stopped pouring in — enough charge had built up that the additional peanuts were repelled by the ones in the can. Here’s a couple of attempts to throw peanuts in.

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You might be tempted to think you could confine a peanut (or any charged particle) this way — all of the charges repel, so you form a potential well which traps the extra charge. Unfortunately it doesn’t work out. The electric field you get will counteract gravity, but there’s no field directed radially inward, at all points, and no way to get one. Electric fields only converge on charges. The best you could get would be a field that was “leaky” — inward at one point, but outward somewhere else. All of this is shown mathematically in Earnshaw’s theorem. It works for magnetic fields, too, with the loophole that it doesn’t apply to diamagnets. (but Earnshaw didn’t know about those)