NUCLEAR INTERVENTION!

This is getting posted a little later than I initially intended; it was a seriously busy weekend.  Additional apologies, since this initially had pictures that are now just hyperlinks.  Evidently, Blogger doesn't care much for images that aren't yours, despite the fact that they are credited where appropriate.  As it goes...

Nuclear Intervention

Have a seat, relax, and be prepared to flex your head a little.  I’d like to stage an intervention about nuclear energy with you.  The recent, tragic events in Japan at the Fukushima-Daiichi power plant weren’t what prompted this; it was the subsequent media reaction to them.  I don’t want to downplay the severity of the situation in Japan nor of the damage that radiation can cause.  Radiation can mean serious business and the situation in Japan is no joke. But the risk of suffering adverse effects here in the US from radiation generated by the disaster in Japan is being blown way out of proportion in the media.  With headlines like “Radioactive Rain on its Way”, or “Malfunctions in Radiation Network Spark Queries”, this is no real surprise.

Take, for example, the headline found in the March 28, 2011 online edition of USA Today:  “Radiation in Boston rain linked to Japan nuclear crisis”.  Despite this incendiary headline, the first paragraph of the article goes on to state:

 “A sample of rainwater in Boston showed very low concentrations of radiation, most likely from the damaged Japanese nuclear power power [sic], according to health officials who say the amount does not pose a safety risk.”

Do you see the problem here?  To me, this pairing seems like rhetorical bait and switch.  At first glance, the headline seems to say, “Oh sweet Jesus, there’s nuclear rain heading for Massachusetts and it’s gonna be a crisis on top of a crisis.”  Then, the article attempts to defuse the headline by assuaging the fears of harm caused by the radiation.  Moreover, the author then attempts to cast doubt on the source of the radiation.

            So should we be concerned at about the possibility of radiation contamination? If the radiation found in Boston rain isn’t from the nuclear disaster in Japan, where did it come from? We’ll look at answers to these questions, but first, I’d like to consult an oracle of sorts. Though this is probably the most un-scientific way a scientist could possibly collect data, I find that the “Comments” section following online news stories is usually a good barometer of just how well a cross-section of the general public understands the issues.  If the reactions seem mostly to agree with prevailing scientific theory, the oracle predicts that most people will understand the theories.  The comments section accompanying this USA Today article is no exception.

When I first read this story on the USA Today Website, I came across this posting by someone with the handle “maineroad”:

“I'm glowing in the rain. I'm glowing in the rain. What a glorious feeling, I'm toxic again. I walk down the lane with a Geiger refrain. I'm glowing, just glowing, in the rain. “

Although the humor is not lost on me, this is precisely kind of reaction that I’d like to address with this intervention.  Perhaps this person is politically opposed to nuclear energy and just attempting to be snarky about it, but my guess is that “maineroad”, like many others, simply does not understand the science behind nuclear energy.

            I can’t blame anyone for not understanding the science behind nuclear energy.  It’s terrifically complicated, and involves all kinds of weird things like half-lives and gluons.  If we see the various kinds of science as being like a collection of all the languages spoken on earth, particle physics would be a language spoken only by some remote tribe rarely contacted by outsiders.  Materials science is another one of those remote tribal languages. They are both like an unholy marriage of physics and chemistry.  So, to help us all better understand this, I’d like to make an attempt to dispel some myths about nuclear energy and provide some clarity about the situation in Japan.

Here’s where the head flexing comes in.  We’ll go from freshman chemistry to senior physics in no time flat, so please bear with me.  As I’ve said, particle physics is a weird and somewhat intimidating area of science, so I’ll spare you some of the gory details.  That being said, it’s necessary to recognize that the minutia are pretty important here, so this will be a truncated account of the physics as we know it.

            I’m not sure where every one is with the way nuclear energy is generated.  Since it’s important to understand this, let’s start with the basics.  First, matter.  All matter can be broken down into atoms, which can be further broken down into protons, electrons, and neutrons.  Each of these particles has a particular charge: electrons have a negative charge, protons have a positive charge, and neutrons have no charge.  Straight out of freshman chemistry, no?  Protons and neutrons can be broken down further into quarks, and scientists have identified around 200 other types of particles as well. 

Although important, quarks and all of these other particles are mostly beyond the scope of what we are attempting to do here.  Don’t worry much about them for now.  If you are interested in learning about particle physics, there are a number of good, readable resources available on the web, like this one:

http://www.particleadventure.org/eternal-questions.html

It might melt your brain a little, but it’s fascinating nonetheless.

Picture: http://www.particleadventure.org/images/page-elements/atom.gif

            Anyhow, mostly these little particles aren’t just floating around randomly and bumping into each other.  They all interact in various ways, the protons and neutrons gathering together to form atomic nuclei, and the electrons orbiting around the nuclei.   The particles link up in an orderly fashion to form the atoms that comprise the physical world.  All of this information is neatly summarized in the periodic table.  Here’s a really nice one:

http://www.webelements.com/

There are four fundamental interactions that govern the way these particles behave: Strong, Weak, Electromagnetic, and Gravity.  Any force you can think of, magnetism, drag forces, friction, and nuclear decay, to name a few, can be attributed to one of these fundamental interactions.  For instance, the electromagnetic force, or E-M force, causes things with like charges to repel and things with opposite charges to attract. 

You might not have guessed, but it’s also the E-M force that is responsible for the fact that you are able to walk.  The E-M force prevents the atoms making up the matter in your bones and tissues, as well as the atoms making up the matter in your shoes and in the floor, from moving around.  Were it not for this interaction, matter as we know it would not exist!  I wonder what Kierkegaard or Nietzsche would have to say about the proposition that life really is just a matter of protons and electrons being attracted to each other?

http://www.particleadventure.org/images/page-elements/residualem.jpg

Since I’m writing this to talk about nuclear energy, let’s talk about the forces that govern radioactivity and nuclear decay.  In nuclear decay, a large atomic nucleus can break apart into smaller nuclei.  An atomic nucleus is just a bunch of protons and neutrons, right? So this makes sense, and a logical follower is that stable nuclei will remain together, while unstable nuclei will tend to break apart, or decay. There are different types of decay, alpha, beta, and gamma being the main ones, each with its own type of associated particle.  The release of energetic particles due to the decay of the unstable atomic nuclei is known as radioactivity. This is what we’re worried about.

Picture: http://www.cartage.org.lb/en/themes/sciences/Physics/NuclearPhysics/Applications/NuclearWeapons/fission_supercritical.gif

The decay process used in electricity generation is known as fission.  In a typical uranium-fuel fission reaction, a stable uranium-235 atom is hit with a slow-moving, or thermal, neutron.  The nucleus absorbs the stray neutron, then becomes the unstable isotope U-236, and splits into two pieces, leaving xenon-140 and strontium-94. This fission event releases energy as heat and gamma radiation, and two additional neutrons.  These two extra neutrons can then go on to strike two more U-235 nuclei, thus starting a chain reaction.  With the proper conditions, scientists can sustain this reaction and generate enough heat to boil water.  The boiling water produces steam, which can be used to spin turbines.  The turbines can then spin generators, which produce electricity.  This is the same process by which we generate electricity by burning coal, but with a different heat source.  Xe-140 and Sr-94 produced by fission are both unstable, and will eventually decay into stable end products. These are called fission products, otherwise known as nuclear waste.

A typical nuclear power generator:

Picture: http://www.freeinfosociety.com/images/science/nuclearenergy1.jpg

Once the fuel in the reactor has undergone enough fission events, a build up of the byproducts occurs, rendering the fuel unusable.  Unfortunately, the waste products from nuclear fission are also highly radioactive, so the spent fuel must be stored somewhere.  Usually at the highly contained, highly shielded reactor site until it’s safe enough to move.  Some of the nuclear byproducts have short life spans, on the order of hours, but can take a really long time for others to decay into something safe, perhaps 10,000 years.  We’re still working out how to store the stuff in the safest possible manner.  There are recent advancements on technologies that would allow us to reclaim the spent fuel and use it to generate more electricity.

Here’s the kicker about nuclear power:  although it produces highly toxic waste as a byproduct, other environmental effects, like CO₂ emissions, are pretty minimal.  They are so small that the emissions level of a nuclear power plant is around that of the renewable energy sources that we currently have. The only other waste product from nuclear energy is heat.  Since the reactor can get really hot, it takes a lot of coolant to prevent it and the fuel from melting down. Much of this heat is used to generate steam and spin the generators that give us electricity. However, a small amount of heat is still discharged into the environment, which can have adverse effects.   

Radiation occurs naturally almost everywhere.  We are constantly being bombarded with radiation from space and radiation found naturally in various substances on earth.  There are many different elements that have radioactive isotopes, or radioisotopes, and these are found all over the place. (An isotope is an atom of an element with the same number of protons and electrons, but a different number of neutrons.) A radioisotope of potassium, K-40, can be found in trace amounts in bananas and in the human body.  Granite and concrete are also mildly radioactive. We frequently use higher doses of radiation in medical procedures like x-rays and in the treatment of cancer.

Picture:  http://www.world-nuclear.org/uploadedImages/org/info/radsources[1].gif?n=4956

 Wait, wait, back up a minute.  If we are constantly subject to radiation from all over the place, how much is too much?  Shouldn’t we be worried about all of the extra radiation coming from the accident at the Fukushima-Daiichi power plant?  

First, let’s talk about how exposure is measured.  The basic unit of radiation dose when absorbed in tissue is the gray (Gy).  One gray represents the deposition of one joule of energy per kilogram of tissue.  Since some types of radiation cause more damage to tissue per gray than others, another unit, the sievert (Sv) is used. You might also see this quantity listed as “rem” (1 Sv = 100 rem). The sievert takes the biological effects of the different types of radiation into account. One gray of beta or gamma radiation has one sievert of biological effect, one gray of neutrons is equivalent to around 10 Sv, and one gray of alpha radiation has an effect of about 20 Sv.  The dosage to humans is typically measured in one-thousandths of a sievert, or millisieverts (mSv).

According to the World Nuclear Organization, public dose limits for exposure from uranium mining or nuclear plants are usually set at 1 mSv/yr above background levels.  In most countries the maximum dose allowed for those who work with radiation is 20 mSv per year. This dosage is also measured with respect to background radiation and usually averaged over five years, with a maximum exposure of 50 mSv in any one year.  The total exposure limit usually doesn’t include any medical exposure, like x-rays or CT-scans. 

Here’s an informal, but reasonably accurate, chart that ought to give you an idea about radiation dosage in context (Note: ionizing radiation is another term for high energy particles and waves, like the ones we’ve been discussing): 

Picture:  

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgJPEUlgtAq7okLwKEUlzA3hssG8dvbSaInLMv9zhwhn8g-lpvENW3SReHB3wpg577DEa2RYdDegTMyW1Erne_Y2hQbYHT09Vco5WnU1LBTDXYAq_vZcRSDUhG8KzxL1Wp9U-wy3lEnj7CY/s1600/radiation.png

        Next, let’s talk about the measures taken to protect humans from radiation levels above that of background. Radiation protection at nuclear power plants and in uranium mining facilities, as well as at every step in the rest of the nuclear cycle, is very highly regulated. Occupational exposure levels are closely monitored.  Generally, there are four ways to protect humans from radiation exposure:

From the World Nuclear Organization’s website:

• Limiting time. In occupational situations, limiting exposure time reduces dosage.
• Distance. The intensity of radiation decreases with distance from its source.
• Shielding. Barriers of lead, concrete or water give good protection from high levels of penetrating radiation such as gamma rays. Intensely radioactive materials are therefore often stored or handled under water, or by remote control in rooms constructed of thick concrete or lined with lead.
• Containment. Highly radioactive materials are confined and kept out of the workplace and environment. Nuclear reactors operate within closed systems with multiple barriers, which keep the radioactive materials contained.

So, if we are concerned with radiation coming from Japan we can clearly see that the shielding and containment protection measures are moot.  But what about the other measures, like limiting the distance to the radiation source and the time of exposure?  And what about the radiation in the Boston rain?  We still haven’t heard about that yet.

As stated, the intensity of radiation decreases with distance from the source.  So, the further away you get from the radiation source, the radiation from the source becomes less intense. Conversely, the closer you get to the source, the more intense the radiation becomes.  If you’ve ever stood next to a fire or put your hand over the burner of a stove, you’ve experienced this effect firsthand.  If the fire is too hot, it will seem cooler when you step away. 

This phenomenon is modeled with an inverse square law, which says that the intensity of radiation, I, at some distance away from the radiation source, d, is equal to the initial intensity, I₀, divided by the square of the distance from the source:

I=I₀/d²

So, for a constant initial intensity, the intensity decreases rapidly as you travel further away from the source. 

Here’s some information from the New York Times about the radiation levels at the Fukushima-Daiichi power plant soon after the earthquake and tsunami struck:

 Picture:

http://graphics8.nytimes.com/packages/images/newsgraphics/2011/0316-japan-quake-radiation/0330-web-RADIATION.jpg

            According to these data, the peak radiation output looks to be about 12 mSv per hour (which is kind of a lot).  Let’s assume, for the sake of argument, that the radiation output remained constant at that level indefinitely.  Think of this like an eternal flame that stays at constant brightness.  Let’s also assume that there isn’t anything in the way to block the radiation from reaching us or to divert its path. To how much radiation from this accident would we then be exposed here in Minnesota? 

Well, Japan is roughly 7000 miles from Minnesota.  If we think of intensity as being measured in mSv per hour, and use the inverse square law, with an initial intensity of 12 mSv per hour, that gives us an approximate radiation intensity here in Minnesota of 2.44 x 10^-7 mSv per hour.  That’s a 2 with six zeroes in front of it!  This level of exposure amounts to about 2 microsieverts per year.  This is about as much radiation as you’d get by standing next to two CRT computer monitors every day, 24 hours a day, for an entire year! 

Radiation can, however, become airborne and travel on the winds. It is just little particles, after all. When radiation does this, it is referred to as “fallout”.  Fallout from atmospheric nuclear testing done in the early part of the 20^th century is still a small part of what makes up background radiation. Though the amount of radiation is still relatively small, this is an item for concern.  Fallout from the Chernobyl accident in 1986 was detected as far away as northern Finland.  For some perspective, the recent accident in Japan has released only a small fraction of what the Chernobyl accident did. 

Despite the tragedy in Japan, and despite other tragedies like the ones at Three Mile Island or Chernobyl, I can’t say for certain whether I think that we should stop looking at nuclear energy as a means to keep our futures electrified.  It certainly has its downsides, but then again so does burning fossil fuels.  We must remember that nuclear technology is still in its infancy.  Even newer technologies, like nuclear waste reclamation and power plants that operate on this reclaimed nuclear waste, may prove to make nuclear energy a safer alternative and reduce our dependence on fossil fuels.  Again, I can’t say which way we ought to go here.  But, I can say this: Love it or hate it, nuclear energy is here to stay.

REFERENCES:

1.     Koch, Wendy (2011). Radiation in Boston rain linked to Japan nuclear crisis. Retrieved 28 March 2011 from USA Today.com: http://content.usatoday.com/communities/greenhouse/post/2011/03/radiation-massachusetts-rainwater-japan-nuclear/1  

2.     World Nuclear Organization online (2011). Nuclear Radiation and Health Effects. Retrieved 28 March 2011 from World Nuclear Organization online: http://www.world-nuclear.org/info/inf05.html  

3.     Lee, Mike (2011). Malfunctions in Radiation Network Spark Queries. Retrieved 28 March 2011 from San Diego Union Tribune Online: http://www.signonsandiego.com/news/2011/mar/28/malfunctions-radiation-network-spark-concern/  

4.     O'Shea, Patrick (2011). Rain will contain more radiation than normal. Retrieved 28 March 2011 from Beaver County Times Online: http://www.timesonline.com/news/transportation/radioactive-rain-on-its-way/article_0779c5e8-59a9-11e0-a326-00127992bc8b.html

5.     http://users.owt.com/smsrpm/Chernobyl/glbrad.html

6.     http://www.borenv.net/BER/pdfs/ber15/ber15-019.pdf