Japan is currently experiencing a nuclear crisis which will go down in history alongside Three Mile Island and Chernobyl (to say nothing of Nagasaki and Hiroshima). But I've noticed that news reports are almost all full of nothing more than sheer speculation about what has actually happened, what is happening right now, and what may happen in the near future at the nuclear reactor complexes which have been affected. There's a reason for this, of course, and the reason is that nobody really knows exactly what is going on. This, however, is not what consumers of news wish to hear. Instead, we get a steady diet of speculation -- without any notification of the speculative nature of what we're being told. And without the speculation even being all that informative.

This is par for the course in any fast-changing event in the media. Whether it's a war or a natural disaster (or any other big and dynamic event), our 24-hour television news media is faced with a problem. Video and factual information trickles in, but in between the video loops you've got to fill up the time with something or another until the next one arrives. Enter the "expert" willing to speculate (often for a hefty fee as a "news consultant"). Because the Japanese disaster story began with an earthquake, followed by a caught-on-camera tsunami, the nuclear disaster story lagged behind these more-familiar disaster stories. Finally, last night, a few actual physicists made it on screen. But their pronouncements were taken as gospel, instead of being properly labeled as speculation, or (at best) "informed guesswork."

I am not going to make this mistake here. I am going to attempt to write about the nuclear disaster in Japan, sitting in the comfort of my own home, and I could get things wildly wrong. Such is the nature of speculation. But I'm also going to attempt to lay out a few things which haven't really been identified in the news reports, as well, in the hopes of at least getting people to start asking the right questions.

My qualifications: a college-level physics knowledge of how a nuclear reactor works, and how fission works. Also, a knowledge of a piece of fiction I strongly recommend to anyone interested in how "scientific" science fiction used to be -- Nerves, written in 1942 by Lester del Rey. This long short story (or short novel) is probably the best thing ever written about a nuclear power plant accident -- and it was written before nuclear power plants even existed. The first controlled nuclear "pile" wasn't built until December of the same year Nerves came out, and the first commercial power plant started operation in Idaho nine years later, in 1951. Nevertheless, the storyline del Ray laid out bears eerie similarities to what is happening in Japan right now, and I heartily recommend it to everyone who loves science fiction (hint: if you can't find a copy of this story, look for the book The Science Fiction Hall of Fame, Volume IIA). I mention this not for any technical knowledge contained in this fictional story, but for how accurately del Rey captured the "chaos theory" aspect of a nuclear accident -- where nobody really knows what the heck is going on.

Getting back to the non-fictional world, let's start with a few basics. A nuclear power plant is composed of three main systems: a "pile" or nuclear reactor, a cooling system, and a way to make electricity. Normally, electricity is generated by using steam to spin turbines which spin a generator. This is the least important of the systems, so we'll just mention it in passing.

The cooling system and the pile are the heart of the matter. The cooling system in the plants we're talking about is nothing more than water. The cooling system also can be an integral part of the electrical generating system, as cold water is pumped in and heated to steam, which powers the generators, but that's a side issue.

The "core" of the plant is the pile. It's called a pile, because the first one was, in essence, a pile of bricks. Nowadays, "rods" are used. Imagine thin rods packed closely together, like a bundle of pencils. Nuclear power isn't that complicated, when you get right down to it. It is merely a matter of putting enough fissile material (uranium, for instance) in close proximity. "Fissile" basically means "splittable," and refers to the atoms splitting into two other elements. When a chain reaction begins, atoms split, and by doing so, spit out excess subatomic particles at high speeds. These crash into other fissile atoms, meaning the process (once started) runs itself (hence "chain reaction"). If these particles do not crash into other atoms, they are spit out as "radioactivity." This is an oversimplification, of course, but it'll do for our purposes.

The rate of the chain reaction is controllable. If it weren't, then nuclear power wouldn't really work. Uncontrolled chain reactions can happen, of course, and these are known as "atomic bombs." If a critical amount of fissile material is present and an uncontrolled chain reaction happens, you get a nuclear explosion, in other words. But, in a nuclear power plant, the reaction is fine-tuned by "control rods" -- usually graphite. This carbon substance "soaks up" extra subatomic particles, and by doing so slows down the overall chain reaction. If the chain reaction is happening too fast, stick a few control rods in the pile and it slows down. If it's happening too slow, withdraw a few control rods and it speeds up. This is a key point which the media has so far been failing to mention much.

Nuclear power, though, doesn't happen directly -- we simply have no easy way of turning all the spitting radioactivity directly into electrons marching through our wires. Instead, a physical method is used to turn the byproduct of the reactor into physical energy which is turned into electrical energy. The byproduct of a nuclear pile is heat. Lots of heat.

This is, of course, where the water comes in. In a conventional (non-nuclear) power plant which creates steam to turn a generator, the steam can either be recycled (cooled down and pumped back into the system as water), or just vented harmlessly to the atmosphere as a byproduct (assuming you've got a large enough supply of cold water to make recycling the steam cost more than it's worth).

The problem with a nuclear reactor, though, is the radioactivity. Radioactivity from the nuclear fuel in the pile has the insidious effect of making everything around it radioactive too -- the steel containment vessel it lives in, the cement surrounding that, human beings working there, and of course, the water which cools it down. Meaning this water can't be freely vented into the air (in normal plant operations) and must be recycled. In fact, most commercial power plants have several layers of water which utilize "heat exchange" systems to contain the radioactivity. The water surrounding the nuclear core turns to steam, for example, and it is then used to turn other water to steam, and this water runs the generator. Then this water (which can become mildly radioactive as well) is sent through another heat exchanger, where non-radioactive water carries the heat away to those giant cooling towers, where the excess heat is bled off into the atmosphere safely. These multiple systems (again, this is an oversimplification) are in place to avoid venting radioactivity into the atmosphere, from the irradiated water.

OK, that was a lot of lead-in, but let's now take a look at what is happening in Japan. The nuclear plants in question were hit by an earthquake, and then a tsunami. [For the sake of clarity, I'm going to speak of a single reactor here, even though multiple reactors are now involved.] The earthquake should have dampened (and, from at least one report, successfully did dampen) down the chain reaction in the pile automatically and immediately. There is supposed to be a system where an accelerometer (a device for measuring acceleration, or "movement") triggers the graphite control rods to automatically all be inserted into the pile when an earthquake hits. So far, there have been no reports that this system did not work as planned (although there have been precious few reports of the control rods at all, so this is still kind of an open question). Assuming this emergency quake system worked perfectly, the pile would have been fully dampened even before the quake ended.

Even with the chain reaction so dampened down, the pile is still hot and still requires cooling. This is where the secondary disaster hit -- as the tsunami reportedly knocked out the backup power system (diesel generators), which cut power to the entire reactor complex -- including the water pumps. What happened next is a two-fold process. The water in the reactor heated up to the point where the pile was (possibly) left exposed to air (instead of being covered with water, to cool it down). While the water was thus turned to steam, it was transformed into its two component elements: hydrogen and oxygen. The pressure built up until the hydrogen exploded (hydrogen is very explosive, as the Hindenburg showed).

We've been seeing these explosions on television, of course. And the word "explosion" in the same sentence as "nuclear power plant" is a terrifying conjunction indeed. As is the repeated use of the term "meltdown."

But this is where all the speculation comes in. Because, from all the reports I have heard, the power is still not back on in any of these reactors. Which means nobody can say with absolute certainty exactly what is going on inside those reactors. A nuclear pile is surrounded by a thick steel containment vessel. No human eyes ever look at it directly, even when the plant is operating normally. Surrounding the steel vessel is a bigger concrete containment structure. Surrounding this is the building the reactor is housed in. Once again, even in normal operation, humans cannot safely look directly at what is going on in the pile. Everything is done remotely. By instruments. Instruments which need power, for the most part. And the power's out.

As I said, this means that nobody has any real hard evidence what's going on in there. Keep this in mind when you hear experts speculating on television.

The biggest speculation right now is whether things are melting or not. Because the pumps failed and the reactor cores seemed to be exposed above their cooling water bath, firemen have reportedly been pumping seawater in to the reactor in a last-ditch effort to cool things down. This raises a number of questions, almost none of which are being addressed in the media. If the pile gets too hot, because it is not being adequately cooled down, the temperature rises abruptly, and the pile itself begins to melt. The pile is made up of several different elements and compounds, all of which melt at differing degrees. The graphite control rods melt at one temperature, and the fuel rods are actually small pieces of uranium covered in ceramic and embedded in a third substance. Once again, each melts at different temperatures.

A real "meltdown" is when the uranium itself begins to turn to liquid. This could also, in turn, melt the bottom of the containment vessel and the concrete containment building. This is what reportedly happened in Chernobyl.

But there is a whole spectrum of possible outcomes, here. None of them are particularly good, but it would be nice if the media began talking about this spectrum responsibly without merely trying to outdo each other in the number of times they can say "meltdown."

The absolute worst case scenario would be that the uranium melts down to a puddle, and then somehow achieves the "critical mass" necessary to create a spontaneous nuclear explosion. This is not likely to happen. Although it takes a frighteningly small amount of uranium to do this, it must be highly purified, contain the correct blend of isotopes, and be very densely packed -- which isn't likely to happen with the fuel used in nuclear reactors. The nightmare of mushroom clouds erupting is almost an impossibility, by design.

But this doesn't mean everything's going to turn out just fine. Because whether the reactor's fuel melts down or not, the question -- no matter what happens on the ground -- is: how much radiation is being vented? Already, radiation exposure has begun. This is likely due to the fact that steam from the cooling system or the explosions of hydrogen were from the primary cooling system -- water used to cool the reactor, which itself is radioactive. But this raises the most important question to be asking right now: where is the seawater steam being vented?

This involves technical answers to questions the media hasn't even asked yet. If seawater is being pumped in to the reactor, exactly how is it being pumped in, and how is the steam being exhausted? If the answer is that they're just pumping water in to a cooling system that has largely been destroyed by explosion, then this means that cooling the reactor core may indeed be possible to achieve, but also that a steady stream of radioactive steam will be released into the atmosphere while this happens -- which could take weeks or even longer.

There may indeed be no other option. It's hard to get physically close to a reactor in the best of times, and when the reactor is buried under the rubble from the explosion of the building on top of it, it may be downright impossible. Venting radioactivity into the air for weeks to come may be the best we can hope for at this point -- especially if it avoids a partial or full meltdown of the core (which would likely cause enormous amounts of radioactivity to be released -- much more than radioactive steam).

So, if were a prominent member of the media who got to sit down with a nuclear expert on air, I would have a few questions for them, at this point, which nobody else seems to be asking (they don't exactly screen for physics knowledge when hiring network anchors, to say the least). The first of which, just to make a point to the audience, would be: "Can anyone say for sure exactly what is happening inside these reactors with 100 percent certainty, or are we all just guessing what is going on?" If the answer to this was anything other than "No, it's all guesswork," then the followup question would be: "How? How does anyone know what's going on in there? Are any instruments still working? Has anyone seen a remote image of what's going on?"

But the real questions are much more important than making this point to the public. The real question would be: "Exactly how much radiation -- in rems, perhaps, or in sieverts -- has the public been exposed to? Exactly how much has been released into the environment?" Radiation, like everything else scientific, is measurable. We all know how big the earthquake was (9.0 on the Richter scale), but I have yet to hear a number of how bad the radiation leaks have been so far. The public at large isn't familiar with the terminology, but it takes about fifteen seconds to explain (usually by comparing things to the dosage from one chest X-ray), and would help quantify what is going on.

The last question I would ask is: "If seawater is being pumped in to flood the core, where exactly is the steam going? I'm assuming that the hydrogen explosion ruined the primary cooling system, so is the water being used to cool the reactor core just being allowed to boil away into the atmosphere? How radioactive is such steam? And how long will such emergency cooling be necessary before a better system can be set up, or is this the last chance we've got to avert a meltdown?"

Speculation is fun, I realize. And it sure does fill up the air time. But the public isn't as stupid as the media normally assumes. While the anchors last night on television were struggling to get up to speed on a subject they are not normally used to pontificating upon (science), we can only hope they get better at it as time goes on. Sooner or later they're going to get tired of repeating "meltdown" over and over, and are going to have to dig into the facts. It's a tough subject to tackle in some ways (tougher even than the normal superlative in these cases, "rocket science"), but in other ways it's really quite simple. A nuclear power plant is a fairly straightforward idea, because the only real "moving parts" in the reactor are subatomic particles. The design is pretty basic, and pretty easy to understand. The disaster scenarios are even fairly easy to understand, as well. But there are a whole spectrum of possible outcomes here. There is indeed a worst case and a best case, and a whole lot of options in between. The media needs to start doing a much better job of understanding the possible outcomes, of explaining the range of possibilities to the public, and of quantifying exactly what is going on (instead of just saying "radiation has been leaked," answer the question "how much?"). All the answers to these questions, at this point, are themselves speculation, of course -- but it would be much more informed speculation than just asking over and over again "is it a meltdown?"

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant