Nuclear Meltdowns

March 14, 2011

There’s been a lot of media buzz in recent days about a few of Japan’s nuclear reactors, which are apparently suffering from a coolant failure and possible meltdown. The 2011 quake is already a disaster, but from the tone of some of these articles, reporters seem to be expecting it to “go nuclear” at any time now, even trotting out the dreaded “Chernobyl” name-drop. This is not honest reporting: it reflects either astonishing incompetence or cold deceptiveness, intended to scare the public out of supporting a promising technology. I’m not going to try to identify the unscrupulous characters who might be responsible (hint: look at the people who sell oil), but I can’t just sit here and watch a meme this deadly infect the world without doing anything about it. This will be like bailing out a cruise ship with a teaspoon, but hey, I gotta try something.

To understand why Chernobyl is a horrible point of reference, we need to start with a brief overview of the physics. Fission reactors generate heat energy by arranging sufficiently “heavy” materials (substances made of large atoms) in such a way that little bits of the atoms start “breaking off” and a stable chain reaction can be achieved. When exposed to the right kind of energy, each fissile atom produces one or more very-fast-moving particles that will eventually smash into other atoms in the fuel and break them apart in turn, thus continuing the reaction. However, according to the curious laws of the quantum universe, at first many of these particles are traveling too fast to successfully break off bits of another atom, and so they must be decelerated by what is called a “neutron moderator” until they are traveling slowly enough to impact the next fissile atoms and continue the reaction.

The neutron moderator effectively determines the rate of the reaction by producing more or fewer of these slow-moving “thermal” neutrons, so its design is of critical importance (pardon the pun) to any supposedly safe reactor. Now the difference between Chernobyl and every other less-dangerous incident should be clear: the reactor at Chernobyl was designed with a notoriously unsafe choice of a moderator, while every operational reactor in Japan has used a very safe choice. Specifically, Japan’s reactors use ordinary water as a moderator. Sure, it’s named as the coolant, but the genius of the design lies in the fact that the water also controls the rate of reaction! If the reactor overheats and the coolant (which is also the moderator) boils away, those fast neutrons maintain their too-high velocity and the chain reaction slows. While this certainly doesn’t eliminate all hazards from the immediate area (did I mention the massive, speeding particles?) the engineers can monitor core pressure from farther away and release some irradiated (very slightly dangerous) steam if it climbs too high, which is exactly what has happened already. At Chernobyl, the reactor used a graphite moderator instead. When it overheated, loss of coolant allowed the reactor to go “prompt critical”, where the chain reaction intensified uncontrollably and exponentially. It ruptured the poorly-designed containment vessel and the hot exposed graphite went up in a fireball, throwing tons of radioactive core materials into the atmosphere. One of these events is not like the other.

Of course, this is not the whole story, as today’s reactors are designed with many additional safety features, but the point is that this difference is indispensible to any intelligent consideration of the risks. Prestigious newspapers might be careful to brush off predictions of a radioactive explosion, and tend to identify dangerous materials leaking through containment into the groundwater as the most serious threat. Even so, there is a conspicuous absence of clarification on the physics whenever Chernobyl is mentioned. The public may expect this kind of fear-mongering and exaggeration from the media, but it is still staggeringly irresponsible when a genuine crisis is happening.

Chernobyl was a disaster of epic proportions, but it was caused by incompetence and greed, not technology. For those who know better, gleefully invoking its memory in order to scuttle safe nuclear power is a terribly evil thing to do.

I don’t want to sound as if I’m criticizing all cautious attitudes in light of the situation (I have one myself). On the other hand, I guarantee that those predicting a fallout doomsday or the end of nuclear power will be pressured to revise their opinions as the crisis is resolved. April 26th was a normal day ruined by irresponsible thugs who abused the scientific method. March 11th will be remembered as a catastrophic day saved by heroes who commanded it.

UPDATE: I really shouldn’t do this, but I’m going to go out on a very narrow limb here and guess that the psychological damage caused by the image of exploding reactor buildings will cause more devastation than a quiet but complete meltdown would have, which makes me wonder a bit about the decision to start pumping in seawater. However, I’m not even close to being qualified to operate one of those things, so don’t trust that opinion under any circumstances.

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