On top of the reporting about one of the 5 most powerful earthquakes in recorded history, which has resulted in over 10,000 deaths and massive disruption in Japan, as well as Tsunamis that swept the pacific, we seem to be focusing on the nuclear power plants. Obviously there is a concern, and in relation to the nuclear power industry, this IS the biggest story since Chernobyl. But should it really be part of every headline about the earthquake?
I started a discussion on Facebook, pointing out a lot of reporters were using words they didn’t understand, to underscore fears that are unrelated to reality. I wasn’t trying to make a political statement about nuclear power, but some interpreted it that way. I do have one, but it’s complicated.
Here, I just want to focus on the words and what they mean. There are concerns, and there is potential danger. But the words being used don’t let people properly weight that danger, and people from the “nuclear power is totally safe” side aren’t really helping, because they carry that message along with their “reassurances.”
Here’s my quick vocabulary, and some potential consequences:
Explosion — none of the plants in discussion are capable of producing a nuclear explosions. Really. Take my word for it. The explosions being discussed could be chemical, as a result of hydrogen splitting and build-up, or steam (which is not technically and explosion) that could result from melting, partial melting, flash criticality, or a rupture in a pressure system somewhere.
Critical — If the word is being used in the technical sense, it means that there is a self-sustaining nuclear reaction occurring. Nuclear reactors go “critical” as part of their normal operations. Criticality means a lot higher heat generation, and you don’t want it to happen if the reactor is not being cooled and monitored. But knowing it is critical doesn’t tell you the magnitude of the problem. Inversely, even if a reactor is not critical, it still generates and enormous amount of heat. Most of the dangers from a nuclear reactor do not require it to be critical.
Meltdown (Partial) — Within the nuclear industry, this is a disaster. To the general public, it really isn’t. If the reactor core experiences distortion as result of heat, that’s a meltdown. Flow is obstructed, and your power generating asset is now a big piece of radioactive trash that you have to store, monitor, and cool until society decides how to deal with nuclear waste.
Meltdown (complete) – Way more serious. But still not in ways most people probably imagine. What melts is the core (fuel rods, cladding, pressure vessel). The molten mess should disperse and cool in the bedding underneath the containment structure, probably creating a ceramic shell around itself. But on the way, it can create other problems: if it goes critical, a radiation flare; if it hits groundwater (or injected seawater breaks containment) a large plume of steam containing radioactive contamination; and if it causes fires, most old plants also have a whole bunch of particulate contamination that would be carried by the smoke.
Meltdown Consequences — I don’t know a lot about the construction of these plants, the surrounding area, or the likelihood of breaking containment, but as a general rule:
If the meltdown causes a criticality flare of some kind (and assuming the normal shielding and containment has been compromised) — the flare would probably not reach local populations, and definitely not past the immediate vicinity which has been evacuated. The flare would also be very brief. However, the workers trying to save the plant could be in bad shape.
If the meltdown splits the cladding and releases a lot of the radioactive gases produced by fission, and these are then vented or otherwise escape from containment, the danger would still be primarily to workers in the immediate vicinity. The gases have short half-lives and decay very quickly.
However, if there is a massive plume of steam or smoke, then there is a potential for longer-lived elements to be carried far. Even if the core itself melts into the bedding, most old nuclear power plants have build-ups of radioactive corrosion products, usually Cobalt 60 (which comes from irradiating Iron 59). Since it has a half-live of over 5 years, and is pretty active, it can be a major problem if spread over a wide area.
Two other phrases that get thrown into the discussion:
Three Mile Island – this is relevant, as TMI was also a water-cooled reactor, and did undergo partial meltdown. However, TMI did not lose a lot of the support systems, and containment remained intact.
Chernobyl — A lot less relevant, as Chernobyl was an air-cooled graphite reactor. The reactor core itself actually burned, producing a huge contamination area. Also, there was very little shielding.