The Fukushima plant: Before the earthquake.
The Fukushima plant: Before the earthquake.Courtesy KEI
Ok, well, there isn’t really such a thing as a nuclear earthquake. “Nuclear Earthquake” just sounds impressive. And I suppose “impressive” is one way to describe what’s happening in Japan right now.

I suppose you’re all aware of the 8.9 (or possibly 9.0) rated earthquake that hit Japan last week (if you aren’t, check out this post), and that the Fukushima nuclear power station there has been severely damaged.

While the country is still trying to put itself together, officials are still trying to get the power plant under control. So what happened, what’s happening, and what’s (probably) going to happen?

Well, a nuclear plant like Fukushima basically operates by using radioactive uranium to boil water. The uranium is always decaying—the number of protons and neutrons it has isn’t stable, so neutrons fly off, causing heat. If the neutrons hit other neutrons in the uranium, they fly off too, causing even more heat. If there’s too much of this neutron-on-neutron action, the uranium will get too hot, melt everything around it, and it’s a disaster. This is what happened at Chernobyl.

To prevent the neutron reaction from getting out of control, and to make sure the uranium produces just the right amount of heat, “control rods” are inserted in with the uranium fuel. The control rods absorb some of the neutrons to keep the reaction under control. When the right amount of heat is being produced, the water around the fuel boils, turns to steam, and spins electric generators. It works out pretty well.

At Fukushima, the control rods were inserted into the uranium as soon as the earthquake started, and they did work—the uranium reaction was shut down. But the decaying uranium had already produced other elements, elements with a lot of heat of their own. So there was a lot of residual heat in the power station.

Normally, water would keep circulating around the hot core, carrying away the residual heat (and turning it into electricity). But between the earthquake and the ensuing tsunami, the power to the water pumps was shut off and the backup generators were disabled. The pumps had backup batteries, but eventually those ran out. That means there was still a lot of heat in the core, but no fresh water to carry it away. The water that was there would continue to heat up until the steam was vented or the vessel containing it simply burst.

Unfortunately, both of those things sort of happened. While purposely venting some of the steam, an explosion happened in the building surrounding one of the cores. According to this site, this is probably because some of the vented water vapor had separated into hydrogen and oxygen, which built up in the building and ignited. This whole situation (the venting and the steam) was radioactive, but not that bad as those things go—the radioactive elements decayed and became stable in a very short time.

The next problem was that with all the venting, the water level around the cores was slowly falling. Without water to take away their heat, the cores could overheat, and eventually melt down. This started to happen, and some more dangerous radioactive products of the uranium started to mix with the remaining water and steam, so officials decided to start pumping seawater into the core. Seawater can get more radioactive than clean water, but it would keep the core cool and under control. And it did.

Today, there was a second explosion at the plant, however. I’m not totally sure what caused this, but it looks like it was again from the accumulation of hydrogen in one of the buildings.

With the uranium reaction under control and the cores under water, the residual heat should eventually dissipate. But the explosions have further damaged the cooling systems, and keeping the multiple cores at the station submerged in seawater has been a challenge. The longer the cores are exposed, the harder it is to control radioactive material already produced by the cores, and the greater the chance of a meltdown occurring at the plant.

Approximately 200,000 people living in the region of the nuclear plant have been evacuated, and it’s still unclear what will happen there. Nothing good certainly, but a meltdown isn’t a sure thing at this point, and even if a meltdown were to occur (again, a meltdown happens when there’s too much heat in the core, and everything around the radioactive fuel melts), the Fukushima plant was built to much higher safety standards than Chernobyl was, and it should contain the damage much more effectively. At Chernobyl, explosions sent radioactive material into the atmosphere and over the surrounding area. At Fukushima, as I understand it, the radioactive products of a meltdown would be contained inside extremely thick, tough containers, which, so far, have not been damaged by the earthquake or the explosions.

There’s more to be said about what will happen, and how this might affect the world’s attitude toward nuclear power, and whether that’s a good thing or not … but that will have to wait for another post.

Update: A Third Explosion at Fukushima
A there's been another explosion at the Fukushima nuclear plant. Now three of the four reactors at Fukushima have experienced an explosion. The previous two explosions were probably caused by a buildup of hydrogen, but it isn't certain whether that was the cause of this explosion as well.

The vents that emergency workers had hoped to use to flood the reactor chamber with seawater were malfunctioning, meaning that the core was dry (and un-cooled) for several hours. The vents finally started working in the early morning, but the chamber wasn't filling with water the way they had hoped, perhaps because of a leak.

A meltdown is still possible, but while radiation levels in the area are considered "elevated," they are low enough that it's very unlikely that the vessels that contain the reactor cores have been breached.

3/15/11 Update: Fire at 4th reactor
Shortly after the explosion at reactor 2 (the third explosion), a fire started at reactor 4. Between the fire and the explosion, radiation levels at the site briefly spiked to about 167 times the average annual dose. Reactor 4 actually wasn't producing power when the tsunami hit, but it did contain a cooling pool for spent fuel assemblies.

Nuclear fuel that has decayed to the point where it's not useful for sustaining a nuclear reaction still produces a lot of heat, and so it's stored in a pool of water for years to deal with the heat and radiation. Reactor 4 at Fukishima has one of these pools, and—just like with the active reactors—it looks like the cooling system was malfunctioning, which allowed the water in the pool to boil away, exposing the spent fuel. The spent fuel likely heated up until it ignited, or caused a fire in the building.

Authorities are now warning people living as far as 20 miles away from the plant to stay inside to avoid any radioactive fallout. As for the emergency workers at Fukushima, CNN's expert says, "Their situation is not great. It's pretty clear that they will be getting very high doses of radiation. There's certainly the potential for lethal doses of radiation. They know it, and I think you have to call these people heroes."

Update: 2 Reactor containment vessels probably cracked
Japanese officials think that the spike of radiation around the Fukushima plant last night might have been associated with a cracked containment vessel in one of the reactors. Today, they think a second container might be cracked as well, and leaking radioactive steam.

Your Comments, Thoughts, Questions, Ideas

JGordon's picture
JGordon says:

There has been a third explosion at Fukushima. More in the updated post above.

posted on Mon, 03/14/2011 - 8:56pm
Anonymous's picture
Anonymous says:

That is super sad. My prayes go out to all of the families, friends, and people in Japan.

posted on Sat, 03/19/2011 - 1:13pm
JGordon's picture
JGordon says:

CNN's video on (some of) what went wrong at the nuclear plant:

posted on Mon, 03/14/2011 - 9:05pm
kieran's picture
kieran says:

that is cool

posted on Sat, 11/19/2011 - 11:34am
JGordon's picture
JGordon says:

There's been a fire at another reactor, probably from the spent fuel pond. (More on that in the second update above.)

CNN is also saying that the cooling systems at the fifth and sixth reactors are not functioning will now. (I had thought there were only four reactors, but I guess there are at least six?)

It seems like there has probably been at least a "partial meltdown" in some of the reactors. We should know in the next 24 hours whether or not there will be a complete meltdown, where the nuclear fuel and its containers melt. If this happens, hopefully the vault-like structures around the reactors will contain the melted fuel and radioactive material, and prevent it from entering the air and water.

posted on Tue, 03/15/2011 - 10:34am
JGordon's picture
JGordon says:

The chairman of the United States Nuclear Regulatory Commission has given an assessment of the situation at the Fukushima plant, and it's much bleaker than what Japanese officials have been saying.

He believes that the pool of water that was covering the spent fuel in the 4th reactor has completely dried, meaning that the fuel is heating up, and releasing lots of radiation (which the water would otherwise have blocked).

The chairman is recommending that people evacuate the area to a radius of about 50 miles, much further from the plant than the Japanese recommendation.

If the pool has dried, it will make recovery operations at all of the reactors much more dangerous, because of the increased radiation levels.

posted on Wed, 03/16/2011 - 3:54pm
Big Gr8pe's picture
Big Gr8pe says:

This is so horrible. First Haiti, Then Japan :( So sad.

posted on Mon, 04/04/2011 - 11:15am
Anonymous's picture
Anonymous says:

it would be cool if you stated more fact and less opinion. :)

posted on Sat, 04/23/2011 - 10:30am
Anonymous's picture
Anonymous says:

that is bad

posted on Thu, 04/28/2011 - 12:09pm
Anonymous's picture
Anonymous says:

thats really sad

posted on Thu, 05/05/2011 - 1:25pm
Anonymous's picture
Anonymous says:

I think finding differnt source of powers is better way for people. Moving out of Nuclear to solar energy and wind energy is the solution.

posted on Sun, 09/11/2011 - 2:43pm
Anonymous's picture
Anonymous says:

well that is just depressing:(but it is interesting...

posted on Mon, 12/26/2011 - 5:03pm
Anonymous's picture
Anonymous says:

this is so cool

posted on Thu, 02/16/2012 - 1:58pm

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