Students with the Department of Nuclear Science and Engineering at MIT have been keeping a really great blog about the ongoing struggle to cool and stabilize the nuclear power plants in Fukushima, Japan. It's my new go-to source for information.
Check out this amazing map. It shows the number of foreshocks, the big quake, and aftershocks, as well their location, date/time, depth, and magnitude. Stick with it: it starts off slowly, but it gets pretty horrifyingly spectacular.
Courtesy KEIOk, 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.
Courtesy NOAASome interesting scientific angles on the recent Japanese earthquake and subsequent human disasters:
Fukushima Nuclear Accident – a simple and accurate explanation. This post is long, but does a great job of explaining exactly how a modern nuclear reactor works, and how engineers plan for natural disasters.
Courtesy Public domain (via Dartmouth)An outbreak of cholera in Haiti is causing doctors and other aid workers concern. Cholera is an infection of the intestines caused by Vibrio cholerae a bacteria often found in contaminated food or drinking water. The bacteria can spread through crowded and unsanitary areas via contact with feces of infected persons. Cholera outbreaks often take place in crowded and impoverished areas, or in war zones. Symptoms include severe abdominal cramps, watery diarrhea, vomiting and rapid dehydration. Left untreated, cholera can be deadly within 24 hours. When detected, treatment involves replenishment of lost fluids and electrolytes. Improved sanitation and personal hygiene practices such as frequent hand washing can help stop the spread of the disease. So far, cholera has killed more than 300 people in Haiti, and most of the nearly 4000 recorded cases have occurred in the region of Arbonite, a rural area unaffected by the 7.0 magnitude earthquake that devastated much of the country last January. The outbreak has been slowing lately, but officials are concerned it could still spread through the hundreds of refugee tent camps located in the overcrowded capital of Port-au-Prince.
Courtesy USGSA fairly strong earthquake measuring 6.9 magnitude (6.7 according to the USGS Earthquake site) caused some panic but so far no reported injuries or major damage to population centers along the Gulf of California. The quake, which struck just before noon local time, was centered about 65 miles south of the coastal city of Los Mochis, and about 6 miles beneath the surface.
Eyjafjallajökull isn't the only volcano to rock our modern world. Thirty years ago today Mount St. Helens erupted in Washington State, making it one of the most spectacular and devastating volcanoes in the history of the United States. For those of us who were not alive or old enough to remember the event, here is a haunting description of the explosion from Boston.com:
"On May 18th, 1980, thirty years ago today, at 8:32 a.m., the ground shook beneath Mount St. Helens in Washington state as a magnitude 5.1 earthquake struck, setting off one of the largest landslides in recorded history - the entire north slope of the volcano slid away. As the land moved, it exposed the superheated core of the volcano setting off gigantic explosions and eruptions of steam, ash and rock debris. The blast was heard hundreds of miles away, the pressure wave flattened entire forests, the heat melted glaciers and set off destructive mudflows, and 57 people lost their lives. The erupting ash column shot up 80,000 feet into the atmosphere for over 10 hours, depositing ash across Eastern Washington and 10 other states."
And for everyone, here are some fabulous Boston.com photos to commemorate the event.
Here's a completely awesome video of a life-sized shake table at the University of California-San Diego used to test building construction designs to withstand earthquakes. Hang on tight, click this link and enjoy. No actual buildings were harmed in the making of this video.
A series of strong earthquakes struck a far western Tibetan area of China on Wednesday, killing at least 400 people and injuring thousands as houses made of mud and wood collapsed, trapping many more, officials said. Fox News.