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About Earthquakes, Tsunamis, and Nuclear Power in General

UPDATE 3:48 PM, Wed, Mach 16:
No coolant remaining in spent fuel pool at Daiichi 4. Melt of uncontained spent fuel rods likely.

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UPDATE:

According to NYT reporter Hiroko Tabuchi some workers remains at the Fukushima Daiichi plant, and reports otherwise were a translation error.
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NOTE: this is a work in progress, but I’m posting now due to the breaking story about the Fukushima Daiichi power plant’s current state.

A press conference was called a few minutes ago (March 15, 10:42 US Eastern Time) in which it was announced that all remaining personnel, including those working on cooling and fire suppression have been evacuated due to rising radiation levels. Some of the unanswered questions that are listed in the full story below are now answered. The reactor cores in Fukushima Daiichi 1 and Fukushima Daiichi 3 have been breached.

The spent fuel pool in Fukushima Daiichi 4 is on fire and cannot currently be doused from the air. Technicians are seeking solutions that will not expose crews to deadly levels of radiation.

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(Everything below was an in-progress post prior to the announcement above, I’ll have to modify/update in the AM)

Millions and millions of us have been riveted by the jumble of dramatic and confusing coverage from Japan – myself included.

***photo here***

It’s heart-wrenching to see the sheer magnitude of the devastation, and more so to hear of ongoing aftershocks, some similar to the quake that wiped out much of Christchurch, New Zealand just a few weeks ago. As of 7:30 PM, March 15, there have been 256 aftershocks between 5.0 and 5.9, 35 aftershocks between 6.0 and 6.9, and 1 aftershock of magnitude 7.1. [***NZ quake photo***]

People far and near are traumatized by such massive events, which tends to lead to a strange dichotomy: we see and read lots of worst-case or best-case thinking, but little analysis. So, I’m going to try to glean some “most likely” reality from the space between the persistent mass of “OMG, worst disaster ever!” and “nothing to see, move along” reporting that seems to have taken over the media.

First, a timeline with some basic background, then information about the nuclear power plant issues and their implications, but before the timeline, some caveats:

1) People in the US are not in any immediate danger.

2) Depending on what happens with the plants over the ensuing days, the particulates in the air, their concentrations, and the movement of air masses, that could change. At the moment, the air that looked like it was headed directly to the West Coast has entered a circular pattern over the Pacific. Exactly which radio-isotopes are in that air mass, at which heights, and what concentration is undetermined.

It could be utterly harmless when it reaches the US or it could pose some health risk. A lot depends on what got sent how high into the atmosphere, how much of it is in there, and how much falls out before it reaches the US.

3) This event is continuing to unfold, and solid information is hard to come by, so I won’t be making any sweeping predictions one way or another. If you’re looking for false certainty in either direction, rather than information, you’ll need to look elsewhere. My goal is to give enough information that you can start to understand the situation and weigh the risks for yourself.

On to the timeline:

1) A freaking massive earthquake hit in the Pacific ocean, just off the coast of northeastern Japan. The latest update based on analysis of seismological readings on Sunday raised the severity to 9.0.

Some parts of the country were lifted as much as 8 feet in the air before slamming back down again – over and over again for a couple of minutes. Imagine what it would feel like to board an elevator, then shoot up a floor, down a floor, up a floor, down a floor, over and over in seconds. That’s what happened to entire communities in Japan during the worst of the earthquake. It’s a testament to their stringent building codes that any buildings in the quake zone survived such extraordinary shaking.

This caused damage to a large number of structures, including power plants. The nuclear power plants in the region were designed to handle quakes significantly stronger than the “typical bad quake” for the region. Unfortunately this quake was many orders of magnitude worse than the design anticipated. A bad quake in the region hovers in the low- to mid- 6.x range. The reactors were designed to handle 7.0 – 7.5.

On the richter scale, a 9.0 earthquake, such as the one this past weekend was 1000 times as strong as the anticipated worst-case of 7.0.

Earthquakes aren’t really an unusual thing in the area – they are so frequent that locals have learned to take them in stride. Accounts like this one are not unusual from survivors:

We were having a good time, almost got to round 12 which in Zombies in a hell of a feat when we broke for a smoke break (save the health trolling) when I noticed the ceiling light was shaking a bit. I yelled out the window “Man, looks like we got a earthquake”. He replied “Not too bad though”, and living in Japan…it wasnt. We get small ones quite frequently, and it normally was not something to panic over.

But it didn’t stop…

And it got stronger…

And there is a moment in an event like this where you go from amused and interested to concerned. Then really concerned. Then only panic and fear.

During the time after the quake, but prior to the tsunami, we have little info about what was going on at the nuclear plants. We know that primary electrical supply was lost. The nuclear plants themselves went into fail-safe auto-shutdown mode (it’s really, really, really good that this part worked, which I’ll explain later), some other types power plants were damaged or destroyed by the shaking.

2) At the nuclear plants that were online at the time of the quake, the systems went into automatic shutdown mode, and the control rods were inserted into the reactors.

This is a really good thing. We wouldn’t be asking “what’s happening?” or “how bad is it?” if those control rods hadn’t been inserted. We would instead be weeping for the thousands upon thousands who had already died from radiation poisoning.

This does not, however, mean that everything is copacetic. It’s possible that not all control rods were completely inserted, and it’s possible that other factors make control rod insertion a bit of a moot point. More on that later…

3) Primary electrical power went out, shutting down the cooling water pumps in the plant.

This was problematic, because even after a plant is shut down, it needs cooling water.

4) The backup generators turned on, pumping cooling water through the plant.

This was good news … for a little while.

5) Then the tsunami struck.


[photo source AP]
Most people think of a tsunami as a single big wave. And it is partly that, but it’s more like the wave equivalent of a super-hurricane. A hurricane isn’t just a bigger thunderstorm. It’s a mass of water and fast moving air that inundates whole regions for hours and hours, with higher-force wind gusts happening over and over throughout the course of the storm.

A tsunami behaves in a similar way, but from below and with far, far more water … and yet more water in place of wind.

In a tsunami, large waves flow across the top of a fast moving, elevated water mass, pummeling any shorelines in the way – flowing up rivers and streams, turning land to water, and plowing through buildings and trees like a great soggy planetary bulldozer. It pulverizes everything in its wake, churning and mashing buildings, vehicles, forests, and everything else like the blades of a gigantic blender.

Tsunamis are caused by earthquakes. The severity of a tsunami depends on which kind of quake happened. This one was caused by the worst kind of quake: one chunk of a tectonic plate slipped under another one, pushing the other upward. This process is called “subduction,” one plate subsides (aka sinks) beneath another, causing the other one to pop up abruptly.

The water in that area was kicked upward with unimaginable force, bashing a massive circular wall of water outward – some of which headed straight into the earthquake-ravaged eastern shore of Japan.

6) The backup generators failed

The story here is mixed – the generators may have been simply flooded with water, or washed away, or their fuel tanks washed away, or some combination of the above at different locations. What we do know is that the arrival of the tsunami brought the end of the backup generators.

7) It was a few hours after this that news started to trickle out about the Fukushima Daiiachi 1 power plant. At 1:30 am US eastern time on Saturday, someone posted via Twitter that there was confirmation of cesium-137 detected around the plant Daiichi 1. This was many hours before the outer shell blew up.

Note: There are multiple nuclear power plants involved in this disaster. Each plant has more than one nuclear reactor. For clarity, the naming convention I’m using is “Location, Plant name, Reactor number.” So “Fukushima Daiiachi 1” means the first reactor at the Daiiachi plant in Fukushima.

The reports of cesium-137 from Fukushima Daiiachi 1 indicated a problem in either the core containment or the spent fuel storage pool. The levels were reportedly small, which would indicate a “small-ish” release, rather than, for example a complete core containment failure. Of course, there’s no knowing how accurate the reports are regarding radiation levels. At the time, they were not stating millisieverts or any other useful measure, simply that there was radioactivity.

Here’s where a diagram might help:


[Image from this post by Richard Cranium – very much worth reading. Be sure to read his initial Q&A, as well.]

The plants are designed with several layers. The outermost layer is mostly to keep the weather out and has almost nothing to do with protection from radiation.

Inner layers are more important – you have an inner containment layer of hardened concrete, then inside that, the core itself (red cigar shape). The core and the inner container sit above another container which has a big bed of graphite in it. Graphite acts sort of like an absorbent sponge for excited atoms, catching them and slowing them down, so they don’t keep the fission process going. The cooling rods mentioned in #2 above are made of graphite.

There is also water – if you look toward the bottom, you see a doughnut of water. This is the reactor cooling water. If you look closely, you can see pipes leading into and out of it. Those are the pipes through which fresh cool water enters and warm exits.

Up top, you can see more water – two gigantic swimming pools. Those hold the “spent fuel rods.” Spent fuel rods are fuel rods that were used up, and are waiting either to be sent for reprocessing or to be placed into some permanent storage (which doesn’t exist, yet). They’re similar to the active fuel rods in the reactor, but are cooler and aren’t in any hurry to start a nuclear fission reaction. They’re still full of radioactive material, and still need to be cooled, but not quite as much as the ones in the core.

Ok, back to the cesium:
Cesium-137 is a byproduct of the radioactive decay of the uranium (or other fuel) in the fuel rods. Its presence in the air indicates that at least some fuel rods in Fukushima Diiachi 1 had become exposed to air for a sufficient period of time for some of the casing to melt. It’s not certain (at least from the coverage I’ve been able to find) whether the exposed rods were in the core, in the spent fuel pool, or some combination of the two.

A fuel rod is basically a hollow tube of zirconium alloy, nicknamed zircalloy, filled with pellets of fuel. In Fukushima Daiiachi 1, the fuel pellets are made of uranium. In other reactors, different fuels may be used.

Even when a reactor is shut down, fuel rods in the core remain hot – both in the radioactive sense and in the temperature sense. The zircalloy casings on the rods are able to withstand temperatures of over 1000 degrees. Unfortunately, the fuel inside the casings tends to be a bit hotter (up to 3000 degrees) for the first few days after a reactor shuts down. You can probably see the obvious problem here, but the solution is fairly simple: draw off the excess heat by continuously pumping cool water though the space.

Sadly, the earthquake eliminated the primary electrical power to the plant, and thus shut off the cooling water pumps. Then the tsunami shut off the backup power. There was reportedly battery power for a short period after the generators died, but the batteries were eventually drained. One report said the US flew in generators, but the US uses a different shape plug than is used in Japan, so making those work was problematic.

In either the core or the spent fuel pools, when new water is not being pumped in, the water already in there heats up, eventually boiling off as steam. This is just like keeping a pot of water on the stove. If you keep nonsensically replacing the water in your teapot with cold water, the water will never boil, and you’re never going to get that cup of tea. If, however, you fill the pot once and let the water stay over the heat for long enough, it will eventually boil. If you forget, and leave your teapot boiling for too long, the water will eventually boil away entirely.

You can probably see where this is going…

Back to Fukushima Daiiachi 1:

While the engineers in the plant scrambled to find ways to make it possible to keep cooling water flowing, the water that was already in the core was heating up and boiling off. At some point, at least some of the fuel rods had no water over at least part of the rod. This meant that the zircalloy casings were no longer being kept below their melt temperature, which in turn means they started melting.

[An aside: we owe these engineers our deepest gratitude and respect. They are knowingly giving their lives to try to save their families, their communities, and any others who could be affected by this tragedy. For Star Trek geeks out there, this is the real world equivalent of Spock in the reactor. In real life, there’s no crisp cinematography, no heart-wrenching background music or poignant last moment, just ordinary people struggling through debris, smoke, dust, noise and heat to control that which does not want to be controlled – at least for a little while.]

Exactly how long the fuel rods were exposed, how many were exposed and how much casing melted is unclear. Not surprisingly, more is worse, less is better – more rods exposed would be worse than fewer exposed. More casings melting would be worse than fewer melting. A larger area of casing melting would be worse than a smaller area. Longer exposure would be worse than shorter periods of exposure.

About all we do know is that at a minimum, some portions of some casings were not cooled for some period of time, resulting in some melting and thus the release of some Cesium-137.

8 ) The outer shell on Fukushima Daiiachi 1 explodes.

This is when the news media panicked. It’s ironic, because in the grand scheme of things, this was nowhere near as big a deal as the quiet release of cesium. But in the world of ill-informed 24-hr news readers, it’s only important if it has “great visuals.”

As people panicked over the big boom, industry experts were trotted out to debunk the concerns of those who were panicking. The panic over the non-critical aspect of the problem gave an opening for the industry to sow the seeds of doubt about any safety concerns.

About the explosion: remember above where I describe the outer shell as something to keep weather out? That’s what blew up. Essentially, the steam inside the building continued heating until it got hot enough for the oxygen and hydrogen in the water molecules to separate. Anyone who has seen footage of the Hindenburg knows about the flammability of hydrogen. When it ignites, you get a sudden rapid expansion of super-heated air, and just like the aftermath of a spark in a house that has a propane or natural gas leak, the building explodes.

The steam that was released by the explosion does have some radioactive particles in it, so this isn’t a good thing – as a matter of fact, it’s pretty bad news for people nearby, especially if they have not taken iodine tablets to protect their thyroid glands, but it’s far different from the reactor core itself exploding.

At least, this is all true of the source cited for the explosion is true. There is a second possibility, however:

It’s possible that the hydrogen/water split due to heat from the spent fuel rods becoming exposed to air. The spent fuel rods don’t have any containment, and they don’t have a big tub o’ cooling graphite into which they can slump if they start to melt.

If the spent fuel rods caused the explosion, then the radiation released won’t be the immediately dangerous nearby iodine-131 that dissipates quickly, it will be the longer-lasting nastier nasties, like cesium-137 (yep, again, but in larger quantities), and strontium-90.

9) Reactor 3 outer shell explodes

10) Reactor 2 outer shell explodes

11) Reactor 4 fire

This is the most worrisome, because this plant was not running at the time of the earthquake and tsunami. The location of the fire is near the spent fuel pool at the top of the reactor, though reports are unclear whether it’s in the pool or something near the pool. This fire is eventually quenched, but the amount of radioactive material released is unclear.

UPDATE: March 15
Reactor 4 caught fire again, this time reports state clearly that the fire is in the spent fuel pool:

Japanese officials told the International Atomic Energy Agency that the reactor fire was in a fuel storage pond — an area where used nuclear fuel is kept cool — and that “radioactivity is being released directly into the atmosphere.” Long after the fire was extinguished, a Japanese official said the pool might still be boiling, though the reported levels of radiation had dropped dramatically by the end of the day.

UPDATE 10:42 PM:
Devastating news – many questions are now answered.
A plan to douse reactor 4 w/water by helicopter has been scuttled due to excessive radiation levels. The official reports of dropping radiation levels were premature.

It is now clear, according to a press conference called by Secretary Edamo, that reactor cores 1 & 3 have been breached, steam is escaping from core 3, and reactor 4’s spent fuel pool is still on fire.

ALL personnel, including those attempting to cool the reactors and deal with the fire have been evacuated.

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Radio-isotopes from the plants:

There are four kinds of isotopes that are likeliest to be emitted by the crippled Fukushima Daiichi plant, as well as the other three that have been taken offline: iodine-131, cesium-137, strontium-90 and plutonium-239. Iodine-131 is, in many ways, the most dangerous of the four, because it can lead to cancer — specifically thyroid cancer — in people exposed to it in the shortest time. Epidemiologists estimate that there were 6,000 to 7,000 cases of thyroid cancer that never would have occurred as a result of the 1986 Chernobyl explosion in Russia. Most of the victims were people who were children at the time of their exposure and developed the disease later.

Strontium and cesium are the next up the danger scale. While iodine tends to concentrate its damage to the thyroid, those two are not nearly so selective. “Strontium is chemicaly similar to calcium,” says Dr. Ira Helfand, a board member for Physicians for Social Responsibility. “So it gets incorporated into bones and teeth and can stay there, irradiating the body, for a long time.” Strontium is most commonly linked to leukemia.

Cesium works in other ways, behaving more like potassium when it’s inside the body — which means it circulates everywhere and can contaminate anything. Cesium doesn’t linger as long as strontium does — it gets excreted in urine over the course of months or years — but that’s more than long enough to cause cancer of the liver, kidneys, pancreas and more. “Basically all of the solid tumors,” says Helfand.

http://climateprogress.org/2011/03/14/third-explosion-reported-3-cooling-systems-failing-3-meltdowns-cant-be-ruled-out-spent-fuel-risk-also-great/

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