The following was written by Plain English Nuclear (originally posted to Facebook at about 12:30am PDT on Wednesday, March 16, 2011).

Subsequent to that post, many people clamored for me to share it publicly.  I have now done so.

From the author: I have a PhD in Nuclear Engineering from the University of California, Berkeley. I am currently employed as a nuclear engineer. I do not work on nuclear power plants; I work on other facilities. But I did study this stuff in school, and I am told I am good at explaining things. (I also have lots of friends who are experts in the nuclear field, and I hope they will correct me when I am wrong.)

——

[Fairly current as of about noonish Pacific time March 15; events since then are sort of haphazardly incorporated.  I'll update as I get the chance, but right now it's bedtime.]

Okay, kids.

This post is open to friends-of-friends.  Feel free to repost if needed, but I don’t really want to open myself up to a wave of comments by strangers alleging this was payback for Pearl Harbor.  (SERIOUSLY WHAT IS WRONG WITH PEOPLE.)

If you don’t know me or my background, here you go:  I’m a nuclear engineer.  I don’t do any work with power plants – I work with other facilities.  But I did study this stuff in school, and I can try to explain it.  If you want an expert, you need to be talking to someone who worked on safety systems for BWRs (boiling water reactors).  (I have lots of friends who are experts like that and I hope they will correct me if I am wrong here.)

This post is written for people who don’t know anything about nuclear reactors.  I have sacrificed detail to provide simple explanations! Not everything here is accurate to the last inch, because I wanted you to be able to actually read the thing.  It’s accurate enough for understanding, I think.  I’m happy to hear suggestions for how to make it better.

The post is also long.  Sorry.

For those of you with short attention spans, I’m gonna get the FAQ stuff out up front, and then provide the long meaty detail stuff down below.

1. I live on the West Coast.  Am I in danger?

No.  Absolutely not.

You won’t even notice except that everyone will keep talking about it for ages, and it’ll take us even longer to get off coal and oil and natural gas because people will be afraid of nuclear power again.  Go outside, get some sunshine (or rain, depending), be grateful for the fact that your city isn’t completely destroyed in an earthquake or a tsunami, hug your loved ones, and then find a way to donate to the relief efforts.

You might get cancer years from now, but it won’t be from this.  It’ll be from smoking or sun damage or plastics or those horrible processed foods with the carcinogens you keep eating.

2. But I saw a fallout map on the internet, labeled “Australian Radiation Services” or “U.S. NRC”!

It’s a hoax.  A really, really mean one.  See http://www.blogotariat.com/node/211958 for one of the best summaries I’ve found.

3. Even if the reactor has a meltdown?  The media keeps saying we’re headed for a meltdown.  Isn’t that a very very bad thing?

Not necessarily.  “Meltdown” is a very broad term – it applies to a range of conditions.  “Meltdown” is basically any time that the fuel gets hot enough that the cladding (the metal wrapper that holds the fuel in place) gets holes in it.  But “meltdown” could mean just one teeny spot on one single fuel pin (the cladding starts to fail at about 2200 degrees F) all the way up to the entire reactor core in a liquid pool on the bottom of the pressure vessel (the fuel itself melts at about 5000 degrees F).  The media seems to think it’s that whole-core thing.  But that isn’t going to happen.

So far they’ve had a partial failure of some of the fuel pins in two of the reactor units, and that’s about where it’s expected to stay.  It may turn out that a third reactor unit also had a partial failure of fuel pins.  This is a sad situation – we try not to have fuel failures, because it’s a giant hassle – but it’s not by itself a dangerous one.  It’s very important to remember that these fuel pins are sealed inside a giant steel pressure vessel, which itself is sealed inside a giant concrete containment structure (you may also hear this called the “drywell”).  Even if the core *did* melt all the way down, either one of those two things on its own would keep the radiation from the melted fuel from getting to the public.

4. But Chernobyl released lots of radiation!

This isn’t like Chernobyl.  You can read why here:
http://news.yahoo.com/s/livescience/20110312/sc_livescience/chernobylscaledisasterveryunlikelyinjapanexpertssay
http://online.wsj.com/article/SB10001424052748704893604576198421680697248.html
http://www.csmonitor.com/World/Global-News/2011/0313/Japan-s-nuclear-crisis-and-Chernobyl-key-differences

Short version:
-         Chernobyl used a different kind of fuel, and its fuel caught on fire and the ash went everywhere in a great cloud that lasted for months in affected areas.  That can’t happen here; for one the fuel can’t catch on fire, so no ash, and for two, any radiation release would be in gaseous form and the cloud would pass over affected areas in hours.
-         Chernobyl didn’t have a containment structure.  These reactors do.

This is more like Three Mile Island, if you insist on picking an accident for comparison.

5. But Three Mile Island was terrible!

Three Mile Island a) didn’t kill anyone, b) didn’t injure anyone, and c) only released a very small amount of radioactive material, mostly gases that went harmlessly into the atmosphere.  (Seriously!  Read about it!)  [1]

During Three Mile Island about half of the core (including fuel) melted and fell to the bottom of the pressure vessel [1].  But it didn’t melt through the steel pressure vessel – in fact it only melted about 5/8 of an inch through the wall.[2]  (A typical pressure vessel is ~6 inches thick.)  And even if it had, it would have had to get through like 6 feet of concrete after that.  (We design it that way.)

Right now our best evidence indicates that yes, a small portion of the cores in Fukishima One Unit 1 and Unit 3 have failed (although we don’t think the fuel has melted, just the cladding), and maybe Unit 2 also.  But it’s thought that the majority of the fuel didn’t melt, and that the cleanup will probably be less difficult than Three Mile Island.

6. But the media says they released radiation, and there’s all these numbers floating about radiation levels, and they evacuated everyone who lives near the reactor.  Can you put this in context?

There were several small, planned releases of slightly radioactive gases.  Each of these radioactivity releases to the environment at Fukushima so far has produced about the level of one dental X-ray if you were standing right over the release and breathing in really hard.  If you weren’t standing right over the release, the particular kind of radioactivity released would have nearly all gone away before the vented gases reached you on the ground.  Even the people on the ship that sailed right into the plume only got a maximum dose about equal to a month of background radiation [6] – that is, the natural radiation you get from living on Earth.

The most recent explosion at Fukushima One Unit 2 and near-simultaneous fire and Fukushima One Unit 4 (about 6 am and 9 am Japan time March 15) did release a one-time gust of radioactive gases that was larger.  Radiation levels at the edge of the nuclear plant briefly spiked to 8217 microSieverts per hour. [10]  How bad is this?  8217 microSieverts is about six times the allowable annual exposure for a member of the public in the U.S.  It would take standing in this kind of radiation for 24 hours before you would be considered to have radiation sickness (with a total dose of 200 milliSievert). [9]  But 8217 microSieverts was the peak of the spike, the total spike lasted less than three hours, and dose rates at the edge of the plant were at 489.8 microSieverts/hr as of 4:30pm Japan time March 15.  (This means you would get your annual dose if you stood there for an hour.  Perspective: This is about the same as smoking 350 packs of cigarettes in a year [12], or living in Denver for a year [15].)

They evacuated people because it was safer that way – just like we evacuate people during tornado and hurricane warnings.  No exposure to the public was expected, but better safe than sorry!

7. But something exploded!  Three times! And it knocked down buildings!

First: There is no way for a nuclear power reactor to explode like an atomic bomb. You just can’t.  Even if you tried.  Explosions can happen at nuclear plants, yes – but they are either mechanical explosions (like pressure building up in a confined space until it pops) or chemical explosions (like a fire setting off a diesel storage tank, or a bunch of hydrogen ending up somewhere that there’s a bunch of oxygen and a spark setting it off like the Hindenberg).  The explosions at Fukushima were not caused by radioactive material.

Now: let’s take a look at what we’ve got right now.  Here’s a typical media graphic (thank you, Daily Mail): http://i.dailymail.co.uk/i/pix/2011/03/15/article-1366341-0B2D7BFA00000578-51_964x678.jpg

Here’s what you need to know:  The fuel is in a steel pressure vessel.  The pressure vessel is in a veeeeeeery thick concrete-and-rebar structure called the containment.  The containment is located in a reactor building, which is another building made of concrete and rebar (though not quite as thick).  On *top* of the reactor building is an additional structure made of steel frame with sheet steel walls.  This structure houses a fuel transfer crane used when they change the fuel in the reactor.

What you see in the picture above is the reactor buildings for Unit 1 through Unit 4 of Fukushima One.  The explosions in Unit 1 and Unit 3 were hydrogen explosions that each happened in the fuel transfer crane areas, blowing the sheet steel off the walls.  Since that structure isn’t designed to withstand explosions, they look pretty rough.  What you can’t see in the photos: the pressure vessels are just fine and the containments are just fine.  (Those structures *are* designed to withstand explosions.)  And the reactor buildings under the steel frames look okay.

Unit 2 had a hydrogen explosion also – but this one was in a thing called a suppression pool, outside the main containment structure but inside the reactor building.  Officials suspect that a small portion of the pressure vessel may have gotten damaged, but this is still unconfirmed.

Unit 4 had a fire inside the reactor building but outside the containment structure.

So contrary to the captions in the photo: no reactor has exploded and no reactor has caught fire.  (Grrrr, bad reporting, Daily Mail!)

By contrast, here’s a picture of an oil refinery in Japan: http://cdn.theatlantic.com/static/infocus/jpq03111/j16_RTR2JQR2.jpg (It’s still on fire, as far as I know.)

8. What’s the worst thing that could happen?  What about the most likely?

My short-version prediction: The fuel in Units 1 and 3 of Fukushima One have been damaged, and the status of the fuel in Unit 2 is unknown.  Fuel in all three of these units could melt further, but the radioactivity will remain contained by the containment structures.  Small amounts of radioactive steam and gases have already been released, and more small releases could occur.  Right now I think 150 people are being monitored for radiation exposure and 23 have been sent for decontamination – but that includes workers.  (Can’t remember a source; would appreciate one.)  Worker injuries (there have already been 15 injuries) will be due to explosions, not radiation.  No harm will come to members of the public.  No harm will come to the environment, except for any little algae and bacteria critters caught up in the seawater they are using for emergency cooling.

The worst thing that could happen is getting a hole in one of the containment structures.  That has possibly happened in Fukushima One Unit 2, due to the hydrogen explosion there.  But radiation levels near this unit fell after an initial spike – which is what you would expect to happen if the suppression pool exploded but the containment held – so their guess is that if there is a hole, it’s actually in the pressure vessel and not the containment structure.  (It’s also expected to be a small hole.)  If there were a hole in the containment structure,   radioactivity carried in liquid coolant could leak out of the hole and into the surrounding reactor building.  Radioactive gases could leak out of the hole and up into the atmosphere.  It’s important to emphasize that the only members of the public who would be at risk in this situation would a) be downwind, and b) probably not get a dose that would kill them or cause cancer – probably a dose closer to 2 or 3 CT scans put together.  I’m not a health physicist, though, so I could be wrong.

There is one complicating factor, though.  If radiation levels from a unit with a hole in the containment structure are too high, it could mean workers trying to make sure the other units at Fukushima One stay shut down would have to evacuate or risk radiation poisoning by staying to operate the reactors.  Probably if this happened they would rotate the workers in on short shifts to minimize exposure.  If workers were completely evacuated, Units 1 and 3 would probably melt down.  Again, as long as the main containment didn’t get compromised, there wouldn’t be a major release of radioactivity.

9. That sounds pretty bad, still.

It is.  It’s never good when people get hurt.  And I bet some investors are going to be mad.  And it’s going to take some work to clean everything up and repair it.  But listen:  this is not the thing that needs your fear and attention right now.
Here’s some perspective: There are over 10,000 missing and presumed dead from the quake and tsunami. [13] Over 3600 people are confirmed as having died in this quake, so far – more than 9/11. Property damage is estimated to be as much as $100 billion, according to some reports. [14]  And aftershocks keep happening.

Quit freaking out about the reactors; freak out about the dead and the wounded.  Freak out about the towns wiped off the coastline.  Get out there and do what you can: donate money, donate time, let Japan know we support them.  And spread good information, not fear.

10. Okay, I’m gonna quit reading now.  That was already too long.

Sure, no problem.  But forward this link to all your non-sciency friends:
http://online.wsj.com/article/SB10001424052748704893604576198421680697248.html

And forward this to your sciency friends:
http://enochthered.wordpress.com/2011/03/13/all-right-its-time-to-stop-the-fukushima-hysteria/

If you want more details, though…

11. Well, okay.  First, I can’t keep all the plants and stuff straight.  Where is the problem?

There are two nuclear plants that we’re primarily concerned with right now: Fukushima Dai-ichi (Fukushima One) and Fukushima Dai-ni (Fukushima Two).  We’ll use the Americanization of these names here because it’ll be a bit easier for English-speakers to keep straight.  Along with a third plant called Onagawa, these two plants were the closest to the epicenter, and are also near the coast.

Fukushima One has six separate nuclear reactors (we call them “units”).  They are numbered: Unit 1 through Unit 6.  Fukushima Two has four units (predictably, Unit 1 through Unit 4).

At the time of the earthquake, Fukushima One Units 1, 2, and 3 were operating.  Fukushima One Units 4, 5, and 6 were shut down for routine maintenance and were not operating.  Fukushima Two Units 1 through 4 were all operating.
As of the last update I saw ([4], 7 pm Japan time March 15):

  • Fukushima One Unit 1 through Unit 3 are pretty bad off and not completely out of the woods.  These reactors will not be usable again when this is all over, but we don’t expect more than partial melting of the cores and limited releases of radioactive gases (like in Three Mile Island).
  • Fukushima One Unit 4 had a hydrogen explosion and subsequent fire in the spent fuel pool and a fire in the reactor building, but the reactor is just fine and was never in danger.  Also, the reactor currently has no fuel in it.
  • Fukushima One Units 5 and 6 are just fine and were never in danger.
  • Radiation levels at the border of Fukushima One were at 489.8 microSieverts/hr as of 4:30pm Japan time March 15.  As stated above, this would give you your annual dose as a member of the public in one hour, and is about equivalent to smoking 350 packs of cigarettes in a year.
  • As for the four units at Fukushima Two: they are all safely shut down.  Unit 3 was never damaged and had a normal shutdown.  Units 1, 2, and 4 are not damaged; originally there were problems with the emergency cooling system, but these problems were fixed quite quickly, and the units are shut down and there is no further danger.  Even though these plants did not have to release any radiation, radiation levels were slightly higher than normal at the border of Fukushima Two (13.7 microSieverts/hr as of 12:00pm Japan time March 15) – perhaps because Fukushima One is nearby?

12. Can you explain – briefly and in plain English, please – how this kind of reactor works?

There are a lot of people who have done this for me.  See the following links:
http://www.boingboing.net/2011/03/12/nuclear-energy-insid.html
http://en.wikipedia.org/wiki/Boiling_Water_Reactor_Safety_Systems
http://enochthered.wordpress.com/2011/03/13/all-right-its-time-to-stop-the-fukushima-hysteria/

My own simplified recap:

For this reactor, the fuel is uranium oxide, which is a ceramic form (one report I saw indicates that one unit might have MOX fuel, which also contains plutonium oxide, but I can’t confirm that).  It’s shaped into mostly-cylindrical pellets that are about as big as the first knuckle on your pinky finger.

The fuel is contained inside cladding.  Cladding is a metal tube, made of zirconium in this kind of reactor, that surrounds a stack of fuel pellets.  It’s capped at both ends so the pellets are completely sealed inside, and it’s about as big around as your pinky finger but ~13 feet long.  Fuel pellets inside one piece of cladding = one fuel pin.

Fuel pins are held in a fuel assembly, which is a metal rack about 6 inches square by 13 feet long that keeps them in the right position.  Fuel assemblies are put into the reactor in another, bigger, rack to form the reactor core.

The reactor core sits down inside a big metal container called a pressure vessel.  It’s made of steel that’s ~6 inches thick.  The pressure vessel has pipes going in at the bottom where coolant comes in, and pipes going out at the top where steam goes out.  It’s also got some vents that only open when engineers tell them to (more on that later).

The coolant is regular water that moves past and through the reactor core (using the spaces in between fuel pins).  Yep!  Regular water.  It’s very, very pure to try to remove any minerals or anything that’s not H2O.  The water never touches the fuel – remember the fuel is sealed inside cladding – so there are no radioactive materials “leaking” into the coolant unless the cladding is damaged.  The water does get exposed to radiation, yes.  But that doesn’t make the water radioactive.  In order for a thing to become radioactive when it’s exposed to radiation, it has to “activate”, and only specific materials can activate.  H2O can’t activate[*], so the H2O going out of the reactor is just plain H2O.  Now, there’s always trace amounts of stuff in the water that *can* activate (like boron), so the coolant is very very slightly radioactive.
[*] Note that this is a simplification.  Oxygen-16 can activate into nitrogen-16, which has a halflife of 7 seconds.  So basically: if you take a cup of water out of a BWR and then sing “Twinkle Twinkle Little Star” it’s pretty much not radioactive anymore.

The reactor works because the reactor core gets hot, and the heat boils the coolant (water), and the steam goes out the top and into the turbine building where it turns a turbine, and the moving turbine runs a generator, and yay electricity!  When the steam goes out the back end of the turbine, it gets condensed back into water and pumped back into the bottom of the reactor to be boiled again in a closed loop.  If you’ve ever seen a tea kettle with the little whirligig on the spout, that’s exactly what happens, only you it’s like you reroute the steam back into the bottom of the kettle.

So we have the reactor core and the coolant inside the steel pressure vessel.  The pressure vessel sits inside a giant thing called the containment structure, made of concrete and lots of steel rebar.  It’s usually 4-8 feet thick.  (That’s a lot, y’all.)  The containment structure is completely sealed up; nothing (not even air) goes in or out unless they intentionally open a hatch.  (The coolant goes in and out through pipes that snake through the containment structure; they are big and huge pipes.)

Now, what makes the fuel hot?  Short answer: Uranium and plutonium in the fuel can fission (break apart), and when they fission, they produce moving particles (neutrons and fission fragments), and the moving particles hit other things, and the hitting-things produces heat.  There are two things that make uranium and plutonium fission: they do it spontaneously at a low level (because they are naturally radioactive [**]), and they do it when neutrons hit them in just the right way.  A fission chain reaction works like this: since fissions create neutrons, and neutrons can create more fissions, if you set everything up just right, you can get a reaction that’s self-sustaining.  That’s what makes a reactor run.  To stop that reaction, you do something that makes the neutrons not hit the fuel as much – in this case, you put control rods in the reactor and the control rods sort of soak up the neutrons that are whizzing around and the whole thing slows down.
[**] Although note! Not all radioactive elements fission; fission is just one way to be radioactive.

Let’s recap for just a second at this point:  There are three physical things standing between the radioactive fuel and someone at the main gate of the plant.  The first is the fuel cladding on each of the fuel pins, made of zirconium.  The second is the pressure vessel, an 6-inch thick steel container.  The third the containment structure, a 4- to 8-foot thick construction made of concrete and rebar.  All of these are air-tight and radioactivity-tight.  There is also the reactor building, also made of concrete, but this one isn’t air-tight.

13. So what happened in the accident?

This description is (generally) of Fukushima One Units 1 through 3.  Fukushima Two Units 1 through 4 started out the same, but they were able to restore cooling much earlier.  (I don’t think they lost their backup diesel generators at all.)
First, the control rods automatically dropped into the core of the operating units in what’s called a scram.  The control rods went all the way in, and brought the fission reaction in the reactor screeching to a low level.  [Safety system #1 (control rods): worked as designed.] At this point the reactors were in “hot shutdown” – the reactor was producing somewhere around 4-7% of full power, and the temperature of the coolant was still at normal operating levels (about 550 F).  The power level in the reactor will normally coast down from there over the next couple days until the power level is around 0.5% of full power.  (You can’t get it to go lower than that without pulling all the fuel out, remember, because the fuel does do some spontaneous fissions.)  This point is called “cold shutdown” – when the temperature of the coolant is less than boiling (212 F).  When you’re in cold shutdown, you almost don’t need to run the cooling system anymore.

During either kind of shutdown, the fuel is still producing heat.  You have to keep the cooling system going the whole time to keep pulling heat away from the fuel so that the fuel doesn’t overheat and damage itself.  BUT you just shut down your reactor that produces electricity, so how are you running your pumps?  Answer: Pumps are usually run using power from the offsite power grid, not your onsite reactor.

It’s expected in earthquakes (and other accidents) that the power grid might get damaged, and that offsite power being supplied to the power station will stop.  So there are backup diesel generators to run everything you need to run onsite: pumps, valves, control panels, etc.  It appears that after the earthquake, the connection to the Japanese power grid dropped (as expected) when the tsunami washed away the power lines.  And the backup diesel generators kicked in. [Safety system #2 (backup diesel generators for cooling recirculation): worked as designed.]

But then after about an hour the diesel generators at Fukushima One failed, reportedly due to damage to the fuel supply from the tsunami.  [Safety system #2 (backup diesel generators for cooling recirculation): temporary problems due to MASSIVE TSUNAMI.]  This meant there was nothing to run the cooling system at Fukushima One Units 1, 2, and 3.  Heat began to build up in the reactors, and the heat boiled the coolant, and the coolant turned to steam, and the pressure began to build up in the pressure vessels.  Why is this a problem?  Two reasons:  one, the increase in pressure could eventually cause your pressure vessel and associated piping to give way (like a popping balloon), and two, fuel that’s not actually underwater gets hotter much faster and could get hot enough that it fails (gets holes in the cladding).  The more coolant that boils into steam, the more the coolant level drops (like boiling a pot of spaghetti), and eventually the reactor would boil dry if you didn’t stop it.  (And then you would melt your spaghetti, I mean fuel.)

This sort of event is also planned for: first, you have some time before things get really iffy (pressure too high or water level too low) during which you can restart cooling, and second, there are a bunch of other things you can do in the meantime.

One of them is you have things that can act as a heat sink – basically large pools of water.  However, they’re sort of one-time use; once you heat them up, you have to cool them down before you can use them again.  These were used and they worked.  [Safety system #3 (automatic depressurization system and isolation condensers): worked as designed.]

One of them is you can add more (cold) coolant while the system is at full pressure.  The pumps to do this run off of steam from the reactor (neat, right? The fact that the reactor is getting hotter automatically powers the thing you need to make it colder).  This ran just fine, and more coolant was put in.  [Safety system #4 (high pressure coolant injection system): worked as designed.]  There’s also a second (less powerful) system that puts more coolant in, that runs off of batteries.  They ran that too.  [Safety system #5 (reactor core isolation cooling system): worked as designed.]  However, the control valves that this new coolant runs through work off of batteries.  After eight hours, the control valves lost power because the batteries ran out.  [Safety system #6 (battery-operated control valves for RCIC line): worked as designed to the end of design lifetime.]  Solution: replace the batteries!  But they ran through all the batteries they had, and were having problems getting more because of all the earthquake damage in surrounding regions.  Hours passed, during which the core kept heating up and coolant kept turning to steam.  Then they got a delivery of portable diesel generators and were able to start a different backup pumping system to top up the coolant in the core.

One of them is you can vent coolant into the space between the pressure vessel and the containment structure.  You open a hatch, and steam goes out, and yay!  Pressure reduced back to safe operating levels.  At this point the steam is still mostly just steam (only very slightly radioactive), because your fuel cladding is still intact.  It’s also trapped in the containment structure and hasn’t been released to the environment yet.  So they vented steam to the containment structure.  [Safety system #7 (pressure vessel venting): worked as designed.]

So there’s lots of stuff that was being done, to buy time to get the cooling recirculation working.  But the longer your reactor sits without cooling, the more you risk the water level dropping to uncover the fuel rods, and the more you risk those fuel rods overheating.  When your fuel rods get uncovered, two things can happen.  One, the cladding can fail – usually because it gets so hot that it can’t take the strain, and it splits open.  Two, even if the cladding doesn’t fail, the high temperatures and the steam can cause it to oxidize – basically, to rust – at an accelerated rate.  This is important because the oxidizing reaction takes H2O and turns it into oxygen (bound up in the zirconium oxide) and hydrogen.

And this is in fact what had happened, while they were sitting there with no power waiting on the delivery of new diesel generators – the cladding in some of the fuel rods failed, exposing the fuel, and the cladding started to oxidize, creating hydrogen.  [Safety system #8 (cladding): functioned as designed for a very long time and then conditions changed causing it to partially fail.]  Now the steam in the reactor was slightly more radioactive, because bits of the fuel were touching the steam, and particles could be picked up and carried with the steam.  But this wasn’t very much radioactivity (way below guidelines for exposures to the public), pressure in the pressure vessel was still rising, and the containment structure was still intact and airtight.  So they made the decision to continue to vent radioactive steam to the containment structure.  [Safety system #9 (containment structure): worked as designed.]

If you keep doing this, eventually pressure will also rise in the containment structure.  So you can vent the containment structure, too.  Many plants have a design where the containment structure can be vented into the reactor building that surrounds the containment, so that you are sequestering any radioactivity.  The reactor building isn’t airtight, but it’ll keep the vast majority of radioactive release from getting out to the environment.  So they vented radioactive steam to the reactor building.  [Safety system #10 (reactor building): worked as designed.]

But remember, the cladding rusting made hydrogen.  Hydrogen, you might recall, is flammable.  So the hydrogen went along with the steam, from the pressure vessel (which had no oxygen gas in it), to the containment structure (which had no oxygen gas in it), to the reactor building (which had normal air in it, and normal air contains oxygen gas).  And if a bunch of hydrogen ends up somewhere that there’s a bunch of oxygen, then it can go off like the Hindenberg (only smaller).

So the next thing that happened was there was a hydrogen explosion in the top of the reactor building for Units 1 and 3 – or rather, in the metal shed at the top of the reactor building, since the reactor building isn’t airtight and all the hydrogen rose.  The shed collapsed, releasing the small amounts of radioactive steam that had been vented there (and more impressively, explosion and loud noises and ooh fire and smoke!).  Important to note at this point: the pressure vessel and containment structure are still intact – there is no direct line from the fuel to the environment.  The only radioactivity that was released was the slightly radioactive steam that they previously chose to vent from the pressure vessel and containment.

At this point they chose to go with another option they had had all along.  This option, however, was sort of the last-choice option:  adding seawater to the pressure vessel, and if needed even filling the containment building structure with it.  This option was designed into the plant as yet another safety system, in case they ever had a situation where they needed mass amounts of coolant in a short time.  And it sure is working:  Units 1 and 3 have stable pressure as of this writing, and water levels appear to be about halfway up the fuel rods and rising; Unit 2 is slightly behind but also improving.  [Safety system #11 (emergency seawater injection system): worked as designed.]  So why didn’t they do this from the start, or at least as soon as they got electricity back to run the pumps?  Because putting nasty, gummy seawater, with minerals and algae and who knows what else, into your nice clean shiny reactor is about like putting sugar in a car’s gas tank.  It’ll stop the car, alright – and then you’ll have a massive repair bill.  Units 1, 2, and 3 at Fukushima One will not run again unless most of the components of the reactor are replaced.

14. So why did I overhear you say to that person that this was actually a success for nuclear power?

First, at magnitude 9.0, this was one of the top ten strongest earthquakes in recorded history.  (Wow!)  The subsequent tsunamis, combined with the earthquake, make this one of the worst natural disasters EVER.  (Also Japan is apparently having a minor problem with a volcano, now.  Guys can’t catch a break.)

The reactors were designed 40 years ago, and in 2008 were certified for ground motion corresponding to about a magnitude 6.7 earthquake right under the plant.[11]  The reason this ground motion was selected was that Japan’s regulatory agency expected (rightly so!) that a ground motion stronger than that had a chance of happening only once in 10,000 years.  We lost the statistical gamble on that one.  But here’s the amazing thing:  the reactors did exactly what they were designed to do: and so did the other nuclear units all over Japan.  Only 7 of the 55 units in Japan [7] had any trouble shutting down, and they were the ones closest to the epicenter.  And the trouble wasn’t even in the reactor, or the containment structure, or the piping – all of these things performed exactly as designed!  The trouble was the tsunami that took out the fuel supply for the backup diesel generators.  Let’s recap with a statement from Steve at Neutron Economy: “What this proves is that in the very worst scenario – a once-in-a-lifetime earthquake beyond the design basis – that the systems can safely contain the integrity of the reactor, particularly with well-trained personnel”. [5]

Second, these plants are 40 years old.  They don’t incorporate all of the safety advances we’ve made since then.  As a matter of fact, I read that these particular plants were already planned to be replaced with newer designs – designs that have passive cooling and wouldn’t have required any electricity to cool the core at all.  (Can’t find the reference right now, sadly.)  The fact that a 40-yearold design survived as well as it did – with no health impact to the public expected – is pretty awesome.

Third, as Rod Adams points out [2], let’s keep this in context with regards to the damage to, and impacts of, the other energy sources in Japan.

Damage from the earthquake and tsunami includes a fire at an oil refinery that is still burning; breaks in a hydroelectric dam, explosions in natural gas systems, and tons and tons of battery and gasoline spills.  There is damage to the environment and danger to people from every form of energy that we use today.

So nuclear’s looking pretty good, right now.  Fear aside, I think we’re going to end up with the least damage to life, health, and the environment out of all the energy sources in use in Japan.  (Except solar.)

15. Where can I get more information?

My best recommended sources for updates right now:

For commentary and help understanding the updates, go to:
http://www.mutantfrog.com/2011/03/15/radiation-safety-update/ – Dunno who this guy is, but he’s doing his research.

For forwarding to your non-sciency friends and relatives, use this:
http://online.wsj.com/article/SB10001424052748704893604576198421680697248.html

And for forwarding to your sciency friends and relatives:
http://enochthered.wordpress.com/2011/03/13/all-right-its-time-to-stop-the-fukushima-hysteria/

16. Show your work!

My references:
[1] http://en.wikipedia.org/wiki/Three_Mile_Island_accident
[2] http://atomicinsights.blogspot.com/2011/03/nuclear-plant-issues-in-japan-are-least.html
[3] http://www.dailymail.co.uk/news/article-1366341/Japan-tsumani-earthquake-America-nuclear-accident-radiation-alert.html
[4] http://www.jaif.or.jp/english/news_images/pdf/ENGNEWS01_1300189582P.pdf
[5] http://neutroneconomy.blogspot.com/2011/03/fukushima-in-laymans-terms.html
[6] http://www.telegraph.co.uk/news/worldnews/asia/japan/8379969/Japan-earthquake-US-aircraft-carrier-sails-into-radioactive-cloud.html
[7] http://www.japannuclear.com/nuclearpower/program/location.html
[8] http://en.wikipedia.org/wiki/Timeline_of_the_Fukushima_nuclear_accidents
[9] http://twitpic.com/49mm4l; see also  http://en.wikipedia.org/wiki/Radiation_poisoning
[10] http://www.world-nuclear-news.org/RS_Possible_damage_at_Fukushima_Daiichi_2_1503111.html
[11] http://www.scribd.com/doc/50728751/New-Microsoft-Word-Document
[12] http://www.physics.isu.edu/radinf/risk.htm
[13] http://news.blogs.cnn.com/2011/03/16/japan-quake-live-blog-death-toll-expected-to-rise-as-crews-reach-more-areas/
[14] http://www.nytimes.com/2011/03/16/business/global/16insure.html?src=busln
[15] http://www.wolframalpha.com/input/?i=490+microsieverts

Posted by PEN at 11:16 AM

Category: Energy, Think Tank

Please use the comments to demonstrate your own ignorance, unfamiliarity with empirical data and lack of respect for scientific knowledge. Be sure to create straw men and argue against things I have neither said nor implied. If you could repeat previously discredited memes or steer the conversation into irrelevant, off topic discussions, it would be appreciated. Lastly, kindly forgo all civility in your discourse . . . you are, after all, anonymous.

5 Responses to “Yet Another Japan Reactor Post”

  1. wongjames61 says:

    can they just put a weigh (right shape) around a long flexible tube and drop it on top of the reactor(s), and pump water from a safer distance for a longer time, afterall they don’t really need a lot of water to cover the used fuel rod ?

  2. KidDynamite says:

    Now Barry – I don’t want to, in your words on the Oehman post: “blindly believe this post, or re-tweet it,” so please enlighten me: is this post also part of the grand GOP pro-nuclear astroturfing conspiracy? Or is this one ok because the author has more nuclear expertise?

    The thesis – that things are nowhere in the realm as bad as the layman would think from reading the 16 point headlines (like the one on NYTimes.com as I type this: “HIGH RADIATION SEVERELY HINDERS EMERGENCY WORK TO COOL JAPANESE PLANT” in the mainstream media – seems very much in line with Oehman’s thesis.

    please help.

  3. Equityval says:

    This post is generally good, but has one gaping flaw – it gives no consideration to the potential for unrestrained release of radiation from the spent fuel pools especially in units 3 and 4 which sit OUTSIDE the containment building. Depending on whether you believe the NRC’s version’s of events or the Japanese govt’s, the pool in unit 4 is either partially empty or totally empty, meaning the fuel is on a path to melting. Moreover, it appears that at least some of the fuel in the pool was not spent, but merely “resting” between stints in the reactor while the it was down for maintenance. Yesterday, TEPCO said there is a remote, but greater than zero chance that the fuel in the pool could reach “recriticality” which for you civilians out there is a nuke weasel word for beginning a fission reaction. In other words a disaster scenario. On a grading scale, we’d have to give this an incomplete and send him back to the library for further work.

  4. JohnathanStein says:

    Author makes a valiant attempt at reasonable explanation — it almost works. After reading, most folk’s would get that nagging feeling he’s a bit too much of a POLLYANNA, and has NOT given clear answers to some basic questions:

    1. OK, so just WHY are reactors on fire, WHAT is burning (when the only possible fuel is radioactive) and how much is being released into the air, settling onto the ground and will contaminate the ocean?

    2. The theme of “Don’t worry, it’s contained” has been heard before — tell me again why are they evacuating the area at all, advising 100,000+ people (with destroyed homes) to stay inside, detecting radiation in Tokyo, pulling most workers out and limiting exposure for those who are left?

    3. This guy has totally ignored the political B.S. factor involved — we haven’t heard the BASIC FACTS of whether/how much radioactive CESIUM, IODINE and STRONTIUM has been released. If they can detect radioactivity in Tokyo, they know more than they’re saying; most of us have gut feel for when something’s false or missing — TPTB over there are sure as heck hiding known facts.

    Yes, it’s all well & good that safety systems all worked in the face of two incredible natural disasters, earthquake and tsunami, but this whole post could & should be reduced to a dozen bullet points — leaving room to analyze and quantify the open questions listed above.

  5. DeDude says:

    As an attempt at trying to defend nuclear power (and it doesn’t really hide that purpose) it is not that bad. As an attempt at explaining what is going on over there it really fails at a lot of levels. The real problems appears to be with the storage pools not the reactors themselves. How can we be sure that the assumption of intact containments are correct. There are still lots of unknowns and unanswered questions. When I see someone who makes the most benign assumptions regarding all the unknowns and unanswered it reminds me of the designers of these plants. They should have presumed the worst to be prepared rather than ignoring worst case scenarios and thinking that the cheap design could work. One simple question is why did the not have emergency generators protected from water, and backup emergency generators placed both in basement and on roof, and a spare set with long cables placed in a separate adjacent building, and another mobile generator on a 4 wheel drive military truck with a huge diesel tank stationed in a protected area 5 miles away up in the mountains. Same thing with water delivery systems they should have had backup of backup of backups knowing how critical access to water and electricity would be. But that require that you remain critical of your own systems rather than developing a defensive attitude. That is why most systems require an independent outside regulator.