Wednesday, March 23, 2011

Making Sense

The nuclear crisis in Japan is scary, a lot of potential for disaster. The fury of media coverage has been nice and I feel for the most part, they are showing a good deal of useful information to explain the situation. Yesterday I sat in on a session led by two nuclear engineers and medical physics expert who gave a no frills assessment.

Surprisingly, the scientific level of these media coverages is pretty intense, lots of jargon. I thought I'd do my part and briefly explain some key elements to nuclear reactors.

What is a nuclear plant?

Power plants using nuclear fuel are just a reinvention of the mousetrap. All power plants do one thing, make steam to drive a turbine. That spinning turbine makes electricity and the means to do that though varies. In reality, all power plants carry the risk of explosion because they all handle high-pressure steam.

Firstly, nuclear reactor plants do not explode on account of their nuclear fuel. There just isn't enough percentage of radioactive substance to trigger the massive explosions we're familiar with.

How do they work?

Nuclear reactors work by using a small yet critical amount of radioactive material that creates a chain reaction. When all of the variable line up the reaction produces heat, which can be used to boil water.

Nuclear power plant cooling towers. These are just big tubes where the steam is recycled. There is a perpetual rain shower inside due to the steam climbing, cooling, and then raining back down. The plant then re-heats the water and makes electricity once more.

Fuel Rods: These are the main source of energy and contain the primary radioactive materials used to create the heat. They are triggered by neutrons. When neutrons are flying around the fuel rods, a lot of energy is being released.

-More info about the entire fission process as a result of neutrons HERE Someone has already said it better than I could.

Control Rods: These are neutron absorbing rods that can be inserted into the chamber where the fuel rods are producing heat. The control rods help stop the bombardment of neutrons and can stop the reaction in the fuel rods all together.

A simple diagram showing the basics of nuclear plant designs

The bottom line: Japan's reactors are in danger due to power failures. The plant's main power supply was damaged as a result of the earthquake and tsunami. The facility did have backup battery power but those eventually ran out. Without the electricity they were not able to keep the water pumps running.

These water pumps are essential in keeping a continuous supply of cool water to absorb the heat and keep things at a manageable temperature. If they cannot be cooled, steam builds and so does the pressure inside the reactor core and housing. The engineers are able to release some of the steam but that is risky because it's a direct release of radioactive materials into the atmosphere.

Some tech'ier stuff:

The Fukushima Daiichi plant reported that once they detected seismic activity they began the fission shutdown process. Inserting the control rods successfully stopped the primary fission process in all 6 reactors. Within the fuel rods though are highly-radioactive elements that continue decaying and radiating large amounts of heat.

There is also the issue of hydrogen gas buildup as a result of water oxidizing with the metals in the reactor. Hydrogen gas is very flammable and can be cause for more troubles.

Something unclear? Science need a little tweaking? Let me know in the comments.


  1. Informative post, Eric. I hadn't seen a clear explanation of the setup, so this was a nice description. Do you have a feel for whether the scientists who work on nuclear power are as worried about outcomes in Japan as the media portrays?

  2. Great job, Eric. I linked to your coverage in my most recent post.

    I do have a question concerning the backup pumps in nuclear plants. Why weren't they effective in this case? I remember reading something about them not activating... Do modern plants have differently engineered backup systems?

  3. Gee -- thanks for turning your authentication thingy off!

  4. Great information, its important to understand how nuclear power works in order to talk effectively about it in terms of energy policy!

  5. Thanks for this breakdown, Eric! There definitely needs to be much more of this kind of explanation to the public, to help them better understand nuclear energy...or any type of energy for that matter. I did an energy field trip last summer, and while I already knew I didn't know anything about energy, I learned how much I actually didn't know!

  6. Is there any other way to cool the rods? When it comes to something with the potential for such potent disaster, you'd think they'd have more safety or backup mechanisms than a few backup batteries that can "run out."

    Also, I appreciate the Simpsons picture. Did you know that every time they show the plant on an episode a bird chirps? Watch/ Listen for it.

  7. Not rods, what I mean is, is there another way to cool the plant?

  8. Thanks for this description, Eric. I had no idea how a nuclear plant worked so this was helpful to read.

    What's your take on the backup battery power situation? It's hard for me to fathom why the plants didn't plan to have a longer supply. Was this simply a matter of poor emergency planning or is there science I'm missing here?

  9. this was an informative post Eric. I think I understood the basic elements of the challenges that a nuclear plantation may cause. I think I agree with Amy's question: the strategy a plantation should use if the battery power fails.

  10. Great post, Eric! For non-sciencey folks like me, you did a great job of explaining in Lehman's terms what nuclear reactors are and the background of the nuclear crisis in Japan at this time. Very scary stuff.

  11. Very clearly told, Eric. I'd like to see you respond to some of the questions in the comment section but the strong response is a real compliment.

  12. To answer a few questions, the plant has backup power supplies but the station where the extra generators are housed was not built for a resultant tsunami as large as the one that hit. In a bad turn of fate, the protective wall around the power generator was something of a ~8.0 proof barrier. The generators were flooded so that left just the batteries which eventually ran out.


    As seen in reports, many of the efforts to cool the reactors were to physically dump water on them. Helicopters would fly over and drop large amounts and firetrucks could spray from afar. These are desperate efforts to keep things under control. Recently, amounts of radioactive water have been measured in the nearby area, evidence that the holding tanks and reactor housing units were damaged and cracked during in the quake.

  13. Well explained, I like the diagrams. I've been seeing a lot of explanations of the process and what has gone wrong at Fukushima in the media. The tension is going to be palpable for some time. The double dose of quake and tsunami spelled doom here, but I understand that they were warned in recent years.

  14. What a great design, I also really appreciate that you decided to do it your way.

    load bank testing & generator maintenance