Its been almost 2 months since the earthquake and tsunami disaster in Japan, and we’re not seeing a lot of coverage of what is going on at the Fukushima nuclear power station these days. So, I’m going to give a brief review of what happened in the first days after the earthquake and tsunami, and then what has been done since then to stabilize the plant. I will write a future post to outline the current plans to continue bringing the situation under control, as well as the impacts on people and the environment. I will assume that anyone reading this has already read my previous posts about Fukushima here and here and here and here, and so I will assume you are familiar with the terms, units and technologies I will be describing. Continue reading
Tag Archives: nuclear power
I hesitate to say it, but it looks like things are beginning to stabilize at the damaged reactors in Japan. Brave New Climate has a round-up of the latest. At least some off-site power is available at the plant, a generator is working, radiation levels are falling, and containment is holding pressure. Call my extremely cautiously optimistic.
MESSENGER will be entering into orbit around Mercury this evening. Watch video from the control room here, along with updates of mission milestones.
And, the UN has passed a resolution to impose a no-fly zone over Libya. And I’m no diplomat, but it seems to authorize airstrikes as well, stopping short only of calling for an invasion. I expect Qadhafi’s tanks and artillery to be taking a beating shortly. Full text here, and BBC overview here.
We live in interesting times.
Contamination – This is what happens when you get radioactive material on you, or anywhere it’s not supposes to be. It sits there giving off radiation that can then harm you. It’s why you see all those folks wearing the full body cloth suits that look like the belong in a hospital or electronics plants. The suit doesn’t stop radiation at all (well, it will stop some kinds, but we don’t need to worry about that right now). It keeps all the radioactive material on the outside of you where the suit can be thrown away. Well, it’ll be bagged and stored as radioactive waste, not just thrown in the can.
Exposure – The amount of radiation that has penetrated an object. This is a measurement of the amount of energy the radiation deposits per unit mass of a material.
Dose – A measurement that approximates how much damage a given exposure of radiation will cause to biological tissue. Different forms of radiation can deposit the same amount of energy into a person, but will cause different amounts of damage.
Sievert – The SI unit for measuring radiation dose. One Sievert, abbreviated Sv, is a lot of radiation, enough to cause radiation sickness. Five Sv can cause up to 50% of people who get that dose to die. A milliSievert is 1/1000th of a Sv, and a microSievert is 1/1,000,000th of a Sv. Dose is cumulative, it adds up over time. For example, if you work in an area with radiation levels of 50 milliSv per hour for 10 hours, wou will have a total acute (short-term) dose of 500 mSv, or 0.5Sv. At Fukushima last I heard they are allowing the workers to get up to 250mSv, up from the normal limit of 100mSv. For perspective, a chest x-ray is about 500 microSv, or 0.5mSv.
Ok, that’s it for now. As always, any questions, ask away.
Got home a bit late tonight, so I’m just going to post some links to stuff I found interesting.
This Slate article is a few days old, so it doesn’t mention some of the more recent bad news about the nuclear reactors in Japan, but it has some good perspective.
Another blog post with corrections to some common misconceptions about the disaster in Japan.
And good ol’ Scientific American has this article on relative radiation release between coal and nuclear plants.
I know everyone is hearing lots of nuclear terminology being thrown around in the news right now, and I wanted to spell out some definitions, as I’ve seen several terms misused by the media. If you really want to see everything spelled out, check out the US Nuclear Regulatory Commision’s definition webpage. I’m going to assume a high-school level of education concerning what an atom is, what its made of etc. Again, as always, please ask for any clarifications if necessary.
Isotope – Elements, like in the periodic table, come in different varieties called isotopes. These isotopes of a material behave chemically exactly the same as each other. For instance hydrogen has three isotopes, H, H2 or deuterium, and H3 or Tritium. They all behave the same, and a small portion of all water actually contains deuterium instead of ordinary hydrogen. Tritium is radioactive, meaning that over time it will give off radiation, in this case a neutron, and become a different atom, deuterium. There are many isotopes for each element, only some of them radioactive. For instance, our bodies need iodine to be healthy. Most of us get this through iodized salt (look in your cupboard). However, nuclear reactors produce a radioactive version called I-131. Because its chemically identical to the normal iodine we need, your body will suck it right up and it will accumulate in your thyroid. However when it gets there it will continue to bombard your body with radiation over time. This is bad. So if you fill your body up with iodine, from tablets or however, you will absorb less of this radioactive iodine.
Radiation – High energy electromagnetic waves (like visible light, but much higher energies) or high-speed sub-atomic particles. Radiation is produced by nuclear reactions like the fission inside a reactor or the decay of radioactive materials (see below). In the nuclear power field, radiation refers specifically to ionizing radiation. This means that the radiation is of a high enough energy to ionize materials, or to strip away the electrons from the atoms in a material. This is bad for living things because these ionized materials in your body, mostly water, are chemically reactive and will damage your cells in a number of ways. This ionized water can also break up DNA in cells, potentially leading to different kinds of cancers. However, radiation can be stopped with different kinds of shielding, depending on the kind of radiation. Also, like a lightbulb is dimmer the further you are from it, the radiation from an object lessens the further away from the object you are, proportional to the inverse of the square of your distance (doubling your distance reduces the radiation by 4 times).
Radioactive Material (RAM) – This is any material that contains a substance that is radioactive. I kinda covered this above under radiation. Radiation is given off by radioactive material. This is the stuff you want to keep contained and away from the public. This is all the nasty stuff inside the fuel rods of a nuclear reactor for example. It also refers to to anything that has been contaminated by any radioactive substance. For instance, if you get some cobalt-60 ( a radioactive metal) on your clothes, your clothes would have to be removed and treated as radioactive material. A lot of the radioactive waste produced by nuclear power plants is of this type of material.
Whew, this is taking more effort than I was expecting. I’ll continue more tomorrow, Chey is probably wondering where I am.
I was going to write a long, in-depth post explaining in detail how a nuclear reactor works and give more info on what is happening in Japan, because I feel the stuff most of you are seeing on TV or online is written by folks with little or no background in nuclear power. I think for the vast majority of normal people, nuclear power is a big unknown. And big unknowns are worrying. The thought that something which is completely undetectable to you without expensive equipment can kill you is a source of many genuine fears. I think the best way to allay those types of fears is by information. The facts. The cold hard truth.
An old friend of mine from the navy, Gabe posted a link on Facebook to another blog that does exactly what I was planning to do. It’s called Brave New Climate, and the author is a published scientist and professor at the University of Adelaide in Australia. I recommend you head over there and do some reading. It’s a bit of a long read, but very useful.
I will do a small post later today or tomorrow just on terminology to clear up some things you may be hearing. Please if you have any question, please ask. This stuff is complicated and difficult to pick up without formal training, so there is no shame in asking what you think is a stupid question. Ask away here on my blog in the comments, on my Facebook, or send me a PM if you don’t want anyone else seeing what you write. I won’t tell unless you let me. Thanks.
The BBC has a pretty decent article on the damage to one of the nuclear powerplants in Japan. The type of reactor involved is a BWR, or boiling-water reactor. The Wikipedia article on these is a bit long, but it operates somewhat like a hot water heater in your house. A nuclear core (2 below) produces heat to boil water (7) into steam (6). That steam is used to spin steam turbines (8 and 9) (like big windmills in theory, but not quite) to produce electricity (10). The steam is then condensed (12) back into water and is sent back into the core (15).
With the earthquake they lost electrical power at the station. This caused the cooling water pumps to stop running. The reactors were automatically shutdown, but because the reactor is full of radioactive material that continues to decay, decay heat continues to heat up the core. They started emergency diesel generators to get those pumps restarted, but those generators apparently cut out shortly after starting. They got temporary generators started eventually for reactors 1 and 2, but not 3.
So, without any cooling, the water left in the core starts to boil off. Think a boiling pot of water. If you put a lid on it, the pressure increases until the lid pops off to relieve that pressure. Reactors have built-in relief valves to relieve this kind of pressure into a containment area. Which appears to be what happened. Here’s where the bad stuff starts. The reactor can get so hot from decay heat that it breaks down the water into hydrogen and oxygen. Well, in this case the hydrogen, oxygen and some spark look to have caused an explosion damaging or destroying the containment (the gray boxes in the above diagrem) for reactor 1, and the fears are it may happen at reactor 3 as well.
This means there may not be a barrier keeping all radioactive material from the reactor from escaping to the environment. The BBC article mentions they’ve detected radioactive cesium. That is potentially very bad. Cesium is a fission product (it is produced by the splitting of uranium fuel atoms) and should be locked up inside the fuel elements inside the core. If we’re detecting it, it might mean that some fuel elements have ruptured. With the possible loss of containment from that hydrogen explosion, we could see the release of some pretty nasty radioactive materials from that reactor.
Now the situation is not hopeless. It sounds like the reactor core and vessel (1) are still intact. The release of radioactive material is most likely from those relief valves I mentioned earlier. So, if you can get the pressure under control so that it doesn’t open the relief valves, you won’t be leaking any radioactive material into the open. The heat produced by the radioactive material in the core decays away exponentially, so as time gone by the situation should get better by itself. Whether that is fast enough to prevent the release of a lot of bad stuff is another story. However, they are apparently flying in spare generators to try and get the cooling pumps running again as well.
So, long story long, this situation is a bit worse than the three-mile island disaster already. It is nowhere near as bad as Chernobyl. I don’t expect things to get much worse at this reactor, but clean-up will be a huge undertaking. Please, ask any questions you might have, and I’ll try to answer them.
EDIT: And as always, it pays to go to the professionals, and not rely on 2nd/3rd hand reports. International Atomic Energy Agency website with updates on Japan.