Another Look at the Nuclear Situation in Japan, Part III
For those following, here is Craig’s third update:
I started these updates when there was not a lot of good information available and when the various media outlets were reporting everything but the science, leaving many people confused. There are a lot of good reports out there now, so I’ve felt less of a need to keep up. The New York Times, NPR, and the BBC are doing a great job on all fronts, so you can read as much as you like on your own, but I did have some things I wanted to discuss.
As far as anyone can tell, the fuel rods have been damaged to some degree, which makes this a partial meltdown. We can’t know for certain what’s going on inside the reactor until it’s cool enough to physically inspect, but we have a good idea. The main way we know that there’s been fuel damage is the presence of cesium-137 and iodine-131 outside of the plants, as far away as 60 miles. These are byproducts of uranium fission but should not be released in ordinary functioning. The damage to the fuel means that the byproducts can mix with the water in the reactor and are getting dispersed into the air in low doses when the steam is vented in order to keep the pressure down. Cesium-137 is chemically similar to potassium (not calcium as I stated in an earlier post) and can take the place of potassium in mussels if ingested; this is, of course, bad because it emits high-energy gamma radiation that is very harmful to the human body. Iodine-131 is chemically identical to regular iodine, which is used in the thyroid gland; the unstable radioisotope similarly emits gamma radiation and is associated with thyroid cancer. That’s why they’re distributing iodine capsules around the evacuation zone: if you take a high dose of regular iodine, your body will incorporate the nonradioactive version where it needs it, and it will not use the radioactive isotope.
The various reactors at Fukushima are emitting radiation 1,200 microSieverts/hour, which is twice the legal level in Japan. Now the legal limit is conservative, so doubling it is not catastrophic, but if the plant continues to emit radiation at this level, there’s evidence that this could lead to higher levels of cancer and birth defects in nearby populations. Although I have explained the dangers of iodine-131 and cesium-137, it is worth noting that most of the radiation being leaked is NOT from those sources, but is rather being produced by tritium (a radioactive isotope of helium) and a couple of other MUCH LESS DANGEROUS sources.
Since the reactors are still very hot and the whole system which usually regulates the temperature by leading away the steam and introducing cold water has stopped functioning, the only way to cool the reactor is to add more and more cold water. My earlier rosy prediction about the level of the disaster was based on the belief that they could get the backup systems to circulate water online relatively quickly, but this was not the case. The tsunami did not just damage the backup generators, but flooded the entire area where all the backup equipment was located, making it even more difficult to set up. The technicians and experts eventually decided that the controlled venting of gases was not good enough and so they flooded the whole reactor with a mixture of seawater (presumably because they’re next to the ocean and it’s available) and boron (sometimes they’ll say boric acid, but that’s just the compound they’re using). Boron absorbs neutrons and is sometimes used to make control rods, so by flooding the reactor with boron they’re essentially increasing the number of control rods to slow down the reactions even more.
They cannot add water indefinitely, however, because that increases the pressure; water becomes steam and if the steam has nowhere to go, the building pressure could damage the reactor vessel. So, they continue to vent gases, some of which goes into containment structures (especially the turbine hall) and some has to go into the atmosphere. A number of processes going on lead to the build-up of hydrogen gas, including the application of heat to water which sometimes splits the atoms apart rather than changing phases to steam. It’s also possible that the damage to the fuel could have allowed for different types of reactions, such as a reaction between the water and zirconium in the reactor, to increase hydrogen production over what we would normally expect. The gases were vented into the turbine hall where the steam to run the power plant would normally go and it’s there (apparently) that the hydrogen exploded. The walls of the turbine hall blew apart the way they were designed to do because otherwise, if they held, pressure would not be sufficiently. According to all reports, the explosion did not damage the containment vessels at either of the two sites where explosions occurred.
When I said that a meltdown was a remote possibility, I was operating under extremely limited information and was thinking about more of the colloquial implications of a meltdown (which makes people think of Chernobyl) rather than the technical definition (by the way, there is no technical definition, but I take it to mean here any damage to the fuel rods caused by heat from loss of cooling). This is not a “complete meltdown”, which refers to one where containment is loss and the core is open and free to spew radiation into the environment. It is a contained partial meltdown, more like Three Mile Island than Chernobyl. The current events are easily the largest nuclear disaster since Chernobyl, itself the largest nuclear disaster in history. It is currently, I think, less hazardous than the Windscale fire of 1957 (yeah, I know you’ve never heard of it), which led to the release of much more radiation than is currently happening and, as far as I can tell baring a further revelation, going to happen.
If the whole experience scares you away from nuclear power, I could completely understand. This could have been and still could become much, much worse. I think it’s worth noting, however, that this is a nightmare scenario: an aging reactor struck by an earthquake and a tsunami, losing coolant, and starting a partial meltdown, and, in fact, partially blowing up, but it’s only releasing twice the legal level of radioactivity. If you think of the number of things that had to go wrong before they had any problems at all, I think it’s quite remarkable.
The process of cooling will continue for weeks to come, and radiation could continue to be released for the entire time. Every time it looks like they have something under control, something new happens, so it’s hard to say. There is not really enough information being released for someone with as little technical knowledge as me to assess the situation any more than this. There are suggestions by experts that the Japanese have made a couple of mistakes during the crisis (primarily waiting too long to start venting gas because they feared public outcry), but most of the mistakes seem to have been of design. The seawalls that are supposed to protect the plant were clearly inadequate for the job. The backup systems were not protected sufficiently and were actually placed in a relatively low-lying area because it was assumed the seawall would protect them. This earthquake was originally deemed an 8.8, but that has been moved up to a 9.0. This change seems insignificant, but the Richter Scale is a base-10 logarithmic scale which means this move by .2 actually represents close to a doubling of the destructive force. No nuclear reactors in Japan are designed to withstand a 9.0 (to be fair, few things in the world are), and the specs are usually something around a 7.something, which is really inadequate for Japan. The location of the facility on the east coast is not ideal because that region is no stranger typhoons and other disasters.
I would also like to restate, for the record, that the nuclear industry in Japan was just emerging from a cloud of scandal and suspicion. The 90s were a rough period for the industry, which a cover-up of the liquid metal sodium fire at the experimental Monju facility (the one that was supposed to be the future of nuclear power and just reopened LAST YEAR), the Tokaimura criticality incident (they mixed some stuff in a bucket and it started a self-sustaining chain reaction!!) and a number of other problems. The degree to which people trust the nuclear authorities and the electric power companies that own the reactors is something of a question mark. This incident will set the industry back quite a bit as people remember (as they do occasionally) that nuclear power has dangers and they don’t like that.