Published in Sendai Earthquake by on March 12th, 2011
I apologize for how long it has taken for me to get this blog post up, and I apologize in advance for answers that may prove to be inaccurate and overtaken by events. I am going to try to answer a number of questions I have received through email and Facebook and queries to this page since the Japanese earthquake struck.
Q: What’s going on with the reactor in Japan?
A: The Fukushima-Daiichi reactors were damaged by the quake and the tsunami that followed. There were six reactors operating at the site, all of them boiling-water reactors (BWRs) built by General Electric between 1970 and 1979. These early BWR designs were not built to the same standards that BWRs and other light-water reactors (LWRs) are built to today, and do not have a full containment system that can hold all of the steam in that would be released from damage in the reactor vessel.
At the time of the quake, only three of the units (1, 2, and 3) were operating. They were immediately shut down. Fission stopped. BWRs don’t use borated water and there was no need to add boron to the coolant. The first unit (FD1) appears to have the most difficulties. These older BWRs need emergency power to cool down safely, and their backup generators were damaged by the tsunami. That seems to be the root of the problem.
Q: What about the radiation released? Is it dangerous?
A: It would appear that some of the nuclear fuel in FD1 has melted and released gaseous fission products to the interior of the reactor. These would include xenon, krypton, and iodine. There are about seven isotopes of xenon that are radioactive and would be released in such an incident, with atomic masses of 133, 135, 137, and 138, along with three isomers, 131m, 133m, and 135m. With the exception of the isomers, each of these xenon atoms will decay into cesium and some into other elements past cesium. There is also krypton but its radioactivity and decay products are of less concern.
Xenon itself is not particularly dangerous. It is a noble gas and is not concentrated in the body. Cesium is more of a concern. Here are the seven decay sequences:
Xenon-131m will decay to stable xenon-131.
Xenon-133m will decay to radioactive xenon-133.
Xenon-133 will decay to stable cesium-133.
Xenon-135m will decay to radioactive xenon-135.
Xenon-135 will decay to very mildly radioactive cesium-135.
Xenon-137 will decay to radioactive cesium-137.
Xenon-138 will decay to radioactive cesium-138 and then quickly to stable barium-138.
Of all of these, the decay of xenon-137 to cesium-137 is probably responsible for the most risk, but xenon-137 decays so quickly that the mobility of cesium-137 is limited. I do not think this poses much risk because it can’t get far. The xenon-135 has a longer half-life (9 hours) but decays to a nearly harmless form of cesium (135). I think this poses almost no risk due to the very long half life of cesium-135.
I apologize for this long explanation but you are going to hear the news about cesium being detected and I wanted to tell you why and what it means.
Q: Is nuclear power unsafe?
A: No. It is far safer than chemical power and renewable power. Look at the burning refineries and gas lines. There are no burning reactors. People are scared of “radiation” and don’t understand what it means. The media makes little attempt to tell them. I am trying to be a resource to help explain because I have had some training in this area. A dam gave way due to the earthquake. That’s not safe either.
Q: What about the radiation? Will I be harmed?
A: No. These isotopes of xenon and krypton and iodine decay quickly. The most dangerous is iodine-131 and the public can be protected during the 30-40 days it will decay by taking potassium iodide pills. These are effective and should be used by people in the evacuation areas.
Q: Will there be fallout? Will it reach the US or China?
A: No, there will be no fallout. It will not reach the US or China.
Q: Why are they detecting all this radiation?
A: Radiation is easy to detect in exceptionally small quantities. You can also identify exactly what nuclide it came from. This is very useful to diagnose what is going on. For instance, if you detect iodine or cesium, you can deduce that these are fission products and there may have been core damage. But simply detecting these isotopes does not mean they are present in sufficient amounts to harm people.
