Japanese Nuclear Problem

There has been an interesting conversational exchange on Hacker News concerning the Japanese nuclear problem. The website is http://news.ycombinator.com/item?id=2316531.

Part of the problem is whether the cores of the three Japanese reactors are still active. That is, whether the cores are still producing heat by atomic fission. One contributor says that continued fission is highly unlikely, because fission has been stopped by the control rods.

However, that is only a guess. The control rods may not have operated properly or have become damaged in some way as to not be able to shut down the fission process.

Atomic fission proceeds by multiplication of neutron emissions. The neutrons are active in forcing fissionable material, such as uranium 235, to undergo fission. Absorb the free neutrons, and the uranium 235 will just sit there. Boron is a known neutron absorber and is normally a constituent of the control rods.

If it is uncertain that fission is still taking place in the three Japanese reactors, the obvious action is to treat with massive amounts of boron. Helicopters can drop boric acid or sodium perborate, which are commercially available in large quantity, on any exposed cores.

So far as I know, a "meltdown" has never occurred. The fear is that if it does, there MAY be an explosions similar to an atomic bomb. If the heat being generated in the core is such as to melt the mass, the boron content of the control rods will likely inhibit any further fission, which is the basis of an atomic explosion. The bottom safe line is treat the whole system with boron compounds, whether the fuel rods are still intact or whether there has been "meltdown".

The question also arises as to the source of the heat, which is still being generated and is attempting to be dissipated by flooding with sea water. Our communicator on the webpage says that heat is being generated from the normal decomposition of radioactive materials previously generated by the fission process. In other words, these reaction products have already been formed. The are normally considered by the nuclear industry as radioactive waste. These radioactive byproducts must undergo their standard lives of decomposition, during which time, they eliminate subatomic particles, some of which are dangerous to humans. However, there is essentially no possibility that they will undergo nuclear chain reaction equivalent to a bomb.

The danger to personnel is exposure to subatomic particles from the decomposition. In normal reactor operation, this is contained by removing the "depleted" fuel capsules, which contain the radioactive byproducts. They are then stored under water for several days as initial radioactivity is reduced and then stored for hopeful reworking.

If the radioactive byproducts escape to the atmosphere, the population at large is subject to where and how far the wind blows the particles before they have reduced their radioactivity to a low level. Therefore, the present Japanese operation is to attempt to keep those radioactive byproducts contained so that the general population is not exposed to significant amounts of subatomic radiation. In this respect, we have some similarity to the Chernobyl incident, where radioactive byproducts were spread over a large population area.

In summary, it appears best to guarantee that fission is stopped in the three reactors by flooding the systems with boron containing compounds. If this is done, it further obviates the danger of an atomic explosion. The main problem is to contain the reactors' radioactive byproducts so that they are not dispersed and will not present a danger to the general population.