Nuclear Power Meltdown in Japan?

As I write this on Sunday evening (U. S. Central Daylight Time), it is Monday morning in Japan, and nuclear engineers continue to struggle with several damaged nuclear power plants in the northern part of Japan. They were damaged in last Friday’s massive magnitude-8.9 earthquake and tsunami. Our prayers and thoughts are with the people of Japan, who are dealing with the worst catastrophe to hit their islands since World War II. It is likely that thousands have died, and about half a million people have been displaced from their homes. Many months will pass before life in Japan returns to something near normal. The question I would like to ask is: will “normal” life in Japan include nuclear power?

To my knowledge, no nuclear plant in the history of the world has ever been subjected to an 8.9-magnitude earthquake before now. Prior to last week’s temblor, Japan was well known for designing nuclear reactors with extremely high standards for safety in the face of all kinds of malfunctions and problems, including earthquakes. The fact that Japan uses nuclear power at all is somewhat impressive, given the fact that it is the only country where people were killed by nuclear weapons in war (Hiroshima and Nagasaki). Conscious of the technology’s history, Japanese nuclear engineers have probably devised the safest possible systems consistent with making a reasonable profit and making a viable contribution to their country’s power industry. But every design has intentional limits, and informed sources say that the plants were not designed to withstand an earthquake the size of the one that hit last Friday.

Despite the magnitude of the shock, it appears that the containment vessels surrounding the radioactive cores have done their job so far. The main problems have been that at several plants, notably the Fukushima No. 1 unit, both the main and the auxiliary electric power failed. Nuclear reactors work by producing huge amounts of heat that is carried away ultimately to make steam that runs electric generators. In pressurized-water reactors (evidently the type in question), the heat is transported by rapidly flowing pressurized water. Any interruption in this flow traps heat in the radioactive core, sending its temperature soaring to the point that the zirconium-encased uranium fuel rods can crack and release radioactive byproducts. The absolute worst-case scenario is not a nuclear-bomb-type of explosion, but a so-called “meltdown” in which the fuel rods melt through the floor of the containment vessel into the ground. The resulting release of radioactive material is a serious problem.

So far, this has not apparently happened. However, short of that ultimate disaster, some other disturbing things can and did occur. Hot zirconium oxidizes, and when it gets in contact with water, a chemical (not nuclear) reaction releases hydrogen gas, which can build up to a concentration that causes a plain old chemical explosion. This has happened in at least one plant, blowing off some of the outer structure of the plant and releasing some radioactive gas. But the amounts are small and nothing like what happened at Chernobyl, for example.

In 1986, an accident at the graphite-moderated nuclear plant in Chernobyl (in the present country of Ukraine) set fire to the graphite and spread deadly amounts of radiation for many miles. By almost any measure, the Chernobyl plant was badly designed, and nothing like the radioactive fire that happened there could occur at the Japanese plants.

Nevertheless, things are still dicey. Even if the nuclear reaction is shut down by emergency flooding or moderator-rod insertion, you still have a tremendous amount of heat to deal with, and the failure of the cooling-water pumps means that the reactors have already overheated and sustained a certain amount of damage. And of course, most of the instrumentation that engineers would normally use to figure out what is going on inside the plants has also gone flooey. Plus, nobody wants to get near the things with radioactive fuel sloshing around. Possibly it is a job for some radiation-hardened robots. If there are any such things, you can bet they have them in Japan and they’re trying to use them now.

A late report mentions that engineers working with at least one plant have thrown in the towel, and are pumping seawater mixed with boron into one reactor vessel. This is a last-ditch emergency measure that will cool the reactor core fast, but will also corrode it to the point of destruction. It’s likely that the reactor was beyond salvaging anyway, but this action seals its fate. At this point, this is an appropriate action that puts public safety ahead of the power company’s investment.

The future of Japan’s nuclear industry may depend on how well the damaged plants are handled, and also how well the news of any releases of radioactivity is dealt with. If the reactor failures were the only problem, it would be a huge crisis, but the Japanese public currently has other things on its mind besides a little radioactive gas floating around amid the devastation of the earthquake and tsunami.

It’s hard to say, but it looks like the Japanese nuclear engineers will handle this situation with courage and good judgment. The reactors will cool, eventually someone will get inside to assess the damage, and some of the power plants will have to be written off. My guess is that Japan will decide to keep using nuclear power, but may increase even further the already rigorous standards for future plant construction, learning from whatever lessons this tragedy has taught us.

Sources: I relied on news reports from CNN at http://www.cnn.com/2011/WORLD/asiapcf/03/13/japan.nuclear.reactors/index.html?hpt=T1 and the Los Angeles Times at http://www.latimes.com/news/nationworld/world/la-sci-japan-quake-reactor-qa-20110314,0,3403230.story.