The simple message from the Fukushima nuclear plant disaster is that unlikely events can and do happen. So when representatives of the nuclear power industry and their regulators re-assure us that modern plants are designed to withstand all "likely" circumstances we should ask them, "Well, what about unlikely circumstances?"
In this article U.S. Nuclear Regulatory Commission Chairman Gregory Jaczko is quoted as saying, "We have a strong safety program in place to deal with seismic events that are likely to happen at any nuclear facility in this country." I'm sure Japanese regulators said the same before recent events.
We should also consider that earthquakes are not needed for crises to occur at nuclear power stations. Neither Three Mile Island nor Chernobyl involved an earthquake. Also, any earthquake strong enough to cause a nuclear emergency will probably have a death toll thousands of times larger from other effects such as building collapses or tsunami. The deaths associated with any problems at nuclear power plants will be very minor in comparison.
But just because nuclear power generation entails risks, does this mean that we should continue to burn coal?
It has been known for 40 years that reactors like those at Fukushima might release radioactive material if they suffered a loss-of-coolant accident. Yet such reactors have been approved and built. (See this Guardian article.) Society has been willing to roll those dice.
Regulators approved those reactors, hoping their faults would never be tested. A score of similar reactors are operating in the U.S. today. Probably they will never be subjected to an unfortunate sequence of events that will cause them to fail catastrophically. But when the industry and their regulators assure us that "nothing can go wrong" they are obviously exaggerating. Things can go wrong, and at Fukushima they have.
The Fukushima disaster illustrates once again how massively complex systems can be destroyed by an unanticipated combination of failures. (See "When Systems Fail It's No Accident" in sister blog Science In Action. Also consider the combination of failures that led to the BP Macondo blowout disaster, described in this post.) Failures of this kind are unavoidable, though fortunately they are rare. (See this Wikipedia list of civilian nuclear accidents--not all of which are disasters.) (Here is an interesting list of structural failures and collapses. Engineering failures are not that uncommon. Dozens of people die from such failures every year on average.)
We don't know yet how much radioactive material will be released from the Fukushima reactors, nor how much disease, death and economic harm may result. Probably the total economic and personal loss due to the reactor failures will be relatively minor--a few billion dollars to Tokyo Electric Power Company, and some tens or hundreds of premature deaths. (There have apparently already been some deaths among workers at the facility, mainly from the effects of the hydrogen explosions, if I interpret the cryptic information coming from TEPCO correctly. Japan has had previous deaths among nuclear industry workers. See Wikipedia article on the Tokaimura accident.)
The cost of coalThis should be balanced against the thousands of deaths annually caused by particulate emissions from coal-burning power plants. Particulates are poison, and cause morbidity and mortality among exposed populations. If you count plants in China the annual toll is probably in the tens of thousands at least. (Here are discussions of health effects of particulates from WRI, EDF and Wikipedia.)
We should also count the deaths among coal miners as a cost of coal-fired electric power. The annual number of coal mine deaths is probably far above the number of deaths that will eventually be attributed to the Fukushima disaster. Twenty-nine coal miners were killed at the Upper Big Branch disaster in the U.S. in 2010. Hundreds of coal miners die in China annually. Mining is dangerous business, probably more dangerous than working at a nuclear power plant. (Of course uranium mining is part of the nuclear fuel cycle, but it may be less dangerous than coal mining.)
(Interestingly the Willow Island construction disaster, the collapse of a cooling tower being built at a coal-fired power plant, killed 51 construction workers. This toll is far greater than that of all nuclear power accidents in U.S. history. Admittedly the coal-fired power industry is much larger than the nuclear power industry.)
The Fukushima disaster is serious, and will do no good to the prospects of the nuclear power industry. If we are going to have nuclear power generation we should figure on the costs of such events. But the risks associated with nuclear power generation, always well known and now sadly demonstrated, need to be balanced against the also-well-known risks associated with other power generation technologies. It is hard to find something worse than coal.