Events in Japan are shocking, impossible to fully comprehend in their magnitude. Inevitably The rethinking of the "nuclear renaissance" has already begun. The New York Times editorial page says it still supports nuclear power as one way to ameliorate carbon emissions and climate change, a "valuable tool." But, it says, "the public needs to know that it is a safe one."

The editorial also contains the best explanation I have read about what is happening inside the reactors.

From early reports, it appears that the troubled reactors survived the earthquake. Control rods shut down the nuclear fission reactions that generate power. But even after shutdown, there is residual heat that needs to be drawn off by cooling water pumped through the reactor core, and that’s where the trouble came.

The nuclear plant lost its main source of electric power to drive the pumps, and the tsunami knocked out the backup diesel generators that were supposed to drive the pumps in an emergency. That left only short-term battery power that is able to provide cooling water on a small scale but can’t drive the large pumps required for full-scale cooling.

Previous nuclear disasters resulted from human error or the failure of human appliances in the absence of natural trauma. We have always known that earthquakes and other natural forces posed a threat to nuclear systems. Now there is terrifying proof.