No commercial nuclear reactors have been ordered in the U.S. since 1978, a year before the Three Mile Island accident. In the aftermath of Chernobyl, moreover, the prospects for nuclear energy have become even bleaker. And yet, say many experts, there is no long-range alternative. The oil crisis has receded but is likely to become a problem again within decades. Coal is still plentiful, but its consequences -- air pollution, acid rain and the threat of global warming caused by the greenhouse effect -- will limit its use. "I'm very concerned about our energy future," says Lyle Wilcox, the Department of Energy's Deputy Assistant Secretary for Nuclear Reactor Research. Without nuclear energy, he claims, "we're left to burning up our national resources."
The Nuclear Regulatory Commission is already looking toward a new generation of safer reactors. Last week, after two years of study, it published a report that includes its first guidelines for advanced reactor designs. Though fairly general, calling for "highly reliable and less complex shutdown and decay heat removal systems" and for "designs that minimize the potential for severe accidents," the implication is specific. Says Commission Chairman Lando Zech: "We should always be focusing on safety."
In fact, several better designs already exist, all of them much less susceptible to disaster than the conventional light-water reactors currently in use in the U.S. But according to M.I.T. Nuclear Engineer Lawrence Lidsky, a consultant on the NRC study, only one of these is truly disaster-proof: the modular high-temperature gas reactor, a prototype of which has already successfully been tested in West Germany. If anything goes wrong, says Lidsky, the MHTGR simply cools down, without releasing any radiation. "It eliminates the accident of greatest concern," agrees Alan Crane, senior associate at the Office of Technology Assessment and co-author of Nuclear Power in an Age of Uncertainty.
When a nuclear reactor is running, its heat comes from the fissioning, or splitting, of the nuclei of uranium or plutonium atoms. These nuclei break apart when bombarded by neutrons, uncharged subatomic particles that are initially provided by a reactor ignition device. The shattered nuclei release energy and emit more neutrons. When uranium atoms are packed closely together, however, as they are in power-plant fuel rods, the neutrons emitted by the splitting nuclei break up other nearby nuclei. Each shattered nucleus contributes more neutrons and heat to what has now become a chain reaction, and the heat is used to produce steam that drives the electrical generators.