How new designs could make nuclear power even more attractive.

Experiments are about to begin on a new form of nuclear power that even eco-warriors might tolerate--if not welcome. It is radically different from the traditional reactor designs that prompt fear and loathing: For one thing, its safety is underwritten by the laws of physics, rather than human ingenuity. Better still, it can use a range of different fuels--including some that would minimize the risk of weapons production by "rogue" nations. But best of all, this new form of reactor can incinerate waste from other reactors, turning today's noxious stockpiles into energy.

Such are the prospects held out by the new reactor, the Accelerator-Driven Subcritical (ADS) system. First proposed in the 1990s by scientists at the Los Alamos National Laboratory and Carlo Rubbia, the Italian Nobel prize-winning physicist, the idea behind ADS is more elegant than its name.

Conventional nuclear power exploits the energy released by the splitting--"fission"--of uranium atoms. Along with energy, this fission process releases neutrons capable of splitting further uranium atoms, triggering a chain reaction. If the numbers of neutrons are held just sufficient to keep the reaction in balance, the result is a steady flow of power that today provides about 17 percent of the world's electricity demand. But if the chain reaction should run out of control, the reactor could overheat and melt down.

The ADS system adopts a different approach to nuclear safety--one that even Homer Simpson could not undermine. The ADS reactor's fuel simply does not generate enough neutrons to sustain a chain reaction. Instead, the reactor is fed with neutrons created by a particle accelerator. Cut off this supply of neutrons--deliberately or accidentally--and the reactor reverts to its natural, somnolent state. A runaway chain reaction is not just unlikely: It is prevented by the laws of physics.

Moreover, the ADS system is a nuclear omnivore, working with fuels that are wholly unsuited to weapons production. To cap it all, an ADS reactor can even consume radioactive waste from conventional reactors

This holy trinity of advantages has made the ADS the subject of intense theoretical research for more than a decade. Now the theory is to be tested in experiments by an international team of scientists at Italy's ...