Planet Of The Year: Nuclear Power Plots a Comeback

The primary purpose of the $3.6 billion nuclear plant that the U.S. Department of Energy wants to build in Idaho Falls, Idaho, is to help replenish America's dwindling supply of tritium, a vital component in atom bombs. But if approved by Congress, the Idaho facility could play an even more important role in the civilian use of nuclear power. For it is based on what proponents claim is a fail-safe technology, one that virtually eliminates the danger of a meltdown.

Nuclear plants have the potential of providing abundant supplies of electricity without spewing pollutants into the atmosphere. But the nuclear- power industry has failed to deliver on that promise, at least in the U.S. Even before the accident at Three Mile Island in 1979, the costs of making atomic power safe were spiraling out of control. Since that episode, the industry has been at a standstill.

What makes the failure all the more disturbing is that it was unnecessary. Engineers have the know-how to build reactors that are demonstrably safer than those now in operation. Moreover, that basic technology has been available for more than 20 years. It was largely ignored in favor of a technology -- the water-cooled reactor -- that had already been proved in nuclear submarines. But water-cooled reactors are particularly susceptible to the rapid loss of coolant, which led to the accidents at both Chernobyl and Three Mile Island.

All nuclear reactors work by splitting large atoms into smaller pieces, thus releasing heat. The challenge is to keep the core of nuclear fuel from overheating and melting into an uncontrollable mass that can breach containment walls and release radioactivity. One way to prevent a meltdown is to make sure the fuel is always surrounded with circulating coolant -- ordinary water in most commercial reactors. To guard against mechanical failures that could interrupt the transfer of heat, most reactors employ multiple backup systems, a strategy known as "defense in depth."

The problem with defense in depth is that no matter how many layers of safety are built into a conventional reactor, it can never be 100% safe against a meltdown. At its Idaho plant, the Energy Department wants to try a different strategy. Rather than construct a giant atomic pile that requires the cooling of large quantities of concentrated fuel, designers propose to build a series of four small-scale, modular reactors that use fuel in such small quantities that their cores could not achieve meltdown temperatures under any circumstances. The fuel would be packed inside tiny heat-resistant ceramic spheres and cooled by inert helium gas. Then the whole apparatus would be buried belowground. Lawrence Lidsky, an M.I.T. professor of nuclear engineering, calls this an "inherently safe" approach: it relies on the laws of nature, rather than human intervention, to prevent a major accident.

The main problem is that the modest electrical output of smaller units makes them less economical, at least initially. But proponents argue that inherently safe plants should prove more cost-effective in the long run. Not only would expensive safety systems no longer be needed, but the units could be built on an assembly line and put into operation one module at a time, enabling utility companies to match operating capacity with demand for power.