THE BURNED OVER DISTRICT

And who hasn't had a grand dream or two. And when you get a couple of hideously rich people to share a common dream, you get the funds to research its possibility.

The quest is for a new kind of nuclear reactor that would be fueled by today’s nuclear waste, supply all the electricity in the United States for the next 800 years and, possibly, cut the risk of nuclear weapons proliferation around the world.

The people developing the reactor work for a start-up, TerraPower, led by Mr. Gates and a fellow Microsoft billionaire, Nathan Myhrvold. So far, it has raised tens of millions of dollars for the project, but building a prototype reactor could cost $5 billion — a reason Mr. Gates is looking for a home for the demonstration plant in rich and energy-hungry China....

Perhaps one of the most intriguing arguments supporters make about Mr. Gates’s reactor is that it could eliminate several routes to weapons proliferation. Iran, for example, says its nuclear program is for peaceful purposes, but it is enriching far more uranium than it needs for power generation. The United States has long said that Iran’s enrichment could lead to a nuclear bomb.

Today’s nuclear reactors run on concentrations of 3 to 5 percent uranium 235, an enriched fuel that leaves behind a pure, mostly natural waste, uranium 238. (A uranium bomb runs on more than 90 percent uranium 235.) In today’s reactors, some uranium 238 is converted to plutonium that is used as a small, supplemental fuel, but most of the plutonium is left behind as waste.

In contrast, the TerraPower reactor makes more plutonium from the uranium 238 for use as fuel, and so would run almost entirely on uranium 238. It would need only a small amount of uranium 235, which would function like lighter fluid getting a charcoal barbecue started.

The result, TerraPower’s supporters hope, is that countries would not need to enrich uranium in the quantities they do now, undercutting arguments that they have to have vast stores on hand for a civilian program. TerraPower’s concept would also blunt the logic behind a second route to a bomb: recovering plutonium from spent reactor fuel, which is how most nuclear weapons are built. Since so much uranium 238 is available, there would be no reason to use that plutonium, TerraPower says.

A very tempting idea.