President Bush unveiled his plan to curb nuclear proliferation yesterday. But a new Energy Department report shows just how tough it's going to be to check the spread of nuclear material. The Department says that tons of highly enriched uranium (HEU), given to countries like Iran and Pakistan during the Cold War, can't be accounted for -- and probably never will be.

In the 1950s, as part of the Atoms for Peace program, the U.S. gave then-friendly countries HEU for their nuclear energy programs -- in exchange for promises not to develop atomic weapons.

Four decades later, the American government decided that trying to recover some of the HEU produced by these foreign nuclear reactors might be sound policy. You know, since HEU can be used to make a nuclear bomb and all.

Good idea. But here's the problem: this program, known as the Foreign Research Reactor Spent Fuel Acceptance Program, addresses only about 30% of the HEU that America gave away.

And of that 30% -- about 5,200 kilograms -- the Energy Department now figures it will only be able to get about about half back.

What's worse, according to the Department, is that there has been "no effort to recover an additional 12,300 kilograms of HEU" given away outside of the Acceptance Program.

Participation in the Acceptance Program was voluntary. So many countries with U.S. produced HEU had chosen not to participate, including Israel, Japan, and France.

That list shouldn't scare anybody, except the most red-faced of the "freedom fries" crowd.

But there are two more countries that should make anybody quiver: Iran and Pakistan.

THERE'S MORE: If the world's nuclear powers agree to the guidelines outlined in Bush's speech, "the world will be a safer place," argues Slate's Fred Kaplan. "The question is: Why should they? What is Bush offering in the way of incentives to keep nuclear wannabes from pursuing their desires or to dissuade nuclear dealers from hawking their wares? Judging from his speech, nothing."