This involved changes in the refuelling system; it was a bid to make it easier to obtain weapons-grade plutonium.

Under pressure from the United States, Taiwan has stopped work on a secret installation that could have been used to obtain plutonium, a main ingredient in nuclear weapons, according to Administration officials.

Opponents said there was a risk that terrorists or hostile countries would try to hijack the ship to obtain plutonium to make bombs.

In contrast, North Korea will have obtained enough plutonium for about 10 weapons on Mr. Bush's watch.

The reactor has been North Korea's main means of obtaining plutonium for weapons.

While there is no way to know with any certainty why the reactor might have been shut down, it has been North Korea's main means of obtaining plutonium for weapons.

But it would be likely to obtain enough plutonium for at least two weapons, and maybe more, if it had begun to master the complex art of reprocessing the rods into plutonium.

First, a bit of history: North Korea may have obtained enough plutonium for one nuclear weapon by halting a reactor in 1989.

Japan intends to obtain plutonium for its breeder reactors by reprocessing the waste from its conventional reactors.

As a result, experts now think that at worst, North Korea obtained only enough plutonium for a single bomb.