North Korea's uranium program is easier to hide

WASHINGTON -- North Korea's decision to enrich uranium rather than Pyongyang's first choice, plutonium, means it is pursuing a nuclear weapons technology that's easier to hide and more reliable, but harder to mount on a missile.

Still, North Korea can put a nuclear warhead on any of its missiles, including those under development that may be able to reach U.S. territory.

"They've clearly demonstrated a missile technology far beyond the range of Japan," said Charles Curtis, president of the Nuclear Threat Initiative, a private group dedicated to stemming the spread of nuclear weapons. "Putting a warhead on a missile isn't a problem for them."

North Korea admitted to a U.S. delegation this month that it had a clandestine nuclear weapons development program aimed at enriching enough uranium to make weapons.

Before agreeing to halt its nuclear weapons program in 1994, North Korea had produced enough plutonium to make at least one bomb, CIA assessments say. U.S. intelligence agencies and Defense Secretary Donald H. Rumsfeld assume Pyongyang made a plutonium weapon or two.

Enough for five bombs

Still more plutonium could be obtained by processing 8,000 spent fuel rods from a nuclear reactor North Korea agreed to shut down as part of the 1994 agreement. Those rods have enough plutonium to make about five nuclear weapons, the U.S. government says.

In the mid-1990s, the United States sealed the rods in canisters meant to keep the North Koreans from extracting the plutonium for weapons. But now that the White House says North Korea has declared the 1994 agreement void, experts worry there's nothing to stop Pyongyang from opening the canisters, processing the rods and making more weapons.

"You have this bomb material sitting there right now that they could reprocess," said Daniel Pinkston, a Korea specialist at the Monterey Institute for International Studies.

Why, then, would North Korea switch to a drive to enrich uranium?

"Enriched uranium is easier to hide," said Gary Milhollin of the Wisconsin Project on Nuclear Arms Control. "Nuclear reactors are fairly difficult to hide, and you need a reactor to make plutonium."

North Korea's apparent plan is to build a series of centrifuges to separate weapons-grade uranium from lower-grade uranium, experts on North Korea's nuclear program and U.S. officials say. Those centrifuges are relatively small, and enriching enough uranium for a weapon would be a slow process.

Simpler design

Uranium bomb designs are simpler and more reliable than those using plutonium. Plutonium weapons require precise measurements, assembly and ignition to work. The United States tested its plutonium bomb design before dropping one on Nagasaki, Japan, at the end of World War II; the uranium-based design of the bomb dropped on Hiroshima wasn't tested.

More uranium than plutonium is needed to make a weapon, however. Crude designs require about 55 pounds of uranium per bomb versus about 17.5 pounds of plutonium.