Small Step in Iran’s Nuclear Effort Suggests Ambitions for a Weapon, Experts Say

Small Step in Iran’s Nuclear Effort Suggests Ambitions for a Weapon, Experts Say
By WILLIAM J. BROAD
Copyright by The New York Times
Published: February 9, 2010
http://www.nytimes.com/2010/02/10/world/middleeast/10iran.html?th&emc=th


Iran’s stated intention to enrich uranium to higher levels is in one sense another incremental act of brinkmanship in a standoff with the West. But nuclear specialists say it also suggests that the country is striving to make real technical progress toward producing a bomb.

The latest step — an order on Sunday to begin enriching uranium to 20 percent — would not itself produce nuclear fuel that could be easily used in a bomb, which generally requires uranium enriched to 90 percent. But the technical leap required to get to 90 percent from 20 percent is relatively straightforward, the specialists say, because enriching uranium in machines known as centrifuges becomes easier at higher levels.

“It’s rather nonintuitive,” said R. Scott Kemp, a centrifuge expert at the Woodrow Wilson School of Public and International Affairs at Princeton University.

On Monday, Iran notified atomic inspectors in Vienna that it would accelerate its enrichment of uranium to 20 percent from its previous levels of roughly 4 percent. Its rationale is that it needs 20 percent fuel for its medical reactor.

On Tuesday, Iranian state news media said the work had begun at the Natanz enrichment plant in the Iranian desert.

Whether Iran’s trouble-plagued nuclear program can successfully enrich uranium to 20 percent or higher levels is not entirely clear, and enriching uranium is just one step in the complex process of making an effective nuclear weapon, if that is what Iran ultimately intends to do. Iran says that its nuclear program is peaceful.

Nuclear experts said that the low level of enrichment of Iran’s existing uranium stock gave the West some assurance that it would take time for Iran to develop a bomb. Every new step toward higher enrichment erodes that margin of comfort.

“The higher the concentration, the easier it gets,” said Houston G. Wood III, a centrifuge expert at the University of Virginia.

The reason lies in the great scarcity of the type of atoms that engineers seek to enrich, or concentrate. Uranium 235 — the kind that easily splits in two, or fissions, in bursts of atomic energy — makes up less than 1 percent of all natural uranium, and engineers spin centrifuges at very high speeds to separate out that rare form.

The early stages of enrichment require more work because so much uranium must be sorted. Mr. Kemp of Princeton likened the process to hunting through a barrel full of blue candies to find a few red ones. “You have to search and search and search,” he said, adding that the hunt gets easier as the number of blue candies falls.

So too with uranium 235. Going from the natural state of 0.7 percent enrichment to roughly 4 percent — as Iran has been doing for years at Natanz in defiance of the United Nations Security Council — requires about 70 percent of the energy needed to concentrate the uranium to the high levels considered necessary for a bomb. Going to 20 percent takes 90 percent of the total energy required — almost to the finish line.

David Albright, president of the Institute for Science and International Security, a private organization in Washington that tracks nuclear proliferation, said the diminishing effort needed to enrich at higher levels meant Iran would need fewer working centrifuges.

Mr. Albright said Iran would need only 500 to 1,000 centrifuges working for six months to enrich uranium from a level of 20 percent to that needed for a bomb, a tiny fraction of the number required to enrich to lower concentrations.

The number of centrifuges is small enough that international inspectors and intelligence agencies would have an “extremely hard” time trying to detect the spinning machines if Iran hid them in a clandestine site, Mr. Albright said.