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ANALYSIS-North Korea looks at new deal of its nuclear cards

SEOUL, Aug 12 (Reuters) - North Korea seems in no rush to restore its old plutonium-producing plant, but that does not mean it has given up on building a bomb and it may now be betting on uranium enrichment instead for its next nuclear bargaining chip.

A switch to uranium would alarm Western powers because it could be done away from the prying eyes of U.S. spy satellites, it may lead to enhanced cooperation with Iran and it could lure customer states keen to start their own nuclear arms programmes.

Analysts say Pyongyang now needs to make crucial decisions about whether it should use its limited resources to rebuild its largely inactive Yongbyon plant, which is designed to produce bomb-grade plutonium, start on a full-scale plan to enrich uranium for weapons or use a combination of both. [ID:nSEO6779]

"It makes little sense to restore an obsolete (plutonium-based) nuclear complex. What makes much more sense is for them to work on the highly enriched uranium (HEU) programme," said a well-informed South Korean government source, who declined to be named.

The North has pursued a plutonium-based programme for decades. This type of programme requires large facilities to produce fuel, a reactor to fire it and a reprocessing plant to separate plutonium from spent fuel rods.

Its Yongbyon plant was being taken apart under a six-country disarmament-for-aid deal that has now all but fallen apart.

"Whether it is restoring Yongbyon or launching a full-scale uranium enrichment programme, North Korea is quite a way off from doing either of these," said Daniel Pinkston an expert on North Korea with the International Crisis Group in Seoul.

North Korea, which has twice tested a plutonium-based nuclear device, has produced enough fissile material at Yongbyon for about six to eight nuclear bombs, experts have said.

It has restored its plant that separates plutonium and is extracting fissile material from spent fuel rods at the plant, which could yield it about one more bomb's worth of plutonium.

After the extraction is finished the North will not have a working plutonium or HEU programme that could supply it with additional fissile material -- unless it makes major investments.

URANIUM A GOOD MATCH FOR NORTH

Enriching uranium offers numerous advantages for North Korea because it does not require massive structures such as a reactor. Instead, it requires a space where thousands of centrifuges can spin and a great deal of time to produce fissile material.

Unlike its plutonium-based programme, enrichment can be done in secret and the country has ample supplies of natural uranium it can use as source materials.

However, experts say that while it is easier to design a standard bomb using HEU, plutonium is a better material to use in a miniaturised nuclear device that can be mounted as a warhead on a missile.

David Albright, head of the Washington-based Institute for Science and International Security, a leading tracker of nuclear proliferation, said there has been no visual evidence yet that the North is rebuilding its demolished cooling tower at Yongbyon, which would indicate plans to fire up its reactor again.

"But I wouldn't conclude it is being abandoned from the mere lack of visual activity," Albright said.

"For example, they may be holding back in case negotiations restart," he added, referring to the now-frozen talks with the United States, China, Japan, South Korea and Japan.

U.S. and South Korean officials said North Korea has previously acquired centrifuges and materials for HEU but experts doubt if Pyongyang, which said earlier this year it had started enriching uranium, yet had anything near a full-scale programme.

TROUBLING IRAN LINK

Going the HEU route would present numerous challenges to global powers because it would likely draw military partners North Korea and Iran closer at a time when Washington is trying to stifle the security threat posed by the two states.

Iran has been a major customer for the North's ballistic missiles and has shown few signs of abiding by U.N. sanctions that restrict most arms dealing with Pyongyang.

"There is a terrifying way that North Korea could overcome its limitation while simultaneously helping another nuclear aspirant: it could work with Iran," Siegfried Hecker, the former head of the U.S. Los Alamos nuclear weapons laboratory, wrote earlier this year for the website of Foreign Policy magazine.

"Pyongyang lacks uranium centrifuge materials, technology, and know-how; Tehran has mastered them. Pyongyang has practical uranium metallurgy capabilities; Tehran has little," said Hecker, one of the few U.S. experts to have visited Yongbyon.

The cash-strapped North, which the United States suspects has sought to sell its nuclear know-how abroad, would also have a new item to market to states wanting to start up their own nuclear arms programmes.

Hecker, a professor at Stanford University, wrote separately in an email this week that it makes little sense at this time for for North Korea to switch from plutonium to HEU because it would take several years to build a programme, even with Iran's help.

"It would make much more sense to restart the ... reactor. The fact that they are not may indicate that they believe their small nuclear stockpile serves as a sufficient deterrent," Hecker said. (Additional reporting by Jack Kim and Christine Kim in Seoul and Mark Heinrich in Vienna; Editing by John Chalmers)

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