North Korea's recent moves to restart a frozen nuclear facility could mean that it is a year or less away from the mass production of nuclear weapons material, analysts say.
By Sarah Buckley
BBC News Online
US officials said in February that satellite photographs indicated work had resumed at the nuclear plant in Yongbyon, which was shut down under an agreement with the US and its allies in 1994.
Analysts warn that processing at Yongbyon could begin only a matter of weeks after it is fully operational.
Spent fuel rods could provide North Korea with several nuclear bombs
But it would take one to two years to produce enough plutonium for a nuclear weapon, they say.
More worrying, however, is that North Korea is thought to have separated plutonium from the plant before it was shut down and stored it in the form of spent fuel rods.
John Large, an independent nuclear consultant, said that the reactor could then simply be used for the final stage of the process - generating other radioactive elements, either tritium or polonium - which are required for the initiation stage of a nuclear weapons device.
"In this case North Korea could have a nuclear weapon ready within a month or so," John Large told BBC News Online.
The CIA believes the 8,000 spent fuel rods North Korea is believed to have stored could be enough to produce one or two nuclear bombs.
North Korea could have a nuclear weapon ready within a month or so
John Large, independent nuclear consultant
The North's Foreign Ministry said on 18 April that it was "successfully reprocessing" the fuel rods. However, the US, Japan and South Korea said they had no indication that this was the case.
John Large said it could be enough for five or six bombs, although he stressed that plutonium was highly unstable and degraded over time, making the task of producing a nuclear weapon all the more difficult.
To make a device, weapons-grade plutonium would have to be separated out from these fuel rods - as it would from the fuel produced in the reactor - by a chemical separation process.
John Large said that there were "two distinctive signatures" that would indicate if reprocessing work had restarted:
A liquid discharge of plutonium into rivers, which could be detected by surveillance planes and submarines
Gaseous output of krypton and iodine from smoke stacks, which could be detected by satellite thermal imagery
North Korea's rationale
The US also says North Korea has admitted to a separate enriched uranium programme.
NORTH KOREA NUCLEAR PROGRAMME
Yongbyon: Five megawatt experimental nuclear power reactor and a partially completed plutonium extraction facility. Activities at site frozen under 1994 Agreed Framework
Taechon: 200-MWt nuclear power reactor - construction halted under Agreed Framework
Pyongyang: Laboratory-scale "hot cells" that may have been used to extract small quantities of plutonium
Kumho: Two 1,000-MWt light water reactors being built under Agreed Framework
A CIA report in November said this could provide "two or more" bombs each year by "mid decade".
North Korea's alleged admission led the US to initiate a halt in fuel aid shipments to North Korea.
North Korea says that it needs to reactivate Yongbyon to compensate for the shortfall in energy caused by the move.
But John Large stressed the Yongbyon reactor was "tiny" at 5 MWt, compared to a commercial reactor which can generate 3,000 MWt.
Yongbyon was therefore not capable of significant electrical power generation, he said.
He also noted that North Korea's recent activity at the plant could not be termed simple political brinkmanship - a knee-jerk reaction to pressure from the US, for example - because "to put all this in place would have taken at least 18 months".
If Yongbyon is used for nuclear weapons production, it only presents a threat to the outside world if North Korea has the capability to launch and deliver nuclear warheads to targets abroad.
This also applies to the handful of nuclear bombs which North Korea may have fabricated over the last decade.
Gary Samore, of the International Institute for Strategic Studies, said that North Korea does have missiles powerful enough to reach Japan and South Korea.
But what is in doubt is whether Pyongyang could build a nuclear weapon small enough to sit on those missiles, he said.
Mr Large disagreed, saying that North Korea's missile programme was probably tailored to carrying weapons of mass destruction.