John Large, who has worked with the Royal Navy, advised Russia on the sunken nuclear submarine Kursk, and is on the UK Nuclear Co-ordinating Group, said that North Korea’s only motive for restarting the reactor was to produce nuclear weapons.

The North Koreans moved 1,000 fresh fuel rods containing uranium to the Yongbyon nuclear reactor yesterday, saying that they wanted to restart it to produce electricity.

The move comes just a week after they unilaterally disabled monitoring equipment and seals put in place by the United Nations’ International Atomic Energy Agency under a 1994 deal with the US in which North Korea promised to stop its nuclear programme in return for supplies of oil.

Pyongyang said that it needed the electricity to compensate for the US suspension of oil shipments after North Korea admitted in October that it was still trying to develop nuclear weapons. The reactor will need a total of 8,000 fresh fuel rods before it can be restarted.

However, Yongbyon produces only 5 megawatts of thermal power, which once converted to electricity and transmitted to cities would be only about 2 megawatts compared with the 1,300 megawatts produced by Sizewell B.

“It’s absolutely nothing, it wouldn’t be of any use, it could just power a few villages,” Dr Large said. There were three possible reasons why they could want to restart the reactor, he said, and each of them would lead to the production of nuclear weapons.

The electricity from the reactor could be used to power a nuclear reprocessing plant also at the Yongbyon complex, enabling the North Koreans to process chemically the 8,000 spent fuel rods that had powered the reactor before it was shut down in 1994.

The North Koreans also dismantled monitoring equipment at the reprocessing plant, which has the facility to separate the spent fuel rods into depleted uranium, and a mixture of plutonium and americium.

That plutonium mixture could be used to produce an atomic bomb within six months to a year. The 8,000 spent fuel rods would produce a minimum of 30kg of plutonium, enough to make seven nuclear weapons.

However, the North Koreans may not have the facilities to handle the americium, which is particularly dangerous, and so may be using the reactor to produce “fresh” uncontaminated plutonium. In that case it would take nine months to a year to produce an atomic bomb.

The third, and most worrying, scenario is that the North Koreans might already have enough plutonium for an atomic bomb, but do not have a nuclear trigger for it.

The UN has never been able to verify how much plutonium the country produced before the reactor was shut down in 1994. Some analysts have speculated that it might have kept enough for two atomic bombs.

In this case North Korea might be restarting the nuclear reactor to produce a “polonium trigger” needed to ignite a nuclear explosion. This would enable it to produce a functioning nuclear weapon within just 30 days.

“All scenarios point to the finishing of the development of nuclear weapons,” Dr Large said. “When you have started producing plutonium, you are reaching the culmination of producing the weapons.”

North Korea’s unstable Stalinist regime has also spent recent years developing a long range missile that would enable it to send bombs as far as Japan. “North Korea has a nuclear weapons development programme on an industrial scale, and the means for delivering them.

“It brings the whole of South-East Asia into political instability,” Dr Large said.

With the collapse of the 1994 deal to stop it producing nuclear weapons, North Korea’s neighbours are left hoping that intense diplomatic efforts can bring the renegade country back in line. “We can never go along with North Korea’s nuclear weapons development,” the outgoing South Korean President, Kim Dae Jung, said yesterday.

“We must closely co- operate with the United States, Japan and other friendly countries to prevent the situation from further deteriorating into a crisis.”

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