Jeffrey LewisYongbyon Shut Down

North Korea has shut down its 5 MWe reactor at Yongbyon, probably to unload spent fuel rods that will be reprocessed to recover plutonium for North Korea’s nuclear weapons program.

Senior North Korean officials recently informed Selig Harrison of the impending shutdown. Unloading the 8,000 fuel rods, which contain enough plutonium for two or more nuclear weapons, will take several months.

The physical evidence for the shutdown is pretty cool. The Institute for Science and International Security released two satellite images (one from Digital Globe) of Yongbyon from January and April. Compare the cooling towers at the bottom of the images.

See what’s different about April? No steam.

Seoul confirmed “through several channels” that North Korea shut down the reactor.

A U.S. official told AP that the shut down could also signal that “the reactor had run into mechanical trouble or that North Korea was bluffing to raise anxieties.” “It is still too murky to tell exactly what the North Koreans are doing,” one senior administration official “who is deeply immersed in the intelligence” told the New York Times.

Paul Adds:

South Korea’s semi-official Yonhap News Agency quotes an unnamed “senior government official” saying that Seoul believes North Korea suspended the reactor operation “temporarily for technical reasons,” but not to remove the fuel rods.

In other news, getting wasted and defecting to North Korea has to be one of the best drinking stories ever.

Paul’s Later Update:

Barbara Slavin has a good article in USAT featuring an interview with NK’s deputy ambassador to the UN. Han Song ryol said the reactor was stopped so NK could

remove the fuel to make bombs and “increase our deterrent” against a possible U.S. attack…


  1. Anders Widebrant (History)

    Any random bozo (hey, I resemble that!) being able to stare down the cooling tower of a North Korean plutonium-producing nuclear power plant is pretty cool. Pretty cool indeed. The internet is strikingly good at stealing cool toys from the government and handing them away for free.

  2. Pavel Podvig (History)

    It would be strange if NK will start removing fuel now. As far as I understand, it could get twice as much plutonium if it keeps the reactor running for an extra year or so.

  3. Jeffrey Lewis (History)

    Yes, if North Korea unloads the fuel rods, I think the decision has to be a political one.

    I mentioned that the Pu is enough for two or so weapons. That estimate is from David Albright. Here is the full paragraph describing his comments:

    He and other experts note that it is uncertain how many weapons the North could produce if it removed the fuel rods, which have been in the reactor for a little over two years. But it would be likely to obtain enough plutonium for at least two weapons, and maybe more, if it had begun to master the complex art of reprocessing the rods into plutonium.

    The last batch of 8,000 fuel rods, according to Albright, contained enough Pu for five nuclear weapons:

    In 1994, North Korea discharged all the irradiated fuel in the 5 megawatt-electric reactor and moved it to a nearby spent fuel storage facility. In total, North Korea discharged about 8,000 fuel rods containing about 50 tonnes of uranium. Based on information from the IAEA, this spent fuel contained about 25-30 kilograms of plutonium. The average burnup of the fuel is about 650 megawatt-thermal-days per tonne of uranium fuel, implying the spent fuel contains about 27 kilograms of plutonium of which about 92 percent is plutonium 239. Assuming that a North Korean nuclear weapon requires about five kilograms of such plutonium, the spent fuel contains enough plutonium to make five nuclear weapons. Some of the fuel may be so damaged or corroded that it cannot be processed in the plutonium separation plant, but estimating this amount is difficult.

    So, North Korea is probably trading a couple of weapons worth of Pu for timing — which I think is reasonable. You?

    I am going to make Steve Fetter teach me to do this calculation.

  4. Pavel Podvig (History)

    If NK had not had some plutonium already, extracting whatever it has in the current batch of fuel sooner rather than later would have made a lot of sense. Otherwise it doesn’t.

    The calculation is really simple – a reactor produces about 1 g of Pu for every MW(t)-day of operation. Assuming that the Yongbyon reactor is 30 MW(t) (which would roughly correspond to the 5 MW(e)) and that it operates about 70% of the time, you would get about 7 kg of Pu a year (30*365*1*0.7).

    But you don’t want to leave fuel in the reactor for too long, since it would accumulate too much Pu-240. The irradiation time is measured by burnup – since the Yongbyon reactor takes about 50 tonnes of fuel, one year of operation (again assuming it operates only 70% of the time) would be equivalent to 0.15 MW(t)-day/kg (30*365*.7/50000). For the two years the reactor has been in operation this time the burnup is about 0.3 MW(t)-day/kg. If the previous batch was exposed to burnup of .65 MW(t)-day/kg, North Korea could let the fuel stay in the reactor for two more years and still get good-quality weapon-grade plutonium. And twice as much of it!

  5. Pavel Podvig (History)

    According to people who just came back from North Korea, the stated NK reason for removing the fuel was the concern about fuel rods – the claim was that these were manufactured before 1994 and it was not clear if they could withstand a full-length campaign (North Koreans said the rods turned out to be fine).