07/23/2009 - 07:39

Is North Korea's reprocessing facility operating?

Hui Zhang

Hui Zhang

Hui Zhang is a physicist and a senior research associate at the Project on Managing the Atom in the Belfer Center...

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In response to a U.N. resolution punishing its nuclear test on May 25, North Korea defiantly threatened on June 13 to weaponize all of its newly separated plutonium. Pyongyang also declared, "More than one-third of the spent fuel rods has been reprocessed to date." However, recent off-site air samples and satellite imagery suggest that North Korea's reprocessing facility isn't operating, casting doubt on Pyongyang's statements. But is it possible that North Korea's reprocessing facility could be in use without detection?

Based on a February 2007 agreement that came out of the Six-Party Talks, North Korea started disabling its plutonium production facilities at the Yongbyon Nuclear Complex that fall, including its 5-megawatt reactor, reprocessing facility, and fuel fabrication plant. About four disablement steps were designed for each facility; among the total of 12 disablement steps, only two were incomplete as of April--unloading all of the spent fuel in the reactor and the removal and storage of the control-rod drive mechanisms.

North Korea finished all four steps designed to disable the reprocessing facility by early 2008, including disabling and removing the drive mechanism for the trolley that transports spent-fuel caskets to the reprocessing facility; cutting two of the four steam lines leading into the reprocessing facility; removing the crane and door actuators that allow the spent fuel rods to enter the reprocessing facility; and removing the drive mechanisms for the fuel cladding, shearing, and slitting machines.

However, in response to U.N. condemnation of its April 5 rocket launch, Pyongyang declared on April 14 that it would reverse all the steps it took in disabling its reprocessing facilities, and on April 24, it confirmed that it had started reprocessing its newly discharged spent rods. Given these declarations, the fundamental question is whether or not Pyongyang could restart its reprocessing facility within 10 days.

It's generally assumed that North Korea would need 2-4 months to restart its reprocessing facility. That said, North Korean scientists and technicians have shown in the past that they can resume reprocessing quickly, something they demonstrated in September 2008 when they recovered all cut cables and disabled reprocessing equipment within two to three weeks. (They did so in response to the Bush administration's hesitancy in removing North Korea from its list of state sponsors of terrorism.)

Moreover, North Korea supposedly applies "direct maintenance" techniques with its in-cell equipment, which involves maintenance through "hands-on operation" (conducted by staff with air masks and multilayered clothing) that's designed to deliver high reliability after the cell has been shut down and the cell equipment has been cleaned and flushed to remove most of the sources of radiation. Furthermore, this staff can work around the clock and operate under considerably poor safety conditions--at least when compared to Western standards. Consequently, North Korean claims of restarting plutonium reprocessing within 10 days shouldn't be completely dismissed on matters of practicality.

On June 13, Pyongyang stated it had reprocessed more than one-third of its spent fuel rods. Is this claim reasonable? Its facility is capable of reprocessing around 110 metric tons of uranium (e.g., Magnox fuel) per line per year, or 220-250 metric tons of uranium per year if both process lines are in use. In addition, North Korea had made some equipment improvements that increased the capacity of the facility by 30 percent. Given Pyongyang's current reprocessing capacity, the entire 50 tons of unloaded spent fuel could be reprocessed within 4-6 months. In fact, as North Korean officials have mentioned, during their 2003 reprocessing campaign, they reprocessed the entire load of spent fuel in less than four months. (See Siegfried Hecker's "The Risks of North Korea's Nuclear Restart.")

Thus, by mathematical deduction, the seven-week period from April 24 to June 13 would be sufficient time for North Korea to reprocess more than one-third of its spent fuel. Pyongyang has every incentive to produce as much plutonium as possible, and its reprocessing of spent fuel is consistent with its current strategy of "enhancing its deterrence by all means." Even if Pyongyang opts to denuclearize at a later date, the more separated plutonium it possesses, the more compensation it could receive in denuclearization negotiations. In all likelihood, North Korea is operating its reprocessing facility at maximum capacity, allowing it to have up to 8-12 kilograms of plutonium by September.

But if North Korea is reprocessing, why aren't the normally detectable signatures apparent? For a reprocessing operation, the most favorable isotope for off-site detection is krypton 85. With its higher fission rate and a relatively long half-life (11 years), a significant quantity of krypton 85 would result from the reprocessing of spent fuel even after several months of cooling.

Given Pyongyang's statements, we can assume that about 20-50 curies of krypton 85 would be released each day it reprocesses. Under normal operation and assuming a 100-percent leak rate of the krypton (North Korea would have no reason to absorb the krypton 85) and a continuous discharge mode (as opposed to holding the krypton 85 for a few days and then discharging it in batches), we can estimate, considering atmospheric dispersion modeling and favorable weather conditions, that the krypton 85 would be difficult to detect from a range outside of 200 kilometers from the reprocessing facilities. Since the North Korean border is far more than 200 kilometers from the reprocessing facility, it shouldn't be surprising that krypton 85 isn't being detected.

What about satellite imagery? Based on its analysis of commercial satellite imagery taken by Digital Globe on May 26, the Institute for Science and International Security reported that the satellite imagery "does not show any steam from the pipes running from the coal-fired plant to the reprocessing plant" and "does not show any smoke from the chimney at the coal-fired plant, nor any plume from the stacks at the reprocessing plant." However, the plume from the stacks at the reprocessing plant mainly would consist of gaseous fissile products (e.g., noble gases such as krypton 85 and Xenon isotopes), which are invisible to the naked eye and certainly not visible through satellite imaging.

The nearby coal-fired steam plant would operate to serve reprocessing operations, but the steam produced during plutonium separation is much less than at later stages, such as when liquid radioactive wastes are treated. Thus, it would be difficult (if not impossible) for commercial satellite imagery to capture the sparse steam, although it could be viewed on-site with the naked eye. Satellite imagery would likely see steam when the plant starts to process liquid radioactive wastes after finishing its plutonium separation--probably in September or later.

Today, though, whether or not this smoke from the chimney of the coal-fired plant can be caught by satellite imaging depends on the size and concentration of the smoke, combustion efficiency of the coal, weather conditions, and visibility (e.g., high winds will make sparse smoke quickly "disappear"). In addition, the top of a coal-fired plant chimney usually features a smaller diameter than that of a cooling tower. These facts suggest satellite imaging isn't an effective way to confirm the operation of a small-scale reprocessing plant. (See "Uses of Commercial Satellite Imagery in FMCT Verification.")

Therefore, the failure of commercial satellite imagery to detect steam/plumes from the reprocessing plant doesn't allow us to definitively conclude that North Korea hasn't resumed reprocessing activities. Furthermore, there is no incentive for the North Koreans to lie about their reprocessing operations. It would be safer to assume what Pyongyang is saying is true. Thus, the international community--in particular the United States and China--must act now to force North Korea to halt plutonium production, stop all weapons tests, and immediately return to the Six-Party Talks.