Jeffrey LewisNew Construction at Yongbyon

Josh Pollack, Dave Schmerler and I have a new analysis of satellite images showing that North Korea is resuming construction at a long-dormant nuclear reactor that, if completed, would increase its production of plutonium for nuclear weapons by a factor of ten.

You can read the full analysis here.

US officials declined to comment on the satellite images, but a source “familiar with the matter” told CNN’s Zach Cohen that “Preparatory activities speak to intent, planning and long held goals.”


Satellite images taken by Maxar show that North Korea is connecting the secondary cooling loop of  the 50 MW(e) reactor to a pumphouse on the river. In the image dated April 20, construction equipment is visible, as are what appear to be pipe segments. By May 7, North Korea had buried the pipe. This is the first unambiguous indicator that North Korea is moving to complete the reactor.

The connection of the cooling loop helps explain other activities seen at the 50 MW(e) reactor in recent years. For example, in May 2021, North Korea demolished a building that we believe was intended to house a cooling pond for spent fuel. The demolition work was observed at the time, but its purpose was ambiguous; did North Korea plan to replace it, or simply to dismantle it? Connecting the secondary cooling loop suggests, in hindsight, that the demolition of the apparent spent-fuel building was an early sign that North Korea intends to complete construction of the reactor. 

It is difficult to estimate how quickly North Korea could complete construction of the reactor.  One major question relates to the overall condition of the reactor building. Although North Korean officials expressed the view in 2006 that it could be repaired, one observer subsequently noted that the building appeared to be in poor condition.  Another question relates to North Korea’s ability to produce key components for this reactor, which is much larger than the 5 MW(e) reactor that North Korea has operated since the late 1980s.

Once complete, the 50 MW(e) reactor would produce about 55 kilograms of plutonium per year, a ten-fold addition to the capacity of the 5 MW(e) reactor currently operating at Yongbyon. This corresponds to at least a dozen new nuclear weapons a year, depending on how much plutonium each North Korean weapon uses.

Increasing plutonium production by about a factor of ten would allow Kim Jong Un to vastly expand North Korea’s stockpile of nuclear weapons in service of both building a large tactical arsenal and equipping long-range missiles with multiple warheads.  Along with North Korea’s preparations to resume nuclear testing, construction work at the 50 MWe reactor underscores the seriousness of Kim Jong Un’s commitment to acquiring a modernized and enlarged nuclear arsenal that would allow North Korea to respond to a US invasion with the preemptive use of large numbers of nuclear weapons.