Satellite images taken by Airbus Defence and Space and analyzed by a monitoring group suggest North Korea has been making rapid upgrades to infrastructure at the country’s only-known nuclear reactor. Watchdog group 38 North says the images were taken on June 21 and show improvements to the nation’s Nuclear Scientific Research Center at a “rapid pace”, despite vague promises of “complete denuclearization” the same month.
Yongbyon is home to reactors used for producing plutonium, which fuels the country’s weapons, and for the generation of electricity for civilian use. The authors caution that these images are not proof that Kim Jong Un has plans to renege on his pledge to the US, but what the updates are for still remains unclear.
"There is actually no agreement in place that obligates specific steps on denuclearization. So far, moves have been unilateral gestures," Jenny Town, research analyst with 38 North, told IFLScience. "Until a deal is in place that specifies steps needed by both parties, I would expect operations to continue at key facilities."
Modifications started in March to the system used to cool the 5-megawatt electric (MWe) plutonium and now looks to be complete from the outside. However, it remains unclear whether the reactor is operating and, if so, at what level.
"Improvements to cooling system infrastructure are important as they should improve production capability of the 5 MWe plutonium and may be needed to bring the ELWR online, which would expand North Korea’s plutonium production program," said Town.

A new channel from the nearby Kuryong River has been dug out. Designed to serve as a cooling mechanism for Yongbyon reactors, the river is at intended design levels and flowing through the dam at capacity. The authors note riverbed dredging continues upstream of the reactor area as well.

Satellite images also show two new buildings near the experimental light water reactor (ELWR), including a four-story engineering building and another unknown structure. 38 North says there is no evidence to suggest operations have begun.
The status of the radiochemical laboratory, where plutonium is separated from fuel rods, is also uncertain, but the report suggests it seems active.

Coal bins at the thermal plant appear to have been somewhat depleted since images were last analyzed in early May, which suggests some sort of operations are continuing. What those operations are, however, are "difficult to discern".

The roof at the uranium enrichment plant seems to be increasing in a stain, which is indicative of continued operations; the staining is caused by water vapor deposits from cooling units for gas centrifuges.

Since late last year, new buildings have been constructed near a presumed radioisotope production facility.
"At least one of these new buildings could be intended to store rail-delivered chemicals to support operations in the main production building, as over the past month, a below-grade pipeline has also been completed that connects them with the main production building, thereby providing a possible means for transferring such chemicals," said the authors, who continue that little else is known about this facility other than it was constructed in 2015 and has since seen various modifications.

Town says attention to the developments reminds leaders that the declaration from the Singapore Summit was not a nuclear deal but instead set the agenda for negotiations.
"The US needs to be ready to provide measures that also meet North Korea’s needs along the way," she said.