North Korea’s Yongbyon nuclear complex has been undergoing continuous modernization and expansion.

38 North, a U.S.-based website that monitors North Korea, reported Sunday that a comparison of commercial satellite images taken in October and November with earlier photos confirmed active improvements throughout the Yongbyon complex.

The website noted that construction activity has been particularly intense this year around a suspected new uranium enrichment building located northeast of the Radiochemistry Laboratory.

Satellite images captured on October 22 and November 13 show that support buildings, which were incomplete in June, have now been finished.

38 North added that since September, six possible heat exchangers have been installed along the southeast side of the main building.