North Korea banned U.N. nuclear inspectors from Nyongbyon in 2009, so it is difficult to know what exactly is happening on the site.
The reactor has been the source of plutonium for the country’s small arsenal of weapons.
North Korea had announced in 2013 that it planned to renovate and restart nuclear facilities, including the reactor which was closed down in 2007.
The website reported continued work at the Experimental Light Water Reactor (ELWR) transformer yard at the site. By the end of 2015, a second transformer was installed in the area, and a new road was also built on the site next to the transformer yard.
The satellite images also show continued activity with vehicles of various sizes being moved around the back of the 5MWe reactor hall. Website 38 North said a reason for the activity could be due to continued maintenance to the site, and the activity may indicate that the reactor is being worked on to bring it back to service.
There are at least three or four buildings in the early stages of construction, according to 38 North.
North Korea has developed two ways to create fissile material for weapons, enrichment of uranium and separation of plutonium. U.S. experts estimate that North Koreans may already have about 10 bombs, but that could grow to between 20 and 100 by the next four years.
Meanwhile, President Obama recently met with the leaders of Japan and South Korea to discuss ways of countering a nuclear attack. Obama called on North Korea to give up its nuclear weapons..
China also agreed to fully carry out recent economic restrictions imposed by the U.N. Security Council against North Korea.
The Associated Press contributed to this report.
