Activity detected at Yongbyon nuclear site: 38 North

An aerial view of the Yongbyon nuclear complex in North Korea in a satellite image analyzed by 38 North, an American think tank, in its report Saturday. [AIRBUS DEFENSE AND SPACE/38 NORTH]

A high level of activity has been detected at North Korea's Yongbyon nuclear complex, suggesting ongoing preparation for a possible nuclear test, a U.S.-based think tank said Saturday.

Washington-based 38 North said recent satellite images of the Yongbyon complex showed "a high level of activity," including signs its 5-megawatt reactor was in continuous operation and new construction was underway near its uranium enrichment plant.

"These developments seem to reflect Kim Jong-un's recent directive to increase the country's fissile material production to expand its nuclear weapons arsenal," the report said.

A satellite image dated March 17 showed ongoing work on a new building near the center's experimental light water reactor (ELWR).

The structure measures approximately 42 meters by 15 meters and has around 20 rooms on the base floor. It will likely serve an administration function, according to the report.

The think tank also detected water discharge from the ELWR in an image dated March 3, suggesting
activity inside the reactor, including normal radioactive decay heat removal "that must be performed when the reactor is shut down for refueling, maintenance or safety-related cooling for various emergency hot shutdown situations."

"Together, the new construction and this recent water discharge seem to suggest that the ELWR is nearing a transition to operational status," it said.

The think tank also detected signs of ongoing construction south of the center's uranium enrichment plant. Enriched uranium is used as fissile material in both nuclear weapons and civilian nuclear energy production.

North Korea conducted six nuclear tests between 2006 and 2017, with many experts warning that the country has completed technical preparations for a seventh test.

The regime continued over the weekend its rhetoric against South Korea and the United States, condemning their joint military training.

"The U.S. and south Korea staged large-scale joint military exercises, Freedom Shield, simulating an all-out war against the DPRK for 11 days from March 13, the longest-ever period," the state-controlled Korea Central News Agency said in its English-language report Sunday, using the acronym for North Korea's full name, the Democratic People's Republic of Korea.

"The U.S. and its followers should never forget the fact that their rival state has possessed the nuclear attack capability in practice as well as the characteristics of the people and army of the DPRK which do not make empty talk."

Seoul and Washington concluded Freedom Shield on March 23, their first large-scale command post exercise in five years, while their ongoing Ssangyong amphibious landing exercise began in Pohang, North Gyeongsang, on March 20.

The latter exercise is scheduled to end Monday.

U.S. Joint Chiefs of Staff Chairman Gen. Mark Milley was supposed to visit Korea last week during the exercises. However, he reportedly canceled his trip at the last minute due to a scheduling conflict with the U.S. Congress.

BY ESTHER CHUNG [chung.juhee@joongang.co.kr]