The International Atomic Energy Agency(IAEA) says a new experimental light water reactor(LWR) in North Korea’s Yongbyon nuclear complex appears to have gone into operation for the first time. 

IAEA Director-General Rafael Grossi revealed the assessment in his opening remarks for the agency’s board of governors meeting in Vienna, Austria on Thursday, citing a strong outflow of water observed from the reactor’s cooling system since mid-October. 

The IAEA chief said that such observation is “consistent with the commissioning of the LWR,” adding that the “discharge of warm water is indicative of the reactor reaching criticality.”

The latest discharge suggests that the North has begun activating a larger LWR than the five-megawatt reactor it has in Yongbyon. 

Grossi said “the LWR, like any nuclear reactor, can produce plutonium in its irradiated fuel, which can be separated during reprocessing, so this is a cause for concern.”

He added that the IAEA cannot confirm the operational status of the LWR as it does not have access to the Yongbyon facility.