The IAEA nuclear watchdog said warm water streaming out of the light-water reactor at North Korea's Yongbyon facility suggests that the plant is operational.
The International Atomic Energy Agency (IAEA) has found that a new nuclear reactor is apparently operational at North Korea's Yongbyon nuclear complex, sparking concern about an additional potential source of plutonium for nuclear weapons.
North Korea has so far used spent fuel from a 5-megawatt nuclear reactor at Yongbyon to meet its plutonium requirements to run its nuclear facility.
However, according to the IAEA, a seemingly new discharge of warm water from a larger light-water reactor suggests that it is also operational.
"The discharge of warm water is indicative the reactor has reached criticality," IAEA chief Rafael Grossi said in a statement on Thursday, meaning the nuclear chain reaction in the reactor is self-sustaining.
Since October, the IAEA has observed a strong outflow of water from the light-water reactor's cooling system, indicative of ongoing employment of the reactor. The presence of warm water is one of the more recent clues, Grossi said.
Concerns over expansion of North Korea's nuclear programme
In 2009, North Korea expelled international investigators so the IAEA does not have access to the country. The agency now relies on satellite imagery for investigating North Korea.
Without access, the IAEA cannot confirm if the nuclear reactor is operational, 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 said, adding that the advancement of North Korea's nuclear program was "deeply regrettable."
A study from the James Martin Center for Nonproliferation Studies (CNS) in California also concluded the reactor could be operational.
It added that it may be "a significant source of nuclear material" for the nuclear weapons program, which is banned by UN Security Council resolutions.
Another study by the Institute for Science and International Security estimated that the light-water reactor "could allow a surge in plutonium quantities at an estimated rate of about 20 kilograms of plutonium per year, a rate four to five times larger than that of the small adjacent reactor."