A new reactor at North Korea's Yongbyon nuclear complex appears to be operating for the first time, the U.N. nuclear watchdog and independent experts said on Thursday, which would mean an additional potential source of plutonium for nuclear weapons.

North Korea has for years used spent fuel from a 5-megawatt nuclear reactor at Yongbyon to produce plutonium for its nuclear arsenal but a telltale discharge of warm water from a larger light-water reactor suggests it is coming online, too, the International Atomic Energy Agency said.

"The discharge of warm water is indicative the reactor has reached criticality," IAEA chief Rafael Grossi said in a statement, meaning the nuclear chain reaction in the reactor is self-sustaining.

The IAEA has not had access to North Korea since Pyongyang expelled its inspectors in 2009. The agency now observes the country mainly using satellite imagery. Without access, the IAEA cannot confirm the reactor's operational status, Grossi said.

The IAEA says it has observed a strong outflow of water from the light-water reactor's cooling system since October, suggesting ongoing commissioning of the reactor. More recent indications are that the water was warm, 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".

 

'SURGE IN PLUTONIUM'

Researchers at the James Martin Center for Nonproliferation Studies (CNS) in California also concluded the reactor is most likely operating, adding that it may be "a significant source of nuclear material" for the nuclear weapons program, which is banned by U.N. Security Council resolutions.

In an April report, the D.C.-based Institute for Science and International Security estimated 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".

That study concluded North Korea may have anywhere from 31 to 96 nuclear warheads, depending on the types of devices being built and which fuel is being used.

News of the reactor's operation comes as North Korean leader Kim Jong Un said an intercontinental ballistic missile (ICBM) test this week showed his country would not hesitate to launch a nuclear attack if an enemy provokes it with strategic weapons.

North Korea has conducted six nuclear tests; the last one was in 2017.

Activity at North Korea's nuclear test site at Punggye-ri has led to months of speculation that it could resume nuclear weapon testing as it seeks to miniaturise warheads for use in ballistic missiles. (Reporting by Francois Murphy in Vienna and Josh Smith in Seoul; Editing by Christopher Cushing and Gerry Doyle)