North Korea has restarted work on second nuclear reactor - report

Following an extended period of inactivity, North Korea has recommenced building work on a second reactor at its controversial Yongbyon nuclear facility, a report by arms control analysts says.

While it wasn't possible to say when the reactor would become operational, the new reactor was 10 times the size of the current one at Yongbyon and could therefore produce 10 times as much plutonium for use in nuclear weapons, one of the report's authors, Jeffrey Lewis, tweeted on Saturday.

"This would make good on Kim's pledge to increase the number of nuclear weapons," Lewis wrote, referring to North Korean dictator Kim Jong Un.

The report on developments at Yongbyon was published by Lewis, Joshua Pollack and David Schmerler of the James Martin Center for Nonproliferation Studies (CNS) on May 10.

North Korea has laid a pipeline connecting the secondary cooling circuit from the 50-megawatt Number 2 Nuclear Power Plant to a pumping station for cooling water on a nearby river, the report said.

The pipeline was buried by May 7 in "the first unambiguous indicator that North Korea is moving to complete the reactor," the report said.

The report estimates the reactor will be able to produce 55 kilogrammes of weapons-grade plutonium a year once it goes online,a vast increase on what the old 5-megawatt reactor could produce.

Pyongyang's interest in ramping up plutonium production suggests it has redoubled it efforts to develop tactical nuclear weapons.

North Korea is subject to international sanctions for its nuclear weapons programme, which has been the source of major international concern for years, particularly for nearby South Korea and Japan.