Explainer-What to know about North Korea's nuclear weapons programme

By Josh Smith

SEOUL (Reuters) - North Korea has disclosed the first photos of a uranium enrichment site designed to produce weapons-grade fuel for its nuclear bombs.

Here's what we know about its growing nuclear arsenal.

WHY IS NORTH KOREA BUILDING NUCLEAR WEAPONS?

North Korea says its arsenal of nuclear weapons and ballistic missiles to carry them are necessary to counter threats from the United States and its allies, which fought the North during the 1950-1953 Korean War.

Pyongyang also often touts the weapons as a matter of national prestige and proof of the country's power.

North Korea has the capability to deliver nuclear weapons on a variety of land-based missile systems, including intercontinental ballistic missiles (ICBMs) with ranges capable of targeting the continental United States, according to the U.S.-based Arms Control Association.

Critics, including those in Washington and Seoul, say the weapons are destabilising, pose a threat to the North's neighbours, and divert resources away from the country's impoverished citizens.

The United Nations Security Council has passed multiple resolutions banning North Korea's nuclear weapons and ballistic missile development, though council members Russia and China have blocked new sanctions and called for existing ones to be rolled back.

HOW MANY NUCLEAR WEAPONS DOES NORTH KOREA HAVE?

State media have shown photos of various types of warheads but North Korea has never disclosed the number of weapons it possesses, and analysts and foreign intelligence agencies have only rough estimates.

In July a report by the Federation of American Scientists concluded that the country may have produced enough fissile material to build up to 90 nuclear warheads, but that it has likely assembled closer to 50.

Lee Sang-kyu, a nuclear engineering expert at South Korea's Korea Institute for Defense Analysis, said North Korea is estimated to have 80-90 nuclear warheads of uranium and plutonium, and that is expected to rise to 166 by 2030.

HOW DOES NORTH KOREA BUILD ITS NUCLEAR WEAPONS?

North Korea has facilities scattered across the country that contribute to its nuclear programme, including mines where raw uranium is gathered, enrichment facilities and nuclear reactors for turning uranium and plutonium into bomb fuel, and weapons assembly plants.

Built in the late 1950s with Soviet aid, the Yongbyon Nuclear Scientific Research Center houses at least three reactors which North Korea says are intended to produce electricity.

It also has a fuel fabrication facility and a plutonium reprocessing plant, where weapons-grade materials can be extracted from spent fuel rods, according to the Nuclear Threat Initiative (NTI), a Washington-based think-tank.

It is one possible location of the enrichment facility shown on Friday. North Korea is also believed to have more centrifuges, including at a site in Kangson.

WHERE DOES NORTH KOREA TEST ITS WEAPONS?

Punggye-ri Nuclear Test Site is in a mountainous region in the far northeast of the country, about 100 km (62 miles) from the border with China.

North Korea has conducted all six of its nuclear tests at the site, in 2006, 2009, 2013, January 2016, September 2016 and September 2017. Analysts doubted North Korea's claim that the January 2016 blast was its first thermonuclear bomb, but believe that such a weapon was likely tested in 2017 in an explosion much larger than previous tests.

All the tests have been conducted in tunnels dug deep under the mountains. There are three visible entrances known as the South Portal, East Portal, and West Portal.

The entrances to those tunnels were blown up in front of a small group of foreign media invited to view the demolition when North Korea closed the site in 2018, declaring a self-imposed moratorium on nuclear weapons tests.

Kim has since said he no longer feels bound by the moratorium, with denuclearisation talks stalled since 2019.

In 2022 satellite imagery showed North Korea working to restore some of the tunnels, raising the prospect of new tests.

(Reporting by Josh Smith; Editing by Stephen Coates)