This week North Korea is scheduled to hold a ‘dismantling ceremony’ at its nuclear test site Mount Mantap, where six nuclear bombs have been detonated in the last 12 years. The ceremony will include collapsing the mountain’s tunnels, which allow access to the mountain’s interior, where the bombs are detonated. Satellite imagery suggests that above-ground structures have already been razed and equipment removed, according to analysis from the website 38 North , a project of the Stimson Center in Washington, DC.

But while some hope North Korea’s move signals genuine willingness to end its nuclear weapons programme, others are sceptical: foreign journalists have been approved to attend the dismantling ceremony, but as yet no independent weapons inspectors. Nature spoke to nuclear engineer Suh Kune-yull of Seoul National University – one of South Korea’s few scientific experts on nuclear weapons – to get a handle on the issues.

The United States has demanded that North Korea’s nuclear programme be subjected to a ‘complete, verifiable and irreversible dismantlement’, or CVID. Is that standard hard to meet?

CVID of North Korea is something that we can only dream of. In reality, that kind of thing can never be realized, because of the nature of the country’s nuclear programme. It may have as many as 50 nuclear weapons. But I don’t think Kim is going to disclose information relating to the whole stockpile, because nobody’s sure how many weapons there are. He could declare 5 to 10, with 45 hidden somewhere underground.

There are close to 10,000 underground shelters or facilities in North Korea where they could be stored. Satellite imagery is not helpful, because they may be hidden 50 metres underground. And most of them are military facilities. Inspectors from the International Atomic Energy Agency may not be granted access.

Even if the country’s nuclear programme is dismantled, its experts still know how to build nuclear weapons. Could the programme be restarted?

That’s the million-dollar question. The nuclear workforce includes close to 10,000 people. Unless there are ways to totally erase their memories, there is going to be a way to reverse dismantlement.

If Kim Jong-un happens to change his mind, the country could rearm itself probably in a matter of six months. There’s uranium ore all over the country. My educated but conservative guess is 20 million tons. I have been privately told by several experts at home and abroad that North Korea may have 5 to ten times as much uranium as the rest of the world combined. It’s enough to fuel the whole arsenal for maybe a millennium. From that point of view, CVID may never be realized. Maybe politically, but not technically.

If inspectors were allowed in to observe Mount Mantap before the tunnels are collapsed, what could they learn?

Tunnel number 2, the northern portal of Mount Mantap, is a smoking gun. It is where five of the six tests, and all the most recent ones, have been conducted. Fission products, such as radioactive caesium, strontium, xenon and krypton, must be still lingering in the tunnel. There must also be some uranium plus plutonium around, because less than 1% of the nuclear material in a bomb gets exploded and the rest of it just scatters.

So the radioactive isotopes can be a great source of information as to how much progress North Korea must have made in the past 20 years, and its future nuclear capability. For instance, should we be able to take direct measurements of the xenon to krypton ratio, we can rather easily and assuredly tell if the bomb was of uranium or plutonium origin. Further, if we were to be lucky enough to find any trace of helium-4 and any remnant lithium, we’d be willing to say the sixth test was indeed a hydrogen bomb.

But I don’t think North Korea is going to allow international inspectors or specialists access to those sites. So we’re going to lose all those details.

What are your concerns about the dismantling process?

If they simply choose to blow the tunnels up, then there’s a way of reusing them. It’s just a matter of digging out the rubble. So that’s not a good idea. We have to do it more completely — for example, seal the tunnels with reinforced concrete, poured at the entrance, so that nobody’s going to get in there. But if they just blow the tunnels up, we won’t be able to make sure nobody’s sneaking in there to remove the rubble.

How did you end up studying nuclear warheads?

When I went to the Massachusetts Institute of Technology in Cambridge for graduate school in the 1980s, I had a chance to get involved in research on nuclear warheads. I started out working on what they call thermohydraulics, which was a mix and match of thermodynamics, heat transfer and fluid mechanics. Just by accident, I was involved in the calculation of the implosion of a plutonium bomb.

I don’t think anybody else in the South Korean nuclear-research community has spent as much time thinking about North Korea’s nuclear-weapons programme as much as I have. South Korea’s research focus is on nuclear power, because we are supposed to be working for the peaceful uses of nuclear technology. Also, we are working under the constraints of the 123 Agreement for peaceful nuclear cooperation between the United States and South Korea, which forbids nuclear-weapons development.

Could South Korean scientists help develop nuclear power for North Korea?

This is something I proposed a couple of months ago in an opinion article for the Korean website Energy Daily . I was referring to the Megatons to Megawatts programme, set up between the United States and Russia in 1993. Uranium that might have been used in warheads in Russia was used to fuel US nuclear power plants. It was a pretty cool example of collaboration, and disarmament.

I was proposing to do the same. We can try to take all of North Korea’s nuclear warheads, and then use them to produce electricity from nuclear reactors that are already in operation. Or we can bring some reactors over the demarcation line. That would be a sign of reunification.