What Might We Learn From North Korea’s Nuclear Test Site?

Kim Jong Un announced that he would close North Korea’s nuclear test site. The Trump administration has greeted this announcement as part of its success in dealing with North Korea.

But North Korea may be doing less than Trump thinks.

The nuclear test site consists of a number of tunnels for underground nuclear explosions and support facilities for that testing. KCNA, the North Korean news agency, has released a list of activities to close the site.

First, explosives will be used to collapse the tunnels, KCNA said. Then, entries to the site will be blocked and all observation facilities, research institutes and guard structures will be removed. Guards and researchers will be withdrawn, and the area surrounding the test site will be closed.

Journalists from China, Russia, South Korea, the United States and the United Kingdom will be invited “in the interests of transparency” to view the site and a dismantlement ceremony scheduled for late May.

Nothing has been said about inviting specialists from the International Atomic Energy Agency or the Comprehensive Test Ban Treaty Organization, who might be able to evaluate how the test site has been used and to what extent it is being deactivated.

There has been speculation that the test site was damaged irreparably by North Korea’s last big test. This is possible, but unlikely.

In the past two weeks, buildings have been removed at the site. It is not clear whether international visitors will be allowed access to the tunnels.

The modifications that are being made to the site are probably to remove indications of the kinds of tests that were done and how the North Koreans obtained information from them. What might be learned if experts had access to the tunnels?

In the announcement that the test site would be closed, subcritical experiments were mentioned for the first time. It would be very likely that North Korea would have done such tests in developing their devices, but this is the first they have admitted it. Subcritical experiments give information about the behavior of fissile and other materials under extreme temperatures and pressures and about the behavior of an entire weapon assembly. There are many ways to do them, and seeing a North Korean experimental setup would reveal much about how sophisticated their program is.

At one time, subcritical experiments required significant amounts of fissile material. The Soviet Union did such experiments at the Semipalatinsk Nuclear Test Site (SNTS), now in Kazakhstan. Some they did in the open, and scattered metallic plutonium on the surface. Others were done in large containers, some of which were in tunnels and others on the surface.

As part of the decommissioning of the SNTS, the US Defense Threat Reduction Agency sealed the tunnels by dynamiting the entrances. This collapsed the tunnel perhaps ten meters in. To retrieve the plutonium, the tunnels had to be opened again. The story is here. The top photo is mine, of one of the collapsed tunnels in the Degelen Mountains.

One question would be whether North Korea did those kinds of experiments.

More modern subcritical experiments can be seen in these two videos. The sound on the second one is annoying, but it’s the only way you can tell something has happened. And there are other possibilities.

Other useful information from the tunnels might be more about the geology of the site and, if possible, isotopic sampling where the tests were done.

The test site can probably be reactivated by mining the collapsed entries to the tunnels, or another test site could be developed elsewhere. It will be prudent to monitor overhead imagery for indications of opening another site.

A part of the arms control community raised questions over verification of Iran’s likely subcritical experiments at the Parchin military base and used them to undermine the Joint Comprehensive Plan of Action, the agreement Donald Trump repudiated. It will be interesting if they insist on similar inspections at the North Korean test site.

Which brings us to the overall question of verification of all steps that North Korea takes in any agreement with the United States. From the tweet I’ve quoted, it’s clear that he has no idea what is required.


Cross-posted to Balloon Juice.