It looks like one outcome of the Hanoi Summit may be that North Korea will follow through on its offer to close the Yongbyon nuclear facility, a pledge made at the Pyongyang Summit with @moonriver365/@thebluehousekr. A thread.

This will be the third shut down of the gas-graphite reactor at Yongbyon. Previous shutdowns lasted from 1994-2003 and 2007-2013. This would be a good outcome, but it is important to be precise about what a shut-down accomplishes and what it does not.

After the November 1994 shutdown, North Korea unloaded spent fuel from the reactor and, after it cooled, allowed NAC Int'l to can that fuel. When North Korea restarted operations at Yongbyon in 2003, it popped open the cans and harvested the plutonium.

The 2007 shutdown was part of the poorly named, multi-step "disablement" process under the Six Party Agreement. North Korea even imploded the cooling tower at US request, but later reconnected the secondary cooling loop to a pumphouse similar to the one in Syria.

Will this shutdown require North Korea to do more than previous shut-downs, which were ultimately reversed? The "D" in CVID was always dismantlement because Republicans used to believe Yongbyon must be dismantled, not merely shut down.

The gas-graphite reactor is now >30 years old. But Magnox reactors can last longer than that. Its possible this is a sweet spot where the reactor is still a proliferation risk to us, but creaky enough that North Korea is willing to part with it. inis.iaea.org/collection/NCL…

One of my hobby horses is insisting North Korea allow international experts to sample the graphite, which would allow us to estimate plutonium production. But I expect that North Korea won't allow that. After all, it sanitized Punggye-ri prior to closure.
tandfonline.com/doi/full/10.10…

Another question relates to the other facilities at Yongbyon. Will North Korea disable the light-water reactor too? Allow inspectors to verify its design? Will it disable the reprocessing, enrichment, conversion and fuel fabrication plants? That's implicit at the moment.

Side note: @ODNIgov believes North Korea has at least two additional enrichment facilities. One near Kangson and third enrichment plant at an undisclosed location. So, this may *slow* the growth of North Korea's fissile material stockpile, but it would not *cap* it.

Recently, a lot of experts have been taken by @SiegfriedHecker's sensible observation that North Korea's more sophisticated designs use tritium that is at least partially produced in the gas-graphite reactor at Yongbyon.

Given the short half life of tritium (12 years), ending production in North Korea would mean that North Korea's stockpile would shrink over time. This would eventually effect North Korea's most sophisticated nuclear designs.
scienceandglobalsecurity.org/archive/sgs05k…

I agree with @SiegfriedHecker that this is a good outcome -- although I would caution we don't have a complete picture of North Korea's sources and stockpile of tritium. Tritium is sold commercially and illicit transfers between proliferators have happened.

There is also the possibility of a covert nuclear reactor. (North Korea very nearly constructed one in Syria in 2006.) But "covert reactors" are often invoked with no evidence for purely partisan purposes, as the unhappy story of Kumchang-ri shows.
nytimes.com/1998/08/17/wor…

There is a lot more to say, although at this point we are waiting for details. So, like my doctoral dissertation, I am not going to finish this thread. I am just going to stop.