Jeffrey LewisMore On Disablement

Top of the reactor core at the Yongbyon 25 MW Reactor,
Photo taken May 1992, courtesy of the IAEA (via ISIS)

The other week, I noted the odd appearance of the word “disablement” in the vocabulary of various State Department officials to describe what North Korea was supposed to do to its 25 MWth reactor at Yongbyon. At the time, I strongly suspected this was a made up word (See: “Disablement, Whatever That Means,” February 19, 2007).

Well, turns out the US national security bureaucracy is trying to figure out what disablement means, too. The question is an interesting one, because we would like to disable the reactor, but in a manner that would permit the IAEA or others to conduct verification and forensics activities to determine the total amount of plutonium produced in the fuel rods.*

Thanks to a friend in the national security community, Arms Control has obtained the Department of Energy’s candidate answer. The two page “official use only” document, entitled On the Issue of Initial Disablement Activities at a Reactor, recommends simply cutting the drive chains that lower the control rods into the core:

[O]nce the control rods are fully inserted in the core and the reactor is safely shut down, one could disable this drive mechanism to prevent the operator from removing the control rods. The simplest way to do this might be to detach or “cut” the drive chains from the control rods. Without the control rods being a connected to the motors, they cannot be removed from the core. And, if the control rods cannot be removed from the core, the reactor cannot be restarted. [Emphasis added]

DOE argues that this is not a permanent or irreversible disablement, but the task of reconnecting the drive chains “would require a reasonable amount of effort from which to recover plant operation.”

Read: Department of Energy, On the Issue of Initial Disablement Activities at a Reactor, March 2006.

*For more on nuclear archeology, see Steve Fetter, “Nuclear Archaeology: Verifying Declarations of Fissile-material Production,” Science and Global Security 3:3-4, 1992.


  1. John Fleck (History)

    As an aside, this is pretty obviously a misuse of the “official use only” designation. As implemented by DOE regulations, it is meant to be applied to documents believed to be exempt from FOIA. There’s nothing in this document that appears to meet any of the FOIA exemptions. But “OUO” is being slapped willy-nilly on DOE documents these days merely to shield them from public view.