Rob Edwards in New Scientist writes about a material called FOGBANK, which is used in US nuclear weapons such as the W76. (Ian Sample in the Guardian also picked it up.)

Edwards’s article contains some speculation on the use of FOGBANK, which is something I’ve been looking into since Frank Munger started asking uncomfortable questions about delays in the W-76 Life Extension Program in January (January 24, January 25, February 12, and March 6).

I believe that FOGBANK is an aerogel used as the interstage material — Howard Morland’s exploding styrofoam — in three thermonuclear designs: the W76, W78 and W80. I believe it is recycled, and will be produced, at the so-called Purification Facility at Y-12.

John Field thinks FOGBANK is an aerogel based on a hypothesis he has about how a thermonuclear secondary works. I suspect he is right for a more mundane reason. Aerogels (that’s one on the right, with a brick sitting on top of it) are extremely low-density materials that feel like polystyrene and look like smoke or fog. Indeed, the nicknames for aerogels include “frozen smoke” and “San Francisco fog.”

Witty bastards in our nation’s nuclear weapons complex, eh?


There are not many official references to FOGBANK, but I’ve collected them for you here. I think they link FOGBANK, ACN, interstage material and the Purification Facility very tightly.

  • A variety of DOE Nuclear Explosive Safety documents describe FOGBANK as a material “used in nuclear weapons and nuclear explosives” along with Lithium hydride (LiH) and Lithium deuteride (LiD), Beryllium (Be), Uranium hydride (UH3), and Plutonium hydride.
  • A Y-12 employee was paraphrased as saying “They’re starting to make things with FOGBANK again after many years of not using it, and it’s a big concern.”
  • NNSA Administrator, Tom D’Agostino, has mentioned FOGBANK twice, linking it to the interstage material of a Navy nuclear warhead and the flammable chemical, Acetonitrile (ACN):

Finally, there is a material that we currently use and it’s in a facility that we built … at Y-12. It’s a very complicated material that — call it the fog bank. That’s not classified, but it’s a material that’s very important to, you know, our life extension activity. And we are spending a lot of money as part of the [LEP] in making — trying to … produce that material, and we are not out of the woods yet. And it’s a material that uses a cleaning agent that is extremely flammable. And in fact, we had to build a separate spillway, external, because if this stuff ever caused a problem we would want — we would have to put it in this area. It’s expensive to operate and maintain that facility.

My ideal world would be — I don’t have to make that material anymore. I don’t have to deal with these chemicals anymore. I can take advantage of outsourcing as — in fact, one of the things on the RRW — in a closed session I would talk about what we would outsource on this — what we think we can outsource on this weapons system that would reduce cost. Want to take advantage of all those things.

[Emphasis mine. Hearing of the Energy and Water Development Subcommittee of the House Appropriations Committee, March 29, 2007]

There’s another material in the — it’s called interstage material, also known as fog bank, but the chemical details of course are classified.

That’s a facility that we currently have right now. It’s a very complicated process. I use that to support the Navy’s program. It takes a tremendous effort to operate this facility. It’s dealing with toxic materials — hazardous to our workforce — but it’s required. It’s the way we did things back in the Cold War. The RRW will allow us to not have to develop and maintain that capability. And that’s very important because that’s got a long-term cost to run and it’s got an impact on our workforce, just like the case material.

[Emphasis mine. Hearing of the Strategic Forces Subcommittee of the Senate Armed Services Committee, March 28, 2007]

We have another material that requires a special solvent to be cleaned. It’s — the chemical term is ACN. But that solvent is very volatile. It’s very dangerous. It’s explosive. And I’m required to use it because that’s what we used 30, 40, 50 years ago, when we made this special material. And so these are the kinds of things that I can eliminate.

[Emphasis mine. Remarks by Thomas D’Agostino at the Woodrow Wilson Center, June 15, 2007]

  • NNSA released a chart (below) on features of the RRW, including the replacement of an “expensive ‘specialty’ material … eliminating need for unique facilities” in the interstage.

  • I believe the so-called “Purification Facility” at Oak Ridge replaced building 9404-11 and is used to recycle and produce FOGBANK. Dennis Ruddy, then-president and general manager of BWXT Y-12, the government’s contractor, said the Purification Facility was used to refurbish a classified material:

“It reprocesses a material that we’re taking out of weapons so that we can reuse it in refurbished weapons. That’s probably all I can say.”

“The material is classified. Its composition is classified. Its use in the weapon is classified, and the process itself is classified,” Ruddy said.

  • John Ainsle, in an excellent backgrounder, quotes a Los Alamos document as stating that the “evaluation of internal gas generation of a Fogbank in a neutron environment was started in FY95.”
  • The Purification Facility uses ACN. On three separate occasions in March 2006, workers evacuated the Purification Facility after alarms went off. According to DOE documents, the Purification Facility is alarmed to monitor for acetonitrile (ACN) levels.
  • Contrary to D’Agostino’s claim that FOGBANK is used to “support the Navy’s program,” I would think three warheads — the W76, the W78, and the W80 — use FOGBANK based on when those warheads were produced.