Fogbank, North Korea’s Hydrogen Bomb and the Reliable Replacement Warhead.

The Reliable Replacement Warhead was a Bush era programme for developing new nuclear warhead designs, which was eventually cancelled but some of its key features live on in the Obama era Interoperable Warhead concept. The RRW programme faced a tough sell in Congress, and arms control and community activist groups mobilised against it. That campaign had a lot to do with the cancellation of the RRW, but Obama’s concern to proceed with nuclear weapons modernisation in a way that didn’t impede his agenda at NPT Rev Cons was also an important factor.

The domestic political factor meant the Reliable Replacement Warhead had to be sold. One means of doing this was to argue that plutonium pits don’t age gracefully so therefore the continued reliability of the legacy stockpile could not be taken for granted. That selling point was shot down by a JASONs study on plutonium pits which demonstrated that they have minimum lifetimes of at least 85 years, and that remaining concerns regarding the reliability of plutonium pits can be handled through stockpile stewardship.

Another argument for the RRW, and therefore against the Science based Stockpile Stewardship Program was that the RRW would be more reliable than continued refurbishment as required because replacing some of the toxic and troublesome to manufacture components of legacy warheads, such as the W76, W78 and W80, would eliminate what we might call problems of tacit knowledge.

But, given the political context at the time, it would not do to simply say this and expect to be taken on trust. Some tangible evidence needed to be provided. One such material, Fogbank, then, briefly, entered centre stage. When in the 1990s the extension of the lifespan of legacy warheads, in the absence of nuclear testing, became a concern it was realised that a key material, Fogbank, would be problematical.

That’s because records were not kept of the process that went into its manufacture, it was a toxic and troublesome substance and as such tacit knowledge was critically important here. This was a problem because the key scientists involved in its manufacture had retired, and to cap things off the plant where it was manufactured, Facility 9404-11 at Y-12, had closed down.

That’s all excellent for showing the weaknesses of Stockpile Stewardship and with the view to developing an argument in favour of the Reliable Replacement Warhead. Here’s a remark from the head of the National Nuclear Security Administration, Tom D’Agostino, demonstrating this

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

Eliminate through the RRW, that is.

In this way, it was eventually revealed that Fogbank is an aerogel, the precise nature and properties of which are of course classified, and is cleaned using acetonitrile which is explosive. Fogbank, it is surmised, is the critical substance used in the interstage of a thermonuclear warhead which couples or channels the radiation from the primary to the secondary so thereby igniting the thermonuclear fuel. Fogbank is what in the image below is depicted as “polystyrene foam.”

Who’s to say that North Korea’s scientists at the Nuclear Weapons Institute weren’t watching this all with keen interest? One suspects that they didn’t have to surmise all for themselves what type of material they needed for the critical interstage of a two-stage thermonuclear weapon. They would have known from the get go that they needed to manufacture for themselves an aerogel cleaned by acetonitrile. This shows why we should not have a generalised incredulity with regard to North Korea’s scientific capabilities.

They weren’t inventing the hydrogen bomb from scratch and they had themselves plenty of information to ensure they didn’t follow blind alleys and take backward steps.

There is of course irony here, for the most lasting impact of the Reliable Replacement Warhead might well be in the interstage of North Korea’s two stage thermonuclear warhead.