Fogbank: That time the US forgot how to make Nukes

The U.S nuclear weapons program is extremely secretive, yet oddly we can still figure some things out about it from the information that is out there. The U.S department of Energy, the government department concerned with the safety and handling of nuclear material, is in charge of one of the largest nuclear stockpiles in the world, and those weapons need to be constantly upgraded and refurbished with newer technologies. Occasionally those technologies get hinted at by politicians when asking for more money, or defending delays, and sometimes its clear that processes to create technologies have been forgotten with engineers retiring. The secret material, publicly refereed to as Fogbank is a great example of this.

Aerial photo of the Y-12 facility
Aerial photograph of the Y-12 facility at Oak Ridge taken around 2007 (Credit: NNSA)

Fogbank first became well known around 2007, when it came to light that it was the root problem behind technical delays in the life extension project for the W76 warhead. This particular warhead is used on the Trident II, submarine launched ballistic missiles. They are known as D5s, and are used by both the U.S Navy, and and the Royal Navy of the UK. It took until 2018 before the W76-1 warheads were finally delivered.

A Trident II (D-5) launch from a submerged Royal Navy submarine
A Trident II (D-5) launch from a submerged Royal Navy submarine. Image from Lockheed Martin, but is a U.S. Department of Defence photo.

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 Fogbank. That’s not classified, but it’s a material that’s very important to, you know, our [W76] life extension activity.

The then NNSA director Thomas D’Agostino, talking to members of the House of Representatives in 2007. He is referring to the Y-12 National Security Complex, located near Oak Ridge.
Y-12 Security Complex
The Entrance building of the Y-12 security complex, a Department of Energy facility located near Oak Ridge (Credit: NNSA).

Late in 2007, D’Agostino described Fogbank as an “interstage material”, which heavily implies that it sits somewhere between the primary and secondary stages of the the two stage thermonuclear weapon. The W76 is a two stage warhead, so would need some sort of material to trigger the second stage. In a thermonuclear bomb, also known as a H-bomb, the first stage creates the easily produced fission reaction (what happens in a nuclear reactor), which creates a superheated plasma at the interstage (the expected role of Fogbank), which then triggers the fusion reaction in the second stage. Fusion is the process that happens in the Sun, and may be the way we power future nuclear reactors.

There’s another material in the [W76] – it’s called interstage material, also known as Fogbank, but the chemical details, of course, are classified,

Thomas D’Agostino speaking to senators late in 2007
NNSA director Thomas D’Agostino in 2009 (Credit: NNSA)

This has obviously lead to many engineers and scientists to comment on possible materials that Fogbank could be. The most common reccuring theme is that it is likely to be an Aerogel, a type of material known as an ultra light gel. Aerogels are extremely light while being surprisingly strong. Invented in the 1930’s, the concept of aerogels have been around for a long time, but it was NASA’s Glen Research Centre that introduced modern methods of manufacture, and even used them on a few space missions such as Stardust. There have been suggestions, such as the one from Jeffery Lewis, an expert on missiles and nuclear weapons, that the code name Fogbank could be a reference to the other nicknames for Aerogels. Names such as “frozen smoke” and “San Francisco fog” have all been used in reference to the light and almost see through solid.

The Stardust dust collector with aerogel blocks. (NASA)
The dust collector with aerogel blocks on NASA’s Stardust spacecraft. (Credit: NASA)

There are a few other things that imply that Fogbank could be an aerogel. In 2007, D’Agostino told legislators that Fogbank’s production process required the material to be purified using “a cleaning agent that is extremely flammable.”. Then in that same year he talked at the Widrow Wilson centre about “another material that requires a special solvent to be cleaned”, potentially the same material, and that the solvent used was identified as “ACN”, the common abbreviation of acetonitrile, a solvent commonly used in aerogel production. He describes the solvent by saying “That solvent is very volatile, it’s very dangerous. It’s explosive.” which describes acetonitrile well.

A 2.5 kg brick is supported by a piece of aerogel with a mass of 2 g.
A 2.5 kg brick is supported by a piece of aerogel with a mass of 2 g. (Credit: NASA/JPL)

More evidence comes from a 2007 briefing slide on a program known as the Reliable Replacement Warhead (RRW), which aimed to develop a new design of warhead to replace a selection of the existing versions. The slide points at an interstage material that is an expensive, “specialty” material that if replaced would eliminate the need for unique facilities. The RRW effort was de-funded in 2008 and cancelled by president Obama the following year.

NNSA slide from a 2007 briefing
The NNSA slide from a 2007 briefing about the RRW program that details the properties of the current interstage material. (Credit: NNSA)

Up until 1989 the Y-12 facility in Oak Ridge had a specialised site known as Facility 9404-11, which was apparently used to create Fogbank. 1989 was the year that the final W76 warhead was finished, so the facility was closed down and a new “purification facility” took its place. The original building was eventually torn down in 2004, and replaced with a new facility, renamed to Facility 9225-3. According to Denis Ruddy, who served as the president of the division of the Babcock and Wilcox Company (BWXT Y-12) that ran the facility between 2000 and 2014, the purification facility reprocessed a material that they were taking out of weapons so that it can be used in refurbished weapons. The material is apparently classified, and the use in the weapon is classified, and so is the process that they follow, unsurprisingly.

It is also public knowledge that this site uses ACN as a part of at least one of the processes going on in it. On three seperate occasions in March 2006, workers had to evacuate the facility after alarms were triggered. According to the Department of Energy, the facility is alarmed to monitor for ACN levels, but it is not confirmed whether the alarms that went off were from ACN. There was also an ACN spill that forced an evacuation of the facility in December 2014, and although there were no injuries, it took months for the facility to get back up and running.

The Purification Facility, also known as Facility 9225-3, at Y-12.
The Purification Facility, also known as Facility 9225-3, at Y-12.

In 2009, in an issue of the Nuclear Weapons Journal, an official publication of the Los Alamos National Laboratory, an article was published that disclosed that there was a decision to restart the manufacture of Fogbank in 2000, and confirmed that it was linked to the W76-1 warhead project. It also revealed that in the years between the projects that the NNSA had lost almost all of its institutional knowledge base regarding the manufacture and development of Fogbank. The article said “Most personnel involved with the original production process were no longer available.” So the newer personnel had to reconstruct the production process from the records. It also mentioned that “a new facility had to be constructed, one that met modern health and safety requirements.” The facility would make sense to be the 9225-3 facility as it stands on the site of the old one. The best part of it all, the new facility, with the new staff using old records to manufacture, created a higher purity final product than the initial W76 warheads used. The problem with this “improved” material was that it was actually too pure,the impurity was actually essential for the final product to work as intended. The process was concluded in 2008, almost a decade after first deciding to restart production, and the W76-1 warheads began that year.

The improved production process
The extremely vauge diagrams shown in the article describing the production process the NNSA initially developed to produce Fogbank in the 2000’s and the improved versions. (Credit: NNSA)

This is one example of how organisations such as the NNSA lose technical institutional knowledge over relatively short periods of time when the technology isn’t being used. They had similar problems with designing high explosive capabilities recently. In March 2020, The director of the Natural Resources and Environment team at the Government Accountability Office, Allison B. Bawden, highlighted that the NNSA had not produced a particular type of high explosives at scale since 1993, and highlighted the issues with Fogbank production as an example. This highlights one issue of governmental technology not being taken on by commercial business to continue. Either way, Fogbank is a prime example of the complexity, and secrecy of nuclear warhead production, and how in that secrecy, technology is lost.