There was a minor dustup on Twitter between my colleague, Jon Wolfsthal, and the Bulletin of Atomic Scientists. Like many discussions on Twitter, 140 characters at a time just didn’t get the job done.

At issue is an important article that Frank von Hippel wrote proposing transparency surrounding subcritical experiments.  Frank’s article was occasioned by a US subcritical test, named Pollux (along with its twin, another experiment named Castor in the Gemini series).  Frank has long argued, rather sensibly it seems to me, for confidence building measures relating to subcritical experiments in the United States, Russia and China.  I have also suggested that such transparency and confidence building measures ought to be an important part of package designed to win Senate ratification of the Comprehensive Nuclear Test Ban Treaty.*

Pollux was a useful chance to revisit these discussions. Allow me to make a series of apparently unrelated observations.

1. Commending NNSA on Transparency

I find it very hard to fault NNSA in terms of transparency, starting with the press release and video. I understand why Frank argues that the video features some unidentifiable equipment, but I think it is possible to identify some of the equipment, especially in the context of many other images released by NNSA relating to subcritical experiments.

The video shows the vessel that contains the subcritical experiment.  Furthermore, it is shot at an angle that shows some of the diagnostics.  If you reverse this image of Armando or the blurry video of Pollux, I believe you can line up both images with the radiography equipment:

But, really, I must be one of a very small number of people who care about such things.  (Even smaller when we remove people named Ivan or Wei.) I welcome, by the way, discussions about what we can make out from the photographs.  I am just working through them myself.

More important, NNSA has also released information about the diagnostic equipment used in the experiment, including bunch of data about the Cygnus Dual Beam Radiographic Facility and Multiplexed Photonic Doppler Velocimeter, which recently won an award. The best part about the MPDV, by the way, is that the fisheye lens is mounted on a cavity probe. (No, I didn’t just win $100 for working “cavity probe” into a blog post.  Why would you ask such a question?) NNSA also releases statistics on the number experiments, by type, on a quarterly basis.  Overall, I think NNSA does a pretty good job of making information available about subcritical testing.

I also understand Frank’s argument that conducting subcritical experiments at a test site –as the US, Russia and China do–”naturally” creates suspicion.  Having said that, U1A is the facility that was designed to accommodate such experiments.  It is the appropriate technical location.  The solution is not to spoil the Arizona wilderness with a green-field underground test facility.  The solution is a further set of transparency and confidence building measures at existing nuclear weapons test sites.

2. Test Site Transparency

What I take to be Frank’s fundamental point is that, even if the Russians and Chinese made similar efforts at transparency, that wouldn’t solve our confidence building problem. He is right.  As I have noted in reference to Russia and Chinese subcritical testing, lack of transparency has added to suspicions of hydronuclear and low-yield testing, both of which would violate the CTBT.  The Russians, in particular conducted a very large number of hydronuclear experiments, which is a reasonable thing to wonder about.

If we are serious about a CTBT, we need to think about how to distinguish between subcritical experiments, which are not prohibited by the CTBT, and hydronuclear ones, which are.

3. Plutonium and Scaled Experiments

Third, and finally, some of my colleagues have claimed that Pollux was the first “scaled experiment” in which plutonium was used in a scale model of the nuclear weapon. Such experiments are not prohibited by the CTBT.  The major question here is one of cost and feasibility, rather than proliferation.   Nick Roth, Hans Kristensen and Stephen Young wrote:

NNSA officials claim that scaled experiments could yield ten times more data points and save money because one large scaled experiment could replace twenty of the smaller hydrodynamic experiments conducted today. Lab scientists maintain that scaled experiments would require major new equipment investments that are not currently planned. At present, U1a in Nevada apparently does not have the diagnostic equipment needed to harvest the additional data generated by scaled experiments.

I would add that the this experiment was the first use of the Multiplexed Photonic Doppler Velocimeter, which may well resolve the issue of diagnostics.  Don Cook claimed in the press release that “Diagnostic equipment fielded by our scientists resulted in more data collected in this single experiment than all other previous subcritical experiments.”  I think it is worthwhile to be cautious about relying on press releases for factual content, but to a first approximation I would argue that getting more data cheaply without violating the CTBT is a good thing.

Random footnote from above.

* I should add that I am pessimistic about the ability of the United States Senate to ratify any treaty, a pessimism only deepened by the shameful debacle that played out on the UN disability treaty.  So pessimistic, I would say, that the Senate’s forfeit of its constitutional responsibilities makes me a strong supporter of pursuing all international agreements, including those involving arms control, through Congressional-Executive Agreements.