|Learning to Contain Underground Nuclear Explosions|
By Dr. Robert R. Brownlee - June 2002
Sometime in 1956 Dr. Alvin Graves, Division Leader of the Test Division at Los Alamos told me that we were going to have to test underground in order to reduce fallout as much as possible. He asked me to see what I could learn about it by making what calculations I could.
The temperatures and pressures generated by a nuclear explosion are such that there was considerable doubt that any underground test buried at a "reasonable" depth could be contained.
In 1956 we were severely limited in computing capabilities-compared to nowadays they were laughable, and miniscule, and arguably nonexistent. I had the equations of state of four materials. They were air and water, aluminum and uranium. As it happens, there is a lot of aluminum in NTS soil, so I called that "earth". I called that of uranium "fire", and the others were air and water, so with earth, air, fire and water, how could I fail?
In attempting to mock up the earth, I had some information about NTS soil densities and water content. I used a cylindrical pipe filled with air of several densities, depending upon the possible use of vacuums. I was allowed considerable freedom to choose other parameters as I wished. For example, what might the efficacy of plugs of various masses be, and where might they be placed for optimum results. I worked regularly with Bill Ogle, the deputy division leader, and we decided to have a first test in an "empty" pipe (cables were present), open at the top. Then we would do a test with a cap, and then do tests with plugs, the first one used to be in the middle of the hole, and the second one at the bottom. Thus we hoped to learn from test to test, acquiring data and information incrementally. Incidentally, the Pascal B test, and those immediately following, had a 4-foot diameter pipe. The cap welded to the top of Pascal B was four inches thick, so was of appreciable mass from a "man-handling" point of view.
The first test of our "series" was Pascal A, with results as documented.
For Pascal B, my calculations were designed to calculate the time and specifics of the shock wave as it reached the cap. I used yields both expected and exaggerated in my calculations, but significant ones. When I described my results to Bill Ogle, the conversation went something like this.
Ogle: "What time does the shock arrive at the top of the pipe?"
Bill was quite delighted with the answer, for he had never before heard a velocity given in terms of the escape velocity from the earth! There was much laughter, and the legend was now born, for Bill loved to report to anybody who cared to listen about Brownlee's units of velocity. He says the cap would escape the earth. (But of course we did not believe that would ever happen.)
The next obvious decision was made. We'll put a high-speed movie camera looking at the cap, and see if we can measure the departure velocity.
In the event, the cap appeared above the hole in one frame only, so there was no direct velocity measurement. A lower limit could be calculated by considering the time between frames (and I don't remember what that was), but my summary of the situation was that when last seen, it was "going like a bat!!"
As usual, the facts never can catch up with the legend, so I am occasionally credited with launching a "man-hole cover" into space, and I am also vilified for being so stupid as not to understand masses and aerodynamics, etc, etc, and border on being a criminal for making such a claim.
I'll add that we learned a lot with our series of low-yield tests. Plugs helped, but the closer to the nuclear device, the better. "Tamping" the device is better yet, and there are some ways to do that which are more clever than others. Mostly we learned that even an empty hole could cause a reduction to the atmosphere of as much as 90 percent, depending on specific design parameters. Later we were to see that if the hole is deep enough and the yield is high enough, an empty hole will close completely, allowing nothing whatsoever out except the initial light, which is not radioactive of course. In time, the tests became very sophisticated-and expensive, but we were able to achieve complete containment for almost every test, and for all but a handful of those that had containment "failures", nothing was detected off site. So I would judge our containment efforts to be quite successful. The case for these views are pretty well laid out in the book Caging the Dragon, by Carothers.
But it took time and money!
Special Thanks to The Nuclear Weapon Archive