In my last post, I discussed the origins of the Reliable Replacement Warhead program (RRW). In this post, I'll look at one example of a change which is being made in the manufacturing of an essential nuclear component, and at what this change means for the debate over RRW.
The component in question here is the "pit," the sphere of plutonium which sits at the heart of a thermonuclear warhead's primary stage.
During the Cold War, pits were made at the Rocky Flats site in Colorado. After Rocky Flats was shut down in 1989, the United States was left without the ability to make new pits for its stockpile.
In 1996, under the leadership of then-director of Los Alamos Siegfried Hecker, the Department of Energy started working on a new pit manufacturing line at Los Alamos’ Technical Area 55 (TA-55). A decade later, replacement pits are finally starting to roll off the line at TA-55. But a debate has broken out over whether or not those pits are functionally the same as those made at Rocky Flats. As a result, the new pits are still waiting to receive their certification for stockpile use.
At the heart of the debate lies precisely the sort of improved manufacturing technique which I mentioned in the last post. At Rocky Flats, plutonium was shaped into pits by stamping, folding and welding, in what’s known as a wrought process. Unfortunately, the wrought process is very infrastructure-intensive, making it good for an industrial-scale facility like Rocky Flats, but less so for a smaller facility like TA-55. The wrought process also creates lots of dangerous plutonium sawdust and shavings, and leaves behind a product with an uneven microscopic texture.
So under Dr. Hecker’s enthusiastic leadership, TA-55 developed a new technique for making pits. The new pits are made using a cast process – that is, molten plutonium (alloyed with some other metals for stability) is poured into pit-shaped molds. The cast process, if done properly, produces a much more uniform product, with less complex equipment and less hazard.
Fast forward ten years.
New pits have been cast and have undergone a gauntlet of tests and computer modeling, but, of course, not underground nuclear tests. Some scientists at the labs, and in the greater nuclear policy community, are ready to certify the pits as functionally equivalent to the Rocky Flats pits in every way. One of these scientists is Raymond Jeanloz, a professor of planetary science at UC Berkeley who does not work at Los Alamos, but is one of the country’s foremost scientific advisors on nuclear issues, and has served as lead author on several JASON studies on stockpile stewardship.
But other scientists are hesitant to certify the pits. They feel that however many tests the cast pits have undergone, they are still irreducibly different from the old wrought pits, and that without a nuclear test, no one can say that they would behave the same. These scientists argue that the new pits should be introduced into the stockpile, but only after the labs have had a chance to modify the warheads to increase their performance margins – that is, only as part of RRW.
Ironically, one of these scientists is Dr. Hecker – the grandfather of the TA-55 pits. He stands by his decision to switch manufacturing techniques, and he insists that the new pits are of excellent quality, but he denies that the labs have been able to test the pits as exhaustively as Dr. Jeanloz claims.
To make matters worse, Dr. Hecker and Dr. Jeanloz disagree just as vehemently on the subject of plutonium aging. Dr. Hecker claims that not enough is known about the different processes which take place as plutonium metal ages to predict safely when aging will begin to affect the dynamics of the pit implosion – and therefore the yield of the warhead primary. He therefore claims that the only responsible thing to do is to replace the current pits after a conservative 50-year shelf-life – and to keep replacing the pits every half-century. This schedule would keep the nuclear labs perpetually busy building, certifying and installing new pits.
Dr. Jeanloz doesn’t buy Dr. Hecker’s claim that plutonium aging is poorly understood. He points out that the nuclear labs have learned so much about plutonium aging just in the last six years that they’re planning on wrapping up a major review of pit lifetimes this coming fall (see page 58 of this report).
Dr. Jeanloz is convinced that the review will give estimates of pit lifetimes "substantially" longer than 60 years. If he's right (and he may not be alone), then there's no need to keep up a high rate of pit production – to say nothing of RRW. Of course, whether the results of that review will be published if the NNSA doesn’t like what it sees is anyone's guess....
Taken as a whole, the dispute between Dr. Hecker and Dr. Jeanloz over pit aging and remanufacture offers a useful behind-the-scenes view of the sorts of arguments which are shaping the technical debate over RRW. Of course, plutonium aging is far from being the only concern behind the drive for RRW. Other parts of the nuclear explosives package, such as the high explosives and the secondary, also raise serious technical concerns. And the political and institutional forces driving RRW, which in some cases have little to do with technical issues, are a whole other subject.
But plutonium science has been, historically, a relatively open field, with much of the progress in the field reported regularly in the open literature. The plutonium aging issue therefore allows us a rare glimpse at the type of scientific and technical debates whose outcomes will determine the future of the nation's nuclear weapons infrastructure and stockpile.
In my fourth and final post on RRW, I'll discuss where RRW stands today, and examine briefly some of the political issues raised by the program.
- Haninah Levine
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Posted by: Rolex at July 2, 2009 03:05 AM