The U.S. last produced nuclear warheads in the 1980s. It cannot presently produce any more. Sandia National Laboratories and other national labs have developed a huge machine to test the old weapons and validate future designs.
The machine, called Scorpius, is one hundred yards in length and will operate 1,000 feet below the Nevada desert. In essence, it’s a giant $1.8 billion X-ray machine which will capture snapshots in time of plutonium as it is compressed with high explosives, creating conditions that exist just prior to a nuclear explosion.
That’s what happens when a nuclear warhead detonates on or over its target. Up until 1992, when a nuclear testing moratorium was agreed to by President George H.W. Bush, underground test implosions of nuclear warheads confirmed the reliability of weapons in the existing nuclear stockpile and the viability of new warhead designs.
Since those days 30-plus years ago, America has relied on computer simulations to theoretically describe the hydrodynamics of plutonium in nuclear warheads as they age.
Those simulations are based on above-ground facility tests of the implosive behaviors of surrogate materials like Tungsten. But their inherent differences with plutonium cannot be accurately accounted for. “Plutonium is a very weird material,” says Jon Custer, Sandia National Laboratories’ Scorpius project lead.
Sandia has designed and is building an electron beam injector that will create the very bright X-ray flashes that Scorpius will use to make images. Other portions of the large, complex machine are being designed and built by teams from Los Alamos and Lawrence Livermore national labs.
The need to confirm the fidelity of the very complex computer models that the U.S. nuclear enterprise has used to validate the functionality of our nuclear stockpile is obvious. They’ve been sitting around for decades.
“If you went back to the [late 1980s] and told anybody working on nuclear weapons that they would still be in the stockpile 40 years later, they would have laughed at you,” Custer says.
The U.S. National Nuclear Security Administration (NNSA) hasn’t simply ignored them, Custer explains.
“It’s been 30 years since we set a [nuclear warhead] off for real. We haven’t done nothing in that time. Between Los Alamos, Livermore, Sandia and all the partners, we’ve spent a lot of time developing tools and techniques to measure everything we can think of. Scorpius is the latest tool that will allow us to compare the [computer] models, in detail, of what should happen to what actually does happen.”
Custer confirms that America has reached the point where it really needs Scorpius to check the functionality of the warheads in its aged stockpile, to bolster confidence in whether they will actually work if needed next year, next month, tomorrow.
Scorpius will do that by taking four to eight X-ray images of imploding plutonium in a three-microsecond window. Plutonium devices representative of warheads in the stockpile will be put through experimental implosions millionths of a second long.
“We do it exactly as a nuclear weapon would do it,” Custer explains. In essence, engineers set off a nuclear reaction and halt it before its cycle ends or “goes critical” – non-explosive testing in keeping with America’s nuclear treaty agreements.
The experiments will be largely automated. A few dozen engineers underground (with more above ground) will control the implosion and operate Scorpius. Numerous other measurements will be recorded during the event as well.
Scorpius is designed to capture X-rays of two subterranean plutonium experiments per year for the next 30 years, a total of 60 events. As such, it is only intended (along with the experiments) to validate the likely performance of a representative sample of the stockpile.
Consider that the U.S. has 3,750 nuclear warheads in its stockpile, 2,000 of which are waiting to be dismantled. Some of the data from the experiments will be used to underpin the design of new warhead technology. Technology in general has moved ahead by leaps and bounds.
Tests with Scorpius are expected to show that newly designed weapons of the future will function if called upon, even though constructed mainly from supercomputer designs and potentially incorporating new materials and unanticipated electronic advances.
Daniel Sinars, director of Sandia’s Pulsed Power Center, said in a press release, “We are entering an era where our modernization programs are going to start making significant changes to the nuclear explosive packages, even if the performance characteristics of the weapons don’t change. That is, they are not ‘new’ weapons, but they may have a lot of new technology.”
As with existing weapons, researchers will compare the X-ray imagery of what is actually happening with plutonium reactions in new devices with what highly sophisticated supercomputer models predict. One might think of Scorpius as a check on virtual design.
How confident is Sandia’s Custer that Scorpius will show that existing model simulations for warheads new or old are accurate?
“I don’t want the modelers to get mad at me,” he jokes. “I think we’re going to be close but I personally would be disappointed if we didn’t see something odd.”
Translating, that means that experts from the national labs are pretty confident that the old nuclear weapons in our stockpile will work as intended. But there could be surprises.
It’s unlikely at present that we’ll get another Scorpius machine even if having it would make solid sense. Cost, as always, is the reason. Custer told me that the perfect Scorpius is actually two machines – situated adjacent to each other at right angles so each event would be captured in two views from different angles and combined in a single rich X-ray.
Such an arrangement was proposed a decade ago, but cost and schedule concerns sunk it. In that respect, Scorpius is a compromise. Nevertheless, Custer thinks it will be effective.
The electron beam injector that Sandia is executing for Scorpius is highly impressive. It takes up approximately 46 feet (14 meters) of space in the machine. As mentioned, it produces the pulses of electrons that create the X-rays that Scorpius will use.
It will pulse the electrons with 22 million volts of power. For comparison, the X-ray machine in your dentist’s office pushes electrons with 50,000 volts. “It’s a lot of electrons accelerated to a very high energy to make a very bright X-ray flash,” Custer enthuses. Scorpius will be a power-hungry machine indeed.
It will be initially operational by 2027 and see its first experiment. By that time the nation may recognize that it needs to manufacture new plutonium for its weapons (something it has not done since 1989).
In the meantime, America needs it to ensure confidence in its nuclear deterrents and to remove any doubt in U.S. adversaries’ minds that our weapons will work, old as they are.
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