Todd Jacobson
NS&D Monitor
12/19/2014
Plutonium shots at Lawrence Livermore National Laboratory’s National Ignition Facility are expected to take place for the first time in January as the National Nuclear Security Administration takes another—somewhat controversial—step on the massive experimental laser system. NNSA weapons program chief Don Cook told Congress last week that the plutonium shots would begin, helping the agency “greatly expand the understanding of plutonium properties in important regimes relevant to NNSA’s mission.”
Lawrence Livermore spokeswoman Lynda Seaver said only a tiny amount of plutonium will be used in the shots—“anywhere between less than one milligram up to 10 milligrams, about the size of a poppy seed”—and would involve non-weapons grade plutonium. Up to 12 shots a year could be performed. “These shots are nothing new,” she said. “They were always a part of NIF’s mission and have been discussed since the 1990s, when NIF was being constructed.”
NIF Offers Unique Capabilities
Thus far, experiments run at NIF have not included plutonium in the shots, using targets consisting of deuterium, tritium and beryllium, but shots involving plutonium are needed to take another step in the understanding of nuclear weapons physics, Cook said. Experiments on plutonium are already conducted at the Nevada National Security Site’s Joint Actinide Shock Physics Experimental Research Facility and on the Z Machine at Sandia National Laboratories, but NIF would allow plutonium to be compressed at “strain-rates” not accessible on other machines, Cook said.
He said scientists have already used dynamic x-ray scattering diagnostics to help measure materials’ structure under high pressure using materials like lead, tantalum and uranium. “It is expected that this platform will successfully produce crystallographic data for the determination of the phase of plutonium at pressures not achieved elsewhere,” Cook said. “Radiographic capabilities at NIF will also allow the determination of other material properties such as strength and equation-of-state at high pressures and high strain rates.”
NNSA Downplays Risks of Pu Shots
While some activist groups have questioned the safety of using plutonium at NIF, Cook downplayed the potential risk of the shot, suggesting that the size of the plutonium planned for the shot had a comparable activity to two household smoke detectors. “The plutonium from the experiments will be totally contained within the target assembly or within the target chamber, and if it were not captured, the exposure to an individual standing at the LLNL site boundary would be less than 0.005% of the dose that individual would receive on a flight from San Francisco, CA to Washington, D.C., and less than 0.03% of the dose that individual would receive from a set of bitewing dental xrays,” Cook said. He said alpha radiation monitoring equipment is being purchased for the facility for $300,000. The plutonium used in the experiments will come from the lab’s existing stocks.
Tri-Valley CAREs, a Livermore-based activist group, has questioned the NNSA’s conclusions about the safety of the shots, noting that an analysis of the risks hasn’t been released. Of significant concern, the group said, is that plans to use an inner containment vessel to capture debris after the shot have bene abandoned, raising questions about contamination for workers and the public, as well as contamination of the target chamber and diagnostic equipment.
The group has also noted that the exact type of plutonium to be used in the experiment has not been specified, though it said it obtained documents indicating that plutonium-242 and 244 would be used, though a mix involving plutonium-239 might also be used. Seaver said only plutonium-242 would be used in the experiments.
