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Research shows nuke weapon pits age gracefully
By The Staff
The National Nuclear Security Administration’s Lawrence Livermore National Laboratory (LLNL) successfully executes the first plutonium shot using the Joint Actinide Shock Physics Experimental Research (JASPER) gas gun at NNSA’s Nevada Test Site. LLNL scientists have done research that proves plutonium has a longer shelf life.
New research uncovered by scientists at the Lawrence Livermore National Laboratory reveals that plutonium can age gracefully.
A story by Arnie Heller in Science and Technology Review gives a synopsis of the history of the research.
The study’s results, announced in late 2006, showed that the slow degradation of plutonium in U.S. nuclear weapons would not affect warhead reliability for decades.
Independent research teams at the two laboratories performed extensive mechanical testing and laboratory-based experiments on aged samples of a plutonium-239 allo y—plutonium mixed with a small amount of gallium to stabilize the material in its delta phase at room temperature.
Alloy samples were taken from 15- to 44-year-old plutonium pits and from plutonium that was artificially aged to 65 years. These tests showed no significant changes in important physical properties such as density and strength. In analyzing the test results, the research teams determined that the minimum lifetime for plutonium pits was at least 85 years — 25 to 40 years longer than previously estimated.
Now, six years later, these same naturally aged samples are 50 years old, and the accelerated alloy samples have reached an equivalent age of 150 years. Both sample lots continue to age gracefully and extremely sensitive tests and high-resolution electron microscope images by Livermore chemists validate the confidence-building conclusions of the earlier study.
“The 2006 report was a work in progress,” said chemist Pat Allen, the deputy program leader for enhanced surveillance and leader of the plutonium aging study. “The 2006 report and recent work continue to show no alarming trends and serve to validate our theories about how plutonium ages. However, we need to keep running tests on naturally aged specimens to see further into the future and make sure there are no surprises.”
Allen said that ongoing monitoring of the accelerated alloys is useful to establish the location of any aging “cliff,” where changes would severely affect performance, even if the cliff did not occur in the near term.
The Los Alamos National Laboratory released the following statement on the findings.
“It’s important to note that this study of plutonium aging is only one area of many that could determine pit lifetimes. Extending the observations from plutonium aging as representative of pit lifetimes neglects to take into consideration all of the other factors and could be easily misunderstood.”
Greg Mello of the Los Alamos Study Group says the new research has some interesting implications.
Livermore’s scientists have done the nation a great service by publishing these results, belated though it is.”
Jay Coghlan of Nuclear Watch New Mexico also weighed in.
“Great news coming out of the weapons labs – the science now shows that the plutonium in U.S. nuclear weapons will age gracefully for at least the first 150 years,” Coghlan said. “That is a 50-65 year bump over the previous assessment, which came out in 2006."