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Los Alamos executes successful hydrotest for W76 maintenance

DOE/Los Alamos National Laboratory : 07 May, 2007  (Technical Article)
Staff from Los Alamos National Laboratory's Dynamic Experimentation Division, supported by hundreds of scientists, engineers, technicians and others from many Laboratory divisions, have successfully executed a major stockpile stewardship experiment.
The hydrodynamic experiment at the Dual Axis Radiographic Hydrodynamic Test Facility, which took place Wednesday afternoon, was the final in a series that has gathered baseline data crucial to the National Nuclear Security Administration's Life Extension Program for the W76 warhead. The W76 is carried on Trident submarine-launched ballistic missiles.

DARHT, the world's most powerful flash X-ray machine, successfully captured a high-resolution X-ray image following detonation of a mock-up of imploding weapon components. The campaign of hydrodynamic experiments at DARHT, coupled with smaller-scale experiments and computer modeling, supports continued maintenance of the W76 without a return to underground testing.

'Preliminary analyses of the radiograph, electronic pin and other data collected by the dedicated team for hydroshot 3612 indicates another complete success,' said Mike Burns, acting deputy associate director for weapons physics at Los Alamos. 'These results are proof of the technical skills of the experimental crew and of DARHT's value to the national stockpile stewardship program.'

Over the next few months, Laboratory researchers will compare the image and data with computer models, closely examine any differences and refine the models so they more accurately represent weapon behavior.

Late next year, NNSA is scheduled to begin manufacturing some W76 components based in part on the data collected in the DARHT experiments. The components used in the experiment were designed and in many cases built by Laboratory staff.

Following an extensive review, those designs will be released for production, Burns said. Once components have been manufactured by the production plants, the hydrotest team will perform confirmatory experiments to ensure that components built in these NNSA facilities perform in the same way as those built for the hydrotests.

'This may have been the most complicated hydrotest ever done at DARHT,' Burns said. Among the many diagnostic tools fielded for the shot, in addition to the radiography machine, were several hundred precisely aligned electronic pins, which measured the contours of the imploding components, an electronic framing camera, neutron generator monitors, temperature monitors, a high-explosive microwave interferometer and Manganin pressure gauges.

DARHT is a high-explosive firing site equipped with a flash X-ray machine that records interior details of dense metal objects to create images of mock-ups of nuclear weapon components at the moment of implosion. Hydrodynamic experiments measure the implosion characteristics of weapon components using simulated materials, which permit scientists to evaluate some crucial aspects of nuclear weapon performance.

The companion experiment in the series, provided a complementary X-ray image and other data of the highest fidelity. Researchers will be able to compare the results from the two hydrotests to improve the quality of the final, war-reserve components. The goal of the entire experimental series is to establish the highest possible level of confidence in the data and computer models that will be the basis for final certification of the refurbished W76.

'Everyone involved was able to apply the lessons learned from the Laboratory's resumption activities to the hydrotest process, so in this shot we improved efficiencies and enhanced our formality, all of which significantly increases our confidence in the data,' Burns said.

Test director for hydrotest 3612 was Christopher Romero of Los Alamos' Dynamic Experimentation Division, and lead experimentalist was Lori Primas of the Hydrodynamics Group. On hydrotest 3625, the test director was Tim Fife of the Dynamic Experimentation Division and lead experimentalist was Scott Watson, currently in Los Alamos' Applied Electromagnetics Group.

Both hydrotests required close, extensive cooperation between the Laboratory and the Los Alamos Site Office of the National Nuclear Security Administration. Several technical divisions at Los Alamos made important contributions to the experiment, supported by the Principal Associate Directorate for Nuclear Weapons Programs. They were the Dynamic Experimentation, Engineering Sciences and Applications, Applied Physics, Manufacturing Systems and Methods, Physics, Materials Science and Technology, Chemistry, Decision Applications, Security and Safeguards, and Health, Safety and Radiation Protection.

The first axis of DARHT has been providing high-quality images of unprecedented resolution and clarity to NNSA's stockpile stewardship program since late 1999 for hydrodynamic experiments and for smaller high-explosives experiments.
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