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September 18, 1997

Darwin Morgan, NV, 702/295-3521
Greg Cook, NV, 702/295-4628
David Schwoegler, Livermore, 510/422-6900
Chris Kielich, DOE HQ, 202/586-5806

Second Subcritical Experiment Conducted Successfully at the Department of Energy's Nevada Test Site

The Department of Energy's Nevada Operations Office today conducted the second subcritical experiment at the Nevada Test Site. The experiment named Holog was conducted safely and preliminary indications are that the experiment was successful.

Sponsored by the Department of Energy's Lawrence Livermore National Laboratory, the Holog experiment was conducted at 1:20 p.m. PDT in the U1A complex, about 960 feet beneath the ground surface. Scientific data obtained from the experiment will allow scientists to answer basic questions about the way plutonium reacts when it's shocked -- which cannot be determined with the required precision by experimenting with substitute materials. The data will help to benchmark complex computer simulations of nuclear weapons performance that will be used to certify the safety and reliability of the Nation's nuclear weapons stockpile without nuclear testing.

Subcritical Experiments are scientific experiments to obtain technical information in support of the DOE program to maintain the safety and reliability of the U.S. nuclear weapons stockpile without nuclear testing. The experiments use chemical high explosives to generate high pressures that are applied to nuclear weapon materials. High speed measurement instruments are used to obtain scientific data on the behavior of the materials. The configuration and quantities of explosives and nuclear materials have been designed so that no nuclear explosion will take place. Thus, the experiments are consistent with the Comprehensive Test Ban Treaty. They are called subcritical because there is no critical mass formed, i.e., no self-sustaining nuclear fission chain reaction occurs. Analysis of data from monitoring instruments confirmed that the Holog experiment remained subcritical.

The U1a Complex is an underground laboratory consisting of a horizontal tunnel about 1,100 feet in length mined in alluvium at the base of a vertical shaft 960 feet beneath the surface. The shaft is equipped with a mechanical hoist for personnel and equipment access, while another vertical shaft about 1,000 feet away provides cross ventilation, instrumentation, utility access and emergency access. The Holog experiment consisted of two simultaneous non-nuclear explosions in a chamber sealed with a two-foot concrete and steel plug from the rest of the tunnel complex. The complex provides a high degree of safety for test site workers and the public and minimizes environmental impacts. The first subcritical experiment in U1a was Rebound, which was conducted in July of this year.

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