July 2, 1997

Chris Kielich/Carmen MacDougall, 202/586-5806
Darwin Morgan, 702/295-3521
Jim Danneskiold, 505/667-1640

DOE Successfully Conducts First Subcritical Experiment

Data Confirms No Nuclear Explosion

The Department of Energy's Nevada Operations Office today conducted the first "subcritical" experiment at the Nevada Test Site, named Rebound. Analysis of data from monitoring instruments confirmed that the experiment remained subcritical, that is, no nuclear chain reaction occurred. Scientists obtained data from the experiment that will be used to support efforts to maintain the safety and reliability of the nation's nuclear weapons stockpile without underground nuclear tests.

Sponsored by Los Alamos National Laboratory, the Rebound experiment was conducted at 10 a.m. Pacific Daylight Time in the U1A complex, a horizontal tunnel mined about 960 feet beneath the ground surface. The purpose of Rebound was to obtain information on the response of plutonium to shock wave compression under different high pressure conditions (several million times atmospheric pressure). Three different explosive assemblies containing a total of about 75 kilograms (160 pounds) of chemical high explosive, an amount comparable to that used in highway construction, provided three different pressure conditions. This explosive energy was directed at about two dozen pieces of plutonium with a total mass of less than 1.5 kilograms (3.3 pounds) with the largest being 70 grams (2.5 ounces).

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.

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 explosive assemblies for Rebound were placed in a small, permanently sealed room mined at the end of a 500-foot long drift that intersects the main tunnel. The complex provides a high degree of safety for test site workers and the public, and minimizes environmental impacts. The shaft was originally mined in the 1960s and a nuclear test named Ledoux was conducted in 1990 in a horizontal tunnel mined from its base.

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