In 1959-1961, subcritical hydronuclear safety experiments were conducted at Technical Area (TA) 49 at the Los Alamos National Laboratory (LANL). These underground experiments were designed and conducted to investigate safety issues. Seventy hydronuclear safety, tracer, and containment test experiments were conducted in 1-m or 2-m diameter shafts at depths ranging between 9 m and 33 m. The subsurface radiological and metals inventory consists of about 40 kg of plutonium, 93 kg of uranium-235, 170 kg of uranium-238, 11 kg of beryllium, and possibly more than 90,000 kg of lead. Explosives used in the experiments consisted largely of TNT, RDX, HMX, and barium nitrate. It is highly likely that the explosives, except for the barium component, were completely consumed by the detonations. Hydronuclear safety test shafts were drilled, test materials were placed at the bottom of the shafts, shafts were backfilled with sand or local crushed tuff, tests were detonated, subsidence in the shafts were backfilled, and cement caps were poured over the test shafts. The diameter of the affected detonation zones is believed to be less than 6 m. Most test shafts were drilled on an 8-m grid spacing in four main areas within TA-49.
