Low-Yield Earth-Penetrating Nuclear Weapons

Robert W. Nelson, "Low-Yield Earth-Penetrating Nuclear Weapons," Science & Global Security, 10, no. 1, (2002): 1-20.
Some senior members of the U.S. government and leaders of America's nuclear weapons labs have recently advocated that the U.S.A. develop a new generation of low-yield earth-penetrating nuclear weapons (EPWs) capable of destroying hardened and deeply buried targets. Because they are intended to detonate below ground and have substantially lower yields than typical weapons in the U.S. nuclear stockpile, it is often assumed that EPWs would produce "minimal collateral damage" and could even be used near densely populated areas. We show here that EPWs cannot penetrate deeply enough to contain the nuclear explosion and will necessarily produce an especially intense and deadly radioactive fallout. A missile made of the hardest steels cannot survive the severe ground impact stresses at velocities greater than about v max ~ 1 km/s without destroying itself. This limits the maximum possible penetration depth into reinforced concrete to about four times the missile length--approximately 12 meters for a missile three meters long. Underground nuclear explosions must be carefully sealed at depths greater than 90 KT 1/3 meters (KT is the yield in kilotons) to be fully contained. At minimum, an earth penetrator creates an open crater or shaft, allowing release of hot plasma and radioactive material in a "roman candle" type explosion. An EPW would most likely excavate a crater of apparent radius R a ~ 50 KT 1/3 m, throwing out a large amount of radioactive dirt and debris. A one kiloton earth-penetrating "mininuke" used in a typical third-world urban environment would spread a lethal dose of radioactive fallout over several square kilometers, resulting in tens of thousands of civilian fatalities.

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