http://www.ucsusa.org/global_security/nuclear_weapons/the-robust-nuclear-earth-penetrator-rnep.htmlTechnical realities:
According to several recent scientific studies, RNEP would not be effective at destroying many underground targets, and its use could result in the death of millions of people.<2>
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RNEP would produce tremendous radioactive fallout: A nuclear earth penetrator cannot penetrate deep enough to contain the nuclear fallout. Even the strongest casing will crush itself by the time it penetrates 10-30 feet into rock or concrete. For comparison, even a one-kiloton nuclear warhead (less than 1/10th as powerful as the Hiroshima bomb) must be buried at least 200-300 feet to contain its radioactive fallout.<3> The high yield RNEP will produce tremendous fallout that will drift for more than a thousand miles downwind. As, Linton Brooks, the head of the National Nuclear Security Administration told Congress in April, "the laws of physics will
far enough to trap all fallout. This is a nuclear weapon that is going to be hugely destructive over a large area" if it goes off underground.
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RNEP could kill millions of people: A simulation of RNEP used against the Esfahan nuclear facility in Iran, using the software developed for the Pentagon, showed that 3 million people would be killed by radiation within 2 weeks of the explosion, and 35 million people in Afghanistan, Pakistan and India would be exposed to increased levels of cancer-causing radiation (see Figure 1).<4>