• Since weapons cannot penetrate very deeply into the ground, destroying deep, hardened targets requires powerful, high-yield nuclear warheads.
• Even a small, low-yield earth-penetrating nuclear weapon will create enormous fallout. The explosion cannot be contained underground. The radioactive debris thrown into the air can drift for miles on the wind.
• There is no guarantee that a nuclear blast will successfully destroy chemical or biological weapons.
• A nuclear attack on a bunker that contains chemical or biological weapons could easily lead to the release and spread of those agents.
• There are current conventional alternatives to the use of nuclear bunker busters.

Q: Why do some advocate the use of nuclear bunker busters?
A: Advocates argue that nuclear weapons are needed to destroy stores of chemical or biological weapons and deeply buried bunkers. But the use of these weapons would lead to severe collateral damage. And, as discussed below, they would not ensure the destruction of chemical and biological agents. Moreover, destroying deep, hardened targets requires very large nuclear weapons that would cause enormous amounts of fallout. Current precision-guided conventional weapons can instead be used to cut off a bunker's communications, power, and air, effectively keeping the enemy weapons underground and unusable until US forces secure them.¹ 

Q: How far can a nuclear bunker buster penetrate? Is this deep enough to contain nuclear fallout?
A: Experiments show that a steel rod hitting the ground at high speed can penetrate at most about four times its length through concrete (e.g., a 10-foot bomb could theoretically go through about 40 feet). However, in order to protect its sensitive components, a nuclear warhead might have to hit the ground at significantly slower speeds, reducing its penetrating capability. The Pentagon's current nuclear bunker buster, the B61-11 bomb, can penetrate only about 20 feet of frozen soil. Because even a one-kiloton nuclear warhead (less than 1/10th the size of the Hiroshima bomb's yield) must be buried at least 200-300 feet to contain its radioactive fallout, there is no way to avoid serious fallout from a nuclear bunker buster.²

Q: Would this explosion cause radioactive fallout?
A: Yes. Shallow nuclear explosions produce especially severe radioactive fallout. The fireball breaks through the surface of the earth, carrying into the air large amounts of dirt and debris, which then fall back to the ground. Even a one-kiloton nuclear warhead that explodes 20 feet underground would eject about one million cubic feet of radioactive debris from a crater the size of ground zero at the World Trade Center.³

Q: Can the radiation or heat of a nuclear blast destroy chemical and biological agents?
A: A nuclear explosion can destroy these agents if they are sufficiently close to the nuclear blast. However, given the difficulty in obtaining data about the precise location and size of underground bunkers, it is difficult to target the agents accurately, or to know how soil or other material might reduce the effect of heat and radiation on the agents. Thus, there is no guarantee that the radiation or heat would destroy all or even most of the chemical or biological agents. Based on that knowledge, the only way to increase the likelihood of destroying the agents is to increase the yield of the attacking nuclear warhead, with a corresponding increase in fallout.⁴ 

Q: Could a bunker-busting nuclear explosion spread chemical or biological agents?
A: Yes. There are two scenarios in which a leak of agents could occur. First, a nuclear weapon exploding near a bunker would disperse chemical or biological agents that were not destroyed, spreading them into the resulting crater and surrounding air. Second, a nuclear weapon exploding farther from an underground storage facility could damage the bunker and the agents' storage containers. The explosion would also create fractures leading to the surface, through which surviving chemical and biological agents could leak into the atmosphere. Because of the difficulties in using a nuclear explosion to neutralize all of the agents reliably, either scenario could result in chemical or biological weapons spreading into the surrounding environment. A recent study predicts that anthrax spread in this fashion would cause even more casualties than the resulting nuclear fallout, which would also be severe.⁵ 

Nuclear bunker buster funding in the FY2004 budget:
The National Nuclear Security Agency (NNSA) is seeking $15 million in additional funding to study the Robust Nuclear Earth Penetrator (RNEP), the Pentagon's current nuclear bunker buster project. Work will soon begin with the FY2003 funding already provided.

Notes
1. See M. Levi, "Fire in the Hole: Nuclear and Non-nuclear Options for Counterproliferation" (Carnegie Endowment for International Peace) at http://www.ceip.org/files/Publications/wp31.asp

2. See D. Wright and L. Gronlund, "Earth-penetrating Weapons" (Union of Concerned Scientists) at http://www.ucsusa.org/global_security/nuclear_weapons/page.cfm?pageID=777

3. See R. Nelson, "Low-Yield Earth-Penetrating Weapons" (Science & Global Security) at http://www.princeton.edu/~globsec/publications/pdf/10_1Nelson.pdf
and S. Drell, R. Jeanloz, and B. Peurifoy, "A Strategic Choice: New Bunker Busters Versus Nonproliferation" (Arms Control Today) at http://www.armscontrol.org/act/2003_03/drelletal_mar03.asp

4. See M. May and Z. Haldeman, "Effectiveness of Nuclear Weapons against Buried Biological Agents Targets" (Center for Security and International Cooperation) at http://cisac.stanford.edu/research/inprogress/mayhaldeman.html

5. Ibid.

For more information, contact:
Stephen Young, Senior Analyst at (202) 223-6133, ext. 112