commentary Dreaming of clean nukes Can the Pentagon defend its plans for new nuclear ?

50% or more reduction in destructive radius. Michael A. Levi But if a ‘containable’ nuclear would Is the US nuclear arsenal sufficient to address deliver such reduced destructive power,might US DOE/SPL today’s security challenges? The Pentagon designers not better focus on delivering a con- apparently thinks not. A new report1 from its ventional warhead to greater depths instead? Defense Science Board (DSB) argues that This leads us to a third problem: the pene- “nuclear weapons are needed that produce tration depths that the DSB promises are much lower collateral damage”. It lends either overly optimistic4 or oddly cautious. support to proposals to build new nuclear Unstated assumptions about the targets can weapons for attacking underground facilities. be misleading. Simply because a device To a point, such ‘ busters’ are nothing can penetrate 30 metres in limestone, it does new — the B-53 bomb, first deployed in the not mean that it will do so in harder granite. early 1960s, can destroy underground targets, Elsewhere, the study looks at how multiple although it creates lethal radioactive fallout bombs dropped into the same hole can make that covers hundreds of thousands of square the hole deeper,but ignores the possibility that kilometres. The new proposals promise more this will make containment more difficult. effective weapons with reduced fallout. But And when the study proposes convincing the DSB overstates the extent to which that is methods for increasing penetration, it begs an possible, and gives the comparative potential Containing underground explosions is not easy. unanswered question. Can these techniques of conventional weapons short shrift. improve penetration of conventional weapons The US Department of Energy insists 400-tonne bomb penetrating 50–55 metres, even further7,rendering a nuclear warhead that, for now, it wants to research, but not and a 3,000-tonne bomb penetrating 100 unnecessary? At one point, the study explains build, exotic new weapons. It contends that metres1.Each of these, the DSB claims, would how a that penetrates 50 this is aimed at sustaining design expertise — destroy facilities roughly twice as far under- metres can destroy targets 100 metres under- but there are reasons for doubt. The Bush ground as the bomb would initially penetrate. ground,and later on the same page asserts that administration’s Nuclear Posture Review2, Those conclusions are unsound.The study a different missile might get 100 metres under- leaked in March 2002, described an aggres- applies data4 that were generated by nuclear- ground — presumably making the first sive approach to nuclear arms, suggesting a weapons tests in Nevada during the cold war. weapon obsolete. Indeed, in its zeal to concoct possible need for new nuclear weapons, and But in the Nevada tests, the hole above the penetration strategies that might contain kilo- the DSB openly discusses deployment. bomb was carefully sealed to prevent fallout — tonne-size bombs, the study strengthens the So far, Congress has been sceptical and in contrast, an earth-penetrating nuclear case for using conventional weapons instead. has cut funding for nuclear weapons3,but the weapon would leave a large hole behind it, This is the essence of the debate. For DSB study could change that. In captivating making containment difficult or impossible5. years, nuclear-weapon scientists have been detail,it describes how new nuclear weapons In addition, any claims about contain- immensely creative in dreaming up ground- could supercharge US capabilities. ment depend on the geology of the target area, penetration schemes to make nuclear Policy-makers should be wary of these rec- but the DSB is not explicit about its choice of weapons powerful yet clean. Most of these ommendations, however, as the claims are targets — implying that its conclusions are ideas will never work, yet they continue to be flimsier than they first appear. more universal than they actually are. For tolerated. Meanwhile, designers of conven- The DSB study begins with impressive example, the standard rule for determining tional arms are subject to intense com- proposals for improving non-nuclear bunker- burial depth from the Nevada tests — the one petition and scrutiny. It is no surprise that busting weapons. Indeed, for what some have the DSB seems to use — is valid for rock with nuclear weapons sometimes seem to have argued only nukes can do,the DSB offers non- low water content.But for explosions in more unlimited potential. But if they are judged by nuclear options that might work just as well. hydrous rocks the weapon would have to be the same standards as other weapons,the case The study then goes on to build a case for how buried deeper to contain the fallout5. in their favour is much harder to make. ■ new nuclear bombs could destroy buried facil- The destructive potential that the study Michael A. Levi is at the the Brookings Institution, ities without killing many people nearby. The claims is also suspect. The DSB requires that 1775 Massachusetts Ave NW, Washington DC unprecedented length and detail of this case is the explosion disable,not destroy,the contents 20036, USA. welcome.But it also exposes critical flaws. of a ‘hardened’ underground facility. This is 1. Report of the Defense Science Board Task Force on Future The modern bunker buster depends on a determined as requiring a shock pressure of Strategic Strike Forces (Department of Defense, Washington missile that penetrates the ground before its 500 bars at the target.But this might not harm DC, 2004) online at www.fas.org/irp/agency/dod/dsb/fssf.pdf 2. Nuclear Posture Review (US Departments of Defense and payload — nuclear or conventional — enemy leaders or their stored weapons stock- Energy, Washington DC, 2001). 6 explodes. Detonating a nuclear weapon piles .There is a contradiction here.The study 3. Kucia, C. Arms Control Today 33, (No. 7) 37 (2003). underground increases its effectiveness,there- claims that the inability of conventional 4. Nelson, R. W. Sci. Global Secur. 10, 1–20 (2002). by reducing the size of the bomb needed. If weapons to deliver destruction is the main rea- 5. Glasstone, S. & Dolan, P. J. (eds) The Effects of Nuclear Weapons 3rd edn, 261 (Departments of Defense and Energy, Washington an explosion is deep and small enough, it may son for needing nuclear arms. But to achieve DC, 1977). be ‘contained’ below the surface, preventing nuclear destruction — rather than disable- 6. May, M. M. & Haldeman, Z. Effectiveness of Nuclear Weapons radioactive fallout. The study concludes that ment — at the same distances, the bomb’s against Buried Biological Agents 19 (Stanford University, a 100-tonne nuclear bomb that penetrates power would have to increase 5- to 15-fold, Palo Alto, 2003). 7. Levi, M. A. Fire in the Hole: Nuclear and Non-Nuclear Options 30–50 metres underground before detonation making containment impossible. By seeking for Counterproliferation (Carnegie Endowment for could be fully contained. The same goes for a a fallout-free design, the study must accept a International Peace, Washington DC, 2002).

892 NATURE | VOL 428 | 29 APRIL 2004 | www.nature.com/nature