12/02/2008 - 07:36

Redefining deterrence: Is RRW detrimental to U.S. security calculus?

Yousaf Butt

Yousaf Butt

Butt is a research professor and scientist-in-residence at the James Martin Center for Nonproliferation...

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Editor's note: The opinions expressed below are solely those of the author and not his employer.

The Reliable Replacement Warhead (RRW) Program proposes to redesign the nuclear explosive package of U.S. nuclear warheads using advanced computer simulations and the experience gleaned from previous weapons tests. The advertised aim of RRW is to enhance warhead safety and security while improving confidence in the stockpile's long-term reliability--allegedly, without any new nuclear explosive tests.1

Currently, the United States possesses roughly 5,700 operationally deployed strategic nuclear weapons; under the Moscow Treaty, this number is planned to shrink to between 1,700-2,200 by December 31, 2012. (Approximately 4,200 warheads are in the reserve stockpile, and their ranks might swell as some of the retired operational warheads could be transferred into the reserve.) A typical U.S. warhead has a yield equivalent to about 100,000-400,000 metric tons of TNT, enough to incinerate a city the size of Washington by blast and fire.2 (By comparison, the Hiroshima bomb had a yield of about 15,000 tons of TNT.) The newest warhead design was fielded 20 years ago, and the United States last carried out an underground nuclear test in September 1992.

According to the National Nuclear Security Administration (NNSA), the current U.S. warhead stockpile is safe, secure, and reliable.3 Its reliability--dominated mostly by the non-nuclear components (cables, valves, pads, cushions, foam supports, electronics, etc.)--is about 98 percent with a high confidence level.4 (Keep in mind, too, that an "unreliable" warhead may still completely destroy a city, as the government considers a warhead with an expected yield of 90 percent or less of its design yield as unreliable.)

In addition, studies by Lawrence Livermore National Laboratory and Los Alamos National Laboratory have concluded that the plutonium pits in the current warheads have a life of at least 85 years, if not a century--a conclusion backed by the JASON group of experts and endorsed by the NNSA.5 It's an important finding that removes any great rush to design and manufacture new warheads.

Nevertheless, in the Bush administration's waning days, the Defense and Energy departments have issued a joint report, "National Security and Nuclear Weapons in the 21st Century," that places a high priority on RRW. They advocate replacing "existing warheads with RRWs of comparable capability that would have advanced safety and security features, be less sensitive to manufacturing tolerances or to aging of materials, and be certifiable without nuclear testing." Unfortunately, the report is rife with logical lapses and unstated assumptions, some of which Hans Kristensen has discussed at the Federation of American Scientists (FAS) website.

Arguably, though, the most egregious conceptual mistake in Energy and Defense thinking is conflating technical warhead reliability with its deterrent value. Because of the massive destruction potential of a nuclear weapon, an adversary's deterrence calculus could hardly be different for, say, a 96-percent reliable nuclear weapon versus a 99-percent reliable weapon. In fact, it's questionable whether it would even be different for a 25-percent reliable weapon versus a 99-percent reliable weapon.6 Switching perspective to the receiving end of a possible massive nuclear retaliatory attack makes the argument more acute: If a country is facing the prospect of several 300-kiloton U.S. warheads destroying its 25 most populous cities, it hardly matters that perhaps one of the weapons will have a suboptimal yield and doesn't completely annihilate the twenty-fifth city.

This deterrent logic is especially pertinent to the RRW debate considering that nuclear targeting practice places more than one weapon on any high-value target, making the probability of annihilation essentially 100 percent whether a single warhead has a 96-percent or 99-percent reliability.7 Ultimately, deterrence is an exercise in psychology, and small differences in the numerical reliability of overwhelmingly destructive nuclear weapons don't have a measurable influence on any adversary's deterrence calculus.

Unlike almost any other type of modern tool, machine, or weapon system, nuclear weapons are purposefully designed not to be used. Therefore, their reliability isn't relevant in the same sense as for a car or computer. As clearly stated in the December 2006 "Deterrence Operations--Joint Operating Concept" document, "The end state for all deterrence operations is decisive influence over the adversary's decision calculus in order to deter aggression and coercion against U.S. vital interests." So even the Pentagon considers the reliability of its nuclear warheads in the context of the perceived deterrent value in an adversary's eyes. Another way to think about it: Consider Chinese or Russian nuclear weapons. Do we know their technical reliability numbers? No. Yet, we still take them very seriously.

Perhaps warhead reliability would be an issue worthy of serious discussion if the current warheads were found to be critically flawed. But from 1958 to 1996, the Stockpile Evaluation Program sampled nearly 14,000 weapons; of these, only about 1.3 percent were found to have failures that would have prevented them from operating as intended.8 Therefore, the metric for the "usefulness" of nuclear weapons shouldn't be reliability, but rather perceived deterrent value. Of course, perceived deterrent value is a psychological metric--incorporating the numerical warhead reliability (if known by the adversary) folded in with the consequences of a nuclear holocaust--but it's worthy of further examination in the context of RRW.

The new Energy/Defense nuclear strategy paper states, "[T]o maintain a credible deterrent at these lower levels, the United States requires nuclear forces that can adapt to changing needs, and a responsive industrial infrastructure that can maintain existing capabilities and manufacture new or replacement components as needed." But since the proposed new weapons will be untested, they will be a marginally less credible deterrent in the eyes of an adversary. Even if the actual numerical reliability of RRWs is higher, the perceived deterrent value of these untested weapons cannot be more than that of empirically tested weapons. Remember, in matters of deterrence, what adversaries believe is more important than what some weapons experts may assert.

This raises another interesting point: What would be the required reliability level of the proposed new warheads? It could only be different from the current weapons by no more than 2 percent, as the current weapons are 98 percent reliable--assuming, of course, that the new warheads are really more reliable than the current warheads. Can a 2-percent difference in reliability really alter an adversary's thinking? And, more importantly, in the absence of testing, how are we to determine the baseline reliability of RRWs? As for the military utility of reliability, does a supposed few percentage point increase in reliability matter when considering the overall destructive power of nuclear weapons? No, especially since the overall reliability of the weapon system is dominated by the intercontinental ballistic missile delivery system--of 2,160 test launches, approximately 15 percent resulted in some type of delivery system failure that would have prevented the warhead from reaching its target.9

Since experts have agreed that the current U.S. stockpile is likely to remain reliable for at least the next 50 years, there's no reason for Energy and Defense to further discuss any potential problems in unclassified documents that may semaphore any alleged weaknesses in the country's nuclear weapons systems to potential adversaries. The current stockpile is a highly credible and effective deterrent in the eyes of any potential adversary for the foreseeable future. To keep it that way, future discussions of warhead reliability should be classified with strict oversight from truly independent experts with appropriate security clearances--i.e., the JASON group.

U.S. strategic planners also ought to pay heed to FAS's Oelrich, who has astutely pointed out that the world-altering ideological prizes that may have been considered worth using nuclear arms over during the Cold War no longer exist. If anything, the interlocking fragility of today's economies acts as a passive--and massive--deterrent between states. For instance, a reason recently given for the implausibility of a U.S.-Israeli attack on Iran's nuclear facilities is that it may drive the price of oil too high.10

Perversely, the new nuclear weapons strategy report effectively threatens to renew testing the already well-tested legacy weapons unless Washington adopts the RRW Program: "Without nuclear testing, at some time in the future the United States may be unable to confirm the effect of the accumulation of changes to tested warhead configurations." This basically amounts to blackmail: Buy the RRW program, we are told, or the Comprehensive Test Ban Treaty cannot be ratified.

But from the perspective of deterrence calculus, there's no plausible argument that would support such renewed testing of empirically certified warhead designs. Says Richard Garwin, a member of the JASON group who is intimately familiar with the RRW Program, "With the passage of time and the improvement in computing tools, I believe that confidence in the reliability of the existing legacy weapons will increase rather than diminish." And Robert Peurifoy, the former vice president of technical support at Sandia National Laboratories has stated, "The present nuclear weapon stockpile contains eight or so nuclear weapon types. That population has enjoyed perhaps 100 successful yield tests. These weapons have benefited from a test base of perhaps 1,000 yield tests conducted during the 40 or so years when nuclear testing was allowed. Is [Defense] really willing to replace tested devices with untested devices?"

This raises another issue ignored by the new Energy/Defense nuclear strategy report: Although the proposed RRW warheads may be certifiable by the weapons laboratories without testing, will all future presidents and generals at the Pentagon also accept an untested weapon in their operational command?11 A similar scenario already occurred in France. Under President Francois Mitterrand, the French accepted untested new nuclear warheads into their submarine-based stockpile based on the results of sophisticated computer simulations. But when Jacques Chirac became the country's president, France conducted a handful of nuclear explosions to make sure that the weapons actually worked. The same thing will likely happen with RRW--at least no one in the U.S. government is offering any guarantees that it won't.

Other motivations cited for pursuing RRW include warhead safety, toxicity, security, and the capability to recruit, retain, and challenge new weapons scientists. Garwin addressed these concerns before the Energy and Water Development Subcommittee of the House Committee on Appropriations in March 2007: "Neither the RRW nor the legacy weapons are likely to be proof against being used as a source of weapon material [for a terrorist]. However, a weapon may be a more difficult target than the hundreds of tons of highly enriched uranium and military and 'civilian' plutonium that could also be the target of terrorist activities." On the subject of the toxic chemicals in the current warheads, Garwin's assessment is particularly salient: "The benefits claimed for RRW in reducing the use of hazardous material might be useful if the legacy weapons were to be replaced, but if they are simply to be preserved and in some instances remanufactured in a scenario of major reductions, an RRW alternative will lead to increased handling of the objectionable materials, as beryllium and other materials are phased out of the stockpile instead of being kept in the form of nuclear weapons."

The argument that RRW is needed to recruit and hone the skills of a new cadre of nuclear weaponeers is also disingenuous. For the most part, the design work has already been completed, rendering the remaining part of the RRW program largely an engineering exercise. Plus, "cutting-edge" nuclear weapons are outmoded and unnecessary--a few tens of uranium-based devices in the operational arsenal of any nuclear weapon state would serve deterrence purposes reliably and adequately.

Contrary to what proponents of untested new warheads assert, the more credible deterrent in the eyes of one's adversary will always be the tested legacy weapons. On the other hand, if the proposed new warheads are eventually tested, this will make it more difficult to stop other nations from doing the same. Either way, the proposed RRW program to develop new but untested nuclear warheads is detrimental to U.S. security.

And before we even think about making new warheads, we need to consider anew what deterrence means and who we may be deterring and from what. As Elaine Bunn of the National Defense University has presciently written, the concept of a credible deterrent needs to be critically reexamined in the post-Cold War era, "[T]he capabilities needed for tailored deterrence go beyond nuclear weapons and the strategic capabilities of the so-called New Triad, to the full range of military capabilities, presence, and cooperation, as well as diplomatic, informational, and economic instruments."

1For definitions of the various terms used, such as "reliability," see the summary of the workshop on the Reliable Replacement Warhead sponsored by the Union of Concerned Scientists (UCS) and American Association for the Advancement of Science (AAAS).
2Lynn Eden, "City on Fire," Bulletin of the Atomic Scientists, January/February 2004, p. 33-43.
3Written statement of Thomas P. D'Agostino, then acting Under Secretary for Nuclear Security and Administrator at the National Nuclear Security Administration (NNSA), before the House Armed Services Subcommittee on Strategic Forces, March 20, 2007.
4UCS and AAAS workshop summary.
5Unclassified NNSA/JASON report on pit lifetime, November 20 2006.
6UCS and AAAS workshop summary; D'Agostino statement. An excellent summary of the logical flaws and omissions in the RRW advocacy has been presented by Ivan Oelrich of the Federation of American Scientists in his response to Rep. Ellen Tauscher's Nonproliferation Review article, "Achieving Nuclear Balance."
7Lynn Eden, "City on Fire."
8General Accounting Office, "Nuclear Weapons: Improvements Needed to the DOE's Stockpile Surveillance Program," GAO/RCED-96-216, 1996. The UCS and AAAS workshop summary noted that specific yield requirements for each weapon type are classified, but generally thought to require detonation under "stockpile-to-target sequence" conditions within 10 percent of their design yield.
9UCS and AAAS workshop summary.
10Christopher Dickey, "The Oil Shield," Foreign Policy, May/June 2006, p. 37.
11Comments by Richard Garwin in his testimony before the Energy and Water Development Subcommittee of the House Committee on Appropriations, March 28, 2007.