The threat of total nuclear annihilation seems to have receded since the demise of the Soviet Union. China, France, India, Israel, Pakistan, the U.K. and even Russia are U.S. allies or, at worst, nonbelligerent competitors with (Russia notwithstanding) limited nuclear arsenals. North Korea and Iran, although both enemies of the U.S., do not as yet possess the weaponry to inflict massive nuclear harm on this nation. In fact, the most pressing nuclear threat appears to be a "dirty bomb"—a conventional explosive packed with radioactive material—or a small nuclear explosive smuggled into the country.

Despite the threat reduction, however, the U.S. retains the weaponry to fight a total nuclear war: roughly 10,000 warheads and bombs. A third of these are warheads—dubbed W76—which, since 1978, have been deployed atop submarine-based ballistic missiles or stored in what is known as the Enduring Nuclear Stockpile, according to Hans Kristensen, director of the Nuclear Information Project at the Washington, D.C.-based Federation of American Scientists (FAS), an organization founded by the creators of the original nuclear weapon in 1945 that has been monitoring the nation's nuclear arsenal ever since. The W76 generates 100 kilotons of explosive force when detonated, the equivalent of 100,000 tons of the chemical explosive trinitrotoluene (TNT). It is designed to obliterate so-called "soft targets," such as ports, garrisons, or factories.

The U.S. plans to retire many of these weapons as part of its nuclear arsenal reductions under the Moscow Treaty on Strategic Offensive Reductions. But the U.S. Departments of Energy (DOE) and Defense (DOD) would also like to replace some of them. And in early March, Lawrence Livermore National Laboratory in California won the initial competition to design the nation's first new nuclear warhead in 20 years. The new weapon would not fulfill a new strategic role in a changed world, but rather replace a portion of the W76 arsenal, due to concern over the aging warheads' ability to retain their full destructive potential in storage.

A government-commissioned independent review by a panel of scientists known as JASON estimated that the plutonium primaries in the current warheads will last a minimum of a century in storage, however, and, therefore, recommended that no action be taken other than routine maintenance, such as replacing surrounding circuitry and parts as they age—a core function of the Lifetime Extension Program the W76s are currently undergoing. Despite the panel's findings and the imminent refurbishments, the Reliable Replacement Warhead (RRW) program, an effort to replace the W76 launched three years ago by the DOE to allay reliability fears, continues.

In an effort to keep the modernization program alive, the Nuclear National Security Administration (NNSA)—a a semiautonomous agency of the DOE in charge of the nation's nuclear weapons—has offered a variety of other rationales, ranging from national security to creating a more environmentally benign weapon. The U.S. Congress is now weighing the fate of the program and whether to fund it as part of efforts to determine what the U.S. nuclear arsenal will look like in the 21st century.

Same Old, Same Old?

During a press conference and subsequent interviews, NNSA officials stressed that the design for the W76 replacement warhead is not a new one. Rather, it is based on a formerly tested weapon that includes a host of new surrounding features. "It's new in the sense that we've never done this before, but it's not new in the traditional arms control sense," says NNSA's John Harvey, director of policy planning staff. "It will have the same form and function as the current weapon."

In fact, the reason the Livermore design triumphed is because it is based on a former design, one detonated underground before the U.S. moratorium on such experiments in 1992. "[The pit] was nuclear tested four times," says Bruce Goodwin, Livermore's associate director for defense and nuclear technologies. "It's the exquisite test pedigree of the baseline for this design that gives very high confidence that it will work as expected."

The new warhead would work much the same as any other fusion bomb. The fissile nuclear pit, or primary, explodes and floods surrounding chemical compounds, known as the secondary, with radiation. This radiation triggers a fusion reaction between the tritium and deuterium isotopes of hydrogen produced by the irradiated compound. A thermonuclear explosion follows.

Only a limited number of such primaries have been tested. "It's the SKUA9 design," Goodwin says, one of a series of primaries created by Livermore during the nuclear testing program simply to test the viability of secondaries, and never produced as a weapon. As a result of this prior testing, this first Reliable Replacement Warhead (RRW1), if built, would require no further detonations, according to the NNSA and Livermore.

It will also provide increased confidence in the weapon's "margin," says J. Stephen Rottler, vice president for weapons engineering and product realization at Sandia National Laboratories in Albuquerque, N.M., which will be responsible for integrating the nuclear explosive into weapons systems such as missiles. Margin is the term used to describe a weapon's ability to avoid failure, such producing as a smaller explosive yield than for which it was designed.

Some scientists argue that the W76 has a low margin of failure because of the thin uranium shell that surrounds its core explosive. It could weaken, particularly as its plutonium core bombards it with radiation over time, subsequently failing to contain the primary fission explosion long enough to generate the high temperatures needed for fusion to take place in creating the secondary hydrogen detonation.

The new warhead will be bigger, thicker and heavier than the W76s, and therefore less likely to allow for that kind of failure, according to both Rottler and Goodwin. "That provides a margin, if you will, as the warhead ages," Rottler says. "The chances of us going underground [to test] again are remote." This is key to the appeal of RRW, because the U.S. government, complying with its treaty obligations, has mandated no return to underground testing.

But critics note that no nuclear weapon in the current U.S. arsenal has ever been manufactured without being tested. "Is there a military commander out there who will ever rely on something that has not been fully tested?" the Federation of American Scientists' Kristensen asks. "So far that has not been the case."

Building a Better Bomb

During the Cold War, the military emphasized packing as many warheads into one weapon as possible to generate maximum explosive yield, while also minimizing the overall weapon's weight to enable maximum range, resulting in weapons like the W76. Now that the Cold War has thawed such considerations are no longer as crucial, weapons designers say, allowing them to add new, heavier features—insensitive high explosives and advanced security technology—to the RRW1.

Insensitive high explosives, which resist detonation except when properly triggered, would improve the safety of handling these weapons in storage. "We have taken insensitive high explosives and slammed it into reinforced concrete blocks at Mach 4. It will not detonate," Livermore's Goodwin says. It is so secure, "you can put a gasoline fire out with it. If you put a blowtorch to it, you can get it to molder."

Further, the W76 lacks permissive action links (PAL), a computerized system that requires appropriate authorization to fire the weapon. "Under refurbishment, if we wanted to improve security interior to the warhead, we would have had to retrofit that into the warheads, which is difficult to do without nuclear testing," NNSA's Harvey says.

The W76 spends the majority of its life aboard submarines or in heavily secured stockpiles, reducing its need for such features, critics note. And the Life Extension Program for other nuclear weapons, such as the B61 gravity bomb, has incorporated added security measures, such as increased encryption, FAS's Kristensen argues. "Here was a weapon that was designed back in the 1960s and 1970s, and when it was first deployed it did not have safety features," he says. "They refit it all on the weapon itself without having to rebuild it. This suggests that you can achieve extraordinarily high levels of safety in current designs without going to a new design."

The U.S. also spent billions of dollars upgrading the security of nuclear weapon storage sites after the September 11, 2001, terrorist attacks, leaving open the question of who is capable of improperly triggering such weapons. "I don't know anyone who believes that the physical security of U.S. nuclear weapons is in doubt," says Ivan Oelrich, FAS's vice president for strategic security programs. The American Association for the Advancement of Science's (AAAS) Nuclear Weapons Complex Assessment Committee, a panel of experts convened to evaluate RRW, agrees, finding no reason to believe that such features would "substantially reduce the current reliance on guns, guards and gates" in its April assessment report.

The NNSA, for its part, believes the new features are necessary for the small amount of time such weapons spend being trucked from site to site to eliminate the threat of hijacking. "It gives us an extra measure that we think is prudent, particularly in transportation scenarios," NNSA's Harvey says.

The "Green" Nuclear Warhead

The RRW1 would also eliminate the need for some of the toxic substances in such weapons, such as beryllium, a light metal that hardens alloys but is also carcinogenic and can cause pulmonary disease. "Because of the release of the weight requirement, we are able to use materials that are heavier but more environmentally benign," Livermore's Goodwin says. "We will be able to eliminate an entire process that produces 96 percent radiological toxic waste that has to be buried and replace it with nontoxic waste that is 100 percent recyclable."

"You replace it with something that quite honestly you could eat and be healthy," he adds. "It is in prosthetic body implants. It's about as biologically benign as any material can be." Because the exact specifications remain classified, however, he was unable to reveal exactly what the benign substance is and its exact purpose in the new weapon.

Building a new nuclear warhead would also entail rebuilding the individual nuclear weapon–producing factories, such as Amarillo, Tex.-based Pantex, Los Alamos's TA-55 or Y-12 in Oak Ridge, Tenn., "antiques," as Goodwin calls them because some date from the 1940s. The Bush administration unveiled plans in April 2006 for a new complex to build all the components of new nuclear warheads—dubbed Complex 2030 for the year set for its completion.

"If you are going to life-extend weapons, you need to recreate the enterprise, the production complex of the 1970s, which is an enormous investment in infrastructure," Goodwin says. "Do you want to reinvest in technologies that in many cases are extremely unpleasant? Or do you want to make the smallest possible enterprise to support a very different deterrent stockpile, a much smaller stockpile?"

But the AAAS panel found that substantial upgrades to the current infrastructure would be needed anyway to carry out the RRW program, including at least a doubling of the current assembling and disassembling work at the Pantex nuclear weapon assembly facility as well as a significant increase in the amount of plutonium pits produced at the TA-55 facility.

The Cost of Nuclear

The NNSA asked for $27.7 million for fiscal year 2007 to research the RRW design. That will rise to $88 million in fiscal year 2008, according to the NNSA's then acting administrator Thomas D'Agostino, and a detailed cost of the entire program should be available before the 2009 budget once the engineers have completed their cost estimates. Until such cost estimates are available, there is no way to determine whether RRW and Complex 2030 present a cost savings or an additional financial burden in the long run compared with simply maintaining a diminished portion of the present arsenal.

Production on the W76 replacement could begin by 2012, depending on how much money Congress provides, Sandia's Rottler says. In the bomb makers's preferred scenario, the RRW1 would replace some portion of the W76s that would otherwise be refurbished as the vast majority are dismantled. This swap would likely take decades, according to the AAAS experts, and would require a commitment of "significant new funds."

"In this year's budget, the NNSA requested $88 million for the first design and development stages of RRW1. Where did [the funding] come from? It came out of the Life Extension Program for the W80," notes Robert Nelson, a senior scientist at the Union of Concerned Scientists, an independent scientific research and advocacy group. "We're worried about the long-term reliability of the stockpile, but to pay for [RRW] we are going to cut the very programs that maintain the reliability of the stockpiles." He adds that by cutting the funding for the maintenance programs for existing weapons: "It makes it impossible to reverse course."

Billions more will be needed to retool the production infrastructure if Congress decides to authorize RRW and Complex 2030, both proponents and opponents say. And members from both sides of the aisle on the House Appropriations Subcommittee on Energy and Water Development have expressed skepticism about the program. "Although a lot of time and energy went into determining the winning design for a new nuclear warhead, there appears to have been little thought given to the question of why the United States needs to build new nuclear warheads at this time," panel chair Rep. Pete Visclosky, (D–Ind.) said in a written statement. "Without a comprehensive defense strategy that defines the future mission, the emerging threats, and the specific U.S. nuclear stockpile necessary to achieve the strategic goals, it is impossible for Congress to appropriate funding for RRW in a responsible and efficient manner."

The RRW W76 replacement is also just the first. "If we're really going to have an impact as to a reduction in the stockpile, we have to address the whole stockpile," Steve Henry, deputy assistant to the secretary of defense for nuclear matters, said at a press conference announcing the design winner. "The RRW1 is to address the first portion, which is a submarine-based W76 replacement."

The NNSA has already launched a feasibility study for a second RRW specifically designed for an air-delivered weapon, according to NNSA's Harvey. A likely candidate for such an RRW2 would be the W78 warhead that sits atop land-based intercontinental ballistic missiles, FAS's Kristensen says. It is nearly as old and also lacking insensitive high explosives and security features.

A Credible Deterrent

But the biggest impact of the replacement weapons program might be on the global nuclear arms situation. Whereas the U.K., France, Russia and China have similar modernization efforts underway or planned, building the RRW1 might provide a dubious signal to the rest of the world as well as potentially provoke accusations of a violation of nuclear nonproliferation and arms control goals. "If the United States, the strongest nation in the world, concludes that it cannot protect its vital interests without relying on new nuclear weapons for new military missions, it would be a clear signal to other nations that nuclear weapons are valuable, if not necessary, for their security purposes, too," Sidney Drell, arms control expert and physicist at the Stanford Linear Accelerator Center said at the American Physical Society Conference in Denver this past March.

Nuclear weapons are intended to be a deterrent, making the price of a particular geopolitical prize that might be seized too costly to bear. Yet, the U.S. has no avowed nuclear enemies as in the days of the Soviet Union and certainly none that would require thousands of nuclear warheads to deter or destroy, according to critics of the RRW plan.

As a result, former secretaries of state Henry Kissinger and George Shultz, former secretary of defense William Perry and former Georgia Sen. Sam Nunn (a former chair of the Senate Committee on Armed Services) have argued for the elimination of such weapons. "We endorse setting the goal of a world free of nuclear weapons and working energetically on the actions required to achieve that goal," they wrote in an editorial that appeared in the Wall Street Journal earlier this year. But the first Reliable Replacement Warhead—and Complex 2030 behind it—is not designed with that goal in mind and, in the absence of policy statements from the current administration, it remains unclear what the role for nuclear weapons—old or new—in the U.S. might be.

But the RRW program may simply be designed to address a more fundamental concern: ensuring that the U.S. retains the capacity to build and field nuclear weapons well into the future. "We want to exercise the scientists and engineers," NNSA's Harvey says. "The folks who did this back in the Cold War are about to retire. We need the next generation to do this and do it now so that they can be mentored by that older generation."

As the Department of Defense's Henry noted: "Based upon our analysis, the expertise is aging faster than the plutonium. And, it's a responsive infrastructure that you rely on to mitigate technical surprise and changes in the geopolitical environment. That responsiveness allows you to trade off numbers of weapons." The true rationale for the Reliable Replacement Warhead program may be reliable replacement scientists, engineers and technicians.

Editor's Note: This article originally incorrectly placed Sandia National Laboratories in White Plains, N.M., rather than Albuquerque, N.M. Also, the JASON report referenced concerned itself solely with the plutonium primaries lifetime not the lifetime of the entire warhead.