The following op-ed by Daryl Kimball, executive director of the Arms Control Association, first appeared in Defense News on March 5, 2007.

Following the end of U.S. nuclear testing a decade and a half ago, some scientists and policy-makers worried that the reliability of U.S. nuclear warheads could diminish as their plutonium cores age. They claimed it would take a decade or more to see if the nation’s weapon laboratories could maintain the existing stockpile of well-tested but aging weapons without further nuclear blasts.

Such concerns led many senators to withhold their support for ratification of the Comprehensive Test Ban Treaty (CTBT) in 1999.

Time has addressed the skeptics’ concerns. For more than a decade, a multibillion-dollar Stockpile Stewardship program has successfully maintained the existing U.S. nuclear arsenal in the absence of testing. As the importance of nuclear weapons in U.S. military strategy has diminished, there has been no need to test new types of nukes.

But now, the Bush administration is asking Congress to fund an ambitious effort to build new replacement warheads, which it claims is needed to avoid plutonium aging problems that could reduce weapon reliability.

In particular, National Nuclear Security Administration (NNSA) officials argue that some warheads in the U.S. stockpile, such as the W76 submarine-launched missile warhead, which were designed to minimize size and weight and maximize yield, have nuclear components that are sensitive to changes due to aging.

In reality, replacement warheads are a solution in search of a problem. Recent findings on plutonium longevity show that the United States can maintain its existing and diminishing nuclear arsenal for decades without new warheads and without resuming nuclear testing. New government studies completed last fall find that the plutonium primaries, or cores, of most U.S. nuclear weapons will have minimum lifetimes of 85 years, about twice as long as previous estimates.

Moreover, the Navy is spending heavily on refurbishing the W76, and it seems implausible that funds would be provided for such a program if it were considered deficient. Instead, it appears that the reliability of existing warheads can be maintained more easily by avoiding unnecessary alterations during refurbishment.

Rather than build new and robust replacement warheads, the reliability of existing warheads can be improved by adding more boost gas to increase the explosive energy of the primary stage of the weapon well above the minimum needed to ignite the secondary, or main, stage.

NNSA argues that more efficient and replacement warheads would be less expensive to maintain than older designs. Indeed, the administration’s request for $118 million for research on replacement warheads in fiscal 2008 may appear to be small in comparison to the government’s $6.5 billion annual nuclear weapons program budget.

But over time, total costs would rise, not fall, because the weapon labs will continue to spend billions to extend the life of existing warheads for the 10 to 20 years needed to build replacements.

NNSA officials also argue they can build replacement warheads that are more reliable and can be certified without nuclear weapon proof testing. While many legislators have their doubts, some believe that if the new warheads are indeed more reliable, this administration or the next one should be more willing to support Senate advice and consent for test ban treaty ratification.

Perhaps. But building a new generation of nuclear weapons to win support for a global test ban treaty intended to help prevent new nuclear arms competition is not only counterintuitive, but politically risky. Given that replacement warheads are still years and billions of dollars away from reality, many test ban treaty skeptics might argue, as they did in 1999, that it is too early to tell whether the new warheads will work reliably and without proof testing.

In fact, confidence in the reliability of the U.S. nuclear stockpile could erode if warhead designs are changed to those not validated by past testing. Nevertheless, NNSA may pursue a design to replace the W76 that consists of various components that have not been previously tested together.

Instead, House and Senate members should shelve Bush’s costly and unnecessary proposals for a new breed of nuclear weapons and approve the CTBT.

Leaders of many key states already doubt the United States and other nuclear-weapon powers intend to pursue their own Nuclear Non-Proliferation Treaty-related disarmament obligations, which include ratification of the CTBT. That shrinking faith erodes the willingness of key non-nuclear-weapon states to fulfill their own NPT obligations, much less agree to measures that would strengthen the beleaguered nonproliferation system.

U.S. leadership on the CTBT would also spur others, particularly China, to follow suit and make it more difficult for them to build new and more dangerous nuclear weapons. The scientific evidence and international security situation calls for a reduction in the role and number of U.S. nuclear weapons, properly funding the surveillance and maintenance of those that remain, and ratification of the test ban treaty.

Daryl Kimball is the executive director of the Arms Control Association in Washington, D.C.