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Scientists See Stockpile Lasting for Decades

Tom Z. Collina

Weighing in on a long-simmering debate within the U.S. government, an influential panel of scientists has found “no evidence” that extending the lives of existing U.S. nuclear weapons leads to reduced confidence that the weapons will work. The panel, known as JASON, found that the “[l]ifetimes of today’s nuclear warheads could be extended for decades, with no anticipated loss in confidence,” according to an unclassified summary of the report.

The study could affect the ongoing Nuclear Posture Review (NPR), which is expected to address whether the United States can maintain its existing warhead designs or might need new ones. By reaffirming that the arsenal can be sustained without nuclear tests, the report could also bolster efforts by the Obama administration to ratify the Comprehensive Test Ban Treaty (CTBT).

“The JASON study offers yet more evidence that the United States can maintain a safe, secure, and effective nuclear arsenal without resorting to nuclear tests,” an Obama administration official said in a Nov. 20 interview. “The burden of proof is now on CTBT skeptics to lay out why the United States must continue to plan for future testing when we have not tested for almost two decades and our weapons experts enjoy a greater understanding of how our nuclear weapons work than at any previous time, thanks to the demonstrable successes of our Stockpile Stewardship Program,” the official said.

However, in a statement e-mailed to Arms Control Today, Rep. Michael Turner (R-Ohio) said, “Setting aside the political pros and cons of CTBT ratification, on [a] technical basis alone the JASON report does not instill confidence that the nuclear security enterprise is in a position to provide long-term sustainment of our nuclear stockpile in a CTBT regime.”

JASON, which had access to classified nuclear weapons design information, reviewed the National Nuclear Security Administration’s (NNSA) Life Extension Program (LEP) at the request of the House Armed Services Strategic Forces Subcommittee, which released the summary Nov. 19. JASON conducted a similar review of the Reliable Replacement Warhead (RRW) program in 2007.

The goal of the LEP is to extend the service lives of existing, well-tested nuclear warhead designs, a process known as refurbishment, without nuclear testing. Congress asked JASON to compare the LEP approach to the RRW program, which calls for “replacing” existing warhead designs with new, untested ones to address concerns that the reliability of today’s warheads could decline as they age. (See ACT, November 2009.)

The U.S. government is extending the life of its existing arsenal because no new warhead types have been introduced since the United States conducted its last nuclear test in 1992. As a result, existing designs are being kept longer than originally planned. Through the LEP, the NNSA has refurbished the W87 Minutemen and W80 cruise missile warheads and the B61-7/11 strategic gravity bomb, is refurbishing all W76 Trident D-5 missile warheads, is planning to refurbish the B61 tactical bomb, and is evaluating what approach to take for the W78 Minutemen and W88 Trident D-5 missile warheads. LEP refurbishment involves swapping older warhead parts with new ones of nearly identical design or that have the same “form, fit, and function,” according to the NNSA. LEPs generally involve the non-nuclear parts of warheads and, in cases such as the B61-7/11 bomb, have included the lithium-deuteride secondary components, also known as “canned subassemblies.”

So far, the LEP has not changed nuclear primaries, which contain plutonium cores, or “pits.” JASON, the NNSA, and Lawrence Livermore and Los Alamos national laboratories, in independent reviews of data gathered by the laboratories, have concluded pits can last 85-100 years or more.

The most prominent advocate of “replacement” warheads has been Secretary of Defense Robert Gates, who in September told the Air Force Association that, “in one or two cases,” the United States would “probably” need “new [warhead] designs that will be safer and more reliable.”

The JASON study, however, found no basis for concerns that warhead aging and efforts to address it reduce reliability. The panel found “no evidence that accumulation of changes incurred from aging and LEPs have increased risk to certification of today’s deployed nuclear warheads” and that current U.S. warheads could last “for decades, with no anticipated loss in confidence, by using approaches similar to those employed in LEPs to date.”

“We welcome the release of the JASON scientific advisory panel’s review of warhead Life Extension Programs,” Strategic Forces Subcommittee Chairman James R. Langevin (D-R.I.) and Turner, the panel’s ranking member, said in a joint statement. “We believe their recommendations provide a sound technical basis to inform subsequent U.S. nuclear weapons policy and program decisions,” they said.

While minimizing concerns about the reliability of life-extended warheads, the JASON report highlights surety as another potential rationale for replacing existing warheads. Gates and others point out that current warheads do not have the latest surety systems, a term that encompasses safety, security, and “use control,” which refers to technologies to prevent the use of lost or stolen weapons. That discussion goes back to 1992, when President George H.W. Bush signed into law a congressionally mandated moratorium on nuclear tests and, at the same time, authorized additional tests for safety and security purposes. Those tests were never conducted because the Air Force and Navy determined that the marginal improvements were not worth the budgetary cost of deploying the new systems.

Events since then may have changed some attitudes. The Sept. 11 terrorist attacks and the Aug. 30, 2007, incident in which the Air Force lost track of six nuclear cruise missiles have focused attention on the vulnerability of nuclear weapons to theft and on improved security and use control. According to congressional staffers, the U.S. military may now be more willing to make expensive operational changes to prevent terrorist acquisition and use, and the NPR is expected to place a high priority on improving the surety of nuclear forces.

JASON did not take a stand on the need for surety improvements. Instead it found that “[f]urther scientific research and engineering development is required,” the summary said. The panel noted that implementation of “intrinsic” surety features, i.e., those inside the nuclear explosive package, would require “reuse or replacement” options. In other words, such changes could not be made through typical refurbishment of existing designs but would have to “reuse” surplus nuclear parts or designs that have already been tested with modern surety features (as the W87 warhead’s design has). Information about security or use control features that would require new “replacement” designs is highly classified.

The panel found that the surety of nuclear weapons carried by strategic bombers could be upgraded using reuse options. That may be a reference to a safety feature known as fire-resistant pits, which are intended to prevent the dispersal of plutonium during an aircraft fire. That feature is used in the most recently developed weapons, including the W87 warhead and the B83 strategic bomb. The panel also noted that upgrading intrinsic surety features in the entire stockpile would “require more than a decade to complete,” which was described as an understatement by one source familiar with the study. As a result, the panel recommended that the potential benefits of surety technologies be assessed “in the context of the nuclear weapons enterprise as a system, including technologies that can be employed in the near term.”

Because changes to warheads utilizing reuse or replacement options may take the weapons beyond previous test experience, “[c]ertification of certain reuse or replacement options would require improved understanding of boost,” the panel said. Boosting, the practice of increasing the yield of a warhead’s primary stage with tritium gas, is one of the most challenging aspects of nuclear weapons physics to simulate in the laboratory.

According to the summary, the report also concluded that the NNSA surveillance program, which is responsible for finding age-related problems with the stockpile and therefore essential to stockpile stewardship, is “becoming inadequate” and that nuclear weapons expertise is “threatened by lack of program stability, perceived lack of mission importance, and degradation of the work environment.” In response, administration officials say that the fiscal year 2011 proposed budget, to be submitted to Congress in February, will include increased spending on NNSA stockpile maintenance activities.

In his e-mail, Turner said the JASON report “raises serious concerns” about the adequacy of the surveillance program and “maintenance of critical expertise and capabilities.”

NNSA spokesman Damien LaVera said in a Nov. 19 written statement that “[t]he JASON’s review confirms the challenges associated with adding performance margin and incorporating modern safety and security features into aging weapons systems, acknowledges the need to preserve our workforce, and reaffirms our long held belief that the strength of the science, technology and engineering at the laboratories and plants is the key to our success.”

LaVera added that “certain findings in the unclassified Executive Summary convey a different perspective on key findings when viewed without the context of the full classified report.” According to congressional staff, the NNSA was referring to possible problems with the stockpile that may be discovered once the surveillance program is improved, otherwise known as “unknown unknowns.”