The Comprehensive Nuclear Test Ban Treaty

A report released in March 2012 by the National Academy of Sciences (NAS) finds that the United States has the technical capabilities both to maintain a secure and reliable nuclear weapons stockpile without nuclear testing, and to monitor clandestine testing by other nations.

The new report is an update of a 2002 report on technical issues associated with the Comprehensive Test Ban Treaty (CTBT), the international treaty to ban all nuclear-explosion testing. The CTBT was negotiated in the 1990s and signed by the United States in 1996, but the Senate declined to ratify it in 1999. The Obama administration has announced that it will pursue ratification of the treaty.

Advances in technology and understanding during the past ten years have significantly strengthened the U.S. ability to maintain its existing nuclear stockpile, according to the report, leaving no technical reason not to participate in the treaty.

The report focuses on four areas, summarized below.

Maintaining the US nuclear stockpile

While noting that sustaining the U.S. arsenal will require a continuing commitment of resources and skilled personnel, the report finds that the United States has a greater technical capability to maintain its nuclear stockpile without nuclear-explosion testing than the earlier report anticipated.

Significant developments over the past decade supporting this conclusion include:

• Recent studies finding that plutonium "pits" (the core of all U.S. nuclear weapons) have a lifetime of at least 85-100 years
• Increases in computing power by a factor of 1,000, which allows better modeling and assessment for weapons programs
• Completion of several major research facilities that help improve our ability to maintain nuclear weapons without additional testing
• Initiatives, such as the production of new W88 pits and life extension programs (LEPs) for W87 and W76 warheads, which show that the U.S. has the capacity to maintain and improve its existing arsenal.
• Two new stockpile surveillance programs for the U.S. arsenal, which will provide better data and diagnostic tools for stockpile stewardship.

Monitoring and verification

The ability to monitor nuclear testing worldwide is essential to the success of the CTBT. There are a number of monitoring systems in existence: the International Monitoring System (IMS), run by the CTBT Organization (CTBTO), national technical means (NTM) of states participating in the treaty, and systems created for other purposes, such as seismic networks used to monitor earthquake activity. The treaty also provides for on-site inspection at the request of signatory states.

Concerns about the effectiveness of monitoring systems helped prevent Senate ratification of the CTBT in 1999. The new NAS report shows that there have been significant improvements in these systems over the past decade, including near completion of the IMS (which was in an embryonic state at the time of the 2002 report), as well as improved satellite capabilities and advances in monitoring techniques that can detect nuclear explosions through their seismic, radioactive, and sonic signatures.

Nuclear tests by North Korea in 2006 and 2009 provided practical tests of these monitoring capabilities: both were detected by seismic sensors and were clearly identified as explosions, not earthquakes. The 2006 test was also detected by radionuclide sensors that detect radioactive particles.

Sustaining US technical capabilities under the CTBT

While the U.S. is technically capable of maintaining its security under the CTBT, budget constraints, bureaucratic inefficiencies, and the difficulty of attracting and retaining top-tier scientific talent create potential challenges for sustaining these capabilities into the future.

The 2012 panel was directed to address this issue, and made several recommendations: better management of nuclear weapons complex facilities; full support for the CTBTO's monitoring and inspection work; continued investment in U.S. monitoring capabilities, including satellites; and safeguards to mitigate potential risks involved in ratifying the treaty.

Most important, the panel repeatedly stresses that "[t]he most serious requirement for sustaining the U.S. stockpile and monitoring capabilities is a clear statement of policy regarding the capabilities that must be maintained, combined with management and support focused on acheiving well-defined technical goals underpinning those capabilities." The panel adds that "the need for such action arises whether or not the United States ratifies the CTBT."

Potential technical advances from nuclear-explosion testing

Like the 2002 report, the current report considers the potential threat to the United States from a state carrying out an undetected nuclear explosion test. However, the report concludes that increases in monitoring capability since then make it unlikely that such a test could go undetected, unless the weapons being tested were of such low capability that they would not present a threat to the U.S. requiring new testing on our part in response.

The most plausible scenario that might require the U.S. to resume testing, the report finds, is that an adversary might develop a capability requiring the U.S. to develop a new kind of nuclear weapon. And this would most likely require the adversary to conduct tests on a scale that current monitoring systems would detect, allowing the U.S. to decide whether it could respond with its current capabilities or would need to invoke the supreme national interest clause and withdraw from the treaty.