however, QMU is explicitly applied only to the (assumed) single-most-important performance measure for each stockpile warhead.

The 2007 annual assessment review was examined in depth by the committee. The use of QMU methodology in the annual assessment review is increasing, and that trend is expected to continue in 2008. The annual assessment reviews include discussions of issues involved in applying QMU and the different views of the national security laboratories where improvements are needed. In the 2007 annual assessment, uncertainty bands were developed using QMU formalism, whereas previously the labs had relied primarily on expert judgment. QMU has not yet been applied to safety, security, or human factors.

In the 2007 assessment, QMU was used to determine how the value and uncertainty of the anticipated primary yield, Yp, compares with those of the minimum primary yield, Yp,min, required for stable secondary performance.

The national security laboratories have made a good start in applying the QMU framework in the annual assessment reviews, but they acknowledge that they still have far to go. Margins, M, and uncertainties, U, should be reported for all critical performance gates.

The committee asked the labs to provide briefings on the use of QMU in the annual assessment process for three specific weapons systems: B61 (Sandia), W88 (Los Alamos), and W80 (Livermore). The use of QMU in these systems is summarized in the following sections.

SANDIA NATIONAL LABORATORIES

In the 2007 annual assessment review, SNL used QMU to assess the firing systems and neutron generators of the B61 system under normal, abnormal, and hostile (e.g., high radiation) environments as a function of component age. It also reported on the use of QMU to analyze the strong link/weak link system for the qualification of the W76 and the B83. For the 2008 annual assessment review, SNL will use a technical basis review team to help identify high-priority components for analysis.

SNL management reported that although its QMU assessments to date have been useful for obtaining a better understanding of margins, there is still a great deal of work to do to understand uncertainties. One senior manager noted that uncertainty quantification is a goal at this point, not a reality. SNL managers also reported that there is not much coordination among the national security laboratories on the selection of components for analysis except in one case: the degradation of neutron generators.

Nevertheless, management noted that the use of QMU has had two notable impacts. First, it is allowing the lab to move away from determin-



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