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1 Overview
Pages 4-17

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From page 4...
... In 1993, Congress and the President directed DOE to "establish a stewardship program to ensure the preservation of the core intellectual and technical competencies of the United States in nuclear weapons."  The Stockpile Stewardship Program's (SSP's) objective was to develop ways to simulate -- with computer models and experiments that remain subcritical -- the various processes that take place during a nuclear weapon explosion and to apply the knowledge gained to extend the life of the existing weapons in the stockpile.
From page 5...
... In general terms, its purpose is to provide a systematic means to apply -- using sophisticated simulation models -- the varied output of the science base of the SSP to the assessment of the nuclear weapons stockpile. This output includes the aboveground nonnuclear and subcritical experiments, data from past underground nuclear tests, and expert judgments of the weapons scientists.
From page 6...
... Nevertheless, QMU is a relatively new component of the program, and both internal and external reviews over the past few years have raised issues about the QMU framework and its application to nuclear weapons assessment. As a consequence, both Congress and the NNSA expressed interest in late 2006 in further evaluation of the QMU framework and its application. Some of the issues driving this interest are the role of expert judgment; the difficulties in quantifying margins and uncertainties for complex systems; the variable quality and quantity of test data that are needed to validate warhead simulation codes that are used to develop good quantitative estimates of margins and uncertainties; and how to properly incorporate statistical considerations into those estimates.
From page 7...
... Nevertheless, dependence on the QMU methodology appears to be growing, leading to increased congressional interest in this aspect of the weapons program. Statement of Task In 2006, as a result of congressional concerns about the methodology, implementation, and likely role of QMU in any potential RRW, the House Armed Services Committee inserted language in HR 5122, the John Warner National Defense Authorization Act for Fiscal Year 2007, requesting the National Academy of Sciences to conduct an independent evaluation of the QMU methodology employed by the national security laboratories and to say whether this methodology could be used to certify an RRW without underground nuclear testing.
From page 8...
... In the FY2008 Consolidated Appropriations Act, Congress denied funding for the RRW program and provided new funding for advanced certification.11 In accompanying language, Congress stated that before any such warhead was developed, "a new strategic nuclear deterrent mission assessment for the 21st century is required to define the associated stockpile requirements and determine the scope of the weapons complex modernization plans." Accordingly, it directed NNSA "to develop and submit to the Congress a comprehensive nuclear weapons strategy for the 21st century." In conjunction with this strategic planning effort, Congress also requested that NNSA "develop a long-term scientific capability roadmap for the national laboratories." In the same legislation, Congress directed NNSA to begin a new Science Campaign called Advanced Certification to address "significant systemic gaps in NNSA's stockpile certification process" and funded this effort at $15 million. In the conference report accompanying the FY2008 Defense Authorization Bill, Congress urged NNSA "to approach the RRW program cautiously, with a commitment to address and resolve all issues as completely 11  U.S.
From page 9...
... BACKGROUND Definition and Current Implementation of QMU This section provides a description of how the QMU methodology is currently being implemented. As was noted above, QMU is an important part of the process by which nuclear weapons computer simulation models, experiments producing no nuclear yield, prior underground nuclear tests, and expert judgment are brought to bear to assess the reliability of the existing weapons stockpile.
From page 10...
... Ultimately these many margins and uncertainties are combined in assess ing the entire nuclear explosive package. QMU has been used for today's nuclear weapons and their predecessors as well as for the RRW design.
From page 11...
... • What joint computational and experimental activities are needed? One fundamental scientific tool is the estimation of uncertainties with sensitivity analyses, as applied to or backed up by an assessment of failure modes, cliffs, mar gins, mining the data from underground nuclear tests, and experimental validation.
From page 12...
... These codes are made up of many physical models describing weapons physics, data from prior underground nonnuclear and nuclear tests, data from subcritical and aboveground experiments, expert judgment, and properties of materials (equations of state, opacity, nuclear reaction cross sections, etc.)
From page 13...
... The codes, along with underground nuclear test data, expert judgment, and aboveground experiments,14 are used to estimate the threshold and lowest expected performance level and, accordingly, the value of the margin for each component or operating 14  Aboveground experiments are by definition subcritical (see Glossary)
From page 14...
... The most difficult part of using the QMU framework for evaluating nuclear weapons performance is identifying, characterizing, quantifying, and aggregating the large number of uncertainties, U, that arise. There are uncertainties in the simulation codes' predicted threshold value and the operating range lower boundary of the margin at each stage of the warhead process.
From page 15...
... Uncertainty is further increased, however, by the fact that underground nuclear test experiments were only rarely conducted at performance thresholds, and data from aboveground experiments extend over a very limited range of the performance space of a nuclear explosion. The codes themselves are sources of uncertainty.
From page 16...
... By using the simulation codes to predict changes in thresholds and uncertainties as components age, estimates can be made of how the performance of the warhead will change over time. Finally, the QMU framework is expected to play an important role in the certification of the reliable replacement warhead design.
From page 17...
... : A White Paper, SAND2006-5001, Albuquerque, N.M.: Sandia National Laboratories (2006)


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