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Simulating Nuclear Explosions under the Comprehensive Test Ban Treaty

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SSMP Program Strategy

"The limitations of the current [experimental/computational] facilities could be accepted [in the past] because underground testing was available, if necessary, to resolve specific issues . . . . New capabilities will improve our ability to simulate the perfor-mance of nuclear weapons and serve as an attraction and training ground for the next generation of nuclear experts." (I-3)

"The nuclear design capability will be maintained by pursuing an understanding of the underlying physics of nuclear weapons and exercising the process of design of nuclear weapons. This includes material properties, hydrodynamics, radiation transport, and neutron transport as well as many other physical processes that occur in the operation of a nuclear weapon. Advanced computational capabilities will be required to adequately address concerns if the design laboratories are forced to deviate from designs that have been verified through nuclear testing."[3] (VII-3)

"Unique capabilities of the Nevada Test Site (NTS) will be utilized to conduct experiments requiring large quantities of high explosive (HE). Other experiments involve special nuclear materials (SNM) driven by HE. Although the principal purpose of these experiments is to provide data for nuclear design laboratory programs, their execution will be very important to an ongoing test readiness posture. Those few capabilities essential for nuclear testing [that are] not used during the experimental program will be exercised periodically to maintain relevant skill bases." (VII-4)

"The end of underground testing will necessitate fundamental changes in the stockpile assessment and certification process. Aboveground experimental facilities that once supplemented underground nuclear testing must be expanded to provide more comprehensive data across a broader range of nuclear processes. Computational modeling, once a tool to facilitate design and evaluation, must now serve as the integrating factor to link aboveground experiments, historical nuclear test data, and design experience into a nuclear predictive simulation capability." (IV-2)

"Experimental programs involving a broad range of existing and advanced facilities will develop the data needed to understand nuclear weapons science at a level more fundamental than was required in the past. The conditions, energies, and densities in the appropriate materials found in many aspects of a nuclear explosion cannot be achieved in the laboratory over the range of needed time or physical scales. Therefore, new experimental facilities -- each having the capability to probe different subsets of these conditions -- must be developed." (IV-2)

"Highly accurate computational simulations of weapons systems will integrate this fundamental understanding, apply it to stockpile issues, and tie it make to experiments and past nuclear tests. The experimental and computational assessment programs must also support the continuing need to evaluate intrinsic and external radiation effects . . ." (IV-2)

"Consistent physical models will be developed representing the essential processes from detonation through the secondary nuclear explosion. These models will be experimentally validated in our research program using new and existing facilities." (IV-6)

"The model validation effort cannot be executed without the high quality experimental data that will be provided by new facilities, especially to address implosion hydrodynamics and high-energy density phenomena. To meet these requirements, investments are being made in new facilities such as the Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility, an Advanced Hydrotest Facility (AHF), the National Ignition Facility (NIF), an Advanced Radiation Source (X-1) and the Atlas pulsed power facility." (IV-4)

"Investments are also being made in supercomputing through the Accelerated Strategic Computing Initiative (ASCI). High-performance computing far beyond our current level must be developed to run the simulations. The shift to computation-based methodologies for assessment and certification will require large improvements in the laboratories' core computational capabilities. ASCI will develop the applications, high performance computers, and problem-solving technologies to feed this core program." (IV-4)

"In addition, some problems could necessitate redesign activities and subsequent certification. It is possible that such design, development, and certification programs could require nuclear testing, a possibility acknowledged in the President's speech of August 11, 1995. [4] . . . .Changes in military requirements may lead to new design requirements, and skilled personnel must be available to execute this work." (I-4)

"This plan provides for the continued development of such weapon components as pits, secondaries, high explosives, detonators, radiation cases, warhead electrical systems, gas reservoirs, and test and handling equipment. Specific efforts in each of these product areas will include advanced development, design, production and assembly activities." (II-6)

". . . and development continues on newer, more capable gas transfer systems and neutron generators for the future." (II-6)

"DOE is maintaining a surge capability to rebuild a larger stockpile." (I-3)

New Weapon Designs and Modifications

"Weapon replacement design options that could be fielded with high confidence without additional nuclear testing will also be developed when necessary. Two candidate designs have been identified for the [Navy] Mk5 delivery system, one reusing an existing pit and one requiring new pit manufacture. These replacement designs would offer alternatives for possible replacement of existing warheads and would be prototyped, which is critical to maintaining our capability to design and fabricate new weapons as required by the Nuclear Posture Review. New experimental and computational capabilities are required to certify these designs without further nuclear testing." (IV-11)

"The New Pit Replacement Option design strategy will be to integrate the nuclear design, engineering design, and manufacturing capabilities in the conceptual stage. This program will also include major elements of a traditional Phase 3 design program, with the exception of nuclear testing. The new experimental facilities and computer modeling and simulation capabilities shown in [figure deleted] are necessary to assess and evaluate the expected nuclear performance." (IV-16)

"The laboratories are currently working on programs to provide new or modified designs that will address current stockpile issues and will exercise a broad range of design skills. These programs include the following:

B61-11 replacement for the B53 gravity bomb. The B61-7 will be modified to replace the B53. [5] This modification will provide enhanced surety [i.e. safety and use control] features relative to the B53. The design and engineering development of the B61-11 will require hydrodynamic testing and engineering functional testing that supports nuclear design capability.

W87 Life Extension Program. The W87 life extension program will require a program of design and evaluation for the physics package, including the assessment required for certification.

B61 Mod 3, 4, and 10 surety upgrades. Proposed modifications to improve the safety of the weapon will require an active nuclear design and laboratory test program to support final evaluation and nuclear certification." (V-9,10)

New Warhead Prototypes

"In addition to the above programs, which are expected to lead directly to stockpile modifications, the nuclear weapons laboratories will conduct prototype programs to provide possible future replacement warhead designs for Navy and Air Force systems. The initial focus for design activities will be the SLBM Warhead Protection Program, a program which is being coordinated among the Navy SSPO [Strategic Systems Program Office] , DOE, and the weapons laboratories." (V-9)

"Two candidate replacement nuclear designs have been identified in this [SLBM Warhead Protection] program. One design would require new pit fabrication, thereby maintaining expertise in new pit technologies. The other would incorporate a reused pit from a retired warhead, providing design and development experience in pit reuse technologies." (V-10)

"Both of the replacement design options will be prototyped and flight tested, but no final development activities will be initiated until a decision is made to proceed. The nuclear design activities of this program will be broadly based and will provide present and future weapons scientists and engineers with the opportunity to exercise the complete set of skills required to design and develop a stockpile warhead." (V-10.)

Warhead Certification

"The term certification refers to a formal process by which the cognizant design laboratories confirm that a warhead or component design conforms to its required military characteristics, with exceptions noted. Certification has historically been associated with the introduction of new warheads into the stockpile …. No new or substantially modified nuclear weapons have entered the stockpile since U.S. nuclear testing ended in September 1992. In the near future, however, several modifications to existing weapons are planned, and they will require certification prior to deployment. These include the B61-11 replacement for the B53, W87 refurbishment, and the replacements for the destructively tested surveillance units of the W88, which will use pits fabricated with a different process than those in the current stockpile.

In addition, future replacements to nonnuclear components will generally employ modified designs. DOE's existing certification process with its peer review agreements provides a framework for these actions." (IV-22, 23)

"With regard to the certification of new designs for the stockpile, existing agreements calling for peer review as part of the DOE certification process are adequate, but a requirement exists to provide sufficient documentation to satisfy [DoD's] DRAAG [Design Review and Acceptance Group] requirements. Additional work is needed to define the level of modification to a current design that should initiate a formal, peer reviewed assessment." (IV-23)

DOE/DoD Joint Flight Testing

"In July 1992 DOE issued a Joint Test Assembly (JTA) design directive. The primary purpose of the directive was to develop an overall philosophy to optimize performance features and address [warhead] environmental [stress] issues on a consistent basis . . . . Included in the JTA design directive is the concept of high fidelity JTAs. High fidelity JTAs are designed to more realistically resemble a nuclear weapon . . . . DOE is currently developing a five-year implementation plan for new JTAs, that will be more in compliance with the design directive." (III-6 and 7)

"A new generation telemetry-based JTA is also being envisioned that will use technology advances to miniaturize the electronics. Modern technology will allow us to design a telemetry package that will fit into the secondary volume of the weapon, leaving a high fidelity denuclearized primary as a component to be tested in flight, or vice versa. In addition to measuring the relatively slow data obtained from current JTAs (e.g. acceleration, strain, temperature, voltage) this package will record the high-rate data. These data are important to the nuclear designers in scoring the implosion. This test might be characterized as a flying hydrotest." (III-12)

"Virtual Testing" Capabilities

"Computer modeling and simulation improvements are currently being implemented and validated in two-dimensional radiation hydrodynamic and explosion codes. In order to completely assess the nuclear performance of the weapons, designers will require computer modeling and simulation improvements in three dimensions." (IV-10)

"The existing empirically based models implemented in our current simulation codes were partially validated through nuclear testing and supporting experiments. However, there are many outstanding issues of fundamental understanding in nuclear weapon science, associated with each stage of weapon operation, that must now be addressed to develop a sufficient basis for weapon assessment and prediction of changes without additional nuclear testing." (IV-24)

"These issues have been prioritized according to the best current evaluation of needs and abilities, and are being addressed systematically. Theoretical models for specific phenomena are being developed and simulated in stand-alone codes. Often they address technical areas, such as instabilities and turbulence, which are not yet formally understood by the general scientific community. New scientific data must be obtained to guide the theoretical development and validation of these models, requiring new experimental capabilities. When validated, the models must then be put into a form that is accurate and efficient for use in our weapon simulation codes." (IV-24)

Predicting Primary Stage Performance

"Direct functional testing can still be performed for most nonnuclear [explosive] weapon system components ….Absent additional nuclear testing, improved models benchmarked against simulation data and validated against data from previous nuclear tests will be the principal basis for assessing the adequacy of electronic and other nonnuclear component behavior in radiation environments." (IV-24)

"A variety of high-explosive driven hydrodynamic experiments using advanced diagnostic capabilities, including high-resolution radiography at multiple times with multiple views, are essential to define the implosion characteristics in the preboost phase or in a safety scenario. Improved theoretical models related to dynamic materials behavior, and fundamental data on particular materials such as high explosives and plutonium, will be essential for adequate modeling and assessment." (IV-26)

"Improved understanding and data related to the dynamic behavior of materials, including age-related changes, will be studied with well-diagnosed experiments using explosive projectile guns, pulsed-power, and lasers. Studies must include understanding of real materials and alloys in manufactured components. Materials science laboratories and tools such as lasers, synchrotron radiation sources, and the application of powerful neutron sources such as LANSCE, will provide much of this important information." (IV-26)

Predicting Late Primary Stage Performance

"The other key technical issues associated with primaries involve the ignition and burn of their boost gas, which are extremely difficult to access experimentally without nuclear testing. Laser and other inertial confinement fusion approaches, and pulsed power experiments may be able to provide an improved understanding of the aspects [sic] of gas burn physics. The data gathered in this complete set of experiments will be essential for evaluating new and evolving computational models of the primary stage behavior." (IV-26)

"The later phases of operation of a primary stage (fission explosion and fusion ignition and burn) rely heavily, in the near term, on physically based advanced computer modeling and simulation and reanalysis of past nuclear test results. As advanced hydrodynamic capabilities like DARHT (and, in the longer term, AHF) become available, they will provide a significant experimental capability to be added to the assessment of primary operation. Pulsed-power, NIF, and other non-laser driven fusion approaches, may be used to provide broader experimental validation of the aspects [sic] of the late phases of primary operation in computer modeling and simulation." (IV-26)

Advanced Dynamic Radiography

"Radiography is an especially important diagnostic for probing performance of primaries at 'nuclear' times. Current facilities at FXR [["Flash X-Ray Facility," Livermore Site 300] and PHERMEX ["Pulsed High Energy Radiographic Machine Emitting X-Rays," Los Alamos] do not have adequate resolution to probe the primary stages in the current stockpile [in their most densely imploded configurations]. The capability of hydrotest facilities will be improved through upgrades (e.g. FXR and Phermex double pulsing), the addition of diagnostics (e.g. the gamma ray camera), and facility improvements (e.g. Contained Firing Facility). (IV-29)

"DARHT [Dual-Axis Radiographic Hydrotest Facility] will provide an expanded hydrotest capability to address both 3D issues and time dependence through the use of two radiographic machines. DARHT will have improved resolution that will allow safety and performance assessments for most stockpile primaries. The AHF [Advanced Hydrotest Facility] will be a subsequent development with multiple axes and multiple times to address performance and safety issues that require a high level of accuracy on the 3-D [three-dimensional] density distribution of materials at nuclear time. New radiographic techniques that do not utilize gamma rays, such as proton radiography, may be necessary to provide this capability." (IV-29)

Predicting Secondary Stage Performance

"However, the high energy-density conditions relevant to secondary performance are extremely difficult to create in a laboratory setting, and most data must be extrapolated to the weapons regime in at least some parameters, requiring the expert judgment of weapons scientists following a careful strategy of fundamental science, scaled experiments, and comparison with past nuclear test data to validate models….laser and pulsed power experiments, as well as computer and simulation modeling advances, are critical to obtaining fundamental physics data that when validated with past nuclear test data, can be used to assess the full nuclear performance of the secondary stage." (IV-27)

"The [computational physics] model validation effort cannot be executed without investment in new experimental measurement capabilities and facilities, especially to address implosion hydrodynamics and high-energy density phenomena. Facilities are also required to provide weapons effects information previously obtained in DNA-sponsored nuclear tests." (IV-27)

"Experimental study of the thermonuclear phase of a weapon explosion is necessary to improve our understanding of the nuclear test database, to evaluate issues identified by stockpile surveillance [e.g. effect of materials degradation on nuclear performance], and to validate new computational modeling and simulation. This work requires experimental facilities that can create hot dense plasmas approaching the physical conditions important to secondaries and some aspects of primary operation. (IV-29)

Plutonium Properties and Dynamic Experiments

"Understanding the properties of plutonium is essential to the accurate modeling of the performance of a primary. Experiments are currently being initiated in the Lyner complex at NTS to experimentally measure the high-pressure equation of state (EOS), strength properties, and response to shock of plutonium. Energy drivers will include high explosives, pulsed power, and gas guns at the NTS and the laboratories." (IV-28)

"A detailed understanding of plutonium material properties will require the application of a variety of state-of-the-art diagnostics (e.g. velocimetry, holography, laser-illuminated high-speed photography, x-ray radiography, and [shorting] pins) as well as diagnostics developed specifically for these experiments. Some plutonium experiments are compatible with above-ground facility capabilities (e.g. diamond anvil, laboratory gas guns, and laser-driven flyer [plate] EOS studies, and can take advantage of additional diagnostic capabilities (e.g. synchrotron radiation sources)." (IV-28,29)

"Dynamic experiments are conducted to understand high explosive (HE) properties, primary and reflected shock structure, and material response, and to examine the effects of engineering features such as welds and surface finish on probable weapon performance. In addition, experiments are conducted to measure the integral performance of complete weapon assemblies to validate models subject to uncertainties from incomplete physics, uncertainties in material properties, computational symmetry assumptions, and the effects of calculations using discrete elements. Hydrotesting of primaries is the only remaining way to test the integral performance of a primary in real weapon geometries." (IV-29)

Improved Computations for Weapons Simulations: The Accelerated Strategic Computing Initiative (ASCI)

"ASCI is envisioned to shift promptly from nuclear test-based assessment methods to computational-based assessment methods. The ASCI program was developed as a surge capability to provide the required dramatic advances in computer hardware and predictive, physics-based modeling and simulation computational tools." ASCI "will extend DOE's computational resources to create an assessment program that does not rely on additional nuclear testing and prototyping capabilities for nuclear weapons." (IV-32)

"The ASCI program plan has four main objectives:

a. Performance: Create highly credible virtual tests to analyze the performance and predict the behavior of nuclear weapons;

b. Safety: Predict with high certainty the behavior of weapon systems in complex accident scenarios;

c. Reliability: Achieve sufficient validated predictive capabilities to extend the lifetime of the stockpile, predict failure mechanisms, and reduce routine maintenance;

d. Renewal: Use virtual prototyping [i.e. 3-D "solid" modeling of weapon components] to reduce the need for testing and production facilities required for stockpile requalification and replacement work." (Appendix B-1)

"ASCI will focus on . . . developing high performance, full-physics, full system, 3-dimensional (3-D) predictive codes to support weapons designs, production analyses, accident analyses, and certifications. Applications in weapons physics, engineering, and manufacturing science will be the main focus of the applications code development effort. Together they will provide the ability to predict the performance of full nuclear weapon systems…" (IV-32)

"Existing codes, constrained to run on current computers, do not have the physics models necessary to accurately simulate the processes and phenomena needed for virtual testing and prototyping. For example, existing codes have several empirical factors that the user must set. These settings are not based on physical understanding of the phenomena in question, but on the judgment of the experienced user in matching past experiments. These empirical factors severely restrict the predictive capability of our codes." (Appendix B-3)

"Removing empirically based factors from the application codes requires an understanding of the physics that the empiricism currently replaces, and requires the creation of new models in the codes to simulate the physics. These new models will have to be verified and validated using different methods and techniques. For example, in the absence of underground testing, the new physics models in the [nuclear explosive] device analysis codes must be validated using advanced aboveground experiments (AGEX) facilities and past underground test data. Similarly, accurate virtual prototyping methods must be developed…" (Appendix B-3)

"The increasing computational power that ASCI will provide will enable calculations of thermomechanical properties, opacity (i.e. a measure of a materials capacity to absorb radiation), and material microstructure that are well beyond our current computational capabilities." (Appendix B-3)

"Strong collaborations with universities will help form a cadre of young scientists trained in defense-related capabilities. Additionally, these collaborative programs, through teaming, competition, and peer review, will fine tune the skills of the personnel conducting the assessment of the stockpile. To address the needs of the stockpile, the foremost science and technology in the world will be utilized." (IV-31)


3. As recently as 1992, the nuclear design laboratories were insisting that confidence could not be sustained even in nuclear-test-proven designs without continued nuclear explosive testing. Now these same laboratories aver that they can make significant changes to these weapons without resort to underground testing -- a startling example of how the "objective" technical requirements of the stockpile can suddenly change with shifting political realities.

4. This speech established the maintenance of nuclear weapons reliability as a "supreme national interest" meriting possible withdrawal from the CTBT.

5. This stockpile modification is already in progress.

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