S&TR March 2012

Extending the Life of an Aging Weapon

6 Lawrence Livermore National Laboratory S&TR March 2012 Life-Extension Program

Extending the Life of an Aging Weapon

Stockpile stewards By law, the directors of the NNSA the warhead’s nonnuclear components. weapons laboratories—Lawrence The announcement was made in a letter Livermore, Los Alamos, and Sandia— from Don Cook, deputy administrator for modernize the W78 provide the secretaries of Energy and NNSA’s Defense Programs. Defense with an annual assessment of the The W78 is used on U.S. Air Force stockpile. Confidence in these assessments Minuteman III intercontinental ballistic warhead for the depends on the laboratories’ abilities to missiles (ICBMs). The Mark 12A reentry evaluate the inevitable changes that occur vehicle encloses the warhead to protect nation’s land-based inside nuclear weapons as they age and it from heat as it speeds through the to effectively deal with any safety or atmosphere. A team of about 30 Livermore performance issues that may arise from physicists, engineers, and chemists are intercontinental ballistic those changes. Stockpile stewardship working on an options study in what is activities enhance understanding of currently planned to be a 10-year effort to nuclear weapons and ensure their safety extend the W78’s service life for another missiles. and performance through a combination 30 years. of theoretical advances, nonnuclear In Congressional testimony in 2011, experiments, supercomputer simulations, Laboratory Director George Miller (now OLLOWING the end of the Cold and stockpile surveillance. When retired) underscored the importance of FWar, the U.S. discontinued design and necessary, life-extension programs (LEPs) the W78 LEP, saying, “The role of any development of new nuclear warheads and are approved to prolong the service life of Life Extension Program is to fix issues halted underground nuclear experiments. an aging warhead and enhance its safety that impact—or will soon impact— In place of underground testing, the and security. overall system effectiveness and take National Nuclear Security Administration LEPs address issues discovered through actions that will extend the stockpile life. (NNSA) pursues stockpile stewardship, routine surveillance and annual stockpile Failure to address these issues can have a comprehensive set of scientific and assessments. components immediate and drastic consequences for engineering activities focused on ensuring are made from various materials including the viability of the deterrent our national that existing U.S. warheads remain high explosives, steel, plutonium, uranium, security strategy relies on. In particular, reliable, secure, and safe. and plastics. Over decades, plastics can it is imperative that we begin the study of break down, metals corrode, and coatings options for refurbishing the W78 warhead deteriorate. A material’s properties may to address evolving issues identified in the The life-extension program (LEP) for the W78 change unpredictably in response to high annual assessment of this weapon system.” warhead (above left) will evaluate options for radiation fields, fluctuating temperatures, “When the W78 was added to the refurbishing the nuclear weapon to address and other environmental conditions to stockpile in 1979, no one anticipated it issues identified with aging components. The which stockpile components are subjected. would not have been replaced 33 years U.S. Air Force deploys the W78 warhead in its In July 2010, NNSA designated later,” says physicist Hank O’Brien, Minuteman III intercontinental ballistic missiles Lawrence Livermore the lead nuclear who leads the W78 LEP for Livermore’s (ICBMs), which are dispersed in hardened silos design laboratory to conduct an LEP on Weapons and Complex Integration (left) to protect against attack. (Courtesy of the Los Alamos–designed W78 warhead, Principal Directorate. “We are seeing Department of Defense.) with Sandia, California, responsible for signs of aging among W78 components,

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although these changes have yet to impact Y-12 National Security Complex, Kansas system reliability. It is important to start City Plant, Pantex Plant, Savannah River the LEP process to prevent this aging issue Site, and Sandia, New Mexico) as they from becoming a real problem.” assess the manufacturability of options for The W78 will be the fourth nuclear components and systems. In particular, weapon system to undergo refurbishment. they want to identify manufacturing In 2004, Lawrence Livermore successfully processes that reduce waste and do not use completed NNSA’s first LEP, refurbishing hazardous materials. the . That effort enhanced the A Project Officers Group, with structural integrity of the warhead and representatives from the Department of extended its life by 30 years. For the Defense, NNSA, Livermore, Sandia, and W87, Livermore and Sandia scientists Los Alamos, meets regularly to assess and engineers developed and certified progress. At the conclusion of phase 6.1, the engineering design and worked Livermore managers will present the closely with NNSA production facilities recommended LEP options to this group. to ensure a cost-effective design and “We are thoroughly analyzing all options ease of manufacture. The W87 effort has to present decision makers with low-risk, served as a model for subsequent LEPs, cost-efficient alternatives,” says O’Brien. including two being conducted by Los “Our findings and recommendations Alamos: the warhead used in Trident are based solely on our best technical II submarine-launched ballistic missiles assessments of cost, risk, and ability to (SLBMs) and the B61 family of nuclear meet stockpile goals.” bombs. (See the table on p. 9.) According to O’Brien, U.S. government LEPs progress through a series policy requires LEP design teams to of phases labeled 6.X. Phase 6.1 is a consider options for refurbishing the concept study, during which scientists existing design, reusing components and engineers explore options, reviewing from other stockpiled designs, and each one’s performance characteristics, implementing nuclear-test-based designs manufacturing issues, and technical that are not in the current stockpile. The challenges; expected improvements Department of Defense also requires LEP in performance margins, safety, and studies to identify and assess options security; and long-term maintenance and that improve safety and security features surveillance requirements. Livermore and that make the warhead adaptable for stockpile stewards expect the W78’s deployment on SLBMs as well as ICBMs. 6.1 phase to conclude this year. It will No new military capabilities or missions then be followed by three phases: option are required. Among the suite of options selection and detailed design and cost identified, the stockpile component reuse studies (6.2), development engineering designs show the most promise to address (6.3), and production engineering (6.4). the LEP requirements cost-effectively and First production of the modified warheads with high confidence in performance. (phase 6.5) is scheduled to begin about 2023, followed by full-scale production Looking to Increase Confidence (phase 6.6). A modern nuclear explosive package As part of phase 6.1, Livermore and includes nuclear and nonnuclear Sandia researchers are working with components that comprise a primary NNSA production agencies (Los Alamos, explosive device and a secondary, both enclosed within a case to confine radiation The Minuteman III ICBM, shown in a flight from the primary explosion. Among test, contains the W78 warhead. (Courtesy of the options being considered as part of Department of Defense.) phase 6.1, designers for the primary and

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secondary are examining ways to increase warhead so it can be adapted to multiple To that end, Livermore engineers are confidence that the weapon will reliably delivery platforms, which would provide working on an advanced mechanical safe achieve its predicted energy release, or a cost-effective hedge against future arming detonator (MSAD). This intricate nuclear yield. problems in the stockpile. nuclear safety component prevents accidental A primary is typically a shell of fissile Many safety and security options or unintended detonation of a warhead. material—called the pit—that is imploded ready for deployment on the W78 are MSADs protect nuclear weapons by by a surrounding layer of chemical high based on results from past nuclear tests. preventing an outside source from using the explosive (HE). Options that entail changes Some features would provide enhanced weapon detonators to successfully ignite the to the weapon’s primary to increase protection from fire, while others would IHE main charge. The miniature notches on confidence in performance make it guard against unauthorized use and attack. an MSAD pattern wheel encode a signal set possible to accommodate insensitive high One safety option being evaluated is a that must be received for the weapon to be explosives (IHEs) and other safety and method to better ensure that the firing operable. This unique signal set ensures that security components to meet U.S. Air Force system commences only when an elaborate naturally occurring signals or an improper requirements. However, says O’Brien, sequence of events takes place. input cannot cause the weapon to function. “We can’t simply swap out IHE for the conventional HE being used in the W78. The primary design must be modified.” Current Weapon Systems in the U.S. Nuclear Stockpile O’Brien explains that the conventional Weapon Type* Delivery system Primary use Service Date added LEP status HE in older weapon systems can be W78 ICBM Minuteman III Surface to surface Air Force 1979 Phase 6.1 sensitive to extreme shocks, which can W87 ICBM Minuteman III Surface to surface Air Force 1986 Completed complicate safeguarding and transport. Livermore designers incorporated a W76 SLBM Trident II (D5) Underwater to surface Navy 1978 Phase 6.6 widely used IHE, triaminotrinitrobenzene SLBM Trident II (D5) Underwater to surface Navy 1989 Future LEP

(TATB), in the design of the W87 ICBM B61-3/4/10 Bomb F-15, F-16 Air to surface Air Force 1979/1990 Phase 6.3 warhead, which includes modern safety features. TATB, however, has not been B61-7/11 Bomb B-52H, B-2A Air to surface Air Force 1985/1996 Phase 6.3 produced in 20 years. Livermore chemists B83 Bomb B-52H, B-2A Air to surface Air Force 1983 Not needed are evaluating current manufacturing -1 Missile B-52H Air to surface Air Force 1982 Delayed techniques that would be more environmentally friendly, should it be *ICBM = intercontinental ballistic missile; SLBM = submarine-launched ballistic missile. decided to use TATB in the refurbished W78 warhead. Advanced safety and security options for the warhead depend on Refurbish Reuse Replace the use of IHE, as well. Physicist Juliana Hsu leads the effort to Performance Limited Large Largest margins improvements improvements improvements understand how the modified W78 could effectively accommodate IHE and other Primary high Retains Enables Enables modified components. She notes that LEPs explosive (HE) conventional HE insensitive HE insensitive HE provide the opportunity to add safety and Added surety for nuclear security features without degrading overall explosive package No Ye s Ye s effectiveness or introducing new military Multiple delivery capabilities. “We will probably have the No Ye s Ye s W78 for the foreseeable future,” she platforms says. As a result, “We will be proposing Production rate Limited by new Not limited by new Limited by new safety and use-control features that were production production production not implemented in the original warhead Green = meets requirement, yellow = partially meets requirement, red = does not meet requirement. design. It makes sense to have the warhead safer and with more effective safeguards.” U.S. government policy requires the W78 LEP to consider three options: refurbishing the existing Hsu adds that physicists and engineers design, reusing components from other stockpiled designs, and using nuclear-test-based designs that are also considering options to modify the are not in the current stockpile. Of the three options, only reuse meets all LEP requirements.

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MSADs are an example of a so-called simulations strong link—rugged mechanical safety allow devices that interrupt the firing chain until physicists certain sensing systems indicate a normal to observe launch sequence. These devices help important safeguard the HE that detonates to begin nuclear- the nuclear detonation. related phenomena nanosecond by nanosecond, with a A Better Look at the Fundamentals level of spatial resolution and a degree of “Stockpile stewardship is becoming physics realism previously unobtainable. scientifically and technically more “We’re bringing substantially more challenging as weapons continue to age computational power to bear on this LEP beyond their original design lifetimes,” compared with the resources we had for the observes O’Brien. However, the physics- W87 LEP,” says O’Brien. “Our codes have based understanding of nuclear detonations much more detail, allowing us to analyze A mechanical safe arming detonator (MSAD) has improved significantly over the past options with even greater precision.” prevents accidental or unintended detonation decade thanks to theoretical advances, Advanced simulations require of a nuclear warhead. Stockpile stewards at experiments, and simulations, together with experimental validation, which, in the Livermore are working on an advanced MSAD the existing nuclear-test database. (See the absence of nuclear testing, is provided for the W78. box on p. 11.) This improved capability by sophisticated nonnuclear experiments. allows weapon scientists and engineers For example, Laboratory physicists to assess with confidence a wide range of Aaron Puzder and Dana Goto designed hydrodynamic experiment at Livermore’s options in the W78 LEP. experimental studies to investigate Contained Firing Facility, which provided Because underground nuclear advanced safety technologies. Those an improved understanding of use-control experiments ceased in 1992, simulations experiments, which were fielded in 2010 technology for consideration in the W78 have become a major tool for assessing and 2011 at the Dual-Axis Radiographic LEP. Physicist Steve MacLaren also won the stockpile and guiding LEP efforts. Hydrodynamic Test Facility at Los an NNSA award for work as lead designer “Compared to the W87 LEP completed in Alamos, provided valuable data for the in high-energy-density experiments on the 2001, we have a much greater technical W78 LEP. National Ignition Facility at Livermore basis for making decisions,” says O’Brien. In 2011, Livermore engineer Chad and the Z-pinch machine at Sandia, New Full three-dimensional, high-fidelity Noble received an NNSA award for a Mexico. Those experiments produced data that validated key stockpile stewardship simulations. The National Boost Initiative (NBI) is also helping scientists better Small-arms fire understand the thermonuclear burn discharged into the process. “NBI is an effort to examine triaminotrinitrobenzene the primary’s performance, or the surrounding a nuclear boost process, in greater detail,” says weapon component Hsu. “The W78 LEP will leverage the does not detonate increased scientific knowledge from this insensitive high this initiative to quantify and potentially explosive. reduce our uncertainties during warhead certification.” Hsu notes that Ray Tolar, a physicist working on the W78 LEP, is also supporting a major NBI milestone. As a result, he will be able to maximize the synergy between the two projects. Livermore physicist Omar Hurricane, who specializes in secondary design, won

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the Department of Energy’s prestigious the solution to our codes,” says Hurricane. Ernest Orlando Lawrence Award for That breakthrough has increased confidence solving a mystery that had confounded in calculations that simulate performance weapon scientists for more than half a for the modified W78 and other warheads. century. For decades, Hurricane says, Weapons scientists continue to scientists had to account for missing benefit from a methodology known energy produced during nuclear tests. as quantification of margins and “There was consistent mysterious uncertainties (QMU). This methodology behavior of nuclear detonations from what draws together the latest data from we measured during underground tests. It simulations, experiments, and theory was OK during the Cold War because we to establish confidence factors for the could do a test and make sure things were key potential failure modes in weapon working properly. With the cessation of systems. QMU helps weapon scientists underground testing, we knew we had to rank the design options identified for the resolve the discrepancy.” W78 LEP. “QMU is a way to quantify our Omar Hurricane received the Ernest Orlando Over a decade, Hurricane led a team performance margins, to help us know Lawrence Award for helping to resolve a long- ranging from 20 to 40 physicists who we’re in the regime where we’re strongly term mystery in weapons physics—accounting worked on two vastly different areas confident,” says O’Brien. “We want for the missing energy produced during of physics. “It was an intense, detailed margins that are sufficiently robust.” nuclear tests. effort,” he says. The team identified the key physical processes involved and built Engineering’s Major Role computational tools to make predictions The LEP effort requires input from complete integration of every component about the physics. They then conducted engineers as much as from physicists. and system, explains Peter Raboin, project experiments to validate their theories. “We Engineers must ensure both the mechanical engineer for the W78 LEP. Raboin notes eventually resolved the problem and applied robustness of the overall system and the that the warhead’s nuclear explosive

Understanding Plutonium

Among all the elements, plutonium is the most mysterious because As part of the W78 LEP, special engineering test facilities it exhibits six different phases (orientations of its atoms) at ambient will help researchers evaluate advanced safety and surety pressure, with a seventh phase under pressure. What’s more, phases features that involve plutonium and uranium. Other facilities readily transform from one to the other and are accompanied by large could help them explore the chemistry of new manufacturing volume changes. In addition, plutonium’s radioactive decay causes methods for the warhead’s plutonium pits. The National Nuclear self-irradiation damage that can change the metal’s properties over Security Administration is changing the manufacturing process time, a matter of concern to stockpile stewards evaluating whether a for plutonium pits because the production facilities of the weapon system should undergo a life-extension program (LEP). Rocky Flats Plant no longer exist. “We need more efficient, Livermore scientists have labored for decades to unravel cost-effective pit manufacturing,” says Chung. “We will have plutonium’s secrets, using a combination of experiments, no underground tests to prove that new manufacturing processes theoretical advances, and simulations. Determining the long-term do not degrade pit performance, so a firmer understanding of behavior of plutonium is important for stockpile stewardship and plutonium is required.” for the eventual dismantlement and disposition of warheads. The Engineering efforts for the W78 LEP will simulate U.S. and Russia have withdrawn thousands of nuclear weapons environmental stresses that components could experience from the from their arsenals, and the excess plutonium recovered from time a warhead is produced until it arrives at a target. These stresses these warheads must be dealt with safely. include being placed and driven on a truck, vibrations experienced “We’ve only studied the basic fundamental properties of at launch and during the flight sequence to a target, and high plutonium metallurgy and properties,” says materials scientist temperatures during reentry through the atmosphere. The planned Brandon Chung. “Many questions remain. It’s very much an tests include spinning components at high speed and subjecting ongoing science.” objects to extreme heat and high gravitational forces.

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package resides in a deployment vehicle be implemented by NNSA production may occur at a very slow rate,” says located in the nose cone of an ICBM. The facilities. In this activity, the Livermore Raboin. “But over 30 years, they can add package and its support structures must be team works closely with Sandia, which up to a considerable amount.” “fit to fly.” is responsible for the nonnuclear O’Brien adds that LEPs in general help “The Department of Defense expects hardware that supports operation of the NNSA maintain the expertise required the W78 to arrive on target intact and nuclear explosive package. Livermore for stockpile stewardship into the future. functioning,” says Raboin. “We pay and Sandia engineers then integrate the (See the box on p. 13.) The special skills very close attention to making sure nuclear and nonnuclear hardware into required for nuclear weapons work are components will survive the flight from fully functional warheads. developed over time through experience launch to target. Parts could potentially Chemists also contribute to this effort and mentoring. The W78 LEP provides the be damaged or break during reentry into by searching for potential problems that Laboratory with an opportunity to develop the atmosphere, when the Mark 12A stem from chemical incompatibilities in the next generation of scientists, engineers, experiences decelerations as high as the widely different materials used in a and technicians to help sustain the nation’s 100 times the force of gravity.” warhead. Such problems could develop nuclear deterrent. To approximate the vibrations over time because components are in during flight, Laboratory engineers use chemical contact with each other and are Best Analysis of Options centrifuges and so-called jerk and shaker situated close to a field of high radiation. “The W78 LEP is a significant tables. By combining such physical Engineers are also mindful of possible development program,” says O’Brien. “It’s experiments with simulations, they mimic changes in the size of gaps separating the biggest effort of this decade for the what happens to the warhead from the components should a material shrink or Livermore weapons program. We’re getting moment it leaves a production facility to expand. “Changes within the warhead ready to present to the U.S. government the point at which it hits a target. our best analysis of options, including Engineers also turn design concepts the advantages and risks of each.” Those Storage prepared by physicists into computer options will address aging issues observed drawings, models, and eventually detailed engineering specifications to Transport

As part of the W78 Assembly LEP, Livermore Pantex engineers will evaluate the benefits of adding safety and security features to the warhead over its complete lifecycle, from fabrication to Deployment deployment. Los Alamos Fabrication Y- 12

Multiple delivery platforms

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Training the Next Generation of Stockpile Stewards

The W78 life-extension program (LEP) presents an excellent “The nation has made an enormous investment in developing opportunity to develop and train stockpile stewards. The program will a cadre of weapons scientists and engineers,” says Shang. “In the help the Laboratory maintain a knowledge pipeline by allowing the past, one way to mastery was achieved by leading and testing next generation of LEP scientists and engineers to work with mentors nuclear devices. Very few of these people remain in our current who have LEP experience. workforce. In today’s era of science-based stockpile stewardship, W78 LEP manager Hank O’Brien notes that neither Livermore mastery is achieved by integrating large-scale simulations with nor Los Alamos can execute all the LEPs needed to sustain the the design work required to field nonnuclear experiments. The nation’s nuclear deterrent. Of equal importance, stockpile stewardship scientists and engineers we hired for the W80 and W87 LEPs are in the absence of nuclear testing vitally depends on the two the technical leaders for the W78 effort. The challenge for us now laboratories providing expert technical review of each other’s work. is to grow a new generation of scientists and engineers so they will To sustain expert judgment, both laboratories must be involved in all have the skills, knowledge, and abilities needed to maintain the elements of stockpile stewardship, and each laboratory must attract, nation’s strategic deterrent.” develop, and retain talented scientists, engineers, and technicians needed to maintain the nation’s nuclear arsenal. The specialized skills 60 and expertise required for nuclear weapons work take a long time to develop through hands-on experience and mentoring. In 2011, 50 Laboratory Director George Miller (now retired) told Congress, “Confidence in the stockpile ultimately depends on confidence in the 40 stockpile stewards at the [National Nuclear Security Administration] labs and production facilities.” With nuclear test experience 30 “The W78 LEP will proceed as the last of the nuclear test- Without nuclear test experience experienced designers will reach the end of their careers, while the first generation of stockpile stewards is in their professional prime, 20 and will develop the next generation,” said Miller. “This program is Number of designers a vital element in maintaining the competency and capability of the 10 Laboratory’s weapons specialists through a project involving design, engineering, and manufacturing.” 0 For the past three years, the Enterprise Modeling Group led 1995 2000 2005 2010 by physicist Cliff Shang has been tracking the skill sets of current Year stockpile stewards at Livermore and projecting needs for the Livermore physicists with nuclear test experience are reaching the end future. Shang notes that the W78 LEP effort is valuable because of their careers, and the first generation of stockpile stewards is in its it “exercises” many key capabilities in the U.S. nuclear security professional prime. The W78 life-extension program is thus critical to enterprise: production plants, design laboratories, and most of all, the Laboratory’s efforts to maintain the skills, knowledge, and abilities the people. required for effective stewardship of the nation’s nuclear deterrent.

in surveillance of W78 units and will feature production centers as the modifications Key Words: B61, intercontinental ballistic warhead designs that increase confidence slowly take shape. missile (ICBM), life-extension program in performance and meet requirements for The result will be a new lease on life for (LEP), mechanical safe arming detonator enhanced safety and security. a warhead that was not designed to remain (MSAD), quantification of margins and Over the next decade, Livermore in service for 40 years. Thanks to the LEP, uncertainties (QMU), stockpile stewardship, stockpile stewards will produce detailed the W78 will have another three decades triaminotrinitrobenzene (TATB), W78, W87. engineering documents, supervise of service life, potentially with advanced advanced experiments, and simulate safety and security features in place and For further information contact Hank O’Brien every proposed modification and new changes that will give stockpile stewards (925) 423-5017 ([email protected]). part in three dimensions. And they greater confidence in its performance. will coordinate closely with NNSA —Arnie Heller

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