Predicting How Weapon Materials Age - S&TR

September 1999

U.S. Department of Energy’s

Lawrence LivermoreNational Laboratory

PredictingHow WeaponMaterials Age

PredictingHow WeaponMaterials Age

Also in this issue: • Determining Radiation Effects to

Chernobyl Cleanup Workers• National Ignition Facility’s Target

Chamber Makes Its Debut

A significant part of Livermore’s work insupport of the Department of Energy’s StockpileStewardship Program is collecting data anddeveloping computer models to predict howcomponents in a stockpiled weapon interact and how rapidly they age. S&TR’s report on this research begins on p. 4. On the cover is an image from one aspect of this research—thecomputed density distribution of ultrafineinsensitive high-explosive powder (TATB) in a weapon component. This research aims tocorrelate observed density variations with thematerial’s age and its performance withmeasured density variations.

About the Cover

About the Review

• •

Lawrence Livermore National Laboratory is operated by the University of California for theDepartment of Energy. At Livermore, we focus science and technology on assuring our nation’s security.We also apply that expertise to solve other important national problems in energy, bioscience, and theenvironment. Science & Technology Review is published 10 times a year to communicate, to a broadaudience, the Laboratory’s scientific and technological accomplishments in fulfilling its primary missions.The publication’s goal is to help readers understand these accomplishments and appreciate their value tothe individual citizen, the nation, and the world.

Please address any correspondence (including name and address changes) to S&TR, Mail Stop L-664,Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, or telephone (925) 422-8961. Our electronic mail address is [email protected]. S&TR is available on the World WideWeb at www.llnl.gov/str/.

Prepared by LLNL under contractNo. W-7405-Eng-48

© 1999. The Regents of the University of California. All rights reserved. This document has been authored by theRegents of the University of California under Contract No. W-7405-Eng-48 with the U.S. Government. To requestpermission to use any material contained in this document, please submit your request in writing to the TechnicalInformation Department, Document Approval and Report Services, Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, or to our electronic mail address [email protected].

This document was prepared as an account of work sponsored by an agency of the United States Government. Neitherthe United States Government nor the University of California nor any of their employees makes any warranty,expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness ofany information, apparatus, product, or process disclosed, or represents that its use would not infringe privately ownedrights. Reference herein to any specific commercial product, process, or service by trade name, trademark,manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring bythe United States Government or the University of California. The views and opinions of authors expressed herein donot necessarily state or reflect those of the United States Government or the University of California and shall not beused for advertising or product endorsement purposes.

SCIENTIFIC EDITOR

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MANAGING EDITOR

Sam Hunter

PUBLICATION EDITOR

Dean Wheatcraft

WRITERS

Arnie Heller, Katie Walter, and Dean Wheatcraft

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George Kitrinos

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Kitty Tinsley

COMPOSITOR

Louisa Cardoza

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Carolin Middleton

S&TR, a Director’s Office publication, is produced by the Technical InformationDepartment under the direction of the Office of Policy, Planning, and Special Studies.

S&TR is available on the World Wide Web atwww.llnl.gov/str/.

2 The Laboratory in the News

3 Commentary by Hal GraboskeLife Performance of Complex Systems

Feature4 A Better Picture of Aging Materials

Fundamental materials science and experiments on components of stockpiled weapons are coming together to produce models that predict the lifetimes of weapon materials.

Research Highlights12 Researchers Determine Chernobyl Liquidators’ Exposure

16 Target Chamber’s Dedication Marks a Giant Milestone

20 Patents and Awards

Abstract

S&TR Staff September 1999

LawrenceLivermoreNationalLaboratory

Printed in the United States of America

Available fromNational Technical Information ServiceU.S. Department of Commerce5285 Port Royal RoadSpringfield, Virginia 22161

UCRL-52000-99-9Distribution Category UC-0September 1999

Page 4Page 16

Page 12

2 The Laboratory in the News

Lab wins six R&D 100 awardsLivermore researchers turned in another strong showing in

the annual R&D 100 awards competition for top industrialinventions, winning six awards. Each year, R&D Magazinepresents these awards to the top 100 industrial, high-technologyinventions submitted to its competition for outstandingachievement in research and development.

Over the past three years, Laboratory scientists, engineers,and technicians have brought home a total of 20 R&D 100awards, and since 1978, they have won 81 of these prestigiousawards. All told, U.S. Department of Energy laboratories won40 of this year’s 100 awards, 10 more than were garnered in1998 by DOE research facilities.

The six Livermore inventions honored are:• The Optical Modulator/Switch provides solutions to the highcost of modulating data onto a laser beam and switching signalsfrom one data channel to another. This invention was developedin association with researchers from AlliedSignal FederalManufacturing & Technology and the University of Marylandat College Park.• Gamma Watermarking is a revolutionary method ofidentifying and authenticating a range of material objects—fromdinosaur bones to priceless objects of art to legal documents andcontracts—with the same quality and legal incontrovertibility asDNA fingerprinting.• The Diode-Pumped Solid-State Green Laser for IndustrialMaterial Processing provides a cost-effective, higher-powerreplacement for lamp-pumped solid-state lasers and hasapplications in laser isotope separation and precision lasermachining.• The Solid-State Power Source for Advanced Acceleratorsand Industrial Applications enables accelerators to greatlyincrease the production of electron beams that in turn are usedto produce bursts of x rays for examining the effects of agingon the nation’s stockpiled nuclear weapons withoutunderground testing. Researchers from Bechtel Nevadacontributed to this invention.• The Atomic Precision Multilayer Deposition Systemprovides a faster, less expensive method for depositingmultilayer thin films to precise, uniform atomic thickness overlarge flat or curved surfaces. It enables rapid development ofall the convex and concave optics needed for extremeultraviolet lithography.• PEREGRINE, a radiation dose calculation system, tackles theproblem of determining the proper radiation therapy dosage byusing models based on fundamental physics principles.PEREGRINE calculates radiation therapy doses of the highestaccuracy for cancer patients.

S&TR will devote its October issue to detailed reports onLawrence Livermore’s award-winning inventions and the teamsthat created them.Contact: Karena McKinley (925) 423-9353 ([email protected]).

Lab helps design Chernobyl robotDepartment of Energy Deputy Secretary T. J. Glauthier

recently dedicated a small but sturdy U.S.-made robot forUkrainians to use in mapping the interior of the Chernobylnuclear power plant, site of the 1986 disaster.

Dubbed Pioneer, the robot was designed by LawrenceLivermore and several other research agencies and was builtby RedZone Robotics Inc. of Pittsburgh, Pennsylvania. Lessthan 1.2 meters tall and resembling a miniature bulldozer, it is expected to endure about two years within the extremelyradioactive remains of Chernobyl rather than the sevenminutes its predecessor lasted before melting andmalfunctioning.

Maynard Holliday, the Livermore robotics expert whoserved as the Pioneer project manager through December1998, noted, “This project is an outgrowth of our cooperationwith the states of the former Soviet Union. This is just onesmall step in giving the Ukrainians state-of-the-art tools tounderstand what they’re dealing with.”

Pioneer is designed to withstand thousands of times moreradiation exposure than humans can tolerate. It could be sentinside Chernobyl within a few months, after Ukrainianscientists are fully trained in its use and after more simulationsare conducted in terrain similar to that in Chernobyl’s rubble-filled interior. Contact: Maynard Holliday (925) 422-3646 ([email protected]).

Teller chair endowed at UC DavisDr. Edward Teller, one of the founders of Lawrence

Livermore National Laboratory and perhaps its most famousemployee, was recognized in mid-June with yet another in along list of honors and awards. A $1-million grant from theFannie and John Hertz Foundation endowed the Edward TellerChair in the University of California at Davis’s Department ofApplied Science.

Teller founded the Department of Applied Science in 1963and served as its chairman until 1966. It is located adjacent toLawrence Livermore and is a prime example of Teller’slifelong interest in science education. Students who participatein the department must submit to a rigorous entry interviewand combine academic studies in applied science with hands-on work at the Laboratory. The faculty includes staff from theUC Davis Department of Engineering and scientists andengineers employed at Lawrence Livermore.

During a news conference following the announcement ofthe endowment, Teller was asked to put the endowment in theperspective of the many honors he has received. Teller replied,“There’s absolutely no award, there’s nothing in the world thatcould be as valuable to me as a plan to better educate our nextgeneration of applied scientists.”Contact: LLNL Public Affairs Office (925) 422-4599([email protected]).

S&TR September 1999

Lawrence Livermore National Laboratory

HE world today is using increasingly complex systemsand taking them for granted. For the scientists and

engineers who design and maintain them, two classes ofsystems present particular challenges: those that operateunder extremely stressful conditions and those that arerequired to operate for extremely long periods of time. Jetaircraft, spacecraft, satellites, and nuclear reactors encounterenormous stresses. Aircraft and spacecraft also oftencontinue to operate for longer than their designed lifetime.We at Lawrence Livermore have been mandated under theDepartment of Energy’s Stockpile Stewardship Program toextend the life of weapons in our nuclear arsenal well beyondthe lifetime for which they were designed. We are alsocollaborating on the design of the Yucca Mountain nuclearwaste repository, which may be required to operate for10,000 years.

For all of these systems, the penalty for failure is high.Injury, death, even major devastation of our planet couldresult from errors made during design, construction,operation, or maintenance. Yet to a certain extent, theseextraordinarily complex and long-lived systems are beyondtesting because we cannot be certain whether we have testedthem well enough or long enough. Nevertheless, atLivermore, we subject weapon parts and components torigorous conditions for extended periods before the weapon is assembled and later during its life in the stockpile. Weunderstand that the stakes are high and that high standards areessential during all phases of the system’s life.

Nuclear weapons typically contain specially developed and unusual materials. Engineered to meet a specific need thatconventional materials could not, these new materials have alimited track record. Researchers have scant informationabout their evolution and about how the many materials willreact with one another sealed in a nuclear weapon or in awaste repository. Incompatibilities that are not apparent overa short time may take on great significance over long periods.

So how do we, as responsible stewards of our nucleararsenal and nuclear waste, respond to these challenges? Forcomplex systems with long lifetimes, our approach

T

3Commentary by Hal Graboske

comprises four integrated elements: prediction, testing,surveillance, and modification.

As described in “A Better Picture of Aging Materials,” the article beginning on p. 4, we are striving to developimproved behavioral and computational models of systemperformance and effective life expectancy using the bestscientific and engineering knowledge and the world’s fastest supercomputers. Only with the powerful computersavailable to us through the DOE’s Accelerated StrategicComputing Initiative can we be confident in the predictionsfor complex systems.

Experimental validation is typically performed initially to determine material properties, again to operationally testcomponents and subassemblies, and finally to test theperformance of an entire subsystem or system. But for nuclearweapons, we cannot perform the third phase of testing in itsentirety. Computational modeling must of necessity replacefull performance testing, previously accomplished throughnuclear experiments. This is where the evolution of validatedage-aware material models will become key to assessing thelife performance of complex systems.

Surveillance incorporates an array of diagnostic techniquesfor monitoring the nuclear stockpile or the nuclear repositoryBecause we no longer monitor performance with nucleartesting, our surveillance of the many materials that make upthe system has taken on new importance.

Data from surveillance and all material and operationaltests are essential for validating our computational modelsand identifying where models need to be changed and limited resources should be focused. Finally, the predictivemodels notify us when modifications are needed in a weapon system before its performance is reduced.

This integrated approach to complex systems is in itself complex. It involves many disciplines and can behandled effectively only by an organization with the depth and breadth of experience of a DOE laboratory suchas Lawrence Livermore.

Life Performance of Complex Systems

■ Hal Graboske is Associate Director, Chemistry and Materials Science.


S&TR September 1999

guidance on the selection and use of thebest available materials for Livermore’snew weapons. Today, the mandate formaterials scientists is more complex: topredict the lifetime of key weaponmaterials and to develop “age-aware”material models for use in codes thatpredict the lifetime of the overallweapon system.

Livermore chemist James LeMay isone of the coordinators assigned to thischallenging set of activities. He and hiscolleagues are focusing primarily on theaging of the many organic materialsused in a weapon. They are alsoexamining the aging of high explosivesand the interactions (compatibility) ofthe many materials in a nuclear weapon.

Data for PredictionsLeMay notes, “True scientific

prediction, as opposed to a statisticalprojection, of how weapon materials ageand interact with one another over timeis difficult. Accurate predictions requireexcellent data, sophisticated models, andpowerful, modern computers.”

The data come from several sources.One is controlled laboratory experimentson weapon materials. They determine theproperties of the materials before theybegin to age, what environmental forcesact upon them while they are enclosed inthe weapon, and how those forceschange the properties that are relevant tothe performance of the system. In otherwords, a major focus of the work is onthe fundamental science of materials.

Another source of data is the detailedcharacterization of components taken

from the stockpile to determine howtheir relevant properties have changed(Figure 1). These measurementssupplement DOE’s Core SurveillanceProgram to verify the safety andreliability of U.S. nuclear weapons.Under core surveillance, weapons areremoved from the stockpile on a regularbasis and disassembled. Componentsare tested to assure that they operate asthey did when the weapon wasassembled. Under the newer EnhancedSurveillance Program, more detailedand fundamental experiments seek outpreviously unknown aging mechanismsthat may affect a material’s lifetime andallow scientists to extrapolate futureaging trends from changes that havealready occurred.

With accurate predictive models,researchers should be able to reduce therequired number of system-levelevaluations, which are expensive.Robust models would reflect whatchemical or physical alterations in amaterial are under way and at whatpoint component or weaponperformance is affected. Surveillancecould then be directed to look forpredicted changes and to findpreviously unanticipated ones, thusproviding a means for continualimprovement and validation ofpredictive models. “We’ve got a longway to go,” says LeMay, “but we havemade considerable progress.”

How Much Change Is OK?Some materials in a nuclear weapon

are designed to be marginally unstable.

4


UCLEAR weapons are complexsystems made of many different

materials and interconnectingcomponents. The materials may interactwith air, moisture, and environmentalhazards during manufacture, shipping,storage, and assembly as well as witheach other once they have beenenclosed in the weapon. They mayweaken, harden, corrode, or even fail.These changes in properties, whetherchemical, physical, or mechanical, are often lumped together under thelabel “aging.”

The shelf life of a nuclear weaponwas not a major issue until the early1990s when the U.S. ceased to developand test nuclear weapons. Before that,new weapons featuring the latesttechnology were regularly designed andbuilt. When a new weapon entered thestockpile, an older one was generallyretired. Now, there are no new weapons,and existing weapons are expected toremain operational for many decades—to perform exactly as designed if theymust ever be used.

The Department of Energy’sStockpile Stewardship Program hasmany facets, one of which is to analyzethe aging processes of the materialsused in nuclear weapons, such as highexplosives, uranium, plutonium, organicmaterials, and polymers. This analysisbuilds on work that materials scientistsat Lawrence Livermore have been doingsince the inception of the Laboratory. Inthe past, they studied how variousmaterials aged and interacted understockpile conditions to provide

N

A Better Picture of Aging MaterialsOur nuclear stockpile is getting older. Livermore scientists are collecting the

data and developing the models needed to predict how much aging is acceptable.

S&TR September 1999

achieved—the weapon will cease to beviable. One or more of its parts mayhave changed just enough or even failedsuch that the weapon no longerperforms as required. An assumption ofLivermore’s materials aging studies isthat there is a slightly earlier pointwhere considerable aging has occurredand yet the weapon still operates asdesigned. LeMay likens it to an olderautomobile that still runs well butwhose brakes are rather worn, whosetires are a bit flat, and whose enginedoes not turn over quite as quickly inthe morning. The important questionsare: Where is that point for a nuclear

5


Materials Aging

When a weapon is assembled, itsarray of components is not inthermodynamic equilibrium.Unfortunately, it is a basic law ofnature that all of the parts in a closedsystem will strive for thermodynamicequilibrium. They will change andperhaps degrade by exchanging energyuntil equilibrium is achieved. In anuclear weapon, that process wouldtake a long time, but some componentschange faster than others and cancause unacceptable aging.

At some point in the degradationprocess—probably long before globalthermodynamic equilibrium is

The high explosives used for initiationmust be somewhat sensitive or they will not detonate. Radioactivity addsanother dimension of instability. Eventhose parts that are theoretically stablecan present difficulties. A bit of oil may be left on a part duringmanufacture. A trace of water vapormight appear in the system, causingcorrosion. A seal might leak and admitoxygen and water. Materials that appearedto be pure at the time of manufacturemay prove to be incompatible and reactwith one another. In all cases, theseaging processes and interactions areextremely slow.

0

0.2

0.4

0.6

0.8

1.0

0Stockpile life, months

Model prediction

Rem

aini

ng r

adiu

s, m

ils

100 200 300 400

Remaininggold wire

Remaininggold wire

Original gold wireOriginal gold wire

(a) (b)

(d )

(c)

Figure 1. A multidisciplinary weapons program team at Livermore has studied the aging of the gold detonator bridgewires in previouslystockpiled weapons. (a), (b), and (c) Cross sections of detonators removed from a previously stockpiled weapon. They illustrate theconversion of the bridgewire from gold to gold indide over the course of about 25 years. Gold indide has mechanical and electricalproperties quite different from those of gold. (d) The predictive model in the graph indicates that these gold bridgewires corrodedramatically as they age. Actual aging data match the predictive model extremely well.

S&TR September 1999

weapon? How much change is OK forthe individual materials in the weapon?

The Materials at HandLivermore-designed nuclear

weapons that reside in the stockpilehave various configurations. But theygenerally incorporate plutonium,uranium, high explosives, plastics,adhesives, foams, and other materialsthat together make the weapon generateits designed yield.

To date, many changes related toaging and to incompatibilities betweenweapon materials have been observed.In the six high explosives used in

various weapons, changes includeswelling, plasticizer migration, binderdegradation, mechanical propertydegradation, adhesive bond rupture, andincompatibilities. In addition, changesrelated to load retention andcompression were found in the polymerfoam cushions that provide paddingbetween various weapon components.

Uranium, plutonium, lithium, andeven gold exhibit surface corrosion.Several materials are affected byradiation from uranium and plutonium.Researchers also found incompletecuring, depolymerization, andhydrogen outgassing in some silicone

6


Materials Aging

compounds. In plastic parts, somepolycarbonate material was degradedby ammonia gas emitted from anearby component. An undesirablystrong adhesion has developedbetween some plastic components.Some adhesives have incompletelycured, some are outgassing, and somebonds have weakened.

Organic materials are a particularconcern. By their very nature, they canbe less stable than many othermaterials. They have weaker bondsand tend to be reactive. They also aremore readily damaged by the radiationthat emanates from uranium andplutonium. Nevertheless, organics arean essential part of a weapon. Someserve chemical functions such ashydrogen “getters,” which absorbdamaging hydrogen in a weapon’shermetically sealed environment.

Other organics (such as siliconestress cushions, adhesives, andcoatings) fill gaps, transmit loads, andmitigate vibration and shock, allowinga weapon to survive what is known asthe stockpile-to-target sequence (STS).A weapon sitting in the stockpileencounters few traumas, but during theSTS, it must endure transport on atruck, temperature changes duringstorage, and perhaps ultimately alaunch and flight from under the wingof a plane, from a submarine, or froma land-based missile silo.

For experiments that examineeverything from bulk materials toindividual atoms, Livermore scientistsare using a unique collection of tools toexamine and test the surfaces andstructure of the many materials thatmake up a weapon. Some of these toolswere developed at Livermore. Otherswere developed elsewhere but modifiedat Livermore for use in the stewardshipof the U.S. nuclear arsenal.

An Explosive IssueMany years ago, Livermore opted to

use insensitive high explosives in its

1.70 1.75 1.80Density, grams per cubic centimeter

1.85 1.90

Figure 2. Using x-ray tomography, Livermore scientists led by Clint Logan have calculatedthe density distribution within a booster pellet made of ultrafine insensitive high-explosivepowder (TATB). The pellet has a radius of 1.9 centimeters and weighs 26.1 grams.

nuclear weapons for greater safety. An insensitive high-explosivecomponent dropped during assembly ordisassembly should not harm personnel,and a weapon that accidentally falls froma truck or even from an airplane shouldnot detonate. But scientists areconcerned that these high explosivesmight lose some of their safetyadvantage as they age. For example,voids in high explosives are necessary todrive the detonation wave. But if voidsincrease in size as the explosive ages, theexplosive may become somewhat lesssafe. High explosives are therefore aprimary focus of Livermore’s work onaging weapons, and many experimentshave been performed over the years.

Because the insensitive highexplosive LX-17 is used in three of thefour Livermore-designed weapons inthe enduring stockpile, its reliability isparamount. Physicist Richard Howelland his colleagues under theleadership of George Overturf haveconducted a number of experiments on LX-17 using positron-annihilationlifetime spectroscopy to search forinterior voids and open volumes assmall as several atomic bond lengthsin diameter. (See S&TR, December1998, pp. 13–17.) Overturf’s team hasused this method to measure changesin the microscopic, open-volume voidsof LX-17’s constituents, including thehigh-explosive powder TATB and its polymeric binder. His goal is to observe changes that occur as aresult of temperature variations andenvironmental stresses duringstockpile life.

Another experiment produced the firstlook at the density of a booster pellet(Figure 2). X-ray computed tomographywas used to examine the density of ahemisphere of ultrafine high-explosivepowder with no binder. This newtomographic technique is being used tocorrelate observed density variations withthe material’s age and its performancewith measured density variations.

Extracting GasesOver a period of years and at

elevated temperatures, the many organicmaterials in a nuclear weapon eventuallyproduce gases at detectable levels. Thereare two types of outgassing: the releaseof gases in the assembly room thatbecome trapped in weapon cracks andcrevices or dissolved in its organiccomponents and the release of gasesinside the weapon that are produced bychemical aging reactions, materialinteractions, or radiation. By eitherroute, organic materials releasecompounds that can corrode metalsand/or interact with and degrade othermaterials and components in the system.In general, outgassing signals theinteraction and possible decompositionof materials in the warhead.

LeMay notes that just assurveillance scientists and engineers

use nondestructive tools to assesschanges in weapons withoutdisassembling them, so docompatibility and aging scientists takeadvantage of nondestructive chemicaltools to assess changes in weaponchemistry and compatibility.

One such tool is solid-phasemicroextraction (SPME, or“speemee”), which Livermore chemistDavid Chambers has adapted toexamine gases for stockpilesurveillance. A syringe needlecontaining a tiny, specially coated fiberis inserted into the headspace of aweapon to sample gases (Figure 3).Gas chromatography and massspectrometry of the tiny sample thensupply data on the contents of theweapon atmosphere. Unlike most othersampling techniques, SPME candeliver high-quality samples of the

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Materials AgingS&TR September 1999

Figure 3. A technician uses an early prototype of the solid-phase microextractor (the devicebetween his hands) to take samples of gases produced by organic materials in a weapon’sheadspace. Analysis of the samples provides indications of material aging.

weapon’s atmosphere to the gaschromatography port with little loss or dilution.

Livermore is the first laboratory touse SPME, a nondestructive technique,to examine weapon gases. With SPME,scientists can obtain an integratedchemical analysis of a weapon’s interiorenvironment, identifying potentialmaterial incompatibilities, identifyingand monitoring aging indicators, andscreening for defects such asincompletely cured adhesive and organicresidues left over from assembly.

Chambers notes that with SPME,otherwise undetectable volatile gasesare now detectable. For example, SPMEwas the first experimental method toreveal relatively large amounts oftoluene in LX-17. Toluene is a solventused in the synthesis of TATB, which isthe primary ingredient in LX-17. Afterproduction, toluene remains trappedwithin TATB’s crystalline structure.Experiments indicate that heating alonedoes not effectively liberate the tolueneunless the LX-17 has been mechanicallystressed. One experiment exposedTATB powder to ultrasonic energy andfound a 500-fold increase in the level oftoluene outgassing. Chambers believesthat toluene levels can be monitored to

determine the chemistry and stress-loading history of the high explosive.

Cushioning the WarheadCellular silicone stress cushions fill

gaps between components, compensatefor manufacturing tolerances ofadjacent components, allow forthermal expansion of components andage-induced swelling of highexplosives, and provide thermalinsulation. For the cushions to performthese jobs successfully, they must exerta specific range of compressive forcesat predetermined maximum andminimum gaps. Because the cushionsfill gaps for the life of the weapon, thelong-term stress behavior of thecushion under load in the chemical andradiation environment of a weapon isan ongoing concern.

LeMay has been examining aging incellular silicone using a form of x-raytomography developed at Livermore bymaterials scientist John Kinney. Thistechnique reveals for the first time theinternal structure of cushions undercompression (Figure 4). It is nowpossible to see how some cells fold intoone another to form “cups” and that cellwall “hinges” spring back after the loadis removed. Some cells move to fill

adjacent cells under compression. X-ray tomographic data can also bemanipulated to show the shape of thecushions’ pores. These images can beused, for example, to determine underwhat range of loads the pores remaininterconnected, thus allowing gases andradiation to percolate through.

Because radiation from adjacentcomponents is constantly bombardingthe cushions and apparentlypercolating through them, LeMay and others are attempting to determinethe damage it may be causing. Only preliminary data are available,because the researchers are stilldeveloping experimental tools that are sensitive enough to characterizeradiation’s effects.

Another Livermore chemist, MehdiBalooch, used temperature-programmeddesorption to study gases desorbed fromsilicone cushions. He found that attemperatures up to 500 kelvins, waterdesorbed at 100 micrograms per gram ofsilicone, with considerably lessdesorption of hydrogen, carbonmonoxide, and carbon dioxide. The realconcern was water, because silica, whichmakes up about 25 percent of thecushions, tends to adsorb water.Outgassing water vapor in a closedenvironment can migrate to other parts inthe warhead and cause corrosion. Thisexperiment—to further understand afundamental property of a commonlyused material in a weapon—demonstratesthe need for basic science in the study ofaging weapon materials.

Hydrogen: The Enemy WithinBalooch is also working with

Wigbert Siekhaus to study the agingprocesses of uranium and lithiumhydride. Specifically, they arestudying the effects of such gases aswater vapor and hydrogen on thesurfaces of these materials: what thereactions are, what products areformed, and how the reactions dependon temperature, gas pressure, and the

8



Unloaded

Unloaded

Pressure = approximately27.6 × 104 pascals (40 pounds per square inch), or about 35 percentcompression

Figure 4. X-ray tomography is revealing for the first time the internal structure of cellular siliconecushions under compression. Note that some cells fold into one another, resulting in a structuralchange should the adjacent cell walls adhere to one another over time.

surface details. They have usedatomic-force microscopy to get aclose-up look at growths on thesurface, modulated molecular-beammass spectrometry to determine the gaseous reaction products and therate of reactions, and temperature-programmed desorption to measure the quantity of adsorbed gases.

“Hydrogen is a major enemy of aweapon,” according Balooch. It isgenerated in a weapon from severalsources and attacks many components.Hydrogen is particularly damaging touranium, reducing its capabilities. If auranium surface is even slightlyoxidized (a process that happens easilyand quickly), it will adsorb hydrogen,prompting the growth of a form ofcorrosion known as hydride pittingalong the uranium’s grain boundaries(Figure 5). Scientists have hadempirical evidence for the hydridingreaction for some time. But the reactionmechanism had never been studied indetail, and a general mechanism had notbeen identified.

A few years ago, Livermoreresearchers demonstrated the fundamentalproperties of the interaction of hydrogenand water vapor with clean uranium atroom temperature and above. Theymeasured the initial sticking probability(low for clean uranium), hydrideformation probabilities, and desorptionkinetics for hydrogen and water vapor.

A more recent experiment examinedthe interaction of hydrogen with uraniumin the presence of impurities designed tomimic conditions in real systems. Tinyplatinum particles measuring just 1 nanometer were deposited on a uraniumsurface. Platinum was used because itbreaks hydrogen bonds to produce atomichydrogen, hydrogen’s most reactive form.When the uranium was exposed tohydrogen, hydrides formed in the vicinityof platinum clusters, expandingnonlinearly over time. Other impuritiescommonly found in uranium may alsostrongly influence hydriding reactions.

A major source of hydrogen in somenuclear devices is lithium hydride. Thereaction of even trace amounts of waterwith lithium hydride generates hydrogen.The team has been using modulated

molecular-beam mass spectrometry tostudy the kinetics of the water–lithiumhydride reaction. As shown in Figure 6,the incoming beam of water vapormolecules and the outgoing hydrogen

9



Figure 5. Atomic-force microscopy shows (a) uranium before hydriding takes place and (b) theformation of uranium hydride along grain boundaries, or hydride pitting.

Figure 6. This schematic shows a modulated molecular-beam mass spectrometer being used tostudy the effects of water vapor on lithium hydride. The beam of water vapor directed at thelithium hydride is turned on and off at brief, regular intervals, as shown in the square pattern of theincoming beam. The outgoing beam of molecular hydrogen has a different shape, indicating abrief residence time in the lithium hydride.

0.5 micrometers

(a) (b)

Molecular beam source Mass spectrometer

Hydrogen

Modulatedwater vapor

beam

Lithium hydride

molecular beam have different shapes,indicating a brief resident time in thelithium hydride. With these experiments,the team will be able to obtain basicinformation about lithium hydride andthe reactions under way, including thesticking probability, reaction probability,elementary surface reaction steps, anddiffusion rates.

Livermore is the only institution inthe world using modulated molecular-beam techniques. Balooch, Siekhaus,and Alex Hamza developed the methodabout 20 years ago while they were atother institutions. According toBalooch, modulated molecular-beamexperiments give the best chemicalkinetic information.

Putting It All TogetherSiekhaus notes that DOE weapons

laboratories have detailed models for

the multitude of reactions that takeplace immediately after a weapon isdetonated but nothing comparable todescribe the life of a weapon beforedetonation. With the relatively shortshelf life that weapons used to have,such models were not necessary. Buttoday they are.

Several years ago, chemist Dan Calefbegan developing a predictive model for one part of a nuclear device usingdata that the experimentalists haveaccumulated on lithium, uranium, gases,and other materials. As LeMay noted,excellent data are important to createsuch models. In a system as small andtight as a nuclear device, trace amountsand slow reactions matter. What seemsto be a small issue can becomemagnified quickly.

According to Calef, “Until recently,decisions about lifetimes tended to be

based on expert opinion and experience.Our goal is to make these decisionsfrom a science-based standpoint.”

His first task is to model thetransport of gases around the system.The originally designed geometry ofthe weapon system and all availableexperimental data are going intoALE3D, a Livermore hydrodynamiccode. He will then examine all thechemical reactions that occur over timeand how these processes change thedesigned geometry. Figure 7 shows astructural change that results frommass diffusion.

Calef is particularly interested in thesmall details in the system, such aspores and gaps between components. Itis in those minute spaces that suchcritical activities as diffusion anddestructive surface chemistry takeplace. With this close-up view, he can

10



(b) Core material in the object reacts and expands

ALE3D models extrusion and surrounding

material distortion

(a) Gas diffuses through the gap

Figure 7. Mass diffusion andstructural distortion as shownin an ALE3D model. In thiscalculation, (a) a solid objectreacts with a gas diffusingthrough a gap. (b) Thereacted solid has a lowerdensity and expands.

determine where problem areas mightbe. From there, he will define any life-limiting components and determine thelifetime of the system.

Livermore weapon models alreadycontain considerable detail, but the detailis of idealized materials. When themodels are based on data from actualconstituent materials and real chemicalreactions, they will be much moreuseful. They can be tweaked to showwhat effect temperature changes, shock,vibration, and other influences have on aweapon. Identifying weak points forfurther experimentation can help toprioritize future research anddevelopment activities. Models couldalso help to identify which parts need tobe replaced and when.

LeMay notes that his group andothers at Livermore must continuallyrefine their approach to characterizingand modeling the aging of Livermore’sweapon materials. As with anymodeling program, there is a strongdynamic between predictive efforts andcontinued experimentation. Even withthe most powerful computers,

modeling needs validation fromexperimental results in an ongoing,iterative process that constantlyrefines modeling results and methods.

LeMay and his colleagues willconstantly be integrating their improvedunderstanding of the aging process intoweapon codes so that changes at thesystem level can be effectively assessed.LeMay concludes that the goal ofscience-based stockpile stewardship—maintaining high confidence in thesafety and reliability of Livermore’sweapons without nuclear testing—requires constant vigilance.

—Katie Walter

Key Words: ALE3D, core surveillance,enhanced surveillance, materials science,modeling, modulated molecular-beamspectroscopy, positron-annihilation lifetimespectroscopy, solid-phase microextraction(SPME), surface chemistry, x-raytomography.

For further information contact James LeMay (925) 423-3599([email protected]).

11



JAMES LEMAY received his B.S. in chemistry in 1980 and hisPh.D. in polymer science in 1984, both from the University ofAkron. He began working at Livermore in 1984. In 1991, hebecame Livermore’s lead scientist for material compatibility issues.He has supported the W89 and W87 weapon programs,dismantlement of the W48 and W79 weapons, stockpile storageissues, and core surveillance activities. He is currently a program

element leader for weapon materials compatibility and aging in the Chemistry andMaterials Science Directorate and is a research and development focus area leader inthe Enhanced Surveillance Program. In 1998, he received a Department of EnergyNuclear Weapons Program award for technical excellence in weapon materials.

About the Scientist

12 Research Highlights S&TR September 1999


N April 26, 1986, an accident at the Chernobyl nuclearreactor in the former Soviet Union released an

enormous number of fission products into the atmosphere andover a large portion of the planet. With about 100 millioncuries released in the 10 days following the initial explosion,the accident was the largest single nonmilitary release ofradioactivity in history—and one of the largest environmentaldisasters ever.

During the first year after the accident, about 25,000people, mainly Soviet Army troops, were dispatched to thesite to clean up the accident. These so-called liquidators wereestimated to have received doses of up to 70 centigrays (a grayis the international unit for measuring absorbed ionizingradiation and is equivalent to 100 rads, or 1 joule perkilogram). In the following three years, another half-millionpeople assisted the effort and are estimated to have receivedlower doses (about 10 to 25 centigrays).

The tasks performed by liquidators included shoveling corematerial off the roof of the undamaged part of the building,operating heavy equipment to contain contaminated soil, andbuilding a concrete sarcophagus around the destroyed reactor.Depending upon the intensity of radiation exposure associatedwith their assigned task, most liquidators received radiationexposures over a period of at least several days, and in somecases over many weeks.

Lawrence Livermore biomedical scientists began studyingthe Chernobyl accident almost as soon as it occurred as part ofa Department of Energy effort to help assess the accident’sbiological effects. The Livermore assistance, which continuestoday, takes advantage of the Laboratory’s longstandingexpertise in evaluating human exposures to ionizing radiationand determining their health risks. Livermore scientists haveforged numerous and often close scientific relationships withtheir Russian and Ukrainian counterparts that endure today incollaborations, mutual assistance, informal communications,and visits.

Techniques to Monitor Damage Lawrence Livermore studies on Chernobyl liquidators have

focused on three techniques—two of them developed atLivermore in the 1980s—that are in wide use today to monitor

genetic damage in people. The techniques are calledbiodosimeters because they measure changes in cells to inferthe biological consequences of the “dose,” or energy depositedin human tissue from ionizing radiation. (In contrast, astandard dosimeter uses a piece of sensitive film that respondsproportionally to ionizing radiation.)

The glycophorin A (GPA) assay was first used to studyChernobyl liquidators who demonstrated immediate symptomsknown as acute radiation sickness. Within days of theaccident, a Livermore group (at that time led by Ron Jensen,now at the University of California at San Francisco) beganreceiving blood samples from people who received highexposures. The evaluation by Livermore’s Richard Langloisfound that the response of GPA to high doses of radiation wassimilar for A-bomb survivors and Chernobyl liquidators. Theinvestigators also found that age and smoking had little effecton the frequency of the GPA null mutants.

The GPA assay measures the number of red blood cellsthat have a change in the M or N form of the GPA gene. Forpeople whose cells have both forms of the gene, damage tothe M form of the gene, for example, can result in a “null”mutation. In such a case, all descendants of that cell fail tomake the M protein. Using flow cytometry and cells stainedwith color-coded antibodies specific to the M and N forms,scientists can study millions of red blood cells from a smallblood sample in a few minutes without the need for cellculturing. (See August 1987 Energy & Technology Review,“A New Assay for Human Somatic Mutations,” pp. 21–26,and April/May 1992 Energy & Technology Review, “TheGlycophorin-A Assay: A Ten-Year Retrospective,” pp. 1–18.)

The second technique measures the frequency of mutationsof the hypoxanthine phosphoribosyltransferase (HPRT) genein lymphocytes. This assay was not invented at Livermore,but Laboratory researchers have greatly expandedunderstanding of the assay’s ability to detect DNA damagefrom ionizing radiation. Livermore biomedical scientist IreneJones performed work in the 1980s using mice to test theassay. She also developed a database on healthy people toserve as a baseline for the frequency and molecular nature ofHPRT mutations.

Researchers Determine ChernobylLiquidators’ ExposureResearchers Determine ChernobylLiquidators’ Exposure

O

A third technique called FISH (fluorescence in situhybridization), which was developed at Livermore and iscurrently used around the world, has been applied toChernobyl liquidators as well as to others suspected ofreceiving ionizing radiation or of being exposed to potentiallydamaging chemicals. FISH measures chromosome damage bydetecting the number of reciprocal translocations, or brokenpieces of chromosomes, in lymphocytes that rejoin in amismatched way. Livermore scientists have shown that thenumber of reciprocal translocations is proportional to exposureto ionizing radiation at low doses. What’s more, unlike somebiodosimeters, including other types of chromosomealterations, the frequency of reciprocal translocations issufficiently stable with time (even over several decades) topermit retrospective dosimetry and can be measuredaccurately at low levels of radiation.

The FISH technique uses chromosomes from culturedlymphocytes. Fluorescent dyes are attached to small pieces of chromosome sequences called probes, which bind tocomplementary sequences of the target chromosomes. The

bound probes reveal the extent of reciprocal translocationsbecause they appear bicolored under a microscope usingfluorescent light (Figure 1) and can thereby be counted easily to determine a person’s likely exposure to ionizing radiation.(See October/November/December 1992 Energy & TechnologyReview, “Chromosome Painting,” pp. 11–26, and theNovember/December 1995 S&TR, “The Genetic Contributionof Sperm: Healthy Baby or Not,” pp. 6–19.)

Applying Biomarkers to Russian LiquidatorsThe usefulness of all three biodosimeters for measuring

small or moderate amounts of ionizing radiation is beingdemonstrated in an eight-year study (1992 to 1999) of a largegroup of liquidators. The study, conducted for the NationalCancer Institute and directed by Livermore scientist IreneJones, focuses on a population of about 300 Russianliquidators who were assumed to have been exposed to doses of about 5 to 25 centigrays. The study also includes 300 matched controls from Russia of about the same age andwith similar smoking histories.

13Radiation EffectsS&TR September 1999


Figure 1. The FISHtechnique attachesfluorescent dyes to smallpieces of chromosomescalled probes, which bind tocomplementary sequencesof target chromosomes.The bound probes revealbicolored reciprocaltranslocations, the numberof which is a strongindicator of exposure toionizing radiation.

14 S&TR September 1999


The results so far show FISH to be sensitive to theexposures of Chernobyl liquidators, with the HPRT assaybeing less sensitive and the GPA assay, which proved highlyvaluable for studies of A-bomb survivors and more highlyexposed Chernobyl liquidators, showing no differencebetween the exposed and control populations (Figure 3). TheLivermore team says its population of liquidators received on average a dose of about 15 centigrays, as determined byFISH. Such a radiation dose is roughly equivalent to agingabout 10 years or to smoking cigarettes regularly. Theexpected health consequences to the population under studyfrom such an exposure are small.

Livermore researcher Jones notes that the sensitivity todetect the effect of radiation exposure is increased by knowingthe age and the smoking habits of the individual, because bothcharacteristics contribute to the damage in their cells.However, she says it is impossible to determine the health riskof any one individual who received a specific amount ofionizing radiation, especially at the lower doses that do notcause acute health effects. Each individual has a differentcomplement of genes that determine how well they can repairdamage from ionizing radiation and other sources. Personalhabits such as smoking, drinking, and diet add to the geneticdamage that accumulates in cells. “It is the sum of all damageand the body’s response to that damage that determines therisk of cancer and other health effects,” she says.

In a separate study led by biomedical scientist Joe Lucas,Livermore researchers applied FISH to a subset ofChernobyl liquidators suspected of receiving a large dose ofionizing radiation. They reconstructed doses for 27Chernobyl liquidators from the frequency of translocationsmeasured in their lymphocytes. Of the 27 individuals, 15 are

Because physical dosimetry was difficult to perform on thehalf-million liquidators, the Livermore team decided toestimate the Russians’ exposure through biodosimetry. Theyalso reasoned that because people have differentsusceptibilities to radiation toxicity, biodosimetry is a moreaccurate indicator of cancer risk than accurate physicaldosimetry. (Physical dosimetry measures radiation incidentupon the body, but biodosimetry measures cellular injuryresulting from that radiation.)

Recognizing Statistical PowerLivermore experts also recognized that the large number of

liquidators would give their study the same kind of statisticalpower that had made previous studies on Hiroshima andNagasaki A-bomb victims important to human radiationbiology. However, it would provide information for differentradiation exposure conditions. While A-bomb survivorsreceived instantaneous external exposures, Chernobylexposures were complex mixtures of internal and externalexposures over a period of time and, in some cases, duringseveral separate work assignments.

To increase the statistical power of dose-effects studies, theLivermore investigators are collaborating with researchersfrom the Applied Ecology Research Laboratory, Ministry ofHealth and Medical Industry of Russia in Moscow; theLaboratory of Radiation Genetics, Central Research Instituteof Roentgenology and Radiology, St. Petersburg, Russia(Figure 2); and the Tula Diagnostic Clinic of the ScientificInstitute of Modern Medical Technologies, Tula, Russia.Blood samples are drawn in St. Petersburg, Moscow, and Tulaand shipped by air to Livermore.

Radiation Effects

Figure 2. Livermore biomedical scientists JimTucker (second row, second from left) andRichard Langlois (second row, far right) recentlyvisited the laboratory of Dr. Irina Vorobstova (frontrow, left) at the Laboratory of Radiation Genetics,Central Research Institute of Roentgenology andRadiology, St. Petersburg, Russia. Visits such asthese have fostered successful collaboration onthe health effects of radiation dose resulting fromthe Chernobyl disaster.

being treated for radiation sickness. The remaining 12 showno medical symptoms.

“FISH has worked extremely well on Chernobyl victims,”says Lucas, one of the original developers of FISH. He notesthat the technique is useful because not every liquidator had adosimeter, and memories of the nature and duration of workassignments for most workers are not reliable.

Questions Still UnansweredCurrent studies at Livermore and at other research centers

are addressing some of the unanswered questions about theassays, such as their sensitivity to low doses, how intensity ofradiation exposure affects the response, the persistence ofchromosome translocations, and the degree to which factorsother than radiation affect them. Jones and her colleagues, forexample, are studying the extent to which the type ofchromosome aberration affects its persistence in human bloodcells, which could change the relationship betweentranslocation frequency determined by FISH and radiationdose as time passes after exposure.

Another major goal of the research will be to understandwhy people differ in the effect that the same dose of radiationhas on their cells. One part of this effort has been started—identifying the differences in the DNA repair gene sequence inpeople. The next big challenge will be to determine how thesedifferences affect the capacity to repair damaged DNA and ifthese differences are related to long-term health.

The Lucas group is collaborating with colleagues atColumbia University on a promising method to detect cellulardamage among the liquidators. The method is based onmeasuring the formation of micronuclei, which are secondaryand much smaller cell nuclei that form in eye cataract tissue asa result of radiation. The group is also working on anenhancement to FISH that is faster, more accurate, and moresensitive by counting individual chromosomes in liquidsuspension instead of on a microscope slide.

In the meantime, Livermore radiation-effects researchersare working with collaborators in Ukraine, Russia, Estonia,and Israel (where some liquidators have immigrated) to applybiodosimeters such as FISH and GPA in their ownlaboratories.

It seems clear that despite its disastrous environmentalconsequences, the Chernobyl accident has spawned deeperunderstanding about the health effects of ionizing radiationand, in the process, spurred stronger international cooperation.

— Arnie Heller

Key Words: biodosimeter, Chernobyl, FISH (fluorescence in situhybridization), glycophorin A (GPA), hypoxanthinephosphoribosyltransferase (HPRT).

For further information contact Irene Jones (925) 423-3626([email protected]) or Joe Lucas (925) 422-6283 ([email protected]).

15Radiation EffectsS&TR September 1999


Figure 3. A Livermore study is using FISH to show that ionizing radiation from the Chernobyl accident has increased the number of chromosometranslocations in (a) the liquidator population compared with (b) a control group. The FISH study also revealed the greater number of translocationsseen in (c) liquidators who smoke cigarettes (solid diamonds) or a stronger tobacco called papirossi (solid squares) compared with (d) the controlpopulation of smokers (open diamonds and squares).

12Upper 95 percent tolerance bounds

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Energy SecretaryBill Richardsonaddresses the crowdthat attended the June 11, 1999,dedication of the National Ignition Facilitytarget chamber.

16 Research Highlights S&TR September 1999


HE June unveiling of a 130-ton (118,000-kilogram)gleaming metal sphere some 10 meters in diameter

marked a much-anticipated and highly celebrated milestonefor the Department of Energy’s National Ignition Facility,now under construction at Lawrence Livermore. A largecrowd of employees and guests, including Energy SecretaryBill Richardson, was on hand for the dedication of the gianttarget chamber for NIF, currently the nation’s largest scienceconstruction project.

The dedication marked the on-time completion of NIF’ssingle largest piece of equipment. The $14.5-millionvessel will serve as the working end of thelargest laser in the world. The outputof NIF’s 192 laser beams willconverge at the precise centerof the chamber, whereconditions of deepvacuum andtemperatures farbelow freezing willsupportexperiments onlydreamed of fordecades.

NIF’s beams will enter the chamber in two-by-two arraysto illuminate 10-millimeter-long gold cylinders calledhohlraums enclosing 2-millimeter capsules containingdeuterium and tritium, isotopes of hydrogen. The two isotopeswill fuse, thereby creating temperatures and pressuresresembling those found only inside stars and in detonatednuclear weapons—but on a minute scale. By recreating theseextreme conditions in a carefully instrumented laboratorysetting, NIF will serve as an essential facility in DOE’sStockpile Stewardship Program to ensure the safety andreliability of the nation’s nuclear arsenal.

Must Last 30 YearsThe job facing a team of engineers from Livermore and Sandia national

laboratories was to design andconstruct a vessel that would last

at least 30 years, withstandearthquakes as well as debris and gamma radiation fromexperiments, maintain deepvacuum and ultrafreezingenvironments required forexperiments, andaccommodate nearly ahundred diagnosticinstruments, 192 beamlines,and associated optics and

equipment—and do it all within budget and on schedule.

Target Chamber’s DedicationMarks a Giant Milestone

T

“There was never any doubt we could build it,” saysLivermore mechanical engineer Dennis Atkinson. In thatrespect, he says, the assignment was similar to other NIFconstruction projects. “They are all challenging, but we know we can accomplish them.”

The engineering team, led by Livermore’s Vic Karpenkoand Dick Wavrik of Sandia National Laboratories, firstconsulted with laser scientists, optical experts, targetphysicists, laser physicists, and facility designers at LawrenceLivermore and Los Alamos national laboratories, theUniversity of Rochester, and the Defense Threat ReductionAgency about their requirements for the target chamber. Theserequirements included the absolute synchronization of laserbeams arriving at the target simultaneously, fixed focal planedistances from the final optics to the targets, close proximityof myriad instruments, and ease of ingress and egress ofsystems to transport, hold, and freeze the tiny targets. Theresult was an 11-centimeter-thick spherical vessel measuringabout 10 meters in internal diameter, with 190 holes ofvarying diameters located over its surface to accommodate the beamlines, diagnostic instruments, and other equipment.

With the final dimensions agreed upon, the engineeringteam reviewed manufacturing options. One idea was tofashion the target chamber from a mosaic of small, identical(1.8- by 1.8-meter) pieces. However, such a mosaicwould require considerable on-site welding and therebyincrease costs.

The team also investigated having the vessel built ina machine shop as two hemispheres and then transportedto Livermore for assembly. That notion was droppedbecause it posed transportation problems, and the vessel,with its complicated distribution of portholes, did notlend itself to being fabricated as two equal hemispheres.

Giant VolleyballThe team finally agreed upon an expanded cube

(6 sides) with 3 plates per side (18 plates total) tominimize welding length and overall cost. The design,looking like a giant volleyball, features 6 symmetricmiddle plates and 12 asymmetric outer plates. Asmanufactured, the 18 aluminum plates measure 2.4 by6.9 meters and weigh about 7.5 tons each.

There was uniform agreement that the vessel shouldbe manufactured from aluminum, specifically thealuminum alloy 5083-0. The same alloy, notes mechanicalengineer Wavrik, is used in harsh marine environments suchas ship superstructures.

The completed vessel was estimated to weigh some 130 tons. An outer concrete skin and final optics would add200 tons each, for a total of nearly 530 tons. Given thatestimate of final weight and the number of holes that neededto be drilled, the designers decided on a plate thickness of

11 centimeters. Although this was more than was needed theoretically, it gave the chamber the strength of a substantial structure in its own right rather than a simplevessel to contain experiments.

A prime consideration was ease of fabricating the 18 plates.“We wanted to make sure we didn’t design something thatwould be difficult to manufacture,” says Atkinson. The teamchose as manufacturing contractor Pitt–Des Moines Inc.,which has extensive experience fabricating vessels, fromnuclear power plants to water storage tanks.

17NIF Target Chamber S&TR September 1999


(a) The target chamber being assembled within a temporary cylindricalsteel structure with a removable roof. This progress photograph wastaken in March 1999 when all of the plates making up the chamberwere in place and some of the 190 portholes to accommodatebeamlines and diagnostic instruments had been cut in it. (b) Thecompleted target chamber being removed from the temporaryassembly structure.

(a)

(b)

18 S&TR September 1999


In addition, workers drilled 118 diagnostic-instrument portswith inner diameters varying from 15 to 70 centimeters.

Achieving Extreme SphericityAt regular steps along the way, the chamber was mapped with

laser surveying instruments to ensure its sphericity. Wavrik notesthat the American Society of Mechanical Engineers specificationfor spherical vessels is for the diameter to measure within 1 percent of specification, or within 10.16 centimeters for the 10-meter-diameter chamber. The Livermore–Sandia

Pitt–Des Moines assembled an international team ofsubcontractors. Manufacturing began in the fall of 1997, when the plates were poured at the Ravenswood AluminumMill in Ravenswood, West Virginia. The plates were shippedto forming subcontractor Creusot–Loire Industries in France,where the plates were heated to 315°C and then shaped in agiant press to the proper spherical geometry.

From France to PennsylvaniaThe formed plates were shipped weekly in pairs from

France to Precision Components Corp. in York, Pennsylvania,where they were trimmed and weld joints were prepared.Three plates at a time were trucked to Livermore. The firstplates to arrive were those with the highest tensile strength to provide a strong base for the entire vessel.

Assembly and welding activities at Livermore wereperformed in a temporary cylindrical steel enclosure looking much like an oil or water tank. Constructed in June 1998, the temporary structure measured 18.3 meters in diameter and 18.9 meters high and rested on a 61-centimeter-thick concrete slab. The enclosure featured a roof to ensure temperature control and keep out rain. The roof was removed only to permit cranes to lift the plates into place as soon as they arrived and for lifting outthe assembled vessel for its dedication and transport to itsfinal home in the target building.

After the bottom three plates were welded together to form a supporting base, the other plates were lowered intoplace and held together with guy wires until welded. Eachwelded seam required 150 passes over a like number of layers of thin aluminum wire for a smooth, nonporous finish.Although time-intensive, this approach minimized thermalstress to the aluminum plates.

The porthole drilling process required laser instrumentationboth to mark the port location and to drill the pilot holes. Mostof the ports are arranged in pairs, one directly on the oppositeside of the chamber from the other. In this way, the twoopposing ports may be used for alignment purposes.

Seventy-one larger holes 1.16 meters in diameter willaccommodate the final optics assemblies (FOAs), the lastelement of the main laser system. An additional port, whichincludes an FOA port, measures 1.67 by 1.16 meters andprovides access for testing nuclear-weapons effects.(Designers have provided the capability to receive andtransport a large diagnostic package to this port.) Weldneckswith thick flanges were secured to the ports to accommodatethe optics assemblies, which will be bolted to the weldnecks.

NIF Target Chamber

specifications called for final measurement within 0.5 percent, or5.1 centimeters in 10 meters. In fact, the assembly crew achieved0.25 percent, or 2.54 centimeters, across the entire diameter.

On June 5, the roof of the temporary enclosure wasremoved, and the target chamber was lifted out by anenormous crane, a 14-story-tall Manitowoc 4600 Ringer.Acquired from DOE’s Nevada Test Site (and transported inpieces aboard 66 trucks), the crane weighs some 900 tons andhas a lift capacity of 600 tons. It will remain on site foradditional heavy-lifting construction jobs on NIF.

The sphere was secured to the crane with a plate loweredvertically into the top port of the sphere and then turnedhorizontally to support the chamber from inside (similar toinstalling a togglebolt). “We all held our breath,” recalledLivermore Director Bruce Tarter, when the chamber was lifted out of the enclosure and then placed on a LampsonCrawler (also borrowed from the test site) as an intermediateanchor for its public dedication.

A few days later, on June 11, the world got a good look at thechamber at the dedication ceremony. The extraordinary structurebecame an instant magnet for employees and visitors alike. AsBritain’s Graham Jordan, Deputy Under Secretary for Scienceand Technology, Ministry of Defense, remarked, the chamberlooked as if it “simply landed one night” from outer space.

The following week, the chamber was hoisted onto amassive concrete pedestal installed inside the target building.Over the next two weeks, a combination of hydraulic jacks,roller assemblies and shims, and finally anchor bolts wereused to adjust the chamber for final alignment and establish its proper elevation and sphere tilt.

This fall the exterior of the chamber will be tested for leaksand then encased in 40 centimeters of concrete with 0.1 percentboron to provide shielding from the neutron and gamma raysproduced by the experiments. The concrete will be appliedover steel rebar tied to the chamber with welded studs.

Following application of the concrete, the chamber’sexterior will be sealed with epoxy paint, and the chamber

will be aligned and hung with the final optics assemblies,which will arrive next year. The chamber is expected to sag a bit from the 400 tons of the concrete shield and optics. As a result, the angle of the FOAs will be adjustedappropriately.

Although an unqualified success in its own right, the target chamber’s completion serves as a striking symbol that NIF is only a few years away from history-makingexperiments as an essential component of DOE’s StockpileStewardship Program.

—Arnie Heller

Key Words: final optics assemblies (FOAs), hohlraum, NationalIgnition Facility (NIF) target chamber, Nevada Test Site, StockpileStewardship Program.

For further information contact Dennis Atkinson (925) 422-6984([email protected]) or Dick Wavrik (925) 422-0415([email protected]).

19NIF Target Chamber S&TR September 1999


The completed targetchamber being lowered intoplace prior to the June 11dedication ceremony. OnJune 17, the chamber washoisted onto its permanenthome, a massive concretepedestal inside the targetbuilding.

20Each month in this space we report on the patents issued to and/orthe awards received by Laboratory employees. Our goal is toshowcase the distinguished scientific and technical achievements ofour employees as well as to indicate the scale and scope of thework done at the Laboratory.

Patents and Awards

Patent issued to

Daniel M. MakowleckiAlan F. Jankowski

Steven T. MayerRichard W. PekalaJames L. Kaschmitter

Edward J. KansaBrian L. AndersonAnanda M. WijesingheBrian E. Viani

Patent title, number, and date of issue

Method of Fabricating BoronContaining Coatings

U.S. Patent 5,897,751April 27, 1999

Capacitor with a Composite CarbonFoam Electrode

U.S. Patent 5,898,564April 27, 1999

Separation of Toxic Metal Ions, Hydrophilic Hydrocarbons,Hydrophobic Fuel, and Halogenated Hydrocarbons and Recovery of Ethanol from aProcess Stream

U.S. Patent 5,906,748May 25, 1999

Summary of disclosure

A method for fabricating boron nitride, cubic boron nitride, andmultilayer boron/cubic boron nitride hard coatings using magnetronsputtering in a selected atmosphere. These hard coatings may beapplied to tools, electronic divices, and engine and other parts toreduce wear on tribological surfaces. These boron coatings containno morphological growth features. For example, the boron is formedin an inert (for example, argon) atmosphere, while the cubic boronnitride is formed in a reactive (for example, nitrogen) atmosphere.The multilayer boron/cubic boron nitride is produced by depositingalternate layers of boron and cubic boron nitride, with the alternatelayers having a thickness of 1 nanometer to 1 micrometer. Theinterfaces of the layers may be discrete or of a blended or gradedcomposition.

Carbon aerogels used as a binder for granularized materials,including other forms of carbon and metal additives, are cast ontocarbon or metal fiber substrates to form composite carbon thin-filmsheets. The thin-film sheets are used in electrochemical energystorage applications, such as electrochemical double-layer capacitors(aerocapacitors), lithium-based battery insertion electrodes, fuel-cellelectrodes, and electrocapacitive deionization electrodes. Thecomposite carbon foam may be formed by prior known processes,but with the solid particles being added during the liquid phase of theprocess, that is, prior to gelation. The other forms of carbon mayinclude carbon microspheres, carbon powder, carbon aerogel powderor particles, and graphite carbons. Metal and/or carbon fibers may beadded for increased conductivity. The choice of materials and fiberswill depend on the electrolyte used and the relative tradeoff ofsystem resistivity and power to system energy.

A process to greatly reduce the bulk volume of contaminantsobtained from a subsurface remediation using an effluent stream.The chemicals used for the subsurface remediation are reclaimed forrecycling to the remediation process. Additional reductions in thebulk volume of contaminants are achieved by destroying thehalogenated hydrocarbons with ultraviolet light and by the completeoxidation of hydrophobic fuel hydrocarbons and hydrophilichydrocarbons. The contaminated bulk volume will arise primarilyfrom the disposal of the toxic metal ions. The entire process ismodular, so if there are any technological breakdowns in one ormore of the component process modules, such modules can bereadily replaced.

Patents


AwardsLivermore scientist Steve Gray has received the Defense

Intelligence Agency Director’s Award for his exceptionalleadership in setting up a sophisticated Web site on aclassified, secure network that combines up-to-dateinformation on foreign proliferation with computational toolsand models.

The program, named Dragon Fury, is now running on aclassified network available to Department of Defensepolicymakers, the intelligence community, and war-fightingcommanders. The Defense Intelligence Agency (DIA) runsthe Department of Defense’s military intelligence operations.

According to the award citation, “Mr. Gray’s dedication tothe Dragon Fury Program has made it possible for senior-leveldefense policymakers, military planners, and combatcommanders to access comprehensive, accurate, and timelyinformation in order to perform their counterproliferationplanning and execution missions. His consistently outstandingleadership and performance have brought great credit uponhimself, the Lawrence Livermore National Laboratory, and theDefense Intelligence Agency.”

Gray is believed to be the first non-DIA employee to receivethis award.

S&TR January/February 1999

A Better Picture of Aging MaterialsThe shelf life of a nuclear weapon was not anissue until the early 1990s when the U.S. stoppeddeveloping and testing nuclear weapons. Existingweapons are expected to remain operational forseveral decades beyond their originally designedlifetime. Livermore is studying the agingprocesses of the many materials that make up anuclear weapon, such as high explosives, metals,and organic materials, with the goal ofdeveloping models that predict the lifetime of individual materials as well as of the entireweapon system. Some experiments areexamining the fundamental nature of thematerials, while others are studying weaponstaken from the stockpile to see how aging isprogressing. The process of compiling this datainto predictive models is just beginning.Contact: James LeMay (925) 423-3599([email protected]).

Abstract

U.S. Government Printing Office: 1999/783-046-80019

Coming Next

Month

Coming Next

Month

Livermore Wins SixR&D 100 Awards

In October, S&TR willreport details about the

winning inventions and theteams that created them.


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