58 Los Alamos Science Number 28 2003

The Pit Production

StoryDouglas D. Kautz, David B. Mann, Richard G. Castro,

Lawrence E. Lucero, and Steven M. Dinehart

In 1993, Los Alamos National Laboratory was asked to return toan important part of its roots. It would once again tackle themanufacturing of the plutonium-bearing pit, a major component

of nuclear weapons. The Manhattan Project pioneers had learned towork with plutonium, perhaps the strangest and most reactive of allthe elements on Earth, and they had built the first pit, testing it inthe Trinity experiment. After World War II, Los Alamos continuedpit manufacturing until 1952, when that mission was transferred tothe newly completed Rocky Flats Plant in Golden, Colorado—seeFigure 1.

Rocky Flats produced thousands of pits year after year until1989, when the Department of Energy (DOE) abruptly ended themanufacture of plutonium components because of environmentalconcerns. Two years later, DOE changed the plant’s official mis-sion from defense programs to environmental remediation andbegan the search for an interim location where pit manufacturingcould be continued on a small scale. Although the United Stateswould eventually have to build a new pit-manufacturing facility toreplace the Rocky Flats Plant, the projected time for its completionwas 2017. Consequently, when Rocky Flats began environmentalremediation in 1991, DOE asked Los Alamos to take on the mis-sion of pit surveillance. And in 1993, the Laboratory was asked totake on pit manufacturing since our facility at Technical Area (TA)55 was the only fully functional plutonium facility in theDOE–Defense Programs complex—see Figure 1.

At the time of transfer, the Laboratory could nominally performalmost all plutonium-processing steps needed to manufacture mostpits in the enduring stockpile; however, close inspection revealed ahost of issues to be solved. Some machining and welding equip-ment, as well as dimensional inspection capabilities, were absent;several processes needed improvement to meet the quality require-ments for the manufacture of war reserve components; and severalprocessing methods had to be converted to fit existing equipment orto meet new regulatory mandates that disallowed the use of RockyFlats technologies. In addition, several pieces of equipment,

although functional, required replace-ment or additional backup capabilityso that the mission could be viable atLos Alamos. Substantial upgradeswere also needed in the processingcapability for nonnuclear compo-nents. Despite many challenges, thepit-manufacturing effort began but asa very small project. Many of the par-ticipants performed several functions,and they focused on developingprocesses rather than product. As theproject matured and needs were betterunderstood, the emphasis shiftedtoward manufacturing pits that wouldbe certifiable, that is, that would meetall the specifications required forinclusion in the enduring stockpile.The successes described here reflectthe dedication of a large number ofpeople in many organizations acrossthe Laboratory. The largest contribu-tors were the Nuclear MaterialsTechnology, Engineering Sciencesand Applications, Materials Scienceand Technology, and Chemistry (for-merly Chemical Science andTechnology) Divisions.

Early Decisions on Materialsand Processes

Early in the project, we made sev-eral major decisions that would influ-ence the entire manufacturingeffort—from preparing the plutoniummetal to fabricating the componentsand assembling the pits. First, wewould reduce the use of variousprocess chemicals to meet environ-mental and waste-processing con-cerns. Next, we would develop newwelding processes for various joints,and finally, we would developmethodologies to ensure that highlyreactive plutonium did not exhibitundue corrosion upon assembly intothe pit. An overriding factor in all ourdecisions was, and remains, the neces-sity to produce pits that are equivalentto those manufactured at Rocky Flats.

The choice of solvents posed aparticularly thorny problem. AtRocky Flats, carbon tetrachlorideand 1,1,1-trichloroethane had beenused in large quantities, but their useat Los Alamos was prohibited by

modern environmental and waste-processing constraints. To developprocessing strategies that employdifferent solvents and minimize theamount needed, we launched severalcompatibility studies with plutonium

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The Pit Production Story

Figure 1. The Rocky Flats Plant and TA-55These pictures are aerial views of the Rocky Flats Plant (top) and TA-55 atLos Alamos (bottom).

and other materials. We not onlydeveloped those strategies but alsocontinued to reduce the waste streamby purifying and reusing the solventswhile ensuring the cleanliness ofcomponents assembled into pits.

The heavy use of lubricants atRocky Flats posed two additionalproblems that we had to avoid. First,the lubricants themselves generatedhazardous waste streams. Second,because plutonium is highly reac-tive, each time a lubricant is used, acleaning step involving large quanti-ties of solvent must follow to ensurethat the plutonium does not reduceto plutonium hydride, in which caseit must be scrapped and reprocessed.Our solution was to reduce the useof lubricants through developmentof a “dry” machining process.Unlike traditional processes, drymachining requires lubricant onlyduring the finishing of parts—referto Figure 2. We also reduced thelubricants in other operations thathad used them during Rocky Flatsprocessing.

Creating the dry machining processtook approximately 18 months andinvolved development of new tools,procedures, machining parameters,and airtight gloveboxes (Figure 3). Wealtered materials processing. At RockyFlats, wrought processing techniqueshad produced the plutonium. Butinstallation of the equipment for thatprocess at the Los Alamos facilitywould have forced major facilitychanges with consequent lengthydelays in acquiring a revised facilityoperating permit. Instead, both ourpit-manufacturing and certificationstaff compared the propertiesachieved through wrought processingand casting and concluded that castmaterial could indeed meet the needsof the weapons community—refer toFigure 3.

To study all replacements forprocess chemicals and materials usedin pit manufacture, as well as theireffects on the materials used in pits,the War Reserve MaterialsCompatibility Board was convened.Once the board found that the new

materials were compatible with the pitmaterials, an extensive quality-controlprogram was instituted to ensure thatno changes occurred in the formula-tion or processing of those materials.That same quality-control programdaily ensures that all materials in themanufacture of pit components meetthe established standards of uniformityand high quality (Figure 4).

A simple example of quality con-trol concerned rubber bands that holda marking mask on the pit. The rubberbands for our first pits were madefrom pure rubber and left no residueson the pit. A second batch receivedfrom the vendor contained an extraingredient that would have left anunacceptable residue on the pit. Thematerials compatibility board studiedthe new material and rejected itsusage for the war reserve product.

This description gives only aglimpse of the many decisions aboutmaterials, processing, and qualitycontrol. Both the production staff andthose in advisory roles workedtogether long and hard to develop and

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The Pit Production Story

Figure 2. The Dry Machining Process(a) The new dry machining process avoids heavy use oflubricants, which are expensive and difficult to dispose ofwhen becoming waste. In this process, no chemicalchanges take place on the surface of the plutonium parts,and thus all the plutonium shavings can be collected forreuse. The dry machining process, therefore, generatesno plutonium waste. (b) Star machinist Dean Martinez isprogramming the T-base lathe to machine a component.

(a) (b)

approve changes in numerousprocesses involved in pit manufac-ture, paving the way for us to meetour production milestones.

The Road to Quality Pits

Early on, the production staff andthe Los Alamos weapons designgroups decided that the major changesin processing should be tested bymanufacturing a series of develop-ment pits and then checking whetherthe processing changes reduced theirfunctionality. We manufactured ninepits for this purpose.

With the first pit, we tested animportant welding process importedfrom Rocky Flats. That test was asuccess. For the second pit, we usedprocesses and tracking systems thatwere available at that early stage andachieved only mixed success, takingthree tries to complete fabricationsatisfactorily. The finished pit wassubjected to an environmental test,and the results were compared withthose from pits manufactured atRocky Flats.

We used the third pit to comparethe surface reactivity of plutoniumfabricated at the Laboratory withthat of pits made at Rocky Flats.During manufacture of the fourth pit,we tested the effectiveness of newcleaning materials chosen to meetnew waste-generation regulations.We exposed the plutonium to larger-than-normal quantities of variousprocessing materials known to bedifficult to remove and then showedthat the new cleaning material,trichloroethylene, could successfullyremove the materials. Postfabricationtesting indicated no significant dif-ferences from pits that had under-gone conventional processing.

Then, in 2000, two major problemscaused significant delays in our fabri-cation schedule. First, during theCerro Grande fire in May, the TA-55

plutonium facility was entombed forthe first time since its opening inDecember 1978 for fireproofingupgrades. After the fire, all pressur-ized gas and fluid lines were tested forleaks in response to a corrective actionfrom a contamination incident that hadoccurred earlier in the year. Afterresolving those issues, we returned tomanufacture a pit that tested theeffects of glovebox atmospheres onthe plutonium material and on the pro-cessing used to remove any reactedmaterial from the plutonium beforefinal fabrication.

Although by that time significantwork had been done to qualify mate-rials and processes, our developmentpits still deviated from any pit thatwould ever be allowed to enter theenduring stockpile. We decided toproduce a series of “standard pits”that were as close as possible to warreserve specifications and process-ing. We made the first in this seriesmainly to exercise the newly formu-lated systems for tracking data andparts. Although several difficultieswere noted during the processing ofthis pit, the lessons learned helped

the project mature greatly. The nextin the development-pit series waspurposely manufactured with severaldefects to test the capabilities of ourmajor nondestructive testingprocesses. We then manufactured asecond standard pit, which trackedmuch better than the first, but theexperience showed that we still hadseveral challenges to overcomebefore we could successfully meetall required product specificationsand quality standards.

The next development-pit testassessed the integrity of Los Alamoscomponents by directly comparingeach one with the correspondingRocky Flats component. After the pitwas successfully fabricated, it wastested to ensure that no reactivity dif-ferences could be discerned betweenthe different materials. Finally, webuilt a third standard pit to check ourquality control and assurance systemsand to demonstrate the efficacy of thelast remaining nondestructive testingprocess.

A long hiatus in fabrication thenensued as the project went throughmajor restructuring. To bring opera-

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The Pit Production Story

Figure 3. Cast Plutonium(a) Shown here is an induction furnace used in the casting process. Induction heat-ing provides good stirring of molten plutonium and a clean atmosphere for process-ing this highly reactive metal. (b) Casting technician Anthony Valdez is setting upthe crucible used in casting.

(a) (b)

tions back up, webuilt two standardpits whose status wecompared with thatachieved for the lastfabricated pit.Although the qualitycontrol and assurancesystems had maturedgreatly during therestructuring activi-ties, the long periodof inactivity had, asexpected, some nega-tive effects on boththe equipment and theprocess operators.Even after the secondpit was fabricated, notall the processingproblems had been fully resolved.

On the other hand, during fabrica-tion of the second pit, we successfullyinstituted a major, new inspectionprocess. That process, although verydifficult to install and prove out, is nec-essary for certifying the quality of fab-ricated components. Its implementationand that of another inspection processallowed us to finally fabricate a prod-uct that was fully compliant with theproduct specifications. All our work onhoning and documenting our processescame together when we manufacturedthe next standard pit. It became theprecursor to a major milestone for theproject, namely, a pit produced withfully qualified processes and qualitysystems as specified in the DOE QC1quality control policy. The final devel-opment pit was a calibration unit fabri-cated with several documented defects;it will be stored and periodically testedto ensure that nondestructive evaluationprocesses are performing in the man-ner expected.

Qualification Pits

The next major milestone was thedelivery of a certifiable pit—a pit that

met all the manufacturing specifica-tions required for placement in thestockpile. Although the pits fabricatedat Los Alamos must still undergo sev-eral engineering and physics testsbefore they can be fully certified andactually placed in the stockpile, allquality control and assurance systemsand process qualifications associatedwith manufacturing will be in place.

In May 2003, the Laboratory com-pleted the first nuclear weapons pit thatmeets specifications for use in the U.S.stockpile. The newly made pit, calledQUAL 1 because it was built with fullyqualified processes, is for use in theW88 warhead, which is carried on theTrident II D5 Submarine-LaunchedBallistic Missile, a cornerstone of theU.S. nuclear deterrent.

The pit production project is restor-ing our nation’s ability to makenuclear weapons, a capability that hadbeen lost when the Rocky Flats Plantwas shut down in 1998.

Looking Forward

Members of the project are alreadyworking on ways to improve both theyield and the efficiency of processing.

We plan to reduce the waste generatedduring plutonium casting by replacingsingle-use fabrication tooling withreusable tooling. We are studyingways to remove a common machiningdefect encountered during turningoperations. We are instituting real-time monitoring on several pieces ofequipment so that process holds nowencountered while waiting for batchresults can be minimized. We are alsoembarking on an in-process monitor-ing strategy to gain much neededprocess-performance data. Havingmoved beyond the certifiable-pit mile-stone, we will institute this type ofrobustness initiative to provide a moreconsistent and higher-quality productto our DOE and Department ofDefense customers. �

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The Pit Production Story

Douglas Kautz graduated from the ColoradoSchool of Mines in 1982 with a bachelor’sdegree in metallurgical engineering andreceived a master’s degree in metallurgicalengineering from the Colorado School ofMines in 1987.Doug worked forRockwellInternational from1982 to 1987, spe-cializing in theprocess engineer-ing of materialsused in nuclearweapons. Fromthere, he moved to LawrenceLivermore NationalLaboratory, working on high-energy-densitywelding research and materials issues withnuclear weapon components until 1994, whenhe became a staff member in the NuclearMaterials Technology Division at Los Alamos,where he is now a deputy leader of the WeaponComponent Technology Group.

Figure 4. Quality Assurance AuditLos Alamos and National Nuclear Security Administrationquality specialists verify that quality assurance systemssupport pit manufacturing.