Engineered Bar Waste Package Design Conceptsfora/67531/metadc628223/...UCRL- JC--106 916 DE92 004657 Engineered Bar_.'er System and Waste Package Design Conceptsfora Potential Geologic

UCRL- JC--106 916

DE92 004657

Engineered Bar_.'er System andWaste Package Design Conceptsfor a

Potential Geologic ReposRory at Yucca Mountain

D.W. Short

D.J. Ruffner

L.J. Jardine

This paper wasprepared for theFOCUS '91

Las Vegas, NV .... . __,.,_ _

September29-October2, 1991 DEC 0 9 log!

JR

Manuscript Date: September 1991Publication Date: October 1991 ,--

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Thisisa preprint ofapaperintended forpublication in a journalorpreceedings. Sincechanges may be made before publication, this preprint is made available with theunderstanding that it will not be cited or reproduced without the permission of theauthor.

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Engineered Barrier System and Waste Package Design Concepts for aPotential Geologic Repository at Yucca Mountain*

D. W. Short D.J. RuffnerLawrence Livermore National Laboratory Lawrence Livermore National Laboratory

, P.O. Box 808, L-622 P.O. Box 808, L-204Livermore, CA 94551 Livermore, CA 94551(510) 422-1287 (510) 422-1754

L. J.JardineLawrence Livermore National LaboratoryP.O. Box 808, L-622Livermore, CA 94551(510) 422-1287

In this paper, we:Abstract

• Provide some background to our conceptual-designWe are using an iterative process to develop preliminary efforts.concept descriptions for the Engineered Barrier Systemand waste-package components for the potential geologic • Describe our conceptual-design process and severalrepository at Yucca Mountain. The process allows multiple preliminary concepts resulting from the process.design concepts to be developed subject to majorconstraints, requirements, and assumptions. Involved in • Discuss the ranking and selection process we willthe highly interactive and interdependent steps of the use to evaluate alternative concepts.process are technical specialists in engineering, metallic

and noametallic materials, chemistry, geomechanics, Backgroundhydrology, and geochemistry. We have developed

preliminary design concepts that satisfy both technical and The Nuclear Waste Policy Act (NWPA) of 1982 creatednontechnical (e.g., programmatic or policy) requirements, an Office of Civilian Radioactive Waste Management

(OCRWM) within DOE with the responsibility for siting,Introduction constructing, and operating a repository for spent nuclear

fuel and high-level radioactive waste (HLW). Pursuant toWe are using an integrated, interactive process to the Act, 40 CFR 191 gave the U.S. Environmental

generate preliminary design concepts for an Engineered Protection Agency (EPA) the responsibility for developingBarrier System (EBS) at Yucca Mountain. This process standards to protect the environment from offsite releasesinvolves functional-analysis techniques to identify the of radioactive material from a repository, and 10 CFR 60functions and mission requirements of the EBS, and an gave the U.S. Nuclear Regulatory Commission (NRC)iterative systems-engineering process to synthesi_._ responsibility for announcing the technical requirementsdescriptions of preliminary design concepts, necessary to license all phases of repository operation. In

1987, Congress amended the NWPA to focus site-Finalization of promising concepts must await data characterization efforts on a site at Yucca Mountain in

that can only be obtained from underground access to the Nevada.proposed repository horizon at Yucca Mountain; weexpect that this horizon will be opened in 1996.1 Until that The NWPA and 10 CFR 60 mandate that radioactivetime, we will use a systems-engineering process to study materials placed in the repository be contained within antwo or more conceptual design configurations. We will engineered barrier system (EBS). As defined by 10 CFR 60,also develop prototypes, as needed, to demonstrate an EBS comprises waste packages stored within anfeasibility of the concepts, underground facility. A waste package is defined as the

*Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore NationalLaboratory under contract No. W-7405-ENG-48.

DI,STRIBHTION... OF THIS DOCUMENT IS UNLIM|TE-D

N/ II::tl /

"waste form and any container, shielding, packing, and Functional Analysis and Mission Requirementsother absorbent materials immediately surrounding anindividual waste container." An underground facility is The functional-analysis approach establishes adefined as "the underground structure, including framework for integrating program-management effortsopenings and backfill materials, but excluding shafts, with technical-requirements analyses to create a unified, "boreholes, and their seals." consistent program. This approach recognizes that, just as

the facilities and equipment comprising the physicalDOE has responded to the requirements of the NWPA waste-management system must perform certain

and related CFRs by drawing up and issuing its Waste functions, so the program-management systems mustPackage Plan, 2 which provides a framework for the design perform certain functions to successfully bring the physicaland implementation of an EBS at Yucca Mountain that can system into being.be shown in an NRC licensing proceeding to meet aliapplicable statutory and regulatory requirements. All We performed a toF-down functional analysis todesign studies conducted under the Plan are to be carried identify the EBS functions and to establish the EBS missionout in accordance with the Management Systems requirements. The breakdown of the functions into the firstImprovement Strategy (MSIS), issued by the Director of four levels is shown in Fig. 1. This functional analysisOCRWM in August 1990, which calls for a rigorous started with the top need, Manage Waste Disposal, andimplementation of systems engineering principles with a flowed down through Dispose of Waste into three majorspecial emphasis on functional analysis, functions, each containing elements for the EBS due to

interface relationships. Fourth-level functions includeThe studies reported in this paper represent a Handle Waste, Contain Waste, Limit Release of

preliminary conceptual-design effort conducted under the Radionuclides, Confirm Performance, Assess Performance,earliest phase of the Waste Package Plan. and Monitor Performance. The geologic repository

interfaces for the EBS include the EBS to the subsurface

Conceptual-Design Studies operations area, the EBS to the Natural Barrier System(NBS), the EBS to the surface operations area, and the

Our conceptual-design studies involve functional internal Waste Package interface with the undergroundanalysis combined with an iterative systems-engineering facility. These interfaces and the boundaries are shown inprocess. 3,4 In this section, we describe: Fig. 2.

• Functional Analysis and Mission Requirements By decomposing the waste-management system, wewere able to define the EBS mission requirements so that

• Concept Synthesis the mission statement contained the objectives andaddressed environments, constraints, and measures of

• Preliminary Concepts effectiveness. The EBS mission is illustrated in Fig. 3. Indoing this az_alysis, we focused on the major constraint

• Requirements Documents that the EBS must be designed using a multibarrier

1ManageWaste

Disposal

I ........ I I I ,,l I Disposaof IWaste1.1 Accept 1_. Transport 1.3 Store I

Waste Waste Waste

II " I

1.4.1 1.4.2 1.4,3 IOperateGeologlc Isolate EvaluateSystem IRepository Waste Performance

-1.4.1.1 Handle Waste .1.4.2.1 Contain Waste .1.4.3.1 Confirm Performance

-1.4.1.2 DevelopSubsurface . 1.4.2.2 Limit Release -1.4.3.2 Assess Performanceopenings

- 1.4.1.3 close Geologic of Radionuclides -1.4.3.3 AssessEnvironmentalRepoaltory . . Compliance

- 1.4.1.4 :_upportGeOlogic - 1.4.2.3 Umlt IncompatibleRepositoryOporetlons HumanActlvltisa -1.4.3.4 Monitor Performance ".

Figure 1. Related functions for the Engineered Barrier System.

.

Boundaries

• Waste PackageJ

Engineered Barrier

Accessible' Environment

Interfaces:EBS to subsurface OPS areaEBS to NBSEBS to surfaceOPS areaWP to underground facility

Figure 2. Geologic repository interfaces for EBS.

I Mission Statement

1

Objectives I Envlr°nments I C°nstralnts ! I EflMeeac_IUvrenSe°fsI

..._ Underground _. Geologicrepository .... NRCstandards"-- Containment disposal forcontaintime_._ Mustmeetoverall

---" Publicopinion releaseIindtto A.E. ._ EPAstandards..._ Limitrelease for releaseto A.E.

rate __. Regulatory m Mustnotprecludeflexibility retrievalpre-closure NRC standards

-- for releaserateto NBS

.._. Performanceshallbe verified

• ..... Containwastefora prescribedtime

_.. Controlreleaseof" R/Nto NBS

Figure 3. EBS mission is characterized by its objectives, environments, constraints, andmeasures of effectiveness.

approach, so that the total system will assure that any The constraints were driven by regulations, policies,releaseof radionuclidesto theaccessibleenvironment and management guidance.The requirementsand .would conform to EPA standards, constraints have many sources, and ali must be considered

if the resulting design-concept description is to beIn generating preliminary concept descriptions, we acceptable. Figure 5 gives examples of regulatory and

translatedthemissionrequirementand known technologi- legalconstraints;programmaticconstraints;functionalcallimitationsintofunctionstobe performedand re- requirements;and limitsofscience,technology,and thequirementsthatdefinehow wellthesefunctionsaretobe environment.performed.Inthisbeginningstageofdevelopment,weused general,nonquantitativeobjectives,environmental In conducting the highly interactiveandassumptions,constraints,and performancemeasures.Both interdependentstepsused todevelopdesign-concepttherequirementsand constraintsevolvedduringthede- descriptions,we drew ontheresourcesofknowledgeablesigndevelopment,startingwithverybroadneeds,then technicalspecialistshaving expertisein engineering,becomingnarrowed,and finishingwithspecificsystem metallic and nonmetallic materials,chemistry,needs,asshowninFig.4. geomechanics,hydrology,and geochemistry.To meet

'::-i:!ii:i!ii.li!ii_:ii,iiii:!-_!i__

Figure4.Therequirementsandconstraintsevolveduringthedesigndevelopment.

regulatoryand llmltso!sclence,

legal constraints _'_ • technology, and(e.g. geologic the environment

.g. material properties,___ state of art, water

reposito _chemistry, permeability)

programmaticconstraints _ife, •

(e.g. regulatory compliance weight limits,strategy, cost and schedule) thickness limits,

choice of materials)

Figure5.EBS conceptdescriptionsmust addressallconstraintsand requirementsand arelimitedbyourunderstandingoftheenvironment,scientificknowledge,andstateoftechnology.

mission requirements for the EBS arid its waste-package Fig. 6 by the arcs cutting each of the four majorcomponents, we used an iterative design concept. We requirement spaces. After describing the system in generalstarted with broad interpretations of the constraints and terms, we were able to be more specific (narrow ourrequirements and with a general understanding of the requirements) and come to closure again. Each source ofscientific and technological limits that applied to the requirements and constraints evolved from broad tosituation. We then developed concepts that allowed us to specific, as represented by the examples in Fig. 7.

: come to closure at each level of specificity, as shown in

limits ofregulatory and science technology,

legal and the environment

programmatic functionalconstraints requirements

Figure 6. Concept development for the EBSand its waste package components is iterative tomeet mission requirements.

programmatic

o : • ; •

Reclulatorvand Legal

_ _lta_i_au i_ _u¢ I.I_S] i_e:rIEP.,_csla_dara d

A [ele__lt_tm,a_di_ ma_ Ii_e_s]I_-_er8_ _el&'l E_#,Wta_.d_rLasl

Functional

I-'] Contain waste for a Iongi '.!me

Limitations of science and technoloqv

A II] I_ltlt b_e]m_at_i_l_ I_,ti'/e_S._;]

Figure 7. Each source of requirements and constraints evolves from broad to specific.

Alternative concepts evolved from each design- To develop design features from the functions anddevelopment session. Minor variations, essentially requirements, we need to describe the operatingdesigners' choices, were possible by choosing such things environments, describe the system phenomena andas alternative waste-package emplacement erientations processes, and incorporate processes and features that can ,(e.g., vertical or horizontal emplacement in an excavated enhance containment and hinder release. Table 1 providescavity, or emplacement directly in the drift). Each a partial listing of some applicable phenomena andparticular choice created more specific requirements, corresponding design features.which could be traded, so that additional design concepts

evolved as a result of trade studies, optimizations, and To generate preliminary concept descriptions, we use ahybrid concepts, tailored systems-engineering process that incorporates 10

iterative steps (Fig. 8):Concept Synthesis

(1) Accommodating a key set of constraints andThe primary functions of the EBSare to contain waste requirements into the concept generation. All EBS

and to limit release of radionuclides to the natural barrier concepts must be designed to address a key set ofsystem. These functions are accomplished by (1) constraints and requirements, including containment ofpreventing or delaying the transport of radionuclides radionuclides for a prescribed period, limits on the releasethrough the surrounding materials; and (2) preventing or rate of any radionuclide, ability to retrieve the waste,delaying movement of gases and liquids to and from the ability to confirm performance, control of criticality,waste, or, if movement occurs, limiting the quantity of provision of unique identification, and materials propertiesgases and liquids in contact with the waste, and interaction.

Table 1. Environmental processes and some correspondin 8 design features.

System Phenomenon/Process Design Features to Enhance or MitigateProcess

Hydrology • LinersFluid flow through fractures • SealantsFluid flow through matrix • Vitrified rock adjacent to emplacementIrnbibition cavity

• Packing materials• "Umbrellas" to divert water

• Drainage schemes to channel water• Emplacement geometry• Containers

Radiation and heat • Heat pipes and active coolingThermal radiation • Thermally activated barriers (e.g.,_-rays, neutrons asphalts, paraffins, chemically bondedConvection ceramics)Conduction • Compatible materialsGeochemical changes high conductivityPhase transformations radiation tolerant

' Waterrelocation temperatureresistantRockstresschanges •Heattailoring,t-radiation-inducedchanges fuelaging

geometricdistribution•Chemicalstabilizers•Mechanicalstabilizers

•High-energyradiation(x-ray,7-ray)barriers

Radionuclide release • Stabilizing buffers used as fillers or .Gaseous release packing to control pHIon exchange • Ion-exchange mediaDissolution of waste • Flocculents

Colloidtransport • Stabilizing/encapsulating matrix "Diffusion *PrecipitationagentsPrecipitation •Low-perme_bilitypackingmaterialsAdvection

/

Table I (cont'd)

System Phenomenon/Process Design Features to Enhance or Mitigate' Process

Container degradation * Stabilizer (buffer) to control pHGeneral corrosion/oxidation * Corrosion-resistant metals/alloys

• Galvanic corrosion * Corrosion-aUowance metals/alloysCrevice corrosion * Galvanic couples, sacrificial anodesStress-corrosion cracking * Crack resistant materialsPitting * Single-phase materials, nonmetallicMicrobial attack materials (oxides, composites, graphites)Crack growth * Joint-free cov.struction, smooth surfaces,Dissolution space-minimal reentrant geometriesAlteration * Fuel aging to reduce temr_exatures

• Lower density per unit area of wastepackages to reduce temperatures

• Compatible packing materialRadionuclide retardation * Low-permeability materials

Chemical bonding * Absorbents/adsorbentsMechanical filtering * Emplacement geometry to maximizeSorption matrix captureMatrix capture * Ion-exchange mediaIon exchange/isotope exchange * Chemically reactive materials to bond

nuclides at local sites

...... "--" [ environment -- [ aria_mo_ I -- or,nh,nc,mocnus

• ¥"I-z I ?

[_SJ k cmn_nce wi_ [_• ] _ [ [_6 J Exmnndnof_ture Intorectlons

/ c,:N /@1 // c_._ rn / v. I // c,_ n K / • I _!

+ 4, 4,Collectconcept dsecriptions Document j_ AssemblSccnceptfeaturesdeecdptioninto

I''• , il i ! IIII'_ Ili i ! i i _J_['i I

' '!,',_i_,;i II' I ' _:._:':_::::"'ii I D

Figure8.A tailoredsystemsengineeringprocessto generatepreliminary conceptdescriptions.

I

(2) Defining the operating environment in terms of to the boiling point of water; cold as less than the boilingthe temperature and presence of water. To focus our point of water; dry as the absence of liquid water; and wetefforts and come to closure, we constrained the design as the presence of liquid water. We chose one of these four

" environment to four fields representing conditions at the fields for each iteration. This approach permitted us toboundary between the EBSand the natural barrier system: easily generate concepts that would be compatible with thehot and dry, cold and dry, cold and wet, and hot and wet. varying conditions that the engineered barrier could seeWe defined hot as,any temperature greater than or equal o;_-: Its expected lifetime.

/

(3) Identifying applicable processes for the given (7) Determining feasibility. We check the feasibility,environment. Examples of these processes include fluid estimate performance, and perform calculations withflow through fractures and matrix; radionuclide simple models. We again refine information needs.retardation through sorption and ion exchange; materialsdegradation through corrosion and microbial attack; and (8) Generatin 8 a records package. For each conceptradionuclide transport through diffusion and dissolution, description, we generate a records package that includesSome of these precesses may not be applicable for an integrated drawing with annotations--e.g., descriptionsparticular environmental fields chosen in the previous of interactions, estimates of performance, preliminarystep. calculations, and judgment calls---and a list of associated

requirements, assumptions, and constraints. We use this

(4) Devising featuzes to mitigate or enhance operable records package to trace design features to higher levels ofprocesses. In this step, we accept or modify the near field functions, requirements, and system descriptions.

and man-made environment, and we define information (9) _hecking for compliance with ali constraints andneeds. For transport processes, we can prevent gas and requi_'ements. We verify that functions, constraints,liquid from reaching the waste; limit entry rate of the gas requirements, and features can be traced through their

' and liquid; limit egre._s rate of the gas and liquid; modify predecessors and parent/child relationships and that nonethe near field and man-made environment to enhance of the higher-level constraints and requirements have beenpositive effects and to mitigate negative effects; and choose overlooked.barriers that limit entry and egress of radionuclides. For

extended life, we can choose materials most resistant to (10) Collecting the preliminary concept descriptionsdegradation; choose materials most comFatible with the for subsequent processing, modification, ranking, andenvironment; add stabilizers to mitigate effects of the selection. Each concept description is reiterated throughenvironment; and modify the environment for the process with modified or new constraints. Eachcompatibility with the materials, concept description is modified for other environmental

fields that were not addressed during the previou_(5) Examining the design featuLres interactions. We iterations. Initial screening rc-',' be done in this step to

examine the interactions of design feature with each other group concept descriptions wtth similar attributes. Thisand with the environment. The features must interact grouping may be helpful in reducing the number ofpositively, and the in situ properties must not compromise concepts to an acceptable number. The level of detail andtheir functions. Any compromise indicates a return to the the duration of the iteration cycles were generally limitedprevious step. We then refine information needs, by available time, cost, and management decisions.

(6) A._sembling the features into an integrated Preliminary Conceptsconcept description. We assemble (synthesize) the featuresand document the ideas by sketching the assembly and

In Figs. 9 through 12, we show four preliminaryannotating the sketch with descriptions and dimensions.concepts that represent diverse ideas, emplacement

Requiran'amts/Constraints _ Processes _ Features

'° "°°Radiation - Shield plug -_-----'-'_--_'_ /M_

shielding _ffiY/// _' _/A_?_:.¢_:_:.'4::;:_'_._:_:_.:'_._'_:_:_:,'_e_:._:i_.;::>.:_:.::_:::_:¢.:::._4::_:_`_:_.:_:::_;:.:¢::_._1._:_:_.:_:.:_+..:_:;:<_..:_.:.: * • :'.':_ '. ".'.

._........ "...... ×.'..'4::.""-' ",_"- _" "_-'-"-_>_._/-"_,,'>'",+" ×_ "_ "_" - >'_'"_i_""'_::', ..... ., • I- • ." •

;:::_.:-;;:_::_)::,_._:_._/,-,.'_:'-_.._._:__:_-.'_:,!_'._:;_._.'-;-_).:_!_'_._/_.',;.'.':r_<:_i:::_:"::_:::,,_._ _ ".. _ " :.

_:___:.-,,_@_,.:-.,._,,_.,_, .,! _:,,:._N_ ......... _g _,_.,-._......_ I_ _!;I""" ..... :""'..'.-,'.;?"":"":..........'_''_"___............_ _ -<"........................*:':_'.;_._._,*..'. _ .... _:_":':*:,_,':,r.,_::'._,_ .::.¢'_i)::":'.,¢':iL':'::.':::_)::':;

_:::::_:_':_:'-":_:_' *::_::_ "--"_: :_;_;-":_,:::'___i::."_;'._"'_X*-,: "",.-'.".".":':.:'.'";......::_.:.'-::-z::_:._::_::_.:.'.,..:,::.._._._'. ,.a_::,::,*,!....... ::,-:.,'_.z_;_:_-x_,,.,...... -:_;'.-.':_',:.._.'-_._ .,.,.:.._,.:,._:.... .,:....,:.............._:,..,..,..,,_,..,.,._,._,_,.,..-,........_ii_::.-.,,.:._,,,..,_.:._:_,.:.,,_,.,._:::::__:_'_...................

"- ,,.-.,-.__,.,_:i_ n_-_:-,_.,.@_ .-_ __i::: "'_................. ,:.,'4._-....'g_ ,..4,.: .... :........."..........._1.2"_i_!._:-2_'_-:'._........._.-:'-'.'-"_.::'.'.._.-,'.._i,,.....................•"_," ' "_.........._...............;:-'..'-';:o;_._':."...%'_.......t_,':"_ _ -_ ".,._:_......... _............... '_;_'*"'..............._._.UO._,.'._:__*i>:_!.".*.."_;".-:',,_:_(b_:! :_"/':_i_:_!.'._,_._,:_,>>.;:::;;:::;_.<_:::::_-4._:....::>:::>_._w ::;_....,_;:,_,%,._z ...::,×>_::,.::::>.:4".>>;::-!_.'-.'.:;:."::$!:_:2:_/.::_!>.z_._::::::::::::::::::::::::::::_:__:.'::_:;i:,_>;->::4"':2

Figure9._aled boreholecontainerconcept.

Requirements/Constraints _ Processes _ Features

, Unique Metal containerIndentlflcatlon

Figure 10. Ceramic container concept.

Requirements/constraints -- Processes--_ Features

Unique Identlficetlon --- Lid

Radiation shielding -- Shield plug

Design, -- Partial cevltyretrievability liner--

Radiation shielding -- Rock aroundcevlty-

Figure 11. Metal multiwaUed container concept.

geometries, and materials. Figure 9 shows a concept that isostatically pressed at 20,000 psi. The cold-pressedincorporates a sealant pumped into the near field to fill container is then placed in another container made of thin

• fissures. The waste is surrounded by a granulated stainless steel, surrounded by granular TiO2, and hotmechanical stabilizing material that is filled with a liquid isostatically pressed at 30,000 psi and 900°C until the TiO2packing material (cementitious, asphaltic, or other). This is compressed to 99% theoretical density. TiO2 is verydesign is applicable only for vertical emplacements, stable in natural groundwater media and is

thermodynamically stable.Figure 10 shows a concept that is independent of

emplacement geometry. The waste is placed in a sealed Figure II shows a multiwalled metal containerthin-walled metal container, surrounded by a ceramic utilizing galvanic couples for extended life. The wastestabilizing matrix (probably A1203), and then cold form is contained in a copper container placed inside a

Requirements/Constraints --_.- Process-_.Featurea

Unique identllleatlon Lid ...____

Radiation .hl.iding Contain.rh _ _.4M "II Slip CaSt '!till. ." '___'_.... _ " ..'"

iii_:_ .::'"_."_W_'_ _:ii: _'_..... _:"_ _'_---"''""" ""

_:__'_'_":__ _ - " ' - - - -_ ..... /" 02M:_ii_i:.'::'::_i!_!_'_".... .. _:.:<>.:::,:.:.:.:::.::!:z..._,._ ..... ._..: ...... ::'::.__._ .mi: ........ _..__ •

._.:i_.... _ ..............._ _. _._. r_ .... _ -_-:_:_:::' _ .]_ _ ._.. .._,,.,.._.... I_,; ........ . _,.... _/.,l--.-t.--

Removable shielding

_,,_ 0

Lifting feature

_ __Optional drift emplacements

Figure 12.. Drift emplaced cast iron concept.

high-nickel-alloy container that, it,, turn, is placed inside a . Defin/.-------_ .e /k_ __wrought-iron outer container. E;_ch container has walls _ Development ofabout 3 cm thick. _ Probabilistic i I Design

r L _election Factors II [. , , ConoeptsFigure 12 shows a drift-emplaced cast-iron cask into

which individual sealed stainless-steel waste containers "_are placed. The iron cask becomes a corrosion-allowance Sei_-_tion

ofbarrier between the waste and the environment. Leader & Analysts

Requirements Documents I ......

i o, ,ooio,A design-requirements document for each of two or Expertsmore selected concepts will be developed, reviewed, and _ Developmentapproved prior to beginning the Advanced Conceptual / Training I of IDesign phase. Interfaces with other parts of thesystem will l of _ Weightingbe identified.Alidesign assumptionswillbe clearlystated Exports _ Factors

' i /for subsequent validation, k.... [ Refinement

o, I /Ranking and Selection ! Selection Factors

' I /Once the final set of concept descriptions has been ! EIIcitatlon

developed, we plan to use a structured,analytical Probabilities

framework to evaluatethe alternativeconcepts.To be _ .....objective, the selection factors must be relevant to I ooo,-'n.,I ]Container |1 Disturbed- i /requirements; must be broad,ind_:pendent,measurable, _ Materlalsl I Des,on i zoe.Bo._avlor I /_

and understood;and must be differentiatedwithoutbias. _x ] Analyslsi ii) I

We have chosen to use Decision Analysis 5 as our _ Aggregation _ / ,analytical framework. This method, which uses the logic , i

flow shown in Fig. 13, will help us determine how well the I Resolution I--. Application _&relative performances of the alternative concepts can be _ of | _ of |

Disagreements | I Weighting Ipredicted over time and will give us a systematic and ' l_ Factors Idocumented decision about the concepts to be carried intothe next design phase of the waste-management program.Decision Analysis methodology has been used extensivelyin the nuclear industry for evaluating the safety of Figure 13. Logic flow for decision analysis method.

reactors, 6,7 and has been advocated for applications in L any sensitivities must be removed, appropriate,mined geologic disposal of radioactive waste. 8,9 Simila_ recommendations will be made for changing themethods have been proposed for the evaluation of waste- requirements that create the sensitivities.package performance. 10 The method is slightly differentthan most other evaluation methods in that the experts

,_ who influence and refh_e the selection factors are trained in Summaryprobability estimation. We will conduct a preliminary

screening to reduce the number of alternatives to a We have developed several preliminary designmanageable set for detailed evaluation, and the experts concepts for an Engineered Barrier System and wastewill then evaluate that set of alternatives, packages to be used at the proposed Yucca Mountain

repository, and we have described a candidate set ofTat)le 2 lists possible factors that may be used in the factors for selecting among alternative design concepts.

evaluation of alternative concepts. After probabilities have However, we cannot complete the design process until webeen elicited, weighting may be applied to each factor, and gain access to the underground horizon at Yuccatotals obtained to tentatively rank alternative concepts. Mountain.

_owever, to reduce the effects of evaluat_)r bias, the

weighting values may be withheld until after the factors We have much work remaining in the Conceptualhave been scored. Design phase. We must iterate present and future design

concepts to sufficient detail to allow reasonable assessmentIf any sensitivities are discovered for the probability of their performance characteristics. Only then can we

estimates, the factors and weights will be reviewed for begin the ranking and selection processes to narrow thepossible modification, and the impact of relaxing the number of concepts to be carried into the Advanced.requirements that cause the sensitivities will be evaluated. Conceptual Design phase of the Waste Package Plan.

o .

Table 2. Examples of selection factors.

Major Are,_ Description Selection Factor

ContainerDesio-n Provideevaluationthatthe Probabilitythat'proposeddesignwillmeet containmentcan bethe "Substantially predicted for 1000 years.Complete Containment"r_u!_'ement of '.0 CFR60.113A. li

Evaluationofabilityofthe Probabilitythatreleasedesigntomeet ratescan be predictedfrom

requirementsforlimited L000 to10,000years.releasefor1,000to10,000

yearsper10CIR 60.113B.

Assuranceretrievabiiity' Probabilityti'lecontainerrequirementscan be met. can be retrievedup to 50

years.

Assesstheinspectability Probabilitythedesigncan

and assurancethatthe be inspectedanddesignmeetsengineering monitored.requirementafterconstruction.

, , , ,

Assesscompliancewith P'robabiii'tythedesignwillhealthand safety meet radiologicalandregulations, safetyrequirements.

Sch,Klule. Probabili'tythatt_eschedulecan bemet.

.... Cosi.' Probabilitythedesigncan'be constructedwithincost.

Container Materials "Assures the materials ' Probability the materialscorrosion behavior can be corrosion properties can bepredicted, predicted over 10,000

yearsi-

.

l,w

Table 2 (cont'd)

t

Major Area Description Selection Factor

Stability of basic material Probability the materialproperties for 10,000 years, will remain stable during

the emplacement period.Assess potential for Probability of microbialmicrobial corrosion of the corrosion not occurring.container.

Assess the potential Probability of creep and/ormechanical degradation fatigue and/ormechanisms, environmental assisted

cracking and/or hydrogenembrittlement or other

pertinent degradationmechanisms will not occur.

Assure adequate strength Probability that selectedand toughness to bear material will remain strongemplacement and retrieval and tough enough during

loads, retrieval perio d.Assess potential fabri_tion Probability the Material canproblems and their impact be fabricated to the designon the performance of the requirements.container.

Disturbed Zone Prediction of near-field Probability the thermalbehavior over 10,000 years, hydraulic behavior of the

near-field can be accuratelypredicted.

Assess influence of design Probability that the near-(thermal load, SF age, etc.) field will remainon the other selection geochemically predictablefactors, i.e., allow a for 10,000 years.geochemically predictableenvironment.

..... Assess the potential for Probability the container orcontainer-geochemical corrosion products will notinteraction, intera_ with surrounding

materials.

References.... 7' .....Sever al Accident Risks: An Assessment of Five U.S.

1. U.S. Department of Energy, Yucca Mountain Project Nuclear Power Plants, Nuclear Regulatory Commission,Office, Waste Package Plan, YMP/90-62, Las Vegas, NV Washington, D.C., NUREG 1150 (1989).(1990). 8. E.J. Bonano, S. C. Hora, R. L. Keeney, and D. von

2. U.S. Department of Energy, Report to Congress on Winterfeldt, Elicitation and Use of Expert Judgment inReassessment of the Civilian Radioactive Waste Management Performance Assessment for High-Level Radioactive WasteProgram, DOE/RW-0247, Washington D.C. (1989). Repositories, Nuclear Regulatory Commission, Washington,

3. L. J. Jardine and D. W. Short, Using a Systems D.C.,NLrREG/CR-5411 (1990).Engineering Process to Develop Engineered Barrier System 9. M.A. Meyer and J.M. Booker, Eliciting and AnalyzingDesign Concepts, Waste Management 91, Tucson AZ, Expert Judgement, A Practical Guide, Nuclear RegulatoryFebruary 24--28, 1991. Commission, Washington, D.C., NUREG/CR-5242 (1990).

Fabrycky, Systems 10. Y.-T. Wu, A. G. Journel, L. R. Abramson, and P. K.4. B. C. Blanchard and W. ,.

Engineering and Analysis (Prentice-Hall, Englewood Cliffs, Nair, Uncertainty Evaluation Methods for Waste PackageNJ, 1990). Performance Assessment, Nuclear Regulatory Commission,

5. R. Keeney and H. Raiffa, Decisions with Multiple Washington, D.C., NUREG/CR-5639 (199l).Objectives: Preferences and Value Tradeoffs (John Wiley & 11. H. Manaktala and C. Interrante, Technical

Sons, New York,1976). Considerations for Evaluating Substantially Complete- ,,,: .... o1_, "Elicitin_: Containment of High-Level Waste Within the Waste Package,6. R. Keeney and u. von ,, ........... _

Probabilities from Experts it, Complex Problems," IEEE Nuclear Regulatory Commission, W_shington, D.C.,_ Trans. Eng. Management 38, 191-'2D1 (1991). NUREG/CR-5638 (1990).