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U N C L A S S I F I E D


Operated by the Los Alamos National Security, LLC for the DOE/NNSA



Donald ReedActinide Chemistry and Repository Science Program

Repository Science and Operations (RSO)Los Alamos National Laboratory

Marcus AltmaierRadiochemistry Division

Karlsruhe institute of Technology, Institute for Nuclear Waste Disposal

7th US/German Workshop on Salt Repository Research, Design, and Operation

Washington DC, September 6-9, 2016

Synergies Between Actinide/Brine Chemistry and Geotechnical Properties

in a Salt Repository Concept“Chemistry/Thermodynamic Database

Summary”

LA-UR-16-26635LA-UR 16- 21447LA-UR 15-27122




Overview

Role/rationale for the Study of Actinide/Brine Systems in a Salt Repository Concept

Repository Design and Geotechnical Issues that Impact Actinide/brine Chemistryo Brine Availability and Flow (Obvious)o Redox-Active Waste/Barrier Componento Strategy for Predictable/Favorable Chemistry

Updates on Actinide/Brine Chemistry Activitieso NEA Pitzer SOAR and Salt Clubo ABC Salt (V) Workshop




Salt Repository Concept: Actinide View

Safety case is most reliant on the geologic isolation expected Self-sealing in < 200 years Little/no interconnected groundwater flow Low reliance on container/canister integrity in PA Performance is somewhat independent of the

wasteform/composition Favorable thermodynamics and chemistry can

be achieved Reducing conditions due to limited oxygen

availability and “designed” reactivity of waste package

Reactive redox control can be used to establish Eh

pH can be “engineered” to be mildly alkaline No meaningful expectation of transport by diffusion

or colloidal processes




Actinide Release Scenario and Calculated DBR ReleaseAppendix PA-2014

• “DBR” is dissolved brine release• Combined E1E2 release is

potentially highest release (but still low overall probability)

• In integrated release CCDF curves, DBR release is most important in the lower probability/high release part of the curve

E1E2 WIPP Deep Drilling Scenario for Release




Rationale for Actinide/Brine Chemistry in a Salt Repository Concept

“Regulatory” reason (WIPP example): We are required to address all “low” probability scenarios in the safety case – so it is a regulatory-driven requirement.

“Sociopolitical” reason: We should be able to explain what is likely to happen to the actinides/radionuclides at all times (before, during and after emplacement) for all repository scenarios. • We need to show that the salt repository concept will

work sufficiently well even if we are wrong about how the geology will function and what future societies may do.

• Site inundation with brine, regardless of how this occurs, likely defines the worse case scenarios.




Should the Salt Repository Concept be Considered for HLW and SF Nuclear Waste?

Current operational issues are an obstacle but the overall long-term safety case is not significantly impacted: WIPP fire and release incident (it was said there would never be

any release from the WIPP) Asse brine seepage issues (it was said there would never be

water/brine in a salt repository) HLW and SF will require that the overall safety case

address the following (beyond TRU or LLW): Much of the WIPP safety case does apply – so WIPP approach is a

good but not sufficient template! Much greater and more diverse radionuclide inventory – so more

than Pu/Am is needed Higher temperature, so it is needed to show that this does not alter

overall performance (leads to drier repository) Higher radiation levels, so this needs to be accounted for more

extensively




Brine Availability and Flow (Obvious)

Geotechnical issues that link to the availability, movement, and composition of water/brine are critical in defining the geochemical conditions:

Temperature and pressure Self-sealing and healing of fractured salt due to the waste

emplacement process Water movement within and out/into the repository Intrusion scenarios and conceptual approach




Mobile Actinide/Radionuclide Concentration

In the WIPP concept, colloidal species contribute to the source term in dissolved brine release (DBR) release scenarios

• Colloidal transport is not a significant issue• Structure and physical properties are not important

solubility of the actinide that reflects pH, inorganic/organic complexation

Actinide concentration added due to colloidal species

Solubility

MineralIntrinsic

MicrobialHumic

Mobile actinide concentration(actinide source term)




Design Input:Favorable Thermodynamics and Importance of

Reducing Conditions

Established by repository design/conceptual model– Self-sealing properties of salt

– Microbial ecology and activity

– Corrosion/waste constituent reactions

Favorable thermodynamics provides higher assurance and reduced uncertainty with respect to repository performance– Actinide speciation and solubility is lowered leading to greater

immobilization

– Overall source term description is simplified.




Plutonium Speciation (Altmaier/Neck – INE)Best Example of Current “Peer” view

Provided curtesy of Marcus Altmaier (KIT/INE). This shows the current view of plutonium speciation for all possible conditions. For the WIPP, only the Pu(III) and Pu(IV) species apply (left side of the Figure).

Altmaier, M., and H. Geckeis, “Plutonium and Actinide Chemistry in Saline Solutions,” Actinide Research Quarterly, 2011 (2), p. 29-32.




Pu-Fe Interaction Studies~ 10 year Data

• Fe2+ is formed from the corrosion of Fe(0)• Colloidal distribution is noted in the carbonate-borate pH area




Possible Oxidation States for Actinides Most likely actinide oxidation states as a function of microbial

activity and the corresponding biogeochemical zone

Actinide Biogeochemical

Zone 89

Ac

90

Th

91

Pa

92

U

93

Np

94

Pu

95

Am

96

Cm

Oxidation States Observed under all Conditions

3 (3)

4

(3)

4

5

3

4

5

6

3

4

5 6

7

3

4 5

6

(7)

3 4

5

6

7?

3 4

5?

6?

Oxic Conditions in Groundwater

3 4 5 6

5

4

5

3 (5)

3

Microbially Active Suboxic Zone

3 4 4 4

6

4 5

3

4

3 3

Microbially Active Anaerobic Zone

3 4 4 4 (3)

4

3

4

3 3

( ) = unstable, ? = claimed but unsubstantiated, bold = most stable




Design Input:Brine Chemistry that Favors Low Actinide Solubility

Chemistry is defined by reaction of the brine with the waste and waste package components (so this can be controlled by design)

Predictability is key/importantMildly alkaline conditions are ideal (pH 9-11)Provide assurance and reduce uncertainty with respect

to repository performance




We need a good/comprehensive model for actinide solubility/concentration

Current repository and site specific thermodynamic data applications rely on estimations, approximations and simplifications done in a way to maintain conservatism with the model.

Simplification can be easier to implement and more explainable to the regulator (therefore better defended)

Circumvents data quality issues (that prevent its inclusion in the NEA databases)

Account for site-specific gaps in data There are specific processes that are difficult to describe in

thermodynamic terms Ultimately the driver for this activity is that it is the right thing to do

scientifically (sociopolitical)




NEA Activities: Actinide and Brine Chemistry

NEA TDB Pitzer State of the Art Report• Literature survey to assess extent and completeness of

available data• Identification of data gaps• Recommend consistency in data collection and analysisM. Altmaier1, D. Costa2, A. Felmy3, H. Moog4, R. Pabalan5, M. Ragoussi2, D. T. Reed6, W. Runde7, P. Thakur8, W. Voigt9

1) KIT-INE, 2) OECD NEA, 3) WSU, 4) GRS, 5) NWTRB, 6) LANL-CBFO, 7) LANL, 8) CEMRC, 9) TUBAF

NEA Salt Club• Integrated effort to establish a unified and self

consistent set of Pitzer parameter and modeling approach




Specific Issues with High Ionic-Strength Thermodynamic data

There is no rigorously thermodynamic approach available, so the Pitzer semi-empirical approach is used

Literature assessment through the NEA is also in progress (State of the Art Report): Number of Pitzer-evaluated binary and

ternary system references sorted by oxidation state. (Altmaier/Fellhauer)

several data gaps exist in current database applications

significant lack of ternary species significant lack of temperature-

variable data for the radionuclide/ actinide data set




Santa Fe NM, April 2013Proceedings of the Third

International Workshop on Actinide and Brine Chemistry in a

Salt-Based Repository (ABC-Salt III)

Carlsbad NM, September 2010Proceedings of the

International Workshop on Actinide and Brine Chemistry

in a Salt-Based Repository (ABC-Salt)

Karlsruhe, November 2011Proceedings of the International

Workshops ABC-Salt (II) and HiTAC 2011

ABC Salt (IV) was held in Heidelberg, April 2015 proceeding under preparation

Actinide and Brine Chemistry in a Salt-Based Repository(ABC Salt) Workshop Series




First Announcement: ABC Salt VActinide and Brine Chemistry in a Salt Repository

Workshop (V) March 26-28, 2017. Convention Center, Ruidoso NM, USA

Workshop Topics for High Ionic-strength Systems• Brine evolution• Brine chemistry• Actinide chemistry • Temperature effects• Microbial effects• Radiolysis • Modeling studies and related

thermodynamic databases

Two-page abstract submittal for each presentation will be required and posters are welcome/ encouraged

Meeting timeline and organizationDecember 2016 Second announcement

and call for abstractsJanuary 2017 Letters of invitation sentMarch 2017 Registration deadline

and tentative agendaRegistration Tentatively ~ $150 Fee: Includes breaks, 3

lunches and one dinnerHotel: A government rate of ~ $100/night is available to meeting participants at the Ruidoso Eleganté hotel, which is co-located with the Ruidoso Convention Center.

This is the fifth in a series of workshops that is centered on actinide and brine chemistrypertaining to the permanent disposal of nuclear waste in a salt repository. Topics generallyrelevant for the description of aqueous chemistry at intermediate to high ionic-strength conditionsare welcome. Emphases in this workshop are an update of ongoing high ionic-strength researchactivities, the extension of this chemistry to elevated temperatures, brine evolution andinteractions, and a special focus on the coordination and issues of efforts to develop a Pitzer-basedmodeling of this chemistry. All who have interest in this high ionic-strength chemistry are invitedto attend and participate in this workshop. A tour of the WIPP facility may be offered onThursday (March 30) after the workshop if there is sufficient interest.

Co-organized by Los Alamos and KIT/INE

ContactsLos Alamos: Don Reed [email protected] 575-234-5559KIT/INE: Marcus Altmaier [email protected] +49 721 608 22592

SponsorshipCEMRC, WIPP/DOE, BMWi, and NEA

Schedule:• First Announcement already sent (~ 1 month ago)• December 2016 – second announcement• January 2017 – letters of invitation sent/abstracts

due• March 2017 – registration and program

Location: Ruidoso New Mexico – USA• Central New Mexico, ~ 2 hours from Carlsbad,

~1 hour from Roswell NM, ~ 1.5 hours from El Paso Texas

• Ruidoso convention center (meeting location)• Meeting/presentation room for ~ 60-70

attendees, co-located room for posters/breaks

• Eleganté hotel – co-located with the convention center

Actinide and Brine Chemistry in a Salt Repository Workshop (ABC Salt V) – March 2017




Brine evolution Brine chemistry Actinide chemistry Temperature effects Microbial effects Radiolysis Modeling studies and related thermodynamic databases

Two-page abstract submittal for each presentation will be required and posters are welcome/encouraged

Workshop Topics: ABC Salt (V)Ruidoso, New Mexico, USA

March 26-28, 2017Contacts: Marcus Altmaier or Don Reed




EXTRA




Research Needs/Simplifications for the HLW/SF Case

Radionuclide and Waste Inventory:• Most actinides, fission products need consideration (broader

assessment is needed since will not be excluded by inventory) • Likely much lower organic content, possibly oxyanions as well• Container material and engineered barrier are not specifiedRedox Control:• Reactive control needed, if Fe, this needs to be demonstrated to

work over the temperature range• Higher radiolysis may preclude the lower Eh’s observed in the

WIPP case – this leads to broader assumptions about oxidation state distributions

Microbial Issues:• These dominate WIPP engineering decisions, but are likely a non-

factor in the near-field (rad levels, temperature, no water)




Research Needs/Simplifications for the HLW/SF Case - Continued

Radionuclide Modeling (Solubility and Speciation): Need to define the source term is still dominated by the low-probability

intrusion scenario (analogous to WIPP) General update of the Pitzer model will be needed (more radionuclides,

significant new Pitzer data available) Greater realism and less conservatism is needed:

• Np(IV) or U(IV) for An(IV) – ie. away from Th(IV)• Higher reliance on hydrolytic speciation and oxyhydroxide solids• Emphasis on inorganic rather than organic complexation (most of

organic issue in the WIPP project goes away) Little to no Pitzer data as a function of temperature




Pu(V/VI) Reduction by Lower-Valent Fe in Brine(with Pu-242)

~ 3-monthAnalyses - all Pu(IV)

~ 6-year Analyses – mostly Pu(III)

XANES analysis performed at the APS, courtesy of Dan Olive and Jeff Terry (IIT)




Pu solubility under reducing conditions in MgCl2 brines

-11

-10

-9

-8

-7

-6

-5

-4

7,5 8,0 8,5 9,0 9,5

- log H+ / molal

log [Pu] / molar

det.lim.

Pu(IV): Pu(OH)4(aq)

Pu(III) from oversaturation, carbonate controlled by Mg-OH-Cl-CO3 phase (Pu(III) in solution, XANES: Pu(III) solid (!)

Pu(III) from oversaturation, carbonate freePu(III) in solution, XANES: Pu(IV) solid

PuO2+x(s) undersaturation, carbonate freePu(III) in solution, Pu(IV) solid

(4 – 582 d)

18020 18040 18060 18080 18100 181200,0

0,4

0,8

1,2

1,6

2,0

PuIIIaq

PuIVaq

PuVIaq

norm

. abs

orpt

ion

[a.u

.]energy [eV]

Pu in 3.5 M MgCl2 + carbonate

3.5 M MgCl2 + Fe + Mg-OH-Cl-(CO3)

Stabilization of Pu(III) solid phases under specific reducing conditions !

Provided curtesy of Marcus Altmaier (KIT/INE). All these data were collected using Pu-242. The different shapes in each color in the Figure on the left represent different time samplings of the same solution (see color coding below).

Altmaier, M., and H. Geckeis, “Plutonium and Actinide Chemistry in Saline Solutions,” Actinide Research Quarterly, 2011 (2), p. 29-32.




Approach to Establish “Mobile” Actinide Concentrations in the WIPP

Assess and track actinide inventory Pu, Am, Cm, U, and Th are potentially important Cm and Np is eliminated as a consideration Available chelating/complexing ligands

Assign oxidation state distribution by expert opinion Built-in conservatism Fe/microbially-induced redox environment that is reducing Support with WIPP-specific data

Establish effective solution concentration Model/measure actinide solubilities using redox-invariant analogs Account for colloidal contribution by process-specific enhancement

factors: intrinsic, bio, inorganic, HA Assign an uncertainty distribution based on literature data review




Summary of Observations: Thorium Brine System

Dissolved species

Nano-filterable species

~Fast Preferentially sorbed (bio, MgO, Fe)

Solid Phase

~slow Influenced by: brine composition carbonate organic complexation

A similar mechanism was proposed in Altmaier, Neck, Fanghanel. Radiochimica Acta 92(9-11), 537-543 (2004).




Phylogenetic tree constructed from WQSP-1 and WQSP-3 16S rRNA encoding sequences retrieved from all samples (raw groundwater = direct (Dir); Aer, IR, and transitional (T))). Tree is rooted to Halorubrum vacuolatum as an outgroup.

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