Title 40 CFR Part 191 Subparts B and C Compliance Recertification Application for the Waste Isolation Pilot Plant Appendix SOTERM-2009 Actinide Chemistry Source Term United States Department of Energy Waste Isolation Pilot Plant Carlsbad Field Office Carlsbad, New Mexico Appendix SOTERM-2009 Actinide Chemistry Source Term Title 40 CFR Part 191 Subparts B and C Compliance Recertification Application 2009 Table of Contents SOTERM-1.0 Introduction ............................................................................................SOTERM-1 SOTERM-2.0 Expected WIPP Repository Conditions, Chemistry, and Processes ......SOTERM-3 SOTERM-2.1 Ambient Geochemical Conditions .....................................................SOTERM-3 SOTERM-2.2 Repository Conditions........................................................................SOTERM-3 SOTERM-2.2.1 Repository Pressure.....................................................................SOTERM-5 SOTERM-2.2.2 Repository Temperature..............................................................SOTERM-5 SOTERM-2.2.3 Water Content and Relative Humidity ........................................SOTERM-5 SOTERM-2.2.4 Minimum Repository Brine Volume...........................................SOTERM-6 SOTERM-2.2.5 DRZ.............................................................................................SOTERM-7 SOTERM-2.3 Repository Chemistry.........................................................................SOTERM-7 SOTERM-2.3.1 WIPP Brine..................................................................................SOTERM-7 SOTERM-2.3.2 Brine pH and pH Buffering.........................................................SOTERM-9 SOTERM-2.3.3 Selected MgO Chemistry and Reactions...................................SOTERM-13 SOTERM-2.3.4 Iron Chemistry and Corrosion...................................................SOTERM-14 SOTERM-2.3.5 Chemistry of Lead in the WIPP ................................................SOTERM-16 SOTERM-2.3.6 Organic Chelating Agents .........................................................SOTERM-17 SOTERM-2.3.7 CPR in WIPP Waste..................................................................SOTERM-19 SOTERM-2.4 Important Postemplacement Processes ............................................SOTERM-19 SOTERM-2.4.1 Microbial Effects in the WIPP ..................................................SOTERM-19 SOTERM-2.4.2 Radiolysis Effects in the WIPP .................................................SOTERM-23 SOTERM-2.5 Changes in WIPP Conditions since the CRA-2004 and the CRA- 2004 PABC ......................................................................................................SOTERM-27 SOTERM-3.0 WIPP-Relevant Actinide Chemistry ....................................................SOTERM-29 SOTERM-3.1 Actinide Inventory in the WIPP .......................................................SOTERM-30 SOTERM-3.2 Thorium Chemistry ..........................................................................SOTERM-33 SOTERM-3.2.1 Thorium Environmental Chemistry...........................................SOTERM-33 SOTERM-3.2.2 WIPP-Specific Results since the CRA-2004 and the CRA- 2004 PABC..................................................................................................SOTERM-35 SOTERM-3.3 Uranium Chemistry ..........................................................................SOTERM-37 SOTERM-3.3.1 Uranium Environmental Chemistry ..........................................SOTERM-38 SOTERM-3.3.2 WIPP-Specific Results since the CRA-2004 and the CRA- 2004 PABC..................................................................................................SOTERM-45 SOTERM-3.4 Neptunium Chemistry ......................................................................SOTERM-47 SOTERM-3.4.1 Neptunium Environmental Chemistry.......................................SOTERM-47 SOTERM-3.4.2 WIPP-Specific Results since the CRA-2004 and the CRA- 2004 PABC..................................................................................................SOTERM-48 SOTERM-3.5 Plutonium Chemistry........................................................................SOTERM-48 SOTERM-3.5.1 Plutonium Environmental Chemistry........................................SOTERM-49 SOTERM-3.5.2 WIPP-Specific Results since the CRA-2004 and the CRA- 2004 PABC..................................................................................................SOTERM-52 SOTERM-3.6 Americium and Curium Chemistry ..................................................SOTERM-54 SOTERM-3.6.1 Americium and Curium Environmental Chemistry ..................SOTERM-55 SOTERM-3.6.2 WIPP-Specific Results since the CRA-2004 and the CRA- 2004 PABC..................................................................................................SOTERM-58 SOTERM-3.7 Complexation of Actinides by WIPP Organic Chelating Agents ....SOTERM-60 DOE/WIPP-09-3424 SOTERM-iii Appendix SOTERM-2009 Title 40 CFR Part 191 Subparts B and C Compliance Recertification Application 2009 SOTERM-3.8 Actinide Colloids..............................................................................SOTERM-60 SOTERM-3.8.1 Actinide Colloids in the Environment.......................................SOTERM-61 SOTERM-3.8.2 WIPP-Specific Results since the CRA-2004 PABC .................SOTERM-63 SOTERM-3.9 Changes in Actinide Speciation Information since the CRA-2004 and the CRA-2004 PABC................................................................................SOTERM-63 SOTERM-4.0 Calculation of the WIPP Actinide Source Term ..................................SOTERM-66 SOTERM-4.1 Overview of WIPP Approach to Calculate Actinide Solubilities ....SOTERM-67 SOTERM-4.2 Use of Oxidation-State-Invariant Analogs.......................................SOTERM-67 SOTERM-4.3 Actinide Inventory and Oxidation State Distribution in the WIPP..SOTERM-69 SOTERM-4.4 Actinide Speciation Reactions Used in the FMT Model..................SOTERM-70 SOTERM-4.4.1 The III Actinides: Pu(III), Am(III), Cm(III) .............................SOTERM-71 SOTERM-4.4.2 The IV Actinides: Th(IV), U(IV), Pu(IV), Np(IV) ...................SOTERM-71 SOTERM-4.4.3 The V Actinides: Np(V)...........................................................SOTERM-74 SOTERM-4.4.4 The VI Actinides: U(VI) ...........................................................SOTERM-75 SOTERM-4.5 Calculations of Actinide Solubility Using the FMT Computer Code .................................................................................................................SOTERM-76 SOTERM-4.5.1 Pitzer Approach for High-Ionic-Strength Brines ......................SOTERM-76 SOTERM-4.5.2 Calculated Actinide Solubilities................................................SOTERM-77 SOTERM-4.6 Calculation of the Effects of Organic Ligands on Actinide Solubility..........................................................................................................SOTERM-79 SOTERM-4.7 Calculation of Colloidal Contribution to Actinide Solution Concentrations .................................................................................................SOTERM-80 SOTERM-5.0 Use of the Actinide Source Term in PA...............................................SOTERM-83 SOTERM-5.1 Simplifications..................................................................................SOTERM-83 SOTERM-5.1.1 Elements and Isotopes Modeled................................................SOTERM-83 SOTERM-5.1.2 Use of Brine End Members.......................................................SOTERM-84 SOTERM-5.1.3 Sampling of Uncertain Parameters............................................SOTERM-85 SOTERM-5.1.4 Combining the Transport of Dissolved and Colloidal Species in the Salado...................................................................................SOTERM-88 SOTERM-5.2 Construction of the Source Term .....................................................SOTERM-88 SOTERM-5.3 Example Calculation of Actinide Solubility ....................................SOTERM-91 SOTERM-5.4 Calculated Dissolved, Colloidal, and Total Actinide Solubilities....SOTERM-91 SOTERM-6.0 References ............................................................................................SOTERM-94 List of Figures Figure SOTERM-1. Molal H+ Concentration Measured as a Function of Time During the Solubility Experiments in 2.67 and 5.15 m MgCl2 Solution ........................................................................SOTERM-12 Figure SOTERM-2. Expected Dominant Actinide Oxidation States as a Function of the Standard Reduction Potential at pH = 7 in Water That is in Equilibrium With Atmospheric CO2.............SOTERM-23 Figure SOTERM-3. NaCl Brine Radiolysis Species and Suggested Mechanism of Production............................................................................SOTERM-25 Figure SOTERM-4. Radiolytic Formation of Hypochlorite Ion in Solutions of Various NaCl Concentrations at a Constant Alpha Activity DOE/WIPP-09-3424 SOTERM-iv Appendix SOTERM-2009 Title 40 CFR Part 191 Subparts B and C Compliance Recertification Application 2009 of 37 GBq/L at pH~12 (Based on Data in Kelm, Pashalidis, and Kim 1999) .........................................................................SOTERM-25 Figure SOTERM-5. Solubility of Amorphous Th(IV) Oxyhydroxide as a Function of Carbonate Concentration in 5 M for pH = 2–8 (A) and pH – 8–13.5 (B)..........................................................SOTERM-36 Figure SOTERM-6. Solubility of Th(OH)4(am)