The Solubility of Actinides in the Near-Field

Ewart, F.T.; Howse, R. M.; Thomason, H. P.; Cross, J E

doi:10.1557/proc-50-701

Cited by 15 publications

(14 citation statements)

References 8 publications

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“…The pH of the resulting mixtures was adjusted with sodium hydroxide or hydrochloric acid. The measured redox potential in the americium experiments was 200 mV (Ewart et al 1986). Aliquots of the equilibrated mixtures were taken and filtered using the technique of Rai (1984).…”

Section: Published Solubility Datamentioning

confidence: 98%

“…Ewart et al (1986Ewart et al ( , 1992 experimentally determined the concentrations of dissolved americium resulting from the equilibration of cement-equilibrated waters that were oversaturated with dissolved Anrn. Values estimated from data reported graphically by Ewart et al (1992, Figure 6) are plotted as filled circles in Figure 4.1 for comparison to the values calculated in our study by computer modeling.…”

Section: Published Solubility Datamentioning

confidence: 99%

“…Their conceptual model involved the use of two solubility-controlling solids to match their measured concentrations of dissolved americium. The model included AmOHCO, and Am(OH), as solubility controls for dissolved americium for the pH ranges from 7 to 9 and 9 to 13, respectively (Ewart et al 1986(Ewart et al , 1992. The combination of solubility controls used by Ewart et al provided a reasonable match to the trend of their measured americium concentrations.…”

Section: --mentioning

confidence: 99%

“…The experiments of Ewart et al (1986Ewart et al ( , 1992 involved the addition of neptunium chloride solutions to cement equilibrated waters in a controlled atmosphere chamber with low CO, contents. Sufficient neptunium solution was added to obtain initial concentrations of dissolved neptunium of 10" M and 3 x lW7 M in the Np V (Ewart et al 1986) and Np N experiments, respectively These initial concentrations are plotted as thin dotted and dash-dotted lines in Figure 4.2.…”

Section: Published Solubility Datamentioning

confidence: 99%

“…Sufficient neptunium solution was added to obtain initial concentrations of dissolved neptunium of 10" M and 3 x lW7 M in the Np V (Ewart et al 1986) and Np N experiments, respectively These initial concentrations are plotted as thin dotted and dash-dotted lines in Figure 4.2. The pH of the resulting mixtures was adjusted with sodium hydroxide or hydrochloric acid.…”

Section: Published Solubility Datamentioning

confidence: 99%

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Effects on radionuclide concentrations by cement/ground-water interactions in support of performance assessment of low-level radioactive waste disposal facilities

Krupka¹,

Serne²

1998

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C o p k r o f h b r t r y~m d r t n d v d r u n d h 8~m m r h t h . N R C~~r AbstractThe U.S. Nuclear Regulatory Commission (NRC) is developing a technical position document that provides guidance regarding the performance assessment of low-level radioactive waste (LLW) disposal facilities. This guidance includes considerations associated with the chemical environment of the vault disposal system and the effects this system may have on the release and mobility of radionuclides. Because the disposal system will contain cementitious materials as structural, waste form, andor bacld'ill materials, the geochemical properties of pore waters buffered by reactions with cement will be very different from those waters associated with the local soil and geology. This environment therefore needs to be considered within the source term calculations if credit is taken for solubility limits andor distribution coefficients for -dissolved radionuclide concentrqtions within disposal units. Geochemical modeling may be used to assess potential chemical conditions in concrete vault disposal units and associated effects on aqueous speciation, solubilities, and sorption of radionuclides that are released from the waste form.In support of NRC7s development of this technical position, two literature reviews were done on information related to the chemical environments associated with the interaction of water with cementitious materials. One review was conducted on methods and associated solid-phase assemblages used to model the composition of pore water resulting from reaction with cementitious materials used in a disposal vault. This literature review also included related information on experimental studies of cemendwater systems, natural analogue studies of cement and concrete, and radionuclide solubilities experimentally determined in cement pore fluids.Based on the results of .this review, geochemical modeling was used to demonstrate the calculation of conservative maximum concentrations for dissolved americium, neptunium, nickel, plutonium, radium, strontium, thorium, and uranium with respect to key geochemical input parameters for two ground-water environments associated with the disposal system. These environments include 1) a cement buffered system, wherein the leachate pH is controlled at values above 10 by the effective buffering capacity of the concrete; and 2) a ground-water buffered system, wherein the leachate pH and related solution parameters are dominated by the local ground-water system.Another literature review was completed on the available data for the sorption potential of selected LLW radionuclides onto "fresh" cement/concretewhere the expected pH of the cement pore waters will equal or exceed 10. The review included data for the radionuclides americium, inorganic carbon, chlorine, iodine, lanthanide elements, niobium, nickel, neptunium, plutonium, radium, strontium, technetium, thorium, and uranium. Based on information gleaned from the literature, a database was developed of preferred minimum distribution coeff...

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Section: Published Solubility Datamentioning

confidence: 98%