Interactions of Ni and Ca at the calcite-solution interface

Torbjörn Carlsson, Hannu Aalto

Research output: Book/ReportReport

Abstract

The performance assessment of repositories for spent nuclear fuel need, among other things, data describing the solubilities of radionuclides in the near field and far field. The solubility limits are often used in order to estimate the maximum concentrations of radionuclides during their possible transport to the biosphere. The solubilities used are mostly the individual solubilities for pure solids of the actual radionuclides. This way of using solubility limits represents a conservative performance assessment where the estimated nuclide concentrations are unrealistically high. This is acceptable from a performance assessment point of view but very unsatisfactory for an optimal design of the repository. In order to make the assessment more realistic, coprecipitation and solid solution formation should be taken into account. Only solids which are, in geological terms, formed in fast reactions need to be considered, which in practice restricts the number of radionuclide scavengers to calcite and iron(III)oxihydroxide. This work focuses on the Ni coprecipitation with calcite. The systems were studied under anoxic conditions and consisted of calcite-saturated 0.05 M NaCl solutions in equilibrium with synthetic calcite. The solutions were initially spiked with 63Ni and 45Ca and the concentrations of these elements were determined using liquid scintillation counting. The Ni coprecipitation was mainly governed by the calcite recrystallization. The results show the extent to which these processes occurred during a 42-day period. Our results indicate that the value of the conditional solubility product for the coprecipitated Ni is at least 4 - 5 orders of magnitude lower than the individual solubility product for NiCO3, and thus a corresponding decrease in the solubility limit for Ni.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages24
ISBN (Print)951-38-4988-0
Publication statusPublished - 1996
MoE publication typeNot Eligible

Publication series

SeriesVTT Tiedotteita - Meddelanden - Research Notes
Number1793
ISSN1235-0605

Fingerprint

solubility
calcite
radionuclide
performance assessment
repository
scavenger
solid solution
anoxic conditions
biosphere
iron
liquid

Keywords

  • radioactive wastes
  • nuclear fuels
  • storage
  • design
  • radioactive isotopes
  • solubility
  • assessments
  • solid solutions
  • environmental effects
  • environmental protection
  • nickel
  • calcium
  • interactions
  • calcite
  • solutions

Cite this

Carlsson, T., & Aalto, H. (1996). Interactions of Ni and Ca at the calcite-solution interface. Espoo: VTT Technical Research Centre of Finland. VTT Tiedotteita - Meddelanden - Research Notes, No. 1793
Carlsson, Torbjörn ; Aalto, Hannu. / Interactions of Ni and Ca at the calcite-solution interface. Espoo : VTT Technical Research Centre of Finland, 1996. 24 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1793).
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Carlsson, T & Aalto, H 1996, Interactions of Ni and Ca at the calcite-solution interface. VTT Tiedotteita - Meddelanden - Research Notes, no. 1793, VTT Technical Research Centre of Finland, Espoo.

Interactions of Ni and Ca at the calcite-solution interface. / Carlsson, Torbjörn; Aalto, Hannu.

Espoo : VTT Technical Research Centre of Finland, 1996. 24 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1793).

Research output: Book/ReportReport

TY - BOOK

T1 - Interactions of Ni and Ca at the calcite-solution interface

AU - Carlsson, Torbjörn

AU - Aalto, Hannu

PY - 1996

Y1 - 1996

N2 - The performance assessment of repositories for spent nuclear fuel need, among other things, data describing the solubilities of radionuclides in the near field and far field. The solubility limits are often used in order to estimate the maximum concentrations of radionuclides during their possible transport to the biosphere. The solubilities used are mostly the individual solubilities for pure solids of the actual radionuclides. This way of using solubility limits represents a conservative performance assessment where the estimated nuclide concentrations are unrealistically high. This is acceptable from a performance assessment point of view but very unsatisfactory for an optimal design of the repository. In order to make the assessment more realistic, coprecipitation and solid solution formation should be taken into account. Only solids which are, in geological terms, formed in fast reactions need to be considered, which in practice restricts the number of radionuclide scavengers to calcite and iron(III)oxihydroxide. This work focuses on the Ni coprecipitation with calcite. The systems were studied under anoxic conditions and consisted of calcite-saturated 0.05 M NaCl solutions in equilibrium with synthetic calcite. The solutions were initially spiked with 63Ni and 45Ca and the concentrations of these elements were determined using liquid scintillation counting. The Ni coprecipitation was mainly governed by the calcite recrystallization. The results show the extent to which these processes occurred during a 42-day period. Our results indicate that the value of the conditional solubility product for the coprecipitated Ni is at least 4 - 5 orders of magnitude lower than the individual solubility product for NiCO3, and thus a corresponding decrease in the solubility limit for Ni.

AB - The performance assessment of repositories for spent nuclear fuel need, among other things, data describing the solubilities of radionuclides in the near field and far field. The solubility limits are often used in order to estimate the maximum concentrations of radionuclides during their possible transport to the biosphere. The solubilities used are mostly the individual solubilities for pure solids of the actual radionuclides. This way of using solubility limits represents a conservative performance assessment where the estimated nuclide concentrations are unrealistically high. This is acceptable from a performance assessment point of view but very unsatisfactory for an optimal design of the repository. In order to make the assessment more realistic, coprecipitation and solid solution formation should be taken into account. Only solids which are, in geological terms, formed in fast reactions need to be considered, which in practice restricts the number of radionuclide scavengers to calcite and iron(III)oxihydroxide. This work focuses on the Ni coprecipitation with calcite. The systems were studied under anoxic conditions and consisted of calcite-saturated 0.05 M NaCl solutions in equilibrium with synthetic calcite. The solutions were initially spiked with 63Ni and 45Ca and the concentrations of these elements were determined using liquid scintillation counting. The Ni coprecipitation was mainly governed by the calcite recrystallization. The results show the extent to which these processes occurred during a 42-day period. Our results indicate that the value of the conditional solubility product for the coprecipitated Ni is at least 4 - 5 orders of magnitude lower than the individual solubility product for NiCO3, and thus a corresponding decrease in the solubility limit for Ni.

KW - radioactive wastes

KW - nuclear fuels

KW - storage

KW - design

KW - radioactive isotopes

KW - solubility

KW - assessments

KW - solid solutions

KW - environmental effects

KW - environmental protection

KW - nickel

KW - calcium

KW - interactions

KW - calcite

KW - solutions

M3 - Report

SN - 951-38-4988-0

T3 - VTT Tiedotteita - Meddelanden - Research Notes

BT - Interactions of Ni and Ca at the calcite-solution interface

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Carlsson T, Aalto H. Interactions of Ni and Ca at the calcite-solution interface. Espoo: VTT Technical Research Centre of Finland, 1996. 24 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1793).