Matrix diffusion model - in situ tests using natural analogues: Dissertation

Research output: ThesisDissertationCollection of Articles

6 Citations (Scopus)

Abstract

Matrix diffusion is an important retarding and dispersing mechanism for substances carried by groundwater in fractured bedrock. Natural analogues provide, unlike laboratory or field experiments, a possibility to test the model of matrix diffusion in situ over long periods of time. This thesis documents quantitative model tests against in situ observations, done to support modelling of matrix diffusion in performance assessments of nuclear waste repositories, which must cover long, even geological time periods. A model testing methodology was developed by combining measurements of long-lived natural decay chains yielding the experimental reference, rock matrix characterisations, and matrix diffusion simulations. Valuable support to matrix diffusion simulations was provided by independent uranium-series disequilibria simulations, done to date radiometrically the accumulated uranium. Repeated model tests, applying the methodology, were carried out at two Finnish natural analogue study sites, the U-Th deposit at Palmottu, and a boulder sample near Hämeenlinna; both sites show elevated natural radioactivity. The deposit at Palmottu is extremely old, while the uranium accumulation in the boulder appears postglacial. The most important lesson learned at Palmottu is that the experimental reference must be conceptually in line with the model being tested. In this view, reconciling the respective concepts of attachment of radionuclides on rock is absolutely essential, otherwise quantitative model testing is pointless. In situ simulations require a complete and consistent site-specific data base for the model, because in model testing even partly generic input data may lead to false conclusions. The boulder sample indicates that recent uranium accumulations are easier to interpret than old ones, because matrix diffusion response is easier to trace, and boundary conditions for the simulations are easier to quantify. The iterative model validation process is a powerful method to refine both theoretical and experimental tools. The tests with the boulder sample support the classical matrix diffusion concept used in performance assessments. The tests at Palmottu indicate, however, a clear need to improve the technique used to obtain the experimental reference.
Original languageEnglish
QualificationDoctor Degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Vuori, Seppo , Advisor, External person
  • Salomaa, Rainer, Advisor, External person
Award date12 Nov 1997
Place of PublicationEspoo
Publisher
Print ISBNs951-38-5208-3
Electronic ISBNs951-38-5209-1
Publication statusPublished - 1997
MoE publication typeG5 Doctoral dissertation (article)

Fingerprint

natural analog
in situ test
matrix
boulder
uranium
performance assessment
simulation
model test
methodology
geological time
model validation
Postglacial
repository
disequilibrium
rock
radioactive waste
radionuclide
bedrock
boundary condition
groundwater

Keywords

  • radioactive wastes
  • groundmass
  • natural analogues
  • in-situ tests
  • matrix diffusion
  • long term tests

Cite this

Rasilainen, Kari. / Matrix diffusion model - in situ tests using natural analogues : Dissertation. Espoo : VTT Technical Research Centre of Finland, 1997. 86 p.
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abstract = "Matrix diffusion is an important retarding and dispersing mechanism for substances carried by groundwater in fractured bedrock. Natural analogues provide, unlike laboratory or field experiments, a possibility to test the model of matrix diffusion in situ over long periods of time. This thesis documents quantitative model tests against in situ observations, done to support modelling of matrix diffusion in performance assessments of nuclear waste repositories, which must cover long, even geological time periods. A model testing methodology was developed by combining measurements of long-lived natural decay chains yielding the experimental reference, rock matrix characterisations, and matrix diffusion simulations. Valuable support to matrix diffusion simulations was provided by independent uranium-series disequilibria simulations, done to date radiometrically the accumulated uranium. Repeated model tests, applying the methodology, were carried out at two Finnish natural analogue study sites, the U-Th deposit at Palmottu, and a boulder sample near H{\"a}meenlinna; both sites show elevated natural radioactivity. The deposit at Palmottu is extremely old, while the uranium accumulation in the boulder appears postglacial. The most important lesson learned at Palmottu is that the experimental reference must be conceptually in line with the model being tested. In this view, reconciling the respective concepts of attachment of radionuclides on rock is absolutely essential, otherwise quantitative model testing is pointless. In situ simulations require a complete and consistent site-specific data base for the model, because in model testing even partly generic input data may lead to false conclusions. The boulder sample indicates that recent uranium accumulations are easier to interpret than old ones, because matrix diffusion response is easier to trace, and boundary conditions for the simulations are easier to quantify. The iterative model validation process is a powerful method to refine both theoretical and experimental tools. The tests with the boulder sample support the classical matrix diffusion concept used in performance assessments. The tests at Palmottu indicate, however, a clear need to improve the technique used to obtain the experimental reference.",
keywords = "radioactive wastes, groundmass, natural analogues, in-situ tests, matrix diffusion, long term tests",
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year = "1997",
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isbn = "951-38-5208-3",
series = "VTT Publications",
publisher = "VTT Technical Research Centre of Finland",
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Matrix diffusion model - in situ tests using natural analogues : Dissertation. / Rasilainen, Kari.

Espoo : VTT Technical Research Centre of Finland, 1997. 86 p.

Research output: ThesisDissertationCollection of Articles

TY - THES

T1 - Matrix diffusion model - in situ tests using natural analogues

T2 - Dissertation

AU - Rasilainen, Kari

N1 - Project code: N7SU00131

PY - 1997

Y1 - 1997

N2 - Matrix diffusion is an important retarding and dispersing mechanism for substances carried by groundwater in fractured bedrock. Natural analogues provide, unlike laboratory or field experiments, a possibility to test the model of matrix diffusion in situ over long periods of time. This thesis documents quantitative model tests against in situ observations, done to support modelling of matrix diffusion in performance assessments of nuclear waste repositories, which must cover long, even geological time periods. A model testing methodology was developed by combining measurements of long-lived natural decay chains yielding the experimental reference, rock matrix characterisations, and matrix diffusion simulations. Valuable support to matrix diffusion simulations was provided by independent uranium-series disequilibria simulations, done to date radiometrically the accumulated uranium. Repeated model tests, applying the methodology, were carried out at two Finnish natural analogue study sites, the U-Th deposit at Palmottu, and a boulder sample near Hämeenlinna; both sites show elevated natural radioactivity. The deposit at Palmottu is extremely old, while the uranium accumulation in the boulder appears postglacial. The most important lesson learned at Palmottu is that the experimental reference must be conceptually in line with the model being tested. In this view, reconciling the respective concepts of attachment of radionuclides on rock is absolutely essential, otherwise quantitative model testing is pointless. In situ simulations require a complete and consistent site-specific data base for the model, because in model testing even partly generic input data may lead to false conclusions. The boulder sample indicates that recent uranium accumulations are easier to interpret than old ones, because matrix diffusion response is easier to trace, and boundary conditions for the simulations are easier to quantify. The iterative model validation process is a powerful method to refine both theoretical and experimental tools. The tests with the boulder sample support the classical matrix diffusion concept used in performance assessments. The tests at Palmottu indicate, however, a clear need to improve the technique used to obtain the experimental reference.

AB - Matrix diffusion is an important retarding and dispersing mechanism for substances carried by groundwater in fractured bedrock. Natural analogues provide, unlike laboratory or field experiments, a possibility to test the model of matrix diffusion in situ over long periods of time. This thesis documents quantitative model tests against in situ observations, done to support modelling of matrix diffusion in performance assessments of nuclear waste repositories, which must cover long, even geological time periods. A model testing methodology was developed by combining measurements of long-lived natural decay chains yielding the experimental reference, rock matrix characterisations, and matrix diffusion simulations. Valuable support to matrix diffusion simulations was provided by independent uranium-series disequilibria simulations, done to date radiometrically the accumulated uranium. Repeated model tests, applying the methodology, were carried out at two Finnish natural analogue study sites, the U-Th deposit at Palmottu, and a boulder sample near Hämeenlinna; both sites show elevated natural radioactivity. The deposit at Palmottu is extremely old, while the uranium accumulation in the boulder appears postglacial. The most important lesson learned at Palmottu is that the experimental reference must be conceptually in line with the model being tested. In this view, reconciling the respective concepts of attachment of radionuclides on rock is absolutely essential, otherwise quantitative model testing is pointless. In situ simulations require a complete and consistent site-specific data base for the model, because in model testing even partly generic input data may lead to false conclusions. The boulder sample indicates that recent uranium accumulations are easier to interpret than old ones, because matrix diffusion response is easier to trace, and boundary conditions for the simulations are easier to quantify. The iterative model validation process is a powerful method to refine both theoretical and experimental tools. The tests with the boulder sample support the classical matrix diffusion concept used in performance assessments. The tests at Palmottu indicate, however, a clear need to improve the technique used to obtain the experimental reference.

KW - radioactive wastes

KW - groundmass

KW - natural analogues

KW - in-situ tests

KW - matrix diffusion

KW - long term tests

M3 - Dissertation

SN - 951-38-5208-3

T3 - VTT Publications

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Rasilainen K. Matrix diffusion model - in situ tests using natural analogues: Dissertation. Espoo: VTT Technical Research Centre of Finland, 1997. 86 p.