Abstract
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Supervisors/Advisors 

Award date  29 Nov 2013 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9789513880972 
Electronic ISBNs  9789513880989 
Publication status  Published  2013 
MoE publication type  G5 Doctoral dissertation (article) 
Fingerprint
Keywords
 nuclear waste
 repository system
 migration
 modelling
Cite this
}
Simplifying solute transport modelling of the geological multibarrier disposal system : Dissertation. / Poteri, Antti.
Espoo : VTT Technical Research Centre of Finland, 2013. 212 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  Simplifying solute transport modelling of the geological multibarrier disposal system
T2  Dissertation
AU  Poteri, Antti
N1  Project code: 82425
PY  2013
Y1  2013
N2  A simplified model was developed to represent radionuclide migration from a deep geological nuclear waste repository system to the biosphere. The modelled repository system is based on the concept of multiple nested transport barriers. The model can be used to assess migration and migration properties of single nuclides (no decay chains) through the repository system. Radionuclide transport processes included to the model are diffusion and sorption in the repository nearfield and advection, matrix diffusion and sorption in the geosphere. A simplified approach to handle solubility limited release of the nuclide from the waste canister is included into the model. The model treats transport barriers as wellmixed volumes. It is also assumed that radionuclide outflow from a barrier can be calculated by negleting radionuclide concentration in the target barrier. Radionuclide transport through the simplified system can be calculated by applying formal analogy of the model to the mathematical model of the radioactive decay chain. Simplifying the barriers as wellmixed volumes suggests that they can be characterised by simple performance measures. Radionuclide outflow from the barrier can be represented by an equivalent flow rate, which is an apparent volumetric flow rate that combined with the radionuclide concentration in the barrier gives the outflow rate of the nuclide. Temporal behaviour of the release rate can be described by two time constants: i) compartment halflife of the nuclide concentration calculated by dividing capacity of the barrier (the total pore volume multiplied by the retardation factor) with the equivalent flow rate and ii) delay time for start of the outflow from barrier after beginning of the inflow to barrier. Performance of the simplified approach to produce actual release rates for different nuclides was tested by modelling C14, I129 and Pu239 using data from the RNT2008 radionuclide migration analysis. Accuracy of the simplified approach is challenged if the nuclide's halflife is not long compared to the time required for the development of perfectly mixed solute concentration field in the barrier. The nuclide and barrier combinations that are prone to this behaviour can be identified by comparing the estimated compartment delay time with the nuclide's radioactive halflife. The simplified model performed well for the C14 and I129, as expected based on the measures above. Early transients of the concentration field in the buffer and in the geosphere are important for the transport of Pu239 in the calculated case. The simplified model gave results for Pu239 that were roughly of the same order of magnitude than the corresponding numerical results.
AB  A simplified model was developed to represent radionuclide migration from a deep geological nuclear waste repository system to the biosphere. The modelled repository system is based on the concept of multiple nested transport barriers. The model can be used to assess migration and migration properties of single nuclides (no decay chains) through the repository system. Radionuclide transport processes included to the model are diffusion and sorption in the repository nearfield and advection, matrix diffusion and sorption in the geosphere. A simplified approach to handle solubility limited release of the nuclide from the waste canister is included into the model. The model treats transport barriers as wellmixed volumes. It is also assumed that radionuclide outflow from a barrier can be calculated by negleting radionuclide concentration in the target barrier. Radionuclide transport through the simplified system can be calculated by applying formal analogy of the model to the mathematical model of the radioactive decay chain. Simplifying the barriers as wellmixed volumes suggests that they can be characterised by simple performance measures. Radionuclide outflow from the barrier can be represented by an equivalent flow rate, which is an apparent volumetric flow rate that combined with the radionuclide concentration in the barrier gives the outflow rate of the nuclide. Temporal behaviour of the release rate can be described by two time constants: i) compartment halflife of the nuclide concentration calculated by dividing capacity of the barrier (the total pore volume multiplied by the retardation factor) with the equivalent flow rate and ii) delay time for start of the outflow from barrier after beginning of the inflow to barrier. Performance of the simplified approach to produce actual release rates for different nuclides was tested by modelling C14, I129 and Pu239 using data from the RNT2008 radionuclide migration analysis. Accuracy of the simplified approach is challenged if the nuclide's halflife is not long compared to the time required for the development of perfectly mixed solute concentration field in the barrier. The nuclide and barrier combinations that are prone to this behaviour can be identified by comparing the estimated compartment delay time with the nuclide's radioactive halflife. The simplified model performed well for the C14 and I129, as expected based on the measures above. Early transients of the concentration field in the buffer and in the geosphere are important for the transport of Pu239 in the calculated case. The simplified model gave results for Pu239 that were roughly of the same order of magnitude than the corresponding numerical results.
KW  nuclear waste
KW  repository system
KW  migration
KW  modelling
M3  Dissertation
SN  9789513880972
T3  VTT Science
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 