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Understanding Processes for Credible Dose Modeling in Geological Repositories

This document examines the necessity for process understanding in the development of effective dose models for geological repositories. Over the past three decades, compartmental representations of surface hydrogeology have been crucial in modeling contaminant concentrations in ecosystems. It discusses the evolution of biosphere models, critical modeling exercises, and the significance of understanding radionuclide transport. The findings suggest that dose effects are not merely linked to discharge points, emphasizing the need for transparency and defensibility in safety assessments and performance evaluations.

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Understanding Processes for Credible Dose Modeling in Geological Repositories

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  1. The need for process understanding in the derivation of a credible dose model for geological repositoriesShulan Xu 2010-01-26

  2. Contents • Introduction • Critical issues • Modelling exercises • Considerations

  3. Introduction Historical development of biosphere models • For thirty years or more, dose models have employed a compartmental representation of the surface hydrogeology to model the dynamic concentration of contaminants in various ecosystems • BIOMOVS I & II, BIOMASS-6 • Landscape models in SR-Can (SKB, 2006) • A number of ecosystems connected • Evolution of site • Dose assessment in the overall assessment • Dose factor, DF, (Sv/yr per Bq/yr) • Defensible, transparent • ACM, • possible impacts

  4. Developments in safety assessment • SSM has initiated research and development projects in the area of performance assessment (PA) modelling a few years ago. • Processes understanding of transport and distribution of radionuclides • Independent modeling capacity to perform replication calculations and development of alternative models/tools to give critical analysis for the safety assessment. • Performance of reviews • SR-97, SR-Can • SAFE, SAR-08

  5. Characteristics of discharge areas • Lake, stream or wetlands • Thick soil layer (QD) • Coincidence with fracture zone

  6. How a size of biosphere object can be identified? Contaminated area Path 2 Path 1

  7. Critical issues • Representation of discharge areas • Process descriptions • Accumulation/GBI • subsurface chemical zonation • Model discretisation

  8. Research and modelling work in 2009 • Project on radionuclide transport through the ”GBI” • Modelling exercises • Effect of accumulation • Effect of different combinations of discharge points

  9. Modelling exercises in 2009 Assume discharge point moving with time due to uplift

  10. a) 0 – 3000 years river lake wetland QD 1 Bq/y b) 3000 – 20000 years Agr. land river lake wetland QD 1 Bq/y Modelling exercises in 2009

  11. Modelling exercises in 2009 Simulated inventory of top soil vs time

  12. Modelling exercises in 2009 Estimates of dose rates for agricultural land compared with doses for different ecosystems.

  13. Findings from modelling exercises • It is not always that the discharge point/object has highest dose effects • A clear link between FEP matrix and PA models is necessary

  14. Considerations • Do we know enough about dilution to make credible dose calculations? • Consensus

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