the need for process understanding in the derivation of a credible dose model for geological...

The need for process understanding in the derivation of a credible dose model

for geological repositories

Shulan Xu

2010-01-26

Contents

Introduction

Critical issues

Modelling exercises

Considerations

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

Microsoft PowerPoint-presentation

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

Characteristics of discharge areas

Lake, stream or wetlands

Thick soil layer (QD)

Coincidence with fracture zone

How a size of biosphere object can be identified?

Path 1

Path 2

Contaminated area

Critical issues

Representation of discharge areas

Process descriptions– Accumulation/GBI– subsurface chemical zonation

Model discretisation

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

Microsoft PowerPoint-presentation

Modelling exercises in 2009

Assume discharge point moving with time due to uplift

Modelling exercises in 2009

0 – 3000 years

3000 – 20000 years

1 Bq/y

1 Bq/y

river

river

lake

lake

wetland

wetlandAgr. land

a)

b)

QD

QD

Modelling exercises in 2009

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

x 104

0

100

200

300

400

500

600

700

800

Time (years)

Inve

ntor

y

(Bq)

Ra-226

C-14Cl-36

Cs-135

I-129

Ni-59Pb-210

Po-210

Simulated inventory of top soil vs time

Estimates of dose rates for agricultural land compared with doses for

different ecosystems.

Nuclides Agricultural

Land/River

Agricultural

Land/Lake

Agricultural

Land/Mire

226Ra 0.7 3 33

36Cl 16 58 10

135Cs 0.4 2.5 17

129I 15 90 21

59Ni 20 140 17

Modelling exercises in 2009

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

Considerations

Do we know enough about dilution to make credible dose calculations?

Consensus