P. Trinchero(1), M. Luna(1), J. Molinero(1), G. Román-Ross(1), F. Maia(1), A. Nardi(1), J. Löfman(2), Petteri Pitkänen(3), L. Koskinen(3)

Coupled Palaehydrogeological Microbial and Geochemical Reactive Transport Model of the

Olkiluoto Site (Finland)

Introduction

(1)Amphos 21 Consulting, (2)VTT Energy, (3)Posiva Oy

Numerical model

References Eronen, M. & Lehtinen, K. 1996. Description of the Quarternary geological history of Romuvaara, Kivetty and Olkiluoto sites (in Finnish with an English abstract). Posiva Oy, Eurajoki, Finland. Working Report PATU-96-74, 37 p. Löfman, J. & Karvonen, T. 2012. Simulations of Hydrogeological Evolution at Olkiluoto. Posiva Oy, Eurajoki, Finland. Working Report 2012-35. Nardi, A., Trinchero, P., de Vries, L., Idiart, A., & Molinero, J. (2012). Coupling multiphysics with geochemistry: The COMSOL-PHREEQC interface. In COMSOL Conference, October, 2012. Parkhurst, D. L., & C. A. J. Appelo (1999), User’s guide to PHREEQC (version 2)—A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations, U.S. Geol. Surv. Water Resour. Invest.,Rep. 99-4259.

Results

• Hydrogeological conditions based on the geometrical configuration and results of existing regional-scale hydrogeological models (i.e. FEFTRA models, Löfman & Karvonen, 2012).

• The model considers three types of initial waters, which define three different hydrochemical zones.

• The domain consist of four Hydrogeological Zones (HZs). • Reactive transport simulations aim at studying the potential for

sulphide generation and key buffering reactions that may control sulphate reduction.

• The paleohydrogeological reactive transport simulations have been carried out using the interface Comsol-Phreeqc (Nardi et al., 2012).

• Dual porosity processes have been included to mimic exchange of mass between the mobile zones and the matrix.

Model features

Conclusions

(1) calcite and pyrite/FeS(am) dissolution/precipitation; (2) aluminosilicates weathering; (3) cation exchange reactions; (4) aqueous redox reactions

HZ-19A

HZ-19C

HZ-19B

BFZ-100

Initial groundwater distribution

Chemical processes considered

• A complex reactive transport model has been successfully implemented and solved.

• The model complexity comes from the geometrical configuration of the

domain (i.e. a set of intersecting planes in a 3D domain), the need to couple the flow conditions to the FEFTRA’s results and the intrinsic complexity of

geochemical reactions.

• The reactive transport model accounts for the exchange of mass between the mobile domain (fractures) and the surrounding matrix blocks.

• The model results, which fit well with measured data at Olkiluoto, help to infer

key information about the buffering capacity of the medium.

Sulfide at 2000 AD

Calcite at 2000 AD

COMSOL geometry

Density field and flow b.c. imported from FEFTRA

Zone 3

Zone 2

Zone 1

Mineral Reaction Log K

FeS(am) FeS + H+ = Fe2+ + HS- -2.95

Calcite CaCO3 = CO32- + Ca2+ -8.48

Albite NaAlSi3O8 +8 H2O = Na+ + Al(OH)4- + 3 H4SiO4 -18.002

illite K0.6Mg0.25Al2.3Si3.5O10(OH)2 + 11.2H2O = 0.6K+ +

0.25Mg2+ + 2.3Al(OH)4- + 3.5 H4SiO4 + 1.2H+

40.267

K-feldspar KAlSi3O8 + 8 H2O = K+ + Al(OH)4- + 3 H4SiO4 -20.573

Siderite FeCO3 = Fe2+ + CO32- -10.89

SiO2(am) SiO2 + 2 H2O = H4SiO4 -2.71

Kaolinite Al2Si2O5(OH)4 + 6 H+ = H2O + 2 H4SiO4 + 2 Al3+ 7.435

Olkiluoto at Eurajoki has been selected as the final repository site

for spent nuclear waste in Finland. This area has been affected, at

regional scale, by land-uplift processes related to the ice withdrawal

These events have resulted in a complex and stratified

heterogeneous hydrochemical system.

The objective of this work was to develop a robust

paleohydrogeological reactive transport (PRT) model that, through a

better understanding of the implications of the past events, might

help to improve the knowledge of the present-day

hydrogeochemical condition conditions at Olkiluoto, thus allowing

to increase the reliability of future predictions.

0 AD 500 AD 1000 AD 1500 AD 2000 AD

FEFTRA – hydrogeological simulations

iCP – palaeohydrogeological RT simulations

• Density field• Flow boundary conditions

0 AD 500 AD 1000 AD 1500 AD 2000 AD

• pH, Eh• Major geochemistry• Mineral consumption• …..

-700

-600

-500

-400

-300

-200

-100

0

100

0 0.002 0.004 0.006 0.008 0.01 0.012

Dep

th [

maw

l]

SO4 [mol/kgw]

S_conservativeS_2000AD_eq_kineticsfield-values (0-200m)field_values (200-400 m)field_values (400-600 m)POSIVA ref. watersinitial waters iCP

-700

-600

-500

-400

-300

-200

-100

0

100

0 0.05 0.1 0.15 0.2 0.25

ele

vati

on

[m

asl]

Ca [mol/kgw]

Ca_2000AD_eq_kin_exchange_phi015

Ca_2000AD_eq_kin_exchange_phi0025

measured_Ca (0-200 m)

measured_Ca (200-400 m)

measured_Ca (400-600 m)

POSIVA ref. waters

initial waters iCP

-700

-600

-500

-400

-300

-200

-100

0

100

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Ele

vati

on

[m

asl]

Cl [mol/kgw]

Cl_2000AD_eq_kin_exchange_phi015Cl_2000AD_eq_kin_exchange_phi0025measured (200-400 m)measured (0-200 m)measured (400-600 m)POSIVA ref. watersinitial waters iCP