A Coupled THMC model of FEBEX mock-up test

1 of 42 Multiphase Flow and Multicomponent Reactive Transport Model of the Ventilation Experiment in Opalinus clay L. Zheng 1* , J. Samper 1# , L. Montenegro 1 , J.C. Mayor 2 E.T.S. Ingenieros de Caminos, Canales y Puertos, Universidad de Coruna, Campus de Elvina s/n 15192 La Coruna, Spain ENRESA, Emilio Vargas 7, 28043 Madrid, Spain Present address: Lawrence Berkeley National Lab, 1 Cyclotron Rd, Berkeley, CA, 94720, USA Corresponding author. E-mail address: jsamper@udc.es (J. Samper) Abstract During the construction and operational phases of a high-level radioactive waste (HLW) repository constructed in a clay formation, ventilation of underground drifts will cause desaturation and oxidation of the rock. The Ventilation Experiment (VE) was performed in a 1.3 m diameter unlined horizontal microtunnel on Opalinus clay at Mont Terri underground research laboratory in Switzerland to evaluate the impact of desaturation on rock properties. A multiphase flow and reactive transport model of VE is presented here. The model accounts for liquid, vapor and air flow, evaporation/condensation and multicomponent reactive solute transport with kinetic dissolution of pyrite and siderite and local-equilibrium dissolution/precipitation of calcite, ferrihydrite, dolomite, gypsum and quartz. Model results reproduce measured vapor flow, liquid pressure and hydrochemical data and capture the trends of measured relative humidities, although such data are slightly overestimated near the rock interface due to uncertainties in the turbulence factor. Rock desaturation allows oxygen to diffuse into the rock and triggers pyrite oxidation, dissolution of