Laurent De Windt

Modeling spent nuclear fuel alteration and radionuclide migration in disposal conditions

A physico-chemical model developed for spent fuel alteration was integrated in a global reactive transport model of a spent fuel disposal system, considering both decaying and stable isotopes, corroded steel canisters, bentonite backfills and a clayey host-rock. Fuel evolution took into account radiolytic-enhanced corrosion and long-term solubility-controlled dissolution as well as instantaneous release fractions. The calculations show that spent-fuel dissolution has no significant alteration effect on the near-field components except an oxidizing plume in the vicinity of the waste packages. The dissolved uranyl species, partly precipitate as schoepite on the fuel pellets, and partly diffuse in the near-field where magnetite and pyrite reduce U(VI) to yield uraninite precipitation. Under disposal conditions, preliminary calculations indicate that steel corrosion may generate sufficient dissolved hydrogen as to react with radiolytic oxidants and inhibit fuel dissolution. The formation of a protective schoepite layer could also reduce the alteration of fuel pellets. Radionuclides migration (Am, Cs, I) in the near-field is discussed in a second stage discriminating between sorption, precipitation and radioactive decay processes. The migration of Cs is translated in terms of cumulative activity profiles useful for integrated performance assessment.

2D simulation of natural gas reservoir by two-phase multicomponent reactive flow and transportDescription of a benchmarking exercise

Different ways of coupling are used to handle the mathematical and numerical difficulties of multiphase multicomponent flow and transport coupled with geochemistry. In absence of analytical solutions for such complex systems, the benchmarking of reactive multiphase simulators is essential for verification and validation of existing methods. This paper presents a reactive transport benchmarking exercise which aims at specifically targeting the numerical capacity of the codes in the context of liquid and gas flow, multicomponent liquid and gas transport, gas solubility, and gaswaterrock interaction. The exercise is based on a description of the long term evolution of the sour gas reservoir. The set of benchmark cases was established to study geochemical, thermo- and hydrodynamical mechanisms; the numerical results of two cases are demonstrated.