Long-term confinement of nuclear waste is one of the main challenges faced by the nuclear industry. Fission products such as Sr-90 and Cs-137, both beta(-) emitters known to induce serious health hazards, represent the largest fraction of nuclear waste. Cement is a good candidate to store them, provided it can resist the effects of irradiation over time. Here, we have investigated the effects of beta(-) decay on cement by performing electron irradiation experiments on different samples. We show that H-2 production in cement, the main effect of water radiolysis, depends strongly on composition and relative humidity. First-principles calculations indicate that the water-rich interlayer regions with Ca2+ ions act as electron traps that promote the formation of H-2. They also show that holes localize in water-rich regions in low Ca content samples and are then able to participate in H-2 production. This work provides new understanding of radiolysis effects in cements.

VL - 100 UR - https://linkinghub.elsevier.com/retrieve/pii/S0008884617302065 JO - Cement and Concrete Research ER - TY - JOUR T1 - Cement As a Waste Form for Nuclear Fission Products: The Case of 90Sr and Its Daughters JF - Environmental Science & Technology Y1 - 2016 A1 - Dezerald, Lucile A1 - Kohanoff, Jorge J. A1 - Alfredo A. Correa A1 - Caro, Alfredo A1 - Roland Jean-Marc Pellenq A1 - Franz-Josef Ulm A1 - Andres Saùl AB -One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of Sr-90 insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its beta-decay on the cement paste structure. We show that Sr-90 is stable when it substitutes the Ca2+ ions in C-S-H, and so is its daughter nucleus Y-90 after beta-decay. Interestingly, Zr-90, daughter of Y-90 and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for Sr-90 storage.

VL - 49 UR - http://pubs.acs.org/doi/10.1021/acs.est.5b02609 IS - 22 JO - Environ. Sci. Technol. ER - TY - JOUR T1 - Cement As a Waste Form for Nuclear Fission Products: The Case of 90 Sr and Its Daughters JF - Environ Sci Technol Y1 - 2015 A1 - Dezerald, Lucile A1 - Kohanoff, Jorge J A1 - Alfredo A. Correa A1 - Caro, Alfredo A1 - Roland Jean-Marc Pellenq A1 - Franz-Josef Ulm A1 - Andres Saùl AB -One of the main challenges faced by the nuclear industry is the long-term confinement of nuclear waste. Because it is inexpensive and easy to manufacture, cement is the material of choice to store large volumes of radioactive materials, in particular the low-level medium-lived fission products. It is therefore of utmost importance to assess the chemical and structural stability of cement containing radioactive species. Here, we use ab initio calculations based on density functional theory (DFT) to study the effects of (90)Sr insertion and decay in C-S-H (calcium-silicate-hydrate) in order to test the ability of cement to trap and hold this radioactive fission product and to investigate the consequences of its β-decay on the cement paste structure. We show that (90)Sr is stable when it substitutes the Ca(2+) ions in C-S-H, and so is its daughter nucleus (90)Y after β-decay. Interestingly, (90)Zr, daughter of (90)Y and final product in the decay sequence, is found to be unstable compared to the bulk phase of the element at zero K but stable when compared to the solvated ion in water. Therefore, cement appears as a suitable waste form for (90)Sr storage.

VL - 49 IS - 22 ER - TY - JOUR T1 - First-principles prediction of kink-pair activation enthalpy on screw dislocations in bcc transition metals: V, Nb, Ta, Mo, W, and Fe JF - Physical Review B Y1 - 2015 A1 - Dezerald, Lucile A1 - Proville, L. A1 - Ventelon, Lisa A1 - Willaime, F. A1 - Rodney, D. AB -

The atomistic study of kink pairs on screw dislocations in body-centered cubic (bcc) metals is challenging because interatomic potentials in bcc metals still lack accuracy and kink pairs require too many atoms to be modeled by first principles. Here, we circumvent this difficulty using a one-dimensional line tension model whose parameters, namely the line tension and Peierls barrier, are reachable to density functional theory calculations. The model parameterized in V, Nb, Ta, Mo, W, and Fe, is used to study the kink-pair activation enthalpy and spatial extension. Interestingly, we find that the atomistic line tension is more than twice the usual elastic estimates. The calculations also show interesting group tendencies with the line tension and kink-pair width larger in group V than in group VI elements. Finally, the present kink-pair activation energies are shown to compare qualitatively with experimental data and potential origins of quantitative discrepancies are discussed.

VL - 91 UR - https://link.aps.org/doi/10.1103/PhysRevB.91.094105 IS - 9 JO - Phys. Rev. B ER -