The predictive power of a classical molecular dynamics simulation is largely determined by the physical validity of its underlying empirical potential. In the case of high-energy collision cascades, it was recently shown that correctly modeling interactions at short distances is necessary to accurately predict primary damage production. An *ab initio* based framework is introduced for modifying an existing embedded-atom method FeNiCr potential to handle these short-range interactions. Density functional theory is used to calculate the energetics of two atoms approaching each other, embedded in the alloy, and to calculate the equation of state of the alloy as it is compressed. The pairwise terms and the embedding terms of the potential are modified in accordance with the *ab initio* results. Using this reparametrized potential, collision cascades are performed in Ni_{50}Fe_{50}, Ni_{80}Cr_{20} and Ni_{33}Fe_{33}Cr_{33}. The simulations reveal that alloying Ni and NiCr to Fe reduces primary damage production, in agreement with some previous calculations. Alloying Ni and NiFe to Cr does not reduce primary damage production, in contradiction with previous calculations.

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.

}, issn = {0013-936X}, doi = {10.1021/acs.est.5b02609}, url = {http://pubs.acs.org/doi/10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J. and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} } @article {133, title = {Cement As a Waste Form for Nuclear Fission Products: The Case of 90 Sr and Its Daughters}, journal = {Environ Sci Technol}, volume = {49}, year = {2015}, month = {Oct-2015}, pages = {13676-83}, abstract = {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.

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}, issn = {1520-5851}, doi = {10.1021/acs.est.5b02609}, author = {Dezerald, Lucile and Kohanoff, Jorge J and Alfredo A. Correa and Caro, Alfredo and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Andres Sa{\`u}l} }