Abstract
Cement is an inexpensive and relatively easily manageable material that is used as a last barrier for nuclear waste disposal. Under these conditions, the cement is in contact with low radiation doses, but there is a distinct possibility of being contaminated with radioactive products. Of particular concern is the medium lived half-life product mathrm {{}^{90}Sr} (28.8 years) due to its ability to replace Ca. mathrm {{}^{90}Sr} undergoes beta -decay to mathrm {{}^{90}Y} which, in turn, beta -decays to stable mathrm {{}^{90}Zr}. In this work, we discuss systematically the chain of non-equilibrium processes that result as a consequence of beta -decay events in cement. We first use density functional-based methods to study the consequences of the sudden increase of the nuclear charge from Z to Z+1, a possible induced ionization and the perturbation of the surrounding electronic charge. Secondly, we use molecular dynamics simulations to study the recoil of the daughter nucleus. Finally, we discuss the damage caused by the ionization cascade produced during the propagation of the beta -electron and the resulting chemical and structural perturbation.Graphic
Highlights
Nuclear fission processes generate a large variety of radioactive products of different lifetimes
To simulate the various aspects of the problem, we have used a variety of methods and codes, uniformly based in density functional theory (DFT)
In order to investigate the structural relaxation induced by the recoil of the daughter nuclei, we performed firstprinciples molecular dynamics simulations within the DFT framework using the Quantum-espresso planewave code [10]
Summary
Nuclear fission processes generate a large variety of radioactive products of different lifetimes. Those with a short half-life, e.g., months to a few years, are relevant during the period of operation of the power plant and, after decommissioning, are managed by storing the used hot fuel for a few years until it can be recycled or buried away. 2, we present the atomic structure of the model cement paste and the details of the different density functional theory (DFT)-based calculation methods used in this work. 3.1, we discuss the consequences of the sudden increase of the nuclear charge (Z) due to βdecay: a possible induced ionization 3.3 we discuss the damage caused by the ionization cascade produced during the propagation of the emitted electron
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