Cesium (137Cs) and technetium (99Tc) are two radionuclides of significant concern in spent nuclear fuel because of their long half-life, high decay energy, and high solubility. Cementitious materials are considered as potential candidates for nuclear waste immobilization. The study of the interaction of radionuclides with the cement matrix is thus essential to determine the capability of cementitious materials to immobilize radioactive isotopes such as 137Cs and 99Tc. Calcium-silicate-hydrate (C-S-H) and calcium-aluminate-sulfate hydrate (ettringite) are two main products of cement hydration in Portland Cement (PC). The interactions of CsCl solution with different crystalline C-S-H structures (9Ã tobermorite, 14Ã tobermorite and jennite) and the interactions of KTcO4 solution with crystalline C-S-H structures (14Ã tobermorite and jennite) and ettringite were studied using Molecular Dynamics (MD) simulations.
MD simulation results indicated that Cs+ ions were mainly adsorbed as inner-sphere complexes at the tetrahedral SiO4 surface ((0 0 1) plane) of 9Ã tobermorite, 14Ã tobermorite, and jennite. The tobermorites showed higher adsorption capacity of Cs+ ions than jennite. Jennite had
weak affinity to Cs+ ions. MD simulation results indicated that TcO4- ions can be adsorbed on the surfaces of 14Ã tobermorite and ettringite. On the octahedral CaO6 surface ((0 0 -1) plane) of 14Ã tobermorite, inner-sphere Tc complexes coexisted with outer-sphere Tc complexes. Co-ion adsorption affected the adsorption of outer-sphere Tc complexes and pushed outer-sphere complexes further away from the surface. On the octahedral CaO6 surface ((0 0 -1) plane) of ettringite, TcO4- ions were mainly adsorbed as outer-sphere complexes. Two types (i.e. type 1: tetragonal geometry and type 2: tetrahedral geometry) of outer-sphere Tc complexes were predicted on both surfaces of 14Ã tobermorite and ettringite. Jennite had no affinity to TcO4- ions.
In conclusion, 9Ã tobermorite and 14Ã tobermorite were better candidates for the immobilization of Cs+ ions than jennite. Ettringite and 14Ã tobermorite also showed better affinity to TcO4- ions than jennite. Ca2+ ions on the surface played an important role and formed complexes with TcO4- ions.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-03282018-153851 |
| Date | 11 April 2018 |
| Creators | Bu, Jingjing |
| Contributors | Hans A. van der Sloot, James H. Clarke, David S. Kosson, Kevin G. Brown, Florence Sanchez |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-03282018-153851/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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