First Principles Study of the Structure and Elastic Properties of Thorium Metal
- PDF / 297,845 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 62 Downloads / 142 Views
First Principles Study of the Structure and Elastic Properties of Thorium Metal Jacob K. Startt and Chaitanya S. Deo Nuclear and Radiological Programs, George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta. GA 30332, U.S.A.
ABSTRACT Thorium has long been considered a possible source of fuel for use in power generating nuclear reactors. While much attention and interest have focused on thorium oxide, metallic thorium alloys were investigated in the past as fuel candidates for fast and thermal breeder reactors. In this work, thorium’s two solid allotropes (face centered cubic α and body centered cubic β) are modelled using Density Functional Theory (DFT). The Vienna Ab Initio Simulation Package (VASP) is used to determine structural and elastic properties, as well as the density of states. The Voigt-Reuss-Hill approximations are used to predict the phases’ bulk moduli, shear moduli, Young’s moduli, and Poisson’s ratios. Four exchange-correlation potentials are used and compared. These are the LDA, the PBE-GGA, the RPBE, and the PBEsol. All potentials showed relatively good accuracy when predicting the lattice constant. The RPBE was the most accurate, slightly over predicting by < 0.2%. The RPBE and the PBE-GGA were the most accurate in predicting elastic properties, performing almost equally, while slightly over predicting most values. INTRODUCTION There has recently been an interest in the development of thorium fueled reactors. Proposed designs include many different reactor types such as heavy water reactors, molten salt reactors, high-temperature gas reactors and some accelerator-driven reactors [1,2,3]. Two promising fuel cycles that have been proposed include a Th-U fuel, in which a starter neutron source is temporarily used to breed U233 in-situ to run a reaction, and a MOX based fuel containing thorium, along with other fissile and fertile isotopes such as U235 and Pu239 [4]. A thorium based fuel cycle could have distinct advantages over uranium. For instance, thorium could allow for a much desired thermal breeder reactor which can be refueled with reprocessed fuel rather than mining for more, reducing cost and extending the lifetime of the fuel supply [5,6]. In addition to operational advantages there are also clear benefits to a thorium fuel cycle from a non-proliferation viewpoint due to the presence of U232 in thorium fuel cycles and the dangerous high-energy gamma rays associated with them. [7] In the present work, metallic thorium is modelled using Density Functional Theory (DFT) [8,9]. Four different exchange-correlation functionals are tested in calculating the lattice constants, elastic constants, various elastic moduli, and density of states.
2447 Downloaded from https:/www.cambridge.org/core. University of Arizona, on 04 Apr 2017 at 07:42:24, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2016.500
THEORY Thorium metal exists in the α (face-centered-cubic) phase at room temperature, tr
Data Loading...
