Phase Stability and Thermodynamic Assessment of the Np-Zr system
| Title: | Phase Stability and Thermodynamic Assessment of the Np-Zr system |
| Author: | Bajaj, Saurabh |
| Abstract: | Metallic fuels have an important role to play in "fast breeder" Gen-IV type nuclear reactors, and U-Pu-Zr is one of the prototypical systems. Because of the variability in fuel chemistry during burn-up, it is important to understand the effect of minor actinides and fission products on phase stability. Within this framework, we present a study on phase equilibria in the binary Np-Zr alloy system on which little work has been published. To resolve the contradictory reports on the ordering/ clustering trends of the bcc phase, a thermodynamic study is performed using the CALPHAD method. The calculated Np-Zr phase diagram is consistent with two sets of data: formation enthalpies of the bcc phase that are calculated with ab initio KKR-ASA-CPA electronic-structure method and lattice stabilities of solution phases obtained from first-principles technique. Another important feature in the Np-Zr alloy system is the non-stoichiometric delta-NpZr2 phase that forms in a hexagonal C32 structure similar to the delta-phase in the U-Zr system and the w-phase in pure Zr. An increase in the homogeneity range of the delta-phase when going from Pu to Np and to U is attributed to a lowering of its heat of formation that is caused by an increase in d-band occupation. Two different possibilities for the stability of the delta- and w- phases have been proposed in the present work. Additionally, calculated changes in enthalpy versus temperature are plotted for two alloy compositions of the Np-Zr system to guide future experimental work in resolving important issues in this system. Finally, an ab initio study, implemented with the L(S)DA U formalism, is performed for pure Np that reveals a transition from a non-magnetic to a magnetic state at a critical U parameter. |
| Subject: |
Metallic fuels
fast-breeder phase equilibria CALPHAD phase diagram electronic-structure first-principles ab initio L(S)DA U |
| URI: | http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8773 |
| Date: | 2010-12 |
Citation
(2010).
Phase Stability and Thermodynamic Assessment of the Np-Zr system.
Master's thesis,
Texas A&M University. Available electronically from
http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2010 -12 -8773.
Files in this item
| Files | Size | Format | View |
|---|---|---|---|
| BAJAJ-THESIS.pdf | 1012.Kb |
View/ |
This item appears in the following Collection(s)
-
Electronic Theses, Dissertations, and Records of Study (2002-present) [10425]
Electronic Theses, Dissertations, and Records of Study Collection
Browse
