Phase Stability and Thermodynamic Assessment of the Np-Zr system
| dc.contributor | Arroyave, Raymundo | |
| dc.contributor | Cagin, Tahir | |
| dc.creator | Bajaj, Saurabh | |
| dc.date.accessioned | 2012-02-14T22:18:29Z | |
| dc.date.accessioned | 2012-02-16T16:20:23Z | |
| dc.date.accessioned | 2017-04-07T19:59:36Z | |
| dc.date.available | 2012-02-14T22:18:29Z | |
| dc.date.available | 2012-02-16T16:20:23Z | |
| dc.date.available | 2017-04-07T19:59:36Z | |
| dc.date.created | 2010-12 | |
| dc.date.issued | 2012-02-14 | |
| dc.description.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. | |
| dc.identifier.uri | http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8773 | |
| dc.language.iso | en_US | |
| dc.subject | Metallic fuels | |
| dc.subject | fast-breeder | |
| dc.subject | phase equilibria | |
| dc.subject | CALPHAD | |
| dc.subject | phase diagram | |
| dc.subject | electronic-structure | |
| dc.subject | first-principles | |
| dc.subject | ab initio | |
| dc.subject | L(S)DA U | |
| dc.title | Phase Stability and Thermodynamic Assessment of the Np-Zr system | |
| dc.type | Thesis |