Binary Pb-Bi (lead-bismuth) eutectic alloys are used as cooling fluid in fourth-generation nuclear reactors like the "Multi-Purpose Hybrid Research Reactor for High-Tech Applications" (MYRRHA), whose project is in final design stage and is to be built in Belgium between 2015 and 2020. As the coolant is inevitably subject to a high neutron flux, a partial transmutation of Pb and Bi into highly radiotoxic Po isotopes will occur. As virtually nothing is known about the ternary Pb-Bi-Po phase diagram, this is a situation in which a theoretical/computational approach becomes an interesting alternative. Knowledge of the phase diagram, coupled with a reliable thermodynamic model, is quite important and useful. Thus, the present proposal aims at a crucial factor related to the occurrence of Po as a contaminant in Pb-Bi alloys, namely, the determination of the ternary Pb-Bi-Po phase diagram, starting from ab-initio electronic structure calculations and CALPHAD modelling of the stable phases. For the ab-initio calculations, we will use the Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method within the Density Functional Theory (DFT), as implemented in the Wien2k computational package. Several binary and ternary compositions and crystal structures will be computed, in order to determine which ones are stable at absolute zero, and, with the inclusion of entropic terms, also at finite temperatures. In this way, we intend to write a thermodynamic database which will describe the ternary Pb-Bi-Po phase diagram, starting from ab-initio data only. This research will be performed in the framework of a bilateral cooperation project between institutions in Brazil and in Belgium.
News published in Agência FAPESP Newsletter about the scholarship: