Binary and ternary Po-containing molecules relevant for LBE cooled reactors at operating temperature

Abstract

Quantum-chemical calculations at several levels of theory were used to assess the stability at different temperatures of a set of 13 binary and ternary Pocontaining molecules that could possibly be formed in an environment with lead, bismuth, oxygen and water. These are conditions that are relevant for a heavy liquid metal cooled fission reactor. The conclusions are that especially PoPb, PbPoO and PoOH and to a lesser extent Po 2 and PoO are stable. These small molecules are likely to be found near the Lead-Bismuth-Eutectic (LBE) coolant at operational temperatures. In contrast Po 3 and PoBi are unlikely to be present under the assumed conditions. Several stability criteria, such as the dissociation into free atoms or into molecular fragments at realistic Poconcentrations or in the thermodynamic limit are discussed at different temperatures. The results obtained with a medium level of theory (Density Functional Theory, PBE0 with Relativistic Effective Core Potentials) show good qualitative correspondence with calculations performed at a much higher level of theory (Multi Reference Configuration Interaction, with spin-orbit coupling and scalar relativistic Hamiltonian). This makes the medium level of theory to be a fair alternative, for obtaining at least qualitative insight, for a high level calculation method which is unfeasible for much larger systems.

Ab initio study of the trapping of polonium on noble metals

“…In order to assess the level of theory that will be required, we compare in In ref. [25], it was already shown that PBE0 succeeds surprisingly well in reproducing the formation energies obtained by the much more accurate MRCI Whereas MRCI and PBE/PBE0 are in fair agreement with each other when 120 no spin-orbit interaction is included (Fig. 1a), this agreement vanishes upon adding spin-orbit coupling (Fig.…”

“…More recently the formation of several polonium-containing 50 molecules, whose existence is expected in a LBE environment, has been studied in Van Yperen-De Deyne et al [25]. In the present work we use density functional theory (DFT) to examine the interaction between a low concentration of monoatomic polonium and the surfaces of the candidate filter materials palladium, silver, platinum and gold.…”

“…In order to prevent a build-up of polonium and other malicious elements 25 in the gas phase, the atmosphere inside MYRRHA's closed reactor vessel will be continuously filtered. Developing appropriate filter systems requires an adequate knowledge of polonium chemistry.…”

Radionuclide Chemistry in Nuclear Facilities Based on Heavy Liquid Metal Coolants: Past, Present and Future

“…The results from SEARCH indicated that while DFT proved to be adequate to describe the adsorption interaction of monoatomic polonium with noble metal surfaces, it is not suitable for a reliable calculation of thermodynamic properties of polonium-containing molecules. [42] Therefore, a combination of more sophisticated methods had to be applied that properly account for electron correlation and the spin-orbit effects that are particularly important for heavy elements such as Pb, Bi and Po. The new calculation routine developed within MYRTE was proven to reliably predict temperature dependent thermodynamic properties of diatomic polonium-containing molecules.…”

Removal of the Homolog Tellurium of Polonium by SiO2 Nanofiber Filter for Lead Alloy-Cooled Reactors

“…Furthermore, a lower trapping temperature meant that the vapor could nucleate and grow on the nanofiber surface, even with a lower degree of subcooling, which also increased the nucleation rate and accelerated the deposition of vapor on the membrane surface. According to relevant studies, the vapor pressure of PbTe is between those of Pb and Bi, indicating that the volatility of PbTe is higher than that of pure Pb and lower than that of Bi [43][44][45][46]. Meanwhile, the melting point of Bi is much lower than that of PbTe; thus, a higher degree of subcooling can be achieved for PbTe.…”