Interaction of krypton and xenon with sodium and activated charcoal: Identification and modeling using gas chromatography and density functional theory

For the online detection of failed fuel pin in Prototype Fast Breeder Reactor (PFBR), Failed Fuel Localization Module (FFLM) facility is designed to probe the sodium (Na) coolant. Fission Gas Sparging Module (FGSM) is retrofitted with FFLM to localize failed fuel subassembly during the dry rupture of the fuel pin. FGSM is used to purge gaseous fission products (krypton (Kr) and xenon (Xe)) from Na, using argon (Ar). In this work, the efficiency of separating inactive Kr and Xe noble gases with Ar purge out of liquid Na, by their collection onto activated charcoal at cryogenic temperatures and the consequent release at high temperatures into the gas samplers was studied using gas chromatography (GC). Studies of the recovery of Xe/Kr separately with and without Na matrix in the FGSM under both static and dynamic conditions were undertaken by sequentially collecting these probe gases along with excess of Ar in different gas samplers which were then estimated using GC. Density Functional Theory (DFT) computations were performed on model Na clusters surrounding Kr/Xe atoms and also on pyrene molecule (a prototype for simulating the spaces within charcoal), trapping Kr and Xe atoms. Experimental observations showed a good correlation with the results obtained from Quantum Theory of Atoms In Molecules (QTAIM), Natural Bond Orbital (NBO), Energy Decomposition (ED), Non-Covalent Interaction (NCI) and Electrostatic Potential (ESP) mapping analyses. Calculated thermochemical parameters affirm the binding of Xe with Na and charcoal to be marginally stronger than that of Kr, consistent with the experimental observations and speculations based on their polarizabilities.