PNNL

Abstract

As part of Flibe Energy, Inc.’s efforts to develop a sustainable fuel cycle for the Lithium Fluoride Thorium Reactor (LFTR), we are developing a chemical processing system for 1) removing the uranium fuel from the fuel salt, 2) removing the lanthanides, and 3) returning the uranium to the cleaned fuel salt. The LFTR’s molten fuel salt is 0.2 mol% uranium (U) in lithium fluoride/beryllium fluoride (2LiF:BeF2 [FLiBe]) because of its high neutron transparency, low melting point (459°C), superior thermodynamic properties, low vapor pressure, and negative temperature coefficient. Our project’s primary objective was to investigate the use of nitrogen trifluoride (NF3) to oxidize, fluorinate, volatilize, and extract U, fission products, and actinides that form volatile fluorides from the used fuel salt. To investigate these extractions, our first challenge in the absence of a FLiBe supplier was to produce laboratory-scale amounts of U-containing FLiBe (FLiBe/U) by first decomposing ammonium beryllium tetrafluoride (ABeF) in a 2-step process to produce BeF2 in an intimate admixture with LiF and uranium tetrafluoride (UF4). Although simple in concept, the FLiBe/U production system required many controls and design elements to minimize fluoride corrosion of structural components, manage the beryllium (Be) chemical risk, monitor process conditions, and remove the ammonia (NH3) and hydrogen fluoride (HF) ABeF decomposition by-products. This article describes the FLiBe/U production system and preliminary ingredient and FLiBe/U characterizations made using x-ray diffraction spectroscopy (XRD), and simultaneous thermogravimetric and differential thermal analysis (TG/DTA).