Removal of bond sodium from Fermi-1 blanket assemblies using a melt-drain-evaporate process

Abstract

A series of runs was performed to demonstrate the removal of bond sodium from full-length unirradiated Fermi-1 radial blanket elements and an entire radial blanket assembly using a melt-drain-evaporate process. The runs were performed in an inert atmosphere glovebox, where the blanket material was breached and loaded into a retort assembly. It was then subjected to elevated temperature and reduced pressure to melt, drain, and evaporate the bond sodium, while simultaneously collecting the sodium distillate in a crucible at the base of the assembly. After each run, the depleted uranium alloy slugs in every element slid out of its cladding, providing the first indication that the blanket material was effectually devoid of sodium metal. Entire columns of depleted uranium alloy slugs and associated cladding from select treated elements were separately subjected to quantitative analyses for residual sodium metal on the element surfaces, yielding removal efficiencies of ≥99.9998%. The remaining uranium alloy slugs and cladding segments from the series of runs were piece-wise immersed in ethanol to react with any residual sodium and provide a visual means of its presence or absence through the corresponding formation of hydrogen gas bubbles or lack thereof. Accordingly, the predominant absence of sodium reactivity on the balance of treated Fermi-1 blanket material was observed. The successful outcome of this demonstration provides a path forward for the treatment and disposal of 34 metric tons heavy metal (MTHM) of irradiated sodium-bonded blanket material from the decommissioned Fermi-1 reactor.