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Predicting the distribution and release of tritium remains a technical challenge for advanced nuclear reactors with molten Flibe (2LiF-BeF2) salt coolants. Tritium transport models, which are currently used to forecast release behavior, are limited by uncertainty in Flibe-related tritium transport properties and by a lack of relevant benchmark experiments to test input parameters and solution methods. A new test facility has been developed at the Massachusetts Institute of Technology Research Reactor (MITR) to irradiate a molten Flibe target in an ex-core neutron beam port to further investigate tritium transport mechanisms at prototypical reactor conditions. The experiment monitored the time-dependent release of tritium from the salt-free surface and the permeation rate of tritium through the stainless steel Flibe-containing test stand. Measured results were benchmarked with a multiphysics tritium transport simulation to resolve complex effects in the test. Trends in tritium release rates from the irradiation were in agreement with the multiphysics simulation of the test, which combined computational fluid dynamics, radiative heat transfer in participating media, and tritium transport in STAR-CCM+. [ABSTRACT FROM AUTHOR]

Corrosion testing of UNS N10003 in molten fluoride salt was performed in purified molten 27LiF-BeF2 (66-34 mol%) (FLiBe) salt at 700°C for 1,000 h, in pure nickel and graphite capsules. In the nickel capsule tests, the near-surface region of the alloy exhibited an approximately 200 nm porous structure, an approximately 3.5 μm chromium-depleted region, and MoSi2 precipitates. In the tests performed in graphite capsules, the alloy samples gained weight because of the formation of a variety of Cr3C2, Cr7C3, Mo2C, and Cr23C6 carbide phases on the surface and in the subsurface regions of the alloy. A Cr-depleted region was observed in the near-surface region where Mo thermally diffused toward either the surface or the grain boundary, which induced an approximately 1.4 μm Ni3Fe alloy layer in this region. The carbide-containing layer extended to approximately 7 μm underneath the Ni3Fe layer. The presence of graphite dramatically changes the mechanisms of corrosion attack in UNS N10003 in molten FLiBe salt. In terms of the depth of attack, graphite clearly accelerates the corrosion, but the results appear to indicate that the formation of the Cr23C6 phase might stabilize the Cr and mitigate its dissolution in molten FLiBe salt. Moreover, a thermal diffusion controlled corrosion model that was fundamentally derived from Fick's second law was applied to predict the corrosion attack depth of 17.2 μm/y for UNS N10003 in molten FLiBe in the pure nickel capsule at 700°C. [ABSTRACT FROM AUTHOR]