Liquid metals forced-convection loops

Because forced-convection loops are costly to construct, it is now the usual practice to operate the loops as permanent testing facilities, with corrosion specimens cycled in and out of the facility. Test specimens of various materials are generally placed in the hot leg, and the effect of the flowing liquid on the specimens is determined from changes in weight, dimensions, composition, mechanical properties, and microstructure. Such an approach yields data on maximum corrosion rates as a function of temperature and liquid metal flow rate. Any attempt to elucidate corrosion mechanisms, however, is hampered by the inability to interrelate dissolution and deposition processes. 

The thermal-convection loops are limited to flow velocities up to about 6 cm s . Where higher velocities are required, the liquid must be pumped, either mechanically or electromagnetically the latter is usually preferred as it avoids the problem of leakage at the pump seal. Basically, these forced-convection systemsconsist of (c) a hot leg, where the liquid metal is... 

Sodium superheat experiments were performed in a forced-convection facility employing system parameters in the range of interest for application to loop- and pot-type liquid metal-cooled fast breeder reactors (LMFBRs). The test section was... 

The time-dependence of void formation in Inconel, as observed both in thermal-convection and forced-circulation systems, indicates that the attack is initially quite rapid but that, it then decreases until a straight-line relationship exists between depth of void formation and time. This effect can 1)0 explained in terms of the corrosion reactions discussed above. The initial rapid attack found for both types of loops stems from the reaction of cliromium with impurities in the molt [reactions (13-1) and (13-2)] and with the FF4 constituent of the salt [reaction (13-3)] to establish a quasi-etiuilibrium amount of CrF2 in the salt. At this point attack proceeds linearly with time and occurs by a mass-transfer mechanism which, although it arises from a different cause, is similar to the phenomenon of temperature-gradient mass transfer observed in liquid metal corrosion. 

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