Silicon mass transfer in sodium loops and the resulting/thermal hydraulic effects

The element silicon in the surface of new, 300 series stainless steel has been shown to rapidly dissolve in sodium above 5250C. It deposits in slightly cooler regions as a crystalline compound with sodium and oxygen. In tests, the deposits have caused increases in hydraulic friction factor (hence, increased pressure loss) of up to 300% at Reynolds Numbers of 144 to 105.Also, they have contributed to local losses of heat transfer rate to 1/10 the original value, at a Reynolds Number of approximately 104. The crystals quickly decompose when out of sodium. Measurements made with a sodium loop (volume = 0.42 m3) include compound solubility vs temperature, loop conditions vs source rates and deposit transfer rates. Laboratory examinations and analyses of the crystals have also been made. The effects of this material have been observed also in a number of other loops. With the data from these studies, such effects are now explained and can be controlled or eliminated by system design and operation