Local sodium boiling experiments in simulated LMFBR fuel subassemblies

Out-of-pile experiments were conducted to examine local sodium boiling in two wire-wrapped 37-pin bundles simulating LMFBR Fuel subassemblies. The fractions of blocked flow area were 26% and 50% respectively. The boiling modes observed in the wake were irregular nucleate, oscillatory and stationary. Three different types of boiling transition were identified from the incipient boiling to the occurrence of dryout. Dryout occurred not in the irregular nucleate boiling mode, but in both the stationary and oscillatory boiling modes. The results showed the existence of two-phase coolability margin in a partially blocked subassembly