Effect of finned structure on critical heat flux (CHF) in downward-face pool boiling

Abstract

Critical heat flux (CHF) plays an important role as the upper limit of heat dissipation process during the in-vessel reactor external reactor vessel cooling (IVR-ERVC). IVR-ERVC is regarded as a very effective way to release the decay heat after the core melt. This severe accident mitigation countermeasure has already been applied in some advanced PWRs and is considered to be used in some advanced BWRs as well. In this paper, experiments of the macro-fin structure positioned on a slope with 5° and 10° downward inclination angle were carried out. The results of the copper bar experiments were then analyzed and compared with the results obtained from a copper bare block experiments which were conducted previously at the same test facility. It was found that the CHF of the finned structure decreased compared with that of the bare surface. This shows that the current CHF data of the bare surface cannot be used directly to the design of new advanced BWRs. The hot/dry spot theory designated for the copper bar was brought up with an attempt to explain the difference of copper bare block and copper bar. Results show that using this theory can explain the decrease of CHF of the copper bar.