Experimental study of the transient boiling phenomenon on a vertically placed ribbon

Abstract

A submersed thin Nickel-200 ribbon experienced exponentially increased power input under prescribed time-constants through Joule heating up to and beyond film boiling for the purpose of simulating and understanding the phenomena that occur during a reactivity-initiated accident in a pressurized water reactor. The ribbon was placed vertically in an isothermal pool of water with no flow at atmosphere pressure and varied degree of subcooling. A programmable direct current power supply was used to generate the desired input Joule heated power transient. The volumetric averaged ribbon temperature was measured by the temperature-resistivity change. High speed photography was utilized to capture the temporal bubble behavior; the photography was synchronized with the power-temperature data to provide as comprehensive empirical information as feasible. The data and images that result from this study objectively capture the heterogeneous spontaneous nucleation (HSN) phenomenon under conditions near and at saturated boiling with short thermal input exponential periods. Additionally, a transition region and region dominated by the hydro-dynamic instability (HI) phenomenon leading to CHF were observed with increasing thermal input exponential periods. For subcooled boiling tests, the temperature overshoot phenomenon was consistently observed. The outcome of this study results in new data not previously available to the scientific community, a comparison of this new data against existing data from previous studies through discussion, and an empirically acquired map of HSN, transition and HI dominated regions leading to CHF.