Modeling the nukiyama curve for water-cooled fusion divertor channels

A conclusive safety assessment of a fusion reactor requires that the thermal response of the divertor assembly is known with a high degree of accuracy. Such accuracy is mandated because the divertor assembly is subjected to the highest levels of incident heat flux within the reactor. In order to accurately predict the thermal response of the divertor's cooling channels, it is necessary to have a complete model of the Nukiyama boiling curve for the water conditions of interest. Currently published models of the Nukiyama curve for fusion divertor channels have only included the regimes of forced convection, partially and fully developed nucleate boiling, and the local CHF. This paper presents a model that includes these pre-CHF regimes and the post-CHF regime of transition boiling. The model is unique because (1) it tightly integrates the respective heat transfer correlations and makes heat transfer predictions for the water conditions and incident heat fluxes that are fusion-specific, (2) predicts post-CHF heat transfer properties for a swirl tape divertor channel, and (3) validates its predictions via comparison with experimental data. Based on these three points, this model is considered as one of the best available methods for predicting the Nukiyama curve for a water-cooled fusion device.