Experimental investigation on quenching behavior during reflooding in a 3 × 3 dual-cooled annular rod bundle

Abstract

The internally and externally cooled annular fuel is an innovative fuel geometry proposal for advanced PWR, which could provide a substantial increase of power density while maintaining or improving safety margins. The quenching behavior of annular fuel during reflood phase in LOCA is more complicated than cylindrical solid fuel, owing to the geometrical difference and the coupling effect of dual-cooling. However, the investigation focusing on quenching characteristics in annular fuel geometry is very little. In the present study, an experimental study on quenching behavior of bottom reflood in a 3 × 3 dual-cooled annular rod bundle was carried out under various test conditions (reflood velocities from 0.025 to 0.15 m·s−1, inlet subcooling from 10 to 80°C, peak cladding temperature from 300 to 900°C, and linear power density from 0 to 1.58 kW·m−1). Self-designed indirect-heating annular rods were employed to provide an axial uniform power distribution in this experiment. It was found that the quenching process on external and internal surfaces of annular rod bundle was almost synchronous. The parametric effects on quenching behavior, i.e. precursory cooling rate, quench front propagation velocity (Vqf) and minimum film boiling temperature (Tmin), were investigated in detail. Earlier occurrence of quenching downstream the grid spacer was also observed under low inlet subcooling and high peak cladding temperature conditions. In addition, several correlations for Tmin were assessed against the present results. Kim correlation was in good agreement with the present data, with the mean absolute errors of 7.81% and 7.55% for outer and inner channels respectively.