Experimental study on transient void behavior in subcooled water during reactivity initiated accidents under low pressure conditions

A series of experiments for fast transient void behaviors during reactivity initiated accidents has been performed with a single simulated fuel rod under the atmospheric pressure condition. A fast-response impedance technique was applied for void fraction measurement. The comparison between the impedance and x-ray techniques indicated that the difference between both techniques was within the allowable range of accuracy for fast transient conditions. Experimental database were obtained, including the onset timing of net vapor generation, local void fraction, water temperature and pressure. The Saha and Zuber model overestimated the experimentally obtained local water subcooling at the onset of net vapor generation. The inlet water subcooling largely influenced the variation of local void fraction. In the case with larger inlet water subcooling, grow and collapse by condensation of voids was repeatedly observed, which suppressed a continuous increase in local void fraction. (authors)