Experimental study on fuel depressurization and its effect on dispersion

Most operating power reactors use oxide fuel in the form of uranium oxide (UO2) which is robust against high temperatures but suffers from poor mechanical performance at high levels of burnup. Currently, the maximum average burnup in light water reactors in the US is limited to prevent severe fuel damage during a hypothetical accident, most importantly the loss-of-coolant accident (LOCA). During a LOCA, high-burnup fuel has been observed to undergo extensive fragmentation, relocation, and dispersal through ruptured cladding, which has the potential to impact both the coolable geometry and long-term cooling of a reactor during such an accident. This paper presents the results from a series of experiments and denotes the approach used to collect such data in which test rods in a mock fuel assembly are filled with a surrogate nuclear fuel and subject to large pressure transients. The resulting deposition of fuel in adjacent subchannels are measured. The results of this study provide an improved method for estimating fuel mass distribution in a reactor core during a LOCA.