Review and analysis of the high-burnup fuel fragmentation and dispersal data: Comparing LOCA test programs

Abstract

A significant amount of data have been collected on high-burnup fuel fragmentation and dispersal; however, the data from various programs have been analyzed using different approaches. These approaches have led to differing observations, which regulators worldwide may interpret as uncertainties, and therefore, the regulators have to incorporate this uncertain transposability to safety application. Consequently, utilities may face overly restrictive regulations that impact their operating conditions and economic viability. Therefore, it is increasingly important to develop a standardized approach to data analysis that accounts for variations in test programs, conditions, and methodologies. Such standardization would improve understanding of the differences in test results and help reduce uncertainties. This paper provides a comprehensive review of data collected from Oak Ridge National Laboratory, Argonne National Laboratory, Studsvik, Japan Atomic Energy Agency, and the Halden reactor. In addition, a standardized approach to analyzing the data will enable a thorough assessment of differences in the data. It was noted that tests performed at Oak Ridge and Argonne generally showed less dispersal than those performed at Studsvik; therefore, test procedures were compared to identify potential differences and their possible impacts on the results. The two datasets were compared to determine the factors contributing to increased dispersal under semi-integral test conditions. The analysis revealed that no single parameter alone governs fuel dispersal; however, the data consistently show that increased cladding deformation is associated with greater fuel mobility and, consequently, a higher likelihood of dispersal. Additionally, two critical data gaps were identified: (1) the impact of plenum volume on rupture temperature and (2) the influence of rupture location on fuel dispersal. Further testing is necessary to better understand these effects, as addressing them could contribute to better assessment of the extent of fuel dispersal.