EVALUATION OF RECENT RIA-SIMULATION EXPERIMENTS WITH THE FALCON FUEL PERFORMANCE CODE

This paper provides a review and analytical assessment of several RIA-simulation experiments performed between 1996 and 2002 on test rods refabricated from high burnup commercial UO2 fuel rods. The evaluation focused on twenty-four (24) RIA-simulation tests, including eight (8) tests with cladding failure, that were performed in the CABRI (REP-Na) and NSRR test facilities on both PWR and BWR rod segments with burnup levels between 45 and 75 GWd/tU. Experimental data, including available PIE reports, were collected, and the experiments were analyzed using the FALCON fuel behavior code to gain insights into the thermal and mechanical state of the test rods during and following the power pulse. The key conclusions from this evaluation are: 1) pellet thermal expansion is the primary PCMI loading mechanism during the early phase of the pulse in LWR UO2 fuel up to a peak pellet burnup of 75 GWd/tU, 2) cladding integrity is controlled primarily by a combination of the hydride phase (hydrogen content, distribution, and orientation) and the cladding temperature, and 3) post-DNB cladding temperature excursions following the power pulse can allow for cladding deformation beyond pellet thermal expansion.