b'Determining the RoleBy providing a separate-effect investigation to fragmentation issues, this project of Fission Gas Bubble Pressureresulted in a remarkable understanding of phenomena causing structural in Fuel Fragmentation Duringmodifications of ceramic fuels at high burnup.Off-normal Conditions:A mechanistic understating of fuel behavior has been acknowledged as a primary need by the international scientific and industrial community A Separate-effect Study in the past decade, particularly in advancing knowledge of the causality of inputoutput relationships for phenomena that impact the economics of the power plant and results in significant economic loss. One example is the limit in discharge burnup that is due to the concerns of fuel fine fragmentation during loss-of-coolant accident of high burnup fuel. In this project, we clarified the role of fission gas bubble pressure in fragmentation under an accelerated schedule. TOTAL APPROVED AMOUNT:Instead of deploying integral irradiation tests that are expensive and take a long $973,500 over 3 years time to implement and execute, we deployed separate-effect studies under controlled conditions to address fuel safety issues and pair the experimental results PROJECT NUMBER:with model developments. At the same time, sensitivity studies from simulations 19A39-061 highlight the most critical parameters that drive fragmentation used to determine PRINCIPAL INVESTIGATOR:the experimental test matrix. Hence, we minimize the number of tests and ensure Fabiola Cappia evaluation of the most significant conditions and increase the impact of testing results. From the experimental side, we induced microstructural modifications, CO-INVESTIGATORS: such as recrystallization or bubble formation by engineering samples through Andrea Jokisaari, INL advanced sintering techniques and ion-implantation, overcoming the issue of high Blair Grover, INL radioactivity. The goal was achieved by partnering with Rensselaer Polytechnic Spencer Parker, INL Institute and Argonne National Laboratory and by developing a dedicated apparatus Jie Lian, Rensselaer Polytechnic Institute devoted to executing fast heating transients at INL, which expanded the laboratorys Kun Mo, Argonne National Laboratory experimental capabilities. New models were implemented at engineering-scale and meso-scale levels to address the fuel fragmentation. The models were used to simulate the project testing conditions and fine-tune the test matrix.Phase-field fracture simulation of a random array of nanoscale bubbles in a 100 nm2 range.(a) The propagated crack is shown in red. Notice how some bubbles display cracks that are not interconnected, while large interconnections exist between other bubbles. (b) The maximum principal stress in the material for bubbles with an overpressure of 200 MPa. The magnitude of the maximum principal stress between two bubbles depends on bubble spacing, with large values occurring between closely spaced bubbles.28'