In a light-water reactor, during the normal operating condition, the UO~2~ nuclear fuel pellets undergo fragmentation primarily due to the presence of thermal stresses, fission gas development, and pellet-clad mechanical interaction. Under Loss of Coolant Accident (LOCA) conditions, a portion of fuel fragments can freely move downwards to the ballooning region due to the significant cladding deformation. The fuel relocation can localize the heat load and in turn, accelerate the cladding balloon and burst process. Cladding burst is of great concern because of the potential for fuel dispersal into the coolant and clad structural stability. In our work, we built up a finite element model considering cladding balloon, fuel relocation, and its resultant thermal feedback during LOCA condition with ABAQUS. The clad balloon model includes phase transformation, swelling, thermal and irradiation creep, irradiation hardening and annealing and other important thermal-mechanical properties. The mass of relocation model was verified against the analytical cases of single balloon and twin balloons. The cladding balloon model combined with fuel thermal conductivity degradation was verified against fuel performance code, FRAPTRAN. Finally, with the evolution of the pellet-cladding gap, the fuel mass relocation was calculated and compared against the IFA-650.4 transient test from the Halden reactor.


Modeling Axial Relocation of Fragmented Fuel During Loss of Coolant Conditions by Using ABAQUS

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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