The UO₂ Power-to-Melt Experiment Performed in the High Burnup Chemistry International Program

In this work, a detailed reevaluation of a past power-to-melt experiment performed within the so-called High Burnup Chemistry project is provided. A pressurized water reactor–type UO₂ fuel rod was base irradiated in Belgian Reactor 3 up to a peak pellet burnup of 60 MWd/kg_U. After base irradiation, the rod experienced a power ramp experiment in Belgian Reactor 2, reaching a ramp terminal level of 70 kW/m (later adjusted to 66 kW/m). Extensive post-irradiation examination was performed after both the base irradiation and the power ramp experiment. After the power ramp experiment, rod cladding failure and local fuel melting were observed. Fuel melting was observed in an 85-mm region around the peak power pellet with a normalized molten fuel radius in the range r/r₀ = 0.20 to 0.27. The threshold power for melting derived from this experiment was 63.0 ± 4.4 kW/m.