Nuclear Mass Defect as the Direct Origin of Sub-Picosecond, Spherically Symmetric Impulsive Pressure Pulses at Fission Scission: The Scission Pressure Pulse Hypothesis and Three Falsifiable Experimental Tests in High-Burnup UO₂ Fuel

This work introduces the Scission Pressure Pulse (SPP) hypothesis, a novel physical framework proposing that the nuclear mass defect at the moment of fission scission acts as a direct source of an ultrafast, spherically symmetric pressure pulse. Unlike conventional models, which attribute fragment acceleration primarily to Coulomb repulsion, this study argues that a sub-picosecond impulsive mechanical event occurs simultaneously, generating extreme transient pressures on the order of 10⁹–10¹² Pa within the surrounding lattice. The hypothesis is motivated by several persistent anomalies observed in high-burnup UO₂ nuclear fuel that remain insufficiently explained by existing theories. These include: the emergence of a characteristic nanoscale grain structure (~100 nm scale), deviations from classical Arrhenius diffusion behavior indicating athermal transport mechanisms, and the stochastic, poorly modeled release of fission gases such as xenon and krypton. Within the SPP framework, these phenomena are reinterpreted as consequences of impulsive, shock-like energy deposition at the instant of mass defect formation, rather than purely gradual or thermally driven processes. The model further extends to explain unexplained damage halo morphologies in fission tracks, attributing them to the overlap of isotropic pressure waves with directional ionization damage. To ensure scientific rigor, the work proposes three independent and falsifiable experimental tests designed to isolate the thermodynamic, spatial, and angular signatures of the proposed pressure pulse. These include: precision calorimetry combined with fragment kinetic energy measurements to detect non-kinetic energy channels, ultrafast X-ray diffraction and acoustic emission techniques to capture transient isotropic strain waves, and angular neutron spectroscopy at perpendicular geometries to identify isotropic emission components. If validated, the Scission Pressure Pulse hypothesis would introduce a previously unrecognized mechanical channel of energy release in nuclear fission, requiring revisions to fuel performance modeling, radiation damage theory, and high-burnup fuel behavior predictions. Rather than replacing established fission physics, it complements existing models by incorporating mass-defect-driven impulsive dynamics as a fundamental component of the scission process.