The Possibility of Local Detonations During Degraded-Core Accidents in the Bellefonte Nuclear Power Plant

It is possible to objectively determine whether a detonation can propagate in a given geometry (volume shape and size, obstacle configuration, degree of confinement) for a given mixture composition (concentrations of hydrogen, air, and steam); this is done by conservatively equating the detonation propagation criteria with the criteria for transition from deflagration to detonation. To reduce the degree of conservatism in this procedure, estimates of the probability of transition to detonation are constructed, based on subjective extrapolations of empirical data. A methodology is introduced that qualitatively ranks mixtures and geometries according to the degree to which they are conducive to transition to detonation. The methodology is then applied to analyzing the potential for local detonations in the Bellefonte reactor containment for a variety of accident scenarios. Based on codecalculated rates and quantities of hydrogen generation and calculated rates of transport and mixing, this methodology indicates a low potential for detonation except for one volume in a few cases.