Fragmentation characteristics of molten materials jet dropped into liquid sodium pool

Characterization of high-temperature nuclear fuel-coolant interactions through X-ray visualization and image processing

“…Intermediate-scale (< 4 kg melt) interactions between prototypic oxide fuel melts and sodium at the BETULLA facility [5] revealed both smooth, high-sphericity debris and fractured particles exhibiting irregular morphologies with significantly enhanced specific surface areas. Similarly irregular debris morphologies were observed for alumina [13] and metallic copper and aluminum melts [7]. The smooth debris population is thought to result from hydrodynamic fragmentation, which is greatly enhanced in the presence of a vapor flux counter-current to the jet [5].…”

“…The FCI is dictated in large part by the initial temperature of the melt-coolant interface, T I , and its relation to the coolant boiling curve and the melting point of the molten fuel material (in this case, steel). Various key temperatures, significant in determining the nature of the FCI [7,45], are summarized in Table 1. The initial interface temperature was estimated using a one-dimensional heat conduction relationship for a semi-infinite geometry, including correction for the latent heat of fusion [7].…”

“…Various key temperatures, significant in determining the nature of the FCI [7,45], are summarized in Table 1. The initial interface temperature was estimated using a one-dimensional heat conduction relationship for a semi-infinite geometry, including correction for the latent heat of fusion [7]. An interface temperature of 1485 K exceeds the coolant saturation temperature by 329 K and lies towards the upper end of the nucleate boiling regime, approaching the departure from nucleate boiling temperature, T I,DN B , at which the critical heat flux is observed [46,5].…”

“…Characterization has thus far been performed for each instantaneous sighting of an object within the X-ray video; however, in order to identify unique melt fragments, without double counting multiple sightings of the same mass, tracking is necessary. The tracking analysis was performed by searching a 7 6 D 0 wide neighborhood around each centroid in the subsequent frame. Where multiple candidate particles were observed within the neighborhood, the candidate most similar in estimated volume was selected.…”

“…The greatly enhanced thermal effusivity ( c p ρλ) of sodium, relative to water, dictates that the initial interface temperature between molten fuel and coolant is closer to that of the coolant. This reduces the potential for stable film boiling at the melt coolant interface [5], although film boiling can still be achieved when the sodium is close to saturation [6] or substantial melt superheats are observed [7]. This implies a departure from the classical explosion model [8,9], characterized by rapid heat transfer in the aftermath of the sudden destabilization of the vapor film [10].…”