Assessment of Debris Bed Formation Characteristics Following Core Melt Down Scenario With Simulant System

Abstract

In a fast reactor safety analysis determination of the molten core conditions when it reaches the core catcher plate is one of the main factors after a postulated MFCI event. If large fragmentation and quenching is accomplished in the coolant column no major problems for main vessel attack would occur. If instead, a significant amount of melt would remain as a solid molten cake, potential for lower head penetration would exist. In the present study towards development of a model for core melting and debris settling on to a core catcher plate, early phase of liquid stream fragmentation progression due to hydrodynamic consideration was investigated with woods metal melt water system. The system selected simulates the hydrodynamic physical properties more closely that of liquid UO2-sodium system. Assessment of debris-bed forming characteristics was carried out with different coolant column and different melt temperatures with melt inventories up to 20 kg released from a nozzle of 8 mm diameter. Bed height, debris spread area, jet break up length and repose angle obtained are presented for a melt release rate of ∼ 600 g/s. Only solidified debris constituted the bed for a melt temperature of 100°C and water temperature of 29 °C, with 720 mm water height. The estimated average bed height, bed porosity and heap repose angle were 15 cm, ∼0.6 and 43° respectively. Solidified central columnar lump of height 30 cm was seen for a water column of 360 mm. Relative bed forming characteristics for melt temperatures of 120 °C and 220 °C are also presented. High speed video imaging was taken to assess the stream break up distance and heap formation dynamics. Bulk coolant temperatures close to the melt stream were also monitored. Dependence of particulate debris and bed characteristics on melt temperature, interaction height and melt inventory have been brought out.

Debris Bed Self-Leveling Mechanism and Characteristics for Core Disruptive Accident of Sodium-Cooled Fast Reactor: Review of Experimental and Modeling Investigations

“…en, the gas-injection method was further employed in the three-dimensional (3D) large-scale self-leveling experiments at Kyushu University, JAEA, and Xi'an Jiao Tong University to diminish the wall effect as well as extend the parametric range (e.g., gas flow rate) for extrapolating the experimental data and findings [32][33][34][35][36][37][38][39][40]. However, recognizing that the debris beds are probably composed of solid fragments and particles with varying sizes and porosities in the hypothetical CDAs of SFR through the interaction between melt and coolant [11,41], various particle components, such as single-size non-spherical particles as well as mixed particles (i.e., mixed-density, mixed-size, and mixed-shape particles), were subsequently applied to form the particle beds for the large-scale macroscopic self-leveling experiments [38-40, 42, 43].…”

Characteristics and Mechanisms of Debris Bed Formation Behavior in Severe Accidents of Sodium-Cooled Fast Reactors: Experimental and Modeling Studies

“…During the past decades, studies focusing on heat transfer within debris beds were performed [32][33][34][35][36][37][38][39][40][41]. In these investigations, in general, the initial debris bed shape was supposed to be homothetically piled [37], cylindrical [38], heap-like [40,41], and Gaussianshaped [39] or conical [16,[42][43][44].…”

Numerical study on sedimentation behavior of solid particles used as simulant fuel debris

“…A 92-mm long nozzle is attached at the lower part of the funnel with its lower end 720 mm from the debris tray (i.e., particle collector plate). The tray has an area of 1104 cm 2 and is located at the bottom of the vessel. The lower end of the nozzle was immersed in the water column of the vessel by maintaining water levels 105 mm above the release point of the nozzle.…”

“…Over the past decades, many researchers have studied the interactions between molten fuel and coolant. They mostly focused on the jet breakup characteristics [2][3][4] jet fragmentation and premixing -and on the debris formation processes [5]. However, there are very little exper- * Corresponding author.…”