Experimental investigation of debris bed relocation behavior by bottom gas-injection

For the core disruptive accident (CDA) of sodium-cooled fast reactor (SFR), the molten fuel or steel is solidified into debris particles, which form debris bed in lower plenum. When the boiling occurs inside debris bed, the flow of coolant and vapor makes debris relocated and flattened, which called debris relocation. Because the thickness of debris bed has great influence on the cooling ability of fuel debris in low plenum, it’s very necessary to evaluate the transient changes of the shape and thickness in relocation behavior for CDA simulation analysis. To simulate relocation behavior, a large number of bottom gas-injection experiments were performed to study the effects of different factors such as particle properties, bed height, gas flow rate, gas injection location and horizontal flow rate on the transient process of debris bed relocation. By analyzing experimental data, we further verified a semi-empirical onset model developed before, which is based on force balance analysis of particles and can reasonably predict the onset of debris bed relocation behavior.