Experimental study on in-vessel debris coolability in ALPHA program

In-vessel debris coolability experiments were performed in ALPHA program at JAERI. Aluminum oxide (Al2O3) produced by a thermite reaction was used as a debris simulant. Approximately 30 and 50 kg of Al2O3 were poured into a pool of nearly saturated water at the ambient pressure of ∼1.3 MPa formed in a lower head experimental vessel. The post-test visual observation and measurement using an ultrasonic technique indicated the formation of a thin porous layer at the vicinity of the surface of the solidified Al2O3 and the interfacial gap between the solidified Al2O3 and the lower head experimental vessel wall. Thermal transient characteristics on the lower head experimental vessel wall observed in the experiments implied that the interfacial gap and the thin porous layer in the solidified Al2O3 layer acted as a thermal resistance during the initial heat-up stage, and water subsequently penetrated into the interfacial gap to effectively cool the lower head experimental vessel wall. The maximum heat flux removed from the experimental vessel was ranged from ∼190 to 360 kW m-2 while the temperature of the vessel wall decreased rapidly. (orig.)