TRIGGERED STEAM EXPLOSIONS WITH CORIUM MELTS OF VARIOUS COMPOSITIONS IN A NARROW INTERACTION VESSEL IN THE TROI FACILITY

摘要

Three triggered steam explosion experiments using corium melts of various compositions were performed in the TROI facility. The interaction vessel was 0.3 m in diameter. The melt compositions were 70:30 (UO_2:ZrO_2) corium, pure zirconia, and partially oxidized corium (UO_2:ZrO_2:Zr:SS = 53.91:23.09:12.00:11.00 in weight percent). The test with 70:30 corium was performed with a 0.95-m-deep water pool under an elevated pressure of 0.205 MPa, while the others were performed with a 1.3-m-deep water pool under atmospheric pressure. The water temperature was maintained at room temperature. The melt mass released to the water pool was ～10 kg for each test. The test with 70:30 corium resulted in a triggered steam explosion, considering the long duration of the dynamic pressure and the large amount of fine debris. The dynamic pressure trace from the steam explosion seemed to be superimposed on that from the external trigger. The test with pure zirconia led to multiple spontaneous steam explosions before any external triggering. The zirconia melt confirmed its explosivity. The spontaneous steam explosion with pure zirconia seems not to be affected by the water depth and diameter of the interaction vessel. The test with partially oxidized corium also resulted in a spontaneous steam explosion before an external triggering. These results are different from the previous TROI tests with 80:20 corium in a narrow interaction vessel of 0.3-m diameter, in which no spontaneous steam explosions occurred. The geometry of the interaction vessel used in these tests does not seem to influence the occurrence of a steam explosion, but the corium composition does affect the triggerability of it.