Core-concrete interactions with overlying water pools

An inductively heated experiment, WETCOR-1, was executed as part of the NRC research program to study and evaluate core debris coolability by overlying water pools. A 34 kg charge material of Al2O3 - CaO was heated to melting at 1850 K within a 32 cm diameter tungsten annulus heated to 2100 K. Ablation of a limestone/common sand concrete basemat was allowed to begin and water at 293 K was then added continuously at 60 liters per minute. Both power and water flow were terminated after a 30 minute test period. The main observations from the WETCOR-1 test were that there was an initial period of vigorous melt-water interaction which lasted for 1-2 minutes and was replaced by a relatively stable crust-water geometry with substantially reduced rates of energy transfer to the overlying water. These rates of energy transfer were insufficient to either quench the melt or to discontinue the pre-established melt pool-concrete ablation process. In summary: The main purpose for performing the WETCOR-1 Test was to ascertain whether or not melt-coolant interactions were unstable for extended periods during the initial interaction period. Extended instabilities might allow for extended periods of very high rates of heat transfer which would result in relatively rapid bulk freezing with very little interaction with the concrete basemat. Extra effort was made in the design and execution of the WETCOR-1 experiment to extend the time for unstable melt-coolant interaction. This included the use of tungsten sidewalls which were heated to temperatures well in excess of the freezing point for the molten pool, the use of slowly freezing oxide materials with relatively high specific heats of 1.3 J/g-K as compared to 0.4 J/g-K for UO2, and the use of a concrete basemat with an established high gas production rate. In addition, the power input to the melt was held to relatively low levels and the melt pool height was relatively shallow. The main observations from the WETCOR-1 Test were that there was indeed an initial period of vigorous melt-water instability but that this period only lasted for 1-2 minutes and was replaced with a relatively stable crust-water geometry with substantially reduced rates of energy transfer to the overlying water. These rates of energy transfer were insufficient to either quench the melt or to discontinue the pre-established melt pool-concrete ablation process. The total energy to the overlying water pool was quantified by measuring the temperature rise in a water supply which was flowing constantly at 60 liters per minute. Initial energy removal rates were 300 kJ/s. These rates steadily dropped to 60 kJ/s after a few minutes and then were relatively constant for the remainder of the test. This total energy must be partitioned among the crucible wall surface area, the tungsten surface area and the melt pool surface area to obtain heat flux information. A quantitative estimate of the energy transfer rates from the debris surface to the water pool is 1.5 MW/m2 initially with an exponential drop to .4 MW/m2 at 8-10 minutes and times thereafter. A comparison of the WETCOR-1 result to previous experiments and analysis indicates that no new dominant phenomena have been identified and that these results are comparable to those for the FRAC, SWISS, and MACE tests. In each of these previous tests there have been only short periods of high energy release, the concrete ablation process has continued, and stable crusts have formed which limited the upward heat flux to.3-.8 MW/m2. None of these tests have defined the regime of coolability where the debris is solidified, all ablation is stopped, and the water pool is able to remove the decay heat power. Our next goal is to analyze the extensive data return from the WETCOR- 1 test and to compare these results to the data return from the MACE program sponsored by EPRI. Future WETCOR tests will be designed to focus on defining and bounding the limit of debris coolability by varying the debris depth, the debris power, and the debris composition