On the applicability of Ishii's similarity parameters to integral system test facilities

This note evaluates the applicability range of Ishii's similarity parameters to integral system test facilities (IST) subjected to slow Small-Break Loss-Of-Coolant Accidents (SBLOCA). It is recognized that the development of Ishii's parameters is theoretically sound and rigorous. However, the range of applicability should be limited to conditions for which the original assumptions hold. For the IST facilities, the major out-of-range application is that Ishii's parameters, developed from the analysis of an open system, are applied to closed integral systems. An enthalpy transport analysis of a closed system demonstrates that such an extrapolation leads to erroneous conclusion. It is shown that two mechanisms which distinguish a closed system from an open system have significant effects on the scaling of system phenomena. One is the interaction/feedback mechanism, which is an inherent characteristics of an integral system. Another is the limited amount of available vapor space in closed systems. (orig.)