The purpose of the Experimental Vacuum Ingress Test Apparatus (EVITA) program is to obtain useful data for safety analysis of serious potential accidents for ITER. The numerical predictions for EVITA have been done by using the MELCOR, PAX, and CONSEN codes under conditions in which temperature is always kept above 273 K. In the EVITA program, high-temperature and high-pressure steam is injected into the vacuum vessel housing the cryogenic plate. Consequently, the phenomena that occur in the vicinity of the impingement surface are expected to be exceedingly transient and complex. The subject of this study is the development of a valid numerical code for the EVITA program. A key point of this study is to describe all of the phenomena, for example, shock-wave propagation and phase change under low pressure. In this study, the C-CUP method is employed, which describes these phenomena. To investigate phenomena with EVITA, numerical analysis had been done with several conditions concerned with input power. As a result, we succeeded in obtaining a fundamental code for the EVITA program as well as interesting views of EVITA.