Development of a system code MEDUSA and its application to the feedwater line break

A computer program, MEDUSA, has been being developed as a thermal-hydraulic analysis tool for the nuclear power plant system. It is based on the COBRA-TF computer program that deals mainly with the two-phase core thermal-hydraulics of the vertical channels. The noteworthy improvement is to introduce the Main Steam Safety Valves and the Pressurized Safety Valves for the Non-LOCA type accident analysis in addition to the features described in the reference [2]. The system analysis capability has been being evaluated by applying the code to the various analyses of the system transients. As a continuing effort from the LOCA analysis [2], Feedwater Line Break (FLB) accident for the typical pressurized water reactor is selected for this study. The analysis results are compared with those of the design code CESEC-III for several important system parameters. This comparison shows that there is no problem to apply the new code to the FLB type accident analysis