Two analyses for Chinshan nuclear power station (CSNPS) show the RETRAN applications in reactor operations. One was used to find the root cause of a reactor trip due to high neutron flux (APRM Hi-Hi). Two of the four turbine control valves failed and closed rapidly. Whether the pressure increase caused the APRM Hi-Hi reactor scram was questioned. An analysis was performed to determine the way to bring unit 1 back to power. The second analysis was conducted to provide an evaluation of the consequences before a plant test planned for late 1994 to consider a design change upgrading recirculation flow control. However, there were concerns about reactor scram during execution of the test and the potential of entering the exclusive region of instability. Sensitivity studies on several different combinations of initial conditions and feedwater flow coastdown curves indicated potential problems with reactor trip and stability.