A code environment based on the CORETRAN and RETRAN-3D codes for the three-dimensional (3-D) kinetic analysis of transients in Swiss light water reactors is currently being developed and implemented within the STARS project at the Paul Scherrer Institute (PSI). As a first step in the application of these codes, an assessment of both codes for the analysis of reactivity-initiated transients in pressurized water reactors (PWRs) was performed. For that purpose, the Nuclear Energy Agency benchmark exercises, consisting of rod ejection and uncontrolled rod bank withdrawal transients, were selected. These analyses showed that very satisfactory results could be obtained with both CORETRAN and RETRAN-3D. In this paper, a summary of the PWR results, along with an emphasis of important modeling options that were identified during that work, is presented. As a second step, it was considered important to assess both codes for boiling water reactor (BWR) reactivity transients. Therefore, in addition, the analysis of a hypothetical beyond-design-basis rod drop accident for a Swiss BWR core at end of cycle is presented in this paper. This transient, which was previously analyzed with another 3-D code at PSI, shows that also for BWRs, both codes give satisfactory results.
