Analysis of Rod Withdrawal at Power (RWAP) Accident using ATHLET Mod 2.2 Cycle A and RELAP5/mod 3.3 Codes

The system code ATHLET (Analysis of THermal-hydraulics Leaks and Transients) is being developed by the Gesellschaft für Anlagen-und Reaktorsicherheit (GRS) mbH in Garching, Germany. In paper, an overview activities performed at Faculty Electrical Engineering Computing (FER), University Zagreb, application transient analyses for NPP Krško (NEK) presented. Newly, NEK input deck released version (Mod 2.2 Cycle A) has been developed. For that purpose, data base maintained FER last two decades primarily development standard RELAP5 was used. model validated analyzing Rod Withdrawal At Power (RWAP) accident nominal power. results steady state calculation as well RWAP were assessed against analysis RELAP5/mod 3.3 code. both calculation, simulated constant reactivity insertion rate equal to 2.4 pcm/sec. analysis, fluid dynamic options tested primary side: a) case with 5 conservation equations mixture level b) two-fluid separate liquid vapour phases all volumes except pressurizer where equations+mixture retained. Steam Generators (SGs) built using basic elements together dedicated separator model. a option thermal mechanical non-equilibrium (6 equations) have shown very good agreement calculation. small differences main physical parameters between models obtained.