RELAP5/mod3.3 Analysis of Natural Circulation Cooldown with One Inactive Loop for Nuclear Power Plant Krško (NEK)

The paper presents the RELAP5/mod3.3 analysis of natural circulation cooldown with one inactive loop for Nuclear Power Plant Krško (NEK). aim is to determine limiting rates during operator recovery actions minimize effect flow stagnation in loop. Since this typical asymmetrical transient, NEK model split reactor vessel was developed (models and core were axially divided two parts) used analysis. several transients cooldown, loop, different time after shutdown (different decay heat) performed. extreme conservative assumptions applied analyses, i.e. complete loss feedwater (FW) auxiliary (AF), including turbine driven (TD) AF pump, has started SG completely dry (inactive). analyses show that rate shall be significantly reduced, and, based on results procedure ES-0.2 “Natural Circulation Cooldown” modified.