Development of the fuel assembly pin-by-pin model in the KORSAR/GP code

This paper presents the pin-by-pin thermal-hydraulic model of the fuel assembly (FA) developed with the KORSAR/GP code. Its application for simulation of separate fuel rods in the FA is demonstrated. Usually the safety margins are calculated using a «hot channel» model for NPP (Nuclear Power Plant) safety analysis. This approach is conservative. The pin-by-pin simulation provides more realistic results and wider safety margins. The new KORSAR/GP pin-by-pin model was cross-validated with the TIGR-SP code which is used by OKB «GIDROPRESS» for FA steady-state operation assessment. DNBR (departure from nucleate boiling ratio) difference between KORSAR/GP and TIGR-SP does not exceed 3%. Thus, the KORSAR/GP pin-by-pin model provides correct results. The nodalization of the developed model consists of parallel 1D hydraulic elements (channels). The cells of these channels are connected to each other by special elements – cross-junctions and turbulent mixing elements (CJ and TM). The paper also deals with the investigation of influence of these elements on DNBR calculation.