Analysis of reactivity transients using a coupled three-dimensional thermal-hydraulic kinetics code

This paper summarizes the current status of Penn State's version of the coupled three-dimensional (3-D) thermal-hydraulic / kinetics TRAC-PF1/NEM code for PWR transient and accident analysis and describes future developments and applications. The TRAC-PF1/NEM methodology utilizes closely coupled 3-D thermal-hydraulics and 3-D core neutronics transient models to simulate the vessel and a 1-D simulation of the primary system. This approach enables one to model in a 'best estimate' manner complex transients involving 3-D effects. An efficient and flexible cross-section generation procedure was recently developed and implemented into TRAC-PF1/NEM. These features make the coupled code capable of modeling PWR reactivity transients, including boron dilution transients, in a reasonable amount of computer time. Three-dimensional studies on hot zero power (HZP) rod ejection and main steam line break (MSLB) transients in at PWR, as well as a LBLOCA accident, have been accomplished using TRAC-PF1/NEM. The results obtained demonstrate that this code is appropriate for the analysis of the space-dependent neutronics and thermal-hydraulic coupled phenomena related to many current safety issues