Improvement of GAMMA+ code for system transient and thermo-fluid safety analysis of sodium-cooled fast reactors

Abstract

The GAMMA+ code was originally developed for the system transient and safety analysis of a high temperature gas-cooled reactor (HTGR). Researches on the extension and improvement of the capability of the GAMMA+ code for applications to a sodium-cooled fast reactor (SFR) have been progressive. This paper summarizes the major items achieved on improvements of the GAMMA+ code to simulate thermo-fluid phenomena in an SFR. These include thermo-physical properties of sodium, empirical models and correlations (i.e., pressure drop and heat transfer correlations), a simplified model for stratified sodium and gas flow, and reactivity feedback models dedicated to an SFR. Such items for the improvement are essential to accommodate the features of an SFR which are different from those of an HTGR. The verification and validation of the improved version of GAMMA+ have been in progress. Initial efforts to verify and validate the improved version of GAMMA+ are also summarized in this paper. The topics of the efforts include conceptual problems having analytical solutions, heat exchanger performances, and a plant trip test of Monju. The results of the verification and validation studies demonstrate the good performance and reliability of the improved version of the GAMMA+ code for analyzing one-dimensional (1-D) as well as multi-dimensional thermo-fluid phenomena in an SFR.