Validation of GAMMA plus code for SFR application using FFTF loss-of-flow-without-scram test results

The GAMMA+ code developed by the Korea Atomic Energy Research Institute (KAERI) for the transient analysis of gas-cooled reactors was significantly improved to accommodate the characteristics of sodium-cooled fast reactors (SFRs). In this paper, to validate GAMMA+, the experimental data from loss-of-flow-without-scram (LOFWOS) test #13 in the Fast Flux Test Facility (FFTF) were used as an integral effect test result for the SFR. A combination of one-dimensional modeling and simplified two-dimensional modeling was employed to model the thermal-fluidic behavior of the FFTF, with the latter applied exclusively to the outlet plenum. A point kinetics model and various core reactivity feedback models were coupled with the thermal-fluidic model to analyze the unprotected loss-of-coolant-flow accident in the FFTF. The comparison of the FFTF test data and GAMMA+ simulation results showed good agreement, as the maximum outlet temperature of the hottest Proximity Instrumented Open Test Assembly (PIOTA) Row 2 was calculated with an accuracy of -2.1 degrees C. The two-dimensional modeling improved the accuracy of predicting the sodium temperature in the primary hot leg and enhanced the understanding of the thermal stratification in the outlet plenum. This study showed that GAMMA+ can contribute to the development of safer and more efficient SFRs as a safety analysis tool.