Sensitivity Study of Calculation for FLECHT-SEASET Tests Using MARS Code

MARS code is a realistic multi-dimensional thermal hydraulic systems code developed by the Korea Atomic Energy Research Institute (KAERI) based on RELAP5 and COBRA-TF codes and is used to analyze the behavior of light water reactor transient. There are two main ways to improve the capability of MARS code in analyzing reflood phenomena: using better models in the source code or performing a sensitivity study to reduce user effect errors. The current paper presents a sensitivity study that was done to improve the capability of the MARS code in calculating reflood phenomena through assessment of FLECHT- SEASET tests. Totally 6 kinds of sensitivity study have been performed for Test 31504, Test 31701 and Test 31805 of FLECHT-SEASET experiment. The main results from this sensitivity study were the high importance of nodalization, grids modeling, using developer option 40 and housing heat structure to peak cladding temperatures and quenching time of reflooding process; their aspects must be considered when analysis of reflooding phenomena in FLECHT-SEASET. This sensitivity study is also useful for MARS code user when modeling and choosing input options to analysis of large break loss of coolant accident in nuclear power plant.