Prediction of Reflood Behavior of Deformed Rods with Non-Deformed Rods in Ather 5×5 Rod Bundle Test Using Mars-Ks Code

An experiment simulating the reflood phenomena with deformed fuel rods array conducted at ATHER 5x5 rod bundle facility is calculated using MARS-KS code in order to validate the code and modeling scheme for the deformed condition following a LOCA. In the experiment, the deformed fuel rods are simulated by the heater rods with sleeves on the outside. To represent properly the rods, the sleeve thermal conductors, the steam gap between the heater rod and the sleeve, the fouling factor into the heat transfer area by contact between adjacent sleeves are implemented. The portion into which the sleeve is installed and the portion not are modeled as separate heat structures. Also the heat loss through the housing of the test section is modeled. Calculations are conducted using one-dimensional models with single channel and two channels and three-dimensional model by ‘multid’ component of the MARS-KS code. From the calculation results, the predictability of the code and the present modeling scheme is discussed in terms of overall response, peak cladding temperature, and time of quenching. Also the differences in phenomena between the deformed rods and un-deformed rods and their reasons are discussed