Two Dimensional Performance Analysis of Small HTR Residual Heat Removal System in DLOFC Condition

This research is aimed to investigate a 10 MWth HTR thermal parameter response to long-term Depressurized Loss Of Force Cooling (DLOFC) accidents. By using two dimensions analysis in radial and vertical direction, comparing to one dimension in radial, the results are expected to be closer to real conditions. The method used is firstly develop a Matlab-based temperature distribution analysis program that solves the two-dimensional conduction equation in cylindrical coordinates and also in a function of time. Using the program, DLOFC simulations were conducted over a period of 588 hours after 200 hours of time needed to reach steady state close to normal operating conditions. It can be evaluated how far the temperature of all reactor components starting from the core to the concrete wall will rise and whether they are within their safety limits. The results show that during DLOFC, temperature of all reactor components increase toward the maximum value before decreasing again. The maximum temperature of the reactor core, reactor vessel and concrete wall are respectively 1080°C, 231°C, and 96.1 °C. The maximum value of the core temperature is reach at 11.1 hours after accident. The water temperature in the cooling panel, for 50 m³ of water volume, has reached its boiling point of 100°C at around 100 hours after DLOFC and decreasing again at the time of 360 hours. Evacuation of the residual heat is not only through the cooling water panel, but also through the three directions of concrete wall, ie top surface, peripheral surface and bottom surface. During DLOFC, the maximum heat power evacuated through top, bottom and peripheral surface are respectively 4.57 kW, 4.84 kW and 29.04 kW. The maximum heat power evacuated by water panel is 52.7 kW. It can be concluded that the reactor remains safe in very long time of DLOFC. (paper)