Experimental and Numerical Investigation into Temperature Distribution of a Simulated PHWR Coolant Channel Under Heatup Condition

The postulated dual-failure accident, i.e., loss of primary coolant flow along with impairment of the emergency coolant injection system, leads to peak fuel temperatures. It is well known that the temperature of the fuel assemblies is one of the significant factors that affect the outcome of an accident. Therefore, the present work aims to thoroughly investigate the thermal response of a single channel under postulated accident conditions. An experimental system was developed to capture the steady-state heat and temperature distribution in a representative 37-element fuel channel for a decay heat of 6.13 kW. Ohmic heating of the fuel rod simulators (FRSs) mimicked the generation of radioactive decay heat. Numerical simulation was also performed using the Fluent 19.1® code, and the discrete ordinates method was used to solve the radiative transfer equation. Based on the experimental results and the simulation results, it was found that the maximum Zircaloy-4 cladding temperature ≈850°C to 870°C was in the center ring. The temperature was found to vary around the circumference for each of the FRSs. Furthermore, the outer ring FRSs that had the lowest temperature developed the highest circumferential temperature gradient. In the pressure tube, the average circumferential temperature gradient obtained from the experiment and the simulation was 3.76°C/radian and 3.85°C/radian, respectively. Between the calandria tube and the moderator, the heat transfer coefficient was estimated to be around 822.3 W/m²‧K.