Numerical study on the effect of moderator depletion on thermal behaviour of fully voided 220 MWe IPHWR channel during LOCA.

• The cooling capacity of moderator decreases with moderator depletion. • The highest temperature reached in the PT for 3500 W/m2 heat input was 1684.3℃. • The highest temperature reached in the CT for 3500 W/m2 heat input was 254.51℃. • Moderator acted as an efficient heat sink up to 20 mm moderator depletion at 3500 W/m2 heat input flux. A steady-state heat transfer analysis is conducted on a completely voided concentric nuclear channel within an Indian pressurized heavy water reactor (IPHWR) to evaluate the temperature distribution in both the pressure tube (PT) and calandria tube (CT), taking into account the depleting moderator condition. The simulations encompass a range of five distinct moderator levels i.e., 10–30 mm at an interval of 5 mm by varying the input heat flux in the fuel bundle at values of 980 W/m2, 1500 W/m2, 2500 W/m2, and 3500 W/m2. The results showed that as the moderator depletes, the temperature difference from top to bottom exhibits an increasing trend in both the pressure tube (PT) and the calandria tube (CT). The maximum top to bottom temperature deviation in the CT was 83.21 %, and in the PT was 0.34 %, at an input heat flux of 2500 W/m2 with 30 mm moderator depletion. The CT is observed to attain a boiling temperature of water at 30 mm moderator depletion for the heat flux of 980 W/m2. Further, for higher heat inputs i.e., 2500 W/m2 and 3500 W/m2, CT attains the temperature more than the boiling point of moderator at initial depletion level which means that the boiling of the moderator starts form the initial depletion level. This scenario may further lead into moderator voiding which may results into the meltdown condition. These results will be helpful to determine the conditions where the temperature rise becomes uncontrollable, and to access the threshold condition for meltdown. [ABSTRACT FROM AUTHOR]