NUMERICAL STUDY ON THERMAL BEHAVIOUR AND MODERATOR BOILING IN TWO NUCLEAR CHANNELS OF IPHWR 220 MWE REACTOR AT DIFFERENT HEAT INPUTS DURING LOSS OF COOLANT ACCIDENT (LOCA)

• Non-uniform temperature distribution at the circumference with maximum at region closer to both the channels. • Maximum temperature of core 2534 °C and 1998 °C of PT at 4500 W/m 2 shows an alarming situation. • Boiling started after 1500 W/m 2 heat flux and Moderator depletion was highest at 4500 w/m 2 . • Upto 4500 w/m 2 moderator acted as an effective heat sink. Indian PHWRs, derived from CANDU designs, are vulnerable to postulated accident scenarios like LOCA with simultaneous ECCS failure. To investigate such conditions, this study analyses the temperature distribution in the pressure tube (PT) and calandria tube (CT) under voided channel conditions using steady-state thermal analysis and ANSYS Fluent at various heat fluxes (900, 1500, 2500, 3500, and 4500 W/m 2 ). The PT showed negligible circumferential temperature variation, while the CT exhibited significant heating near neighbouring channels. As heat flux increased, the moderator surrounding the CT progressively heated and eventually began to boil beyond 1500 W/m 2 . Boiling was more intense near the lower region of channel 1 and the upper region of channel 2. The trend in boiling behaviour remained consistent across different heat fluxes, although the onset occurred earlier at higher flux levels. These findings highlight critical thermal behaviour under accident-like conditions and can support safety evaluations of reactor designs.