The moderator in the Calandria of a CANada Deuterium Uranium (CANDU) reactor serves as a backup heat sink in a Loss of Coolant Accident (LOCA) combined with a Loss of Emergency Coolant Injection (LOECI) accident scenario. This requires that the heat from the fuel be transferred through the ballooned/sagged Pressure Tube and the contacted Calandria Tube (CT) to the moderator. Increasing the heat transfer to the moderator will enhance the safety of the reactor by increasing the margin to Calandria Tube Rupture and ensuring the fuel is cooled. Conceptual designs were assessed to determine their potential for increasing heat transfer to the moderator in accident scenarios. Three different design options for a CT have been investigated using numerical simulation techniques. The CT design options include fins or ribs of different sizes and combinations. The fins and ribs provide improved heat transfer. Analyses results have shown that the design options yield an increased heat transfer with a minimal impact on moderator flow. The analysis has determined that the ribbed design option is superior in terms of heat transfer enhancement.

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