The diagram of the CANDU in Figure 3.6 shows the positioning of the two re­fueling machines at either end of one of the horizontal channels. Each machine is a pressure vessel that can be connected to the ends of the horizontal channel, becoming pressurized to system pressure when a plug at the end of the chan-

NEW IRRADIATED IRRADIATED FUEL FUEL FUEL ASSEMBLY DISMANTLING BUFFER STORE Figure 7.3: Fuel-refuel sequence for AGRs.

nel is removed. Each refueling machine contains a magazine that can hold ei­ther spent fuel (at the discharge end) or fresh fuel (at the inlet end). A ram is used to push the fuel bundles through the channel. The success of these refu­eling machines has contributed significantly to the very high load factor (pro­portion of time for which the reactor is at power) achieved in the C^NDU reactors as a result of on-load refueling. For a typical 600-^W(e) reactor, ap­proximately 70 fuel bundles are changed each week. The fuel in the machines is cooled by means of a flow of heavy water taken from the main reactor coolant circuit and passed through the machines back into the fuel channels.