The Korea Atomic Energy Research Institute (KAERI) has been developing a dual-cooled annular fuel for the power uprate of 20% in an optimized pressurized water reactor (PWR) in Korea, OPR1000. The dual-cooled annular fuel is configured to allow the coolant flow through the inner channel as well as the outer channel. Several thermal-hydraulic issues exist for the application of the dual-cooled annular fuel to OPR1000. One of the key issues is the hypothetical event of inner channel blockage because the inner channel is an isolated flow channel without the coolant mixing between the neighboring flow channels. The inner channel blockage could cause the Departure from Nucleate Boiling (DNB) in the inner channel that eventually results in a fuel failure. A long lower end cap for the annular fuel was invented to provide flow holes by perforating the side surface of the end cap body. The side holes in the lower end cap are expected to supply a minimum coolant in the inner channel in order to prevent the DNB occurrence in the event of partial or even complete blockage of the inner channel entrance. But due to very unusual shape of the lower end cap, it is difficult to estimate the flow resistance of the side flow holes using empirical equations available in the open literatures. Experimental and computational fluid dynamics (CFD) study were performed to investigate the bypass flow through the side holes of the end cap in the case of complete entrance blockage of the inner channel. The form loss coefficient in the side holes was also estimated by using the pressure drop along the bypass flow path.

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