Abstract
The objective of present study is to evaluate and to increase the effective coolant flow rate of VHTR (Very High Temperature gas-cooled Reactor) core whose thermal output is 50MW and core outlet gas temperature is 950°C, without changing the sizes of the core and fuel element, Four types of fuel element are discussed, they are two flange type pin-in-block fuel elements which have 18 fuel rods (P 18) and 36 fuel rods (P 36), a flange type multihole fuel element (MH 8) and a dowel type pin-in-block fuel element (P 15).The flow distribution analysis was carried out by flow network code which calculated coolant pressure, flow rate and temperature. As the result, the followings were obtained:Effective coolant flow rate (Weff) became lower in the order, MH 8, P 36, P 18 and P 15 fuels. Weff of the P 15 fuel was the lowest, because crossflow loss coefficient of dowel type fuel element was lower than that of flange type. Weff of the P 36 fuel was higher than that of the P 18 fuel, because of larger total cross section of coolant flow channels. Weff of the MH 8 fuel was higher than that of the P 36 fuel, because of larger equivalent diameter of the channels.This analysis clearly revealed that the effective coolant flow rate increased by using the fuel element with large values of crossflow loss coefficient, cross section and equivalent diameter of coolant flow channels.
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