LOWER STRUCTURE OF REACTOR FUEL ASSEMBLY AND THIMBLE SCREW FOR FUEL ASSEMBLY

摘要

PROBLEM TO BE SOLVED: To well attain a cooling function of non-nuclear fuel core structure and a limiting function of coolant flow during scram by improving a thimble screw connecting a guide thimble and a lower nozzle in a fuel assembly for pressurized water reactors. SOLUTION: In the fuel assembly, having a guide thimble for guiding a control rod and the lower nozzle, the thimble screw 30 connecting the guide thimble lower end and the lower nozzle, has a center axis part 33 provided with a thread face 41 screwing in the guide thimble and a head part 31 with a diameter larger than the fitting hole of the lower nozzle and a valve part 35. The center axis part 33 is provided inside a penetration water hole 53 and a guide hole which extends to the axis direction. The valve part 35 is provided with a valve box 45 and an inside valve ball 47, so as to allow the upward flow F of coolant and limit the downward flow.