COUNTER MEASURE FOR FOREIGN ARTICLE FOR LOWER NOZZLE OF 17x17 TYPE PWR FUEL ASSEMBLY

摘要

PROBLEM TO BE SOLVED: To prevent invasion of line foreign articles into a fuel assembly by minimizing the projection area of the lower nozzle flow path of a 1717 type fuel assembly to a lower core plate and controlling the posture of the foreign materials. SOLUTION: On a filter member put in between a fuel rod and a lower nozzle plate, a multitude of hollow upper projections 7 projecting upward from the lower part of each fuel rod and a multitude of lower projections 8 projecting downward from each crossing point of grid plate of the lowest support grid are formed. In each upper projection 7 a flow hole 9 is formed within nearly the projection area of the fuel rod positioning above it in vertically downward direction and in each lower projection 8 a low hole 10 is formed within nearly the projection area of the crossing point of grid plate positioning above it in vertically downward direction. The plate thickness of the filter member is specified to be ca. 15 mm, the angle of elevation of the upper projection to be ca. 62.5 degrees and the shape and dimension of the flow hole are specified to fit to the 1717 type fuel assembly.