Top nozzle for nuclear fuel assembly having spring insert hole improved in fastening stability and method of manufacturing the same

A method of manufacturing a top nozzle for a nuclear fuel assembly, the method comprising:

• forming a fastening pin hole in a vertical direction through an upper surface of a spring clamp that is provided on the top nozzle;
• forming a spring insert hole in the spring clamp in an insert direction of a hold-down spring unit by using an electro-discharge machining process;
• coupling the hold-down spring unit to the spring clamp to insert an end of the hold-down spring unit into the spring insert hole;
• and
• casting a main body of the top nozzle before the forming of the fastening pin hole, the main body comprising a coupling plate coupled to a guide thimble of the nuclear fuel assembly, and a perimeter wall protruding upwards from a perimeter of the coupling plate, wherein the spring clamp is provided on an upper surface of the perimeter wall,
• wherein the forming of the fastening pin hole comprises forming an elliptical pin head seat into an elliptical shape to form an upper end of the fastening pin hole, and
• wherein the forming of the spring insert hole by using the electro-discharge machining process comprises forming a premachined hole through the elliptical pin head seat before the electro-discharge machining process is conducted.