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

Abstract

A top nozzle for a nuclear fuel assembly and a method of manufacturing the top nozzle are provided. The top nozzle can include a coupling plate, a perimeter wall and a hold-down spring unit. The coupling plate can be coupled to a guide thimble of the nuclear fuel assembly. The perimeter wall can protrude upwards from the perimeter of the coupling plate. A spring clamp can be provided on the upper surface of the perimeter wall. The hold-down spring unit can be mounted to the upper surface of the perimeter wall in such a way to couple a corresponding end of the hold-down spring unit to the spring clamp. A fastening pin hole can be vertically formed through an upper surface of the spring clamp. A spring insert hole into which the hold-down spring unit can be inserted and formed by electro-discharge machining in an insert direction of the hold-down spring.

1 - 9 . (canceled) 
     
     
         10 . A top nozzle for a nuclear fuel assembly, the top nozzle comprising:
 a coupling plate coupled to a guide thimble of the nuclear fuel assembly;   a perimeter wall protruding upwards from a perimeter of the coupling plate, the perimeter wall comprising a spring clamp provided on an upper surface of the perimeter wall;   a hold-down spring unit mounted to the upper surface of the perimeter wall;   a fastening pin hole vertically formed through an upper surface of the spring clamp; and   a spring insert hole located in the spring clamp, the spring insert hole being formed by electro-discharge machining in an insert direction of the hold-down spring unit,   wherein an end of the hold-down spring unit is inserted into the spring insert hole.   
     
     
         11 . The top nozzle as set forth in  claim 10 , wherein the coupling plate and the perimeter wall are integrally formed by casting into a single body. 
     
     
         12 . The top nozzle as set forth in  claim 10 , wherein the fastening pin hole has an elliptical pin head seat formed in the upper surface of the clamp and defines a part of the spring insert hole. 
     
     
         13 . The top nozzle as set forth in  claim 12 , wherein the spring insert hole is formed by forming a premachined hole having a cross-section less than a cross-section of the spring insert hole and by conducting an electro-discharge machining process. 
     
     
         14 . The top nozzle as set forth in  claim 12 , further comprising:
 a fastening pin provided with a head having a shape corresponding to the elliptical pin head seat, the fastening pin being configured to be inserted into the fastening pin hole to hold the hold- down spring unit.   
     
     
         15 . 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; and   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.   
     
     
         16 . The method as set forth in  claim 15 , 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.   
     
     
         17 . The method as set forth in  claim 15 , 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.   
     
     
         18 . The method as set forth in  claim 15 , further comprising:
 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.   
     
     
         19 . A top nozzle for a nuclear fuel assembly, the top nozzle comprising:
 a coupling plate coupled to a guide thimble of the nuclear fuel assembly;   a perimeter wall protruding upwards from a perimeter of the coupling plate, the perimeter wall comprising a spring clamp provided on an upper surface of the perimeter wall;   a hold-down spring unit mounted to the upper surface of the perimeter wall;   a fastening pin hole vertically formed through an upper surface of the spring clamp;   a spring insert hole located in the spring clamp, the spring insert hole being formed by electro-discharge machining in an insert direction of the hold-down spring unit,   wherein an end of the hold-down spring unit is inserted into the spring insert hole,   wherein the coupling plate and the perimeter wall are integrally formed by casting into a single body,   wherein the fastening pin hole has an elliptical pin head seat formed in the upper surface of the clamp and defines a part of the spring insert hole, and   wherein the spring insert hole is formed by forming a premachined hole having a cross-section less than a cross-section of the spring insert hole and by conducting an electro-discharge machining process; and   a fastening pin provided with a head having a shape corresponding to the elliptical pin head seat, the fastening pin being configured to be inserted into the fastening pin hole to hold the hold-down spring unit.   
     
     
         20 . 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.